WO1988001085A2 - Fiber optics communication link for remote mobile vehicle - Google Patents

Abstract

A fiber optics communication link (20) for a remote mobile (22) vehicle employs a single strand of optical fiber (26) to convey control data from a stationary control station (24) to the vehicle and to simultaneously convey environmental data generated by transducers carried by the vehicle back to the control station. At the control station, the received optical signals are converted to an electrical form and demodulated to recover the environmental data. Additionally, encoded and modulated optical signals corresponding to the control data are provided to the second combiner/splitter (56) for transmission via the fiber to the first combiner/splitter (36). At the vehicle the received optical signals are converted to electrical form, decoded and demodulated to recover the control data, and used to control the vehicle and transducers. Frequency multiplexing is used in different directions along the single fiber in order to eliminate noise due to reflections along the optical path.

Description

FIBER OPTICS COMMUNICATION LINK FOR REMOTE MOBILE VEHICLE

The present invention is directed to a fiber optics communication link for a remote mobile vehicle, and more particularly to a communication link which employs a single strand of optical fiber for conveying control data from a stationary control station to the vehicle and for conveying environmental data from the vehicle to the stationary control station.

Not infrequently; it is desirable to. conduct an investigation for gathering environmental data in a region that may be hostile to human observers. For example, it may be desirable to investigate a feature on the sea floor, or to monitor temperature and toxic fumes at an industrial fire. Moreover, even if physical danger to an observer is not present, the observer's efficiency may be increased if he can conduct his investigations at one or more remote locations without moving from a stationary control center.

Remotely controlled vehicles frequently employ a radio link between a human controller and the vehicle.

Familiar examples include R/C airplanes and cars which are used as amusement devices, but remotely controlled vehicles having practical applications are also known. Radio controlled vehicles, however, suffer from several disadvantages when they are used as mobile platforms for environmental sensors. For example, environmental data transmitted by radio back to the controller may be distorted by electromagnetic interference, so that the data becomes unreliable. Furthermore, it is easy for unauthorized people to receive the transmitted data, so that security may be a problem. Finally, the difficult government licensing procedures associated with radio communications are frequently burdensome.

A microfilmed paper by K. Niederhofer et al., "A Bidirectional Fiber Optic Link for Guided Missiles," (Manuskript fur Tagungsband der IDEE '82 [Manuscript for convention proceedings of the IDEE '82], May 18th - 20th, 1982 in Hannover, Federal Republic of Germany), discloses an antitank missile which is controlled from a launching platform via an optical communication link. The link conveys a video signal to the launching platform and a command signal to the missile. The paper comments that it is not practicable to use a separate optical fiber for each direction of transmission, but that there are two basic methods of signal separation — wavelength multiplexing and time division multiplexing — which permit a single fiber to be used. Niederhofer et al. disclose an experimental arrangement which employs the time division multiplexing technique, with the command signal being sent to the missile during the vertical blanking interval of the video signal from the missile. At the missile is a single LED which, serves as both a transmitting element and a receiving element, and at the launching platform is an optical coupler which links a transmitter and a receiver to the single fiber.

In the optical communications art the term "wavelength multiplexing" means that different colors provide different optical channels. For example, an optical transmitter which is connected to a fiber and which emits information (analog or digital) using light of a given color can communicate with any optical receiver whichis connected to the fiber and which is responsive only to light of that given color, regardless of whether the fiber also carries other optical signals at different colors. An optical transmitter includes a light-emitting element which receives an electrical signal and generates light having an intensity which varies with the electrical signal. Similarly, an optical receiver includes a light-sensitive element which receives the light and generates an electrical signal whose voltage corresponds to the intensity of the incoming light. Light-emitting elements are commercially available which emit light at a limited range of wavelengths (e.g., laser diodes), but light-sensitive elements (e.g., photodiodes) tend to be sensitive to a broad range of wavelengths. For this reason, in wavelength multiplexing the optical signals carried by a fiber must be optically separated before reaching the light-sensitive elements of the optical receivers. For example, Niederhofer et al. disclose an optical communication link wherein a single fiber joins two dichroic couplers, with one coupler receiving light at a first wavelength from an optical transmitter and distributing light at a second wavelength to an optical receiver, and with the other coupler receiving light at the second wavelength from an optical transmitter and distributing light at the first wavelength to an optical receiver. The result is that each optical receiver is responsive to only one of the optical transmitters.

Dichroic filters and diffraction gratings may also be employed to separate optical channels when wavelength multiplexing is employed. However, the optical elements needed for wavelength multiplexing tend to be relatively expensive. In time division multiplexing, on the other hand, some type of timing control is needed in order to ensure timing allocations, and this both increases complexity and limits the data transfer rate on the individual channels.

The primary object of this invention is to provide a communication link for remote control of a vehicle via a single strand of optical fiber from a remote control station. With this object in view, the present invention resides in a communication link for conveying environmental data generated at a vehicle to a control station and for conveying control data generated at the control station to the vehicle, the vehicle having motors responsive to the control data for moving the vehicle, comprising a first optical combiner/splitter disposed at said control station and having first, second, and third light ports; a second optical combiner/splitter disposed at said vehicle and having first, second, and third light ports; optical fiber for providing a single optical path which optically connects said first light ports of said first and second combiner/splitters characterized by first electro-optic array disposed at said vehicle for transmitting said environmental data in optical form to said second light port of said second combiner/splitter, said environmental data in optical form having at least one first frequency channel; second electro-optic array disposed at said control station and connected to said second light port of said first combiner/splitter for receiving and displaying environmental data, said second electro-optic array being responsive to said at least one first frequency channel; third electro-optic array disposed at said control station for transmitting said control data in optical form simultaneous with said transmittal of said environmental data to said third light port of said first combiner/ splitter, said control data. in optical form having at least one second frequency channel that is different from said first frequency channel; and fourth electro-optic array disposed at said vehicle and connected to said third light port of said second combiner/splitter for receiving control data for said vehicle and said motors, said fourth electrooptic array being responsive to said at least one second frequency channel, said at least one first frequency channel and said at least one second frequency channelconnected to frequency multiplexing circuitry to isolate said environmental data signals and said control data signals. The preferred embodiment of the indention will be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic block diagram of a vehicle and control station system which includes the fiber optics communication link of the present invention;

Figure 2 schematically illustrates an optical combiner/splitter;

Figure 3 illustrates the remote vehicle and stationary command station used with an embodiment of the fiber optics communication link of the present invention; Figure 4 is a schematic block diagram of circuitry at the stationary control station of the embodiment of Figure 3; Figures 5A-5F are waveform diagrams used for explaining the encoding and decoding of control signals employed in the embodiment of Figure 3;

Figure 6 is a schematic block diagram of circuitry at the remote vehicle in the embodiment of Figure 3; Figure 7 is a schematic block diagram of a motor control circuit in Figure 6;

Figure 8 is a side view of the fiber reel illustrated at the back of the vehicle in Figure 3;

Figure 9 is a side view of the motor control sensor board employed in Figure 8 to sense the position of the fiber tension control arm; and

Figure 10 is a schematic diagram of a motor drive circuit for supplying or taking up fiber from the reel of Figure 8 in response to the position of the fiber tension control arm. Figure 1 illustrates the general form of the fiber optics communication link 20 of the present invention, which includes elements both in vehicle 22 and instationary, control station 24, along with optical fiber 26 between vehicle 22 and station 24. Although fiber 26 will be referred to as a single fiber since it provides a single optical path (in contrast to two or more fibers to provide parallel optical paths), in practice optical couplers 27 (only one of which is illustrated) may be provided to optically connect the ends of different fiber segments. Disposed at station 24 are control data generators 28, which permit an operator at station 24 to generate signals for steering vehicle 22 and signals for selectively controlling environmental data acquired by vehicle 22. The signals from generators 28 are provided to control data encoder 30, which encodes the signals and employs the encoded signals to modulate a carrier in order to prepare them for transmission to vehicle 22 via a plurality of time division multiplexed control channels having the same channel frequency. The signals are provided to optical transmitter 32, which converts the signals to their optical equivalents and provides them via optical fiber 34 to a light port of combiner/splitter 36. Combiner/splitter 36 additionally receives multi-channel environmental data signals in optical form from vehicle 22 via fiber 26, and provides these signals to optical receiver 38 via optical fiber 40. Each channel of environmental data has its own channel frequency, which is different from the channel frequency of the control channels. Receiver 38 transforms the optical signals to corresponding electrical signals which are provided to environmental data demodulator 42, which separates the data channels. The demodulated signals are then delivered to environmental data display 44 or other data utilization devices such as data recorders (not illustrated).

Optical transmitters and receivers with multiple channel capabilities are commercially available under the trademark "Wavelink" from Grass Valley Group, Inc., P.O.

Box 1114, Grass Valley, California 95945, Model 3290/91.

From the foregoing discussion it will be notedthat combiner/splitter 36 includes a light port for receiving from fiber 34 optical signals to be conveyed via fiber 26, and a light port for delivering to fiber 40 optical signals which have been received via fiber 26. The physical structure of such a combiner/splitter is shown schematically in Figure 2, which illustrates a pair of optical fibers that have been fused at intermediate region

46. Fiber portions 48 and 50 are disposed at one side of region 46 and fiber portions 52 and 54 are disposed at the other side. Neglecting minor losses, half of the power of a light beam which enters the end of fiber portion 50 (for example) is distributed to fiber portion 52, and the other half is distributed to fiber portion 54. A negligible amount of this incoming light is distributed to fiber portion 48. If light beams were exposed to the ends of both fiber portions 48. and 50 simultaneously, half of the light of each beam would be distributed to each of fiber portions 52 and 54. Furthermore, the device is symmetrical. That is, a light beam entering the end of fiber portion 52 (for example) would be equally distributed to fiber portions 48 and 50.

To use the device illustrated in Figure 2 as combiner/splitter 36 in Figure 1, one of the four fiber portions -- say, fiber portion 48 -- would be optically terminated in a non-reflecting manner. The other three fiber portions 50-54 would then be optically connected to fibers 26, 40 and 34, respectively. With such connections it will be apparent that optical signals entering combiner/ splitter 36 from fiber 34. will be conveyed, at approximately half power, to fiber 26, with none of the signal being distributed to fiber 40. On the other hand optical signals entering combiner/splitter 36 from fiber 26 will be equally distributed to fibers 34 and 40. The portion of the optical signal delivered to fiber 34 is simply ignored by optical transmitter 32, which is not equipped to detect the light. It should be noted that, due to the previously- described symmetrical effect, combiner/splitter 36 cansimultaneously send optical data to vehicle 22 and receive optical data from vehicle 22 without interference. That is, optical signals from vehicle 22 do not interfere with optical signals from station 24 even if such signals occur simultaneously and at the same optical wavelength. However, as a practical matter which will be discussed in more detail later, simultaneous transmissions in different directions and at the same optical wavelength result, in noise due to signal reflections at discontinuities in the optical path.

A combiner/splitter suitable for use in the present invention is commercially available from Max-light Optical Waveguides, Inc., 3035 N. 33rd Drive, Phoenix, Arizona 85017, Model C2X2-200.

With continuing reference to Figure 1, located at vehicle 22 is a splitter/combiner 56 which accepts optical signals from and provides optical signals to fiber 26. Optical fiber 58 delivers optical signals from combiner/ splitter 56 to optical receiver 60, where the optical signals are converted to their electrical counterparts. Thereafter the signals are conveyed to control data decoder 62, which demodulates and separates the control channels, and thence to vehicle controller 64, which controls motors (not illustrated in Figure 1) to move the vehicle and any manipulative appendages thereto.

Environmental data generators 66, preferably including at least one television camera in addition to other analog and digital environmental transducers, provide signals for environmental data controller 68. Control data decoder 62 is connected to environmental data controller 68 in order to.permit the operator at control station 24 to select or otherwise control the data generators 66. The signals are modulated by environmental data modulator 70 to provide a plurality of environmental data channels at different frequencies, and the modulated signals are then provided to optical transmitters 72. The optical signals are thereafter delivered by optical fibers 74 tosplitter/combiner 56. As has been previously discussed, light travelling in one direction along the optical components does not interfere with light that is travelling in the opposite direction, even if the wavelength is the same. However, reflections occur at discontinuities along the optical path, where the index of refraction changes suddenly. Couplers such as 27 (and others, not illustrated, which might in practice be employed) create such discontinuities. Moreover a discontinuity is provided at the end of fiber 34 that is connected to transmitter 32, the end of fiber 40 that is connected to receiver 38, the end of fiber 53 that is connected to receiver 60, and the end of fiber 74 that is connected to transmitter 72. The result of these reflections is that an optical signal from transmitter 32, for example, will be reflected at reduced intensity back along fiber 26 and thence, via combiner/splitter 36 and fiber 40, to receiver 38. The reflection problem could be avoided in the optical domain either by time division multiplexing, so that receiver 38 would be inoperative while transmitter 32 is transmitting, or by wavelength multiplexing, so that transmitter 32 emits light having a color to which receiver 38 is not sensitive. However in the present invention noise arising from incidental reflections is not avoided in the optical domain, but is instead removed in the electrical domain by frequency division multiplexing. That is, the reflections are converted to electrical signals by receiver 38, but the noise is subsequently removed by filtering.

Figure 3 illustrates a top plan view of a remote vehicle 76 and a front elevational view of a stationary control station 78 which can be used with a specific embodiment of '& fiber optics communication link of the present invention. The vehicle 76 includes a chassis 80 to which axles 82 and 84 are fixedly mounted. Wheels 86 and 88 are rotatably mounted at the ends of axle 82, wheel 86 having a pulley 90 affixed to the inner side thereof and vheel 88 having a pulley 92 affixed to the inner side thereof. Wheels 94 and 96 are rotatably mounted at the ends of axle 84, with pulley 98 being affixed to wheel 94 and with pulley 100 being affixed to wheel 96. Reversible DC motor 102 is affixed to chassis 80 and is provided with a shaft 104. Shaft 104 is received by reduction gear box 106, which is fixedly mounted on chassis 30 and which has a shaft 108 that rotates more slowly than, motor shaft 104. Pulley 110 is fixedly mounted at the end of shaft 108, and drive belt 112 is wrapped around pulleys 92, 110, and 100 to rotate wheels 88 and 96 in unison when motor 102 is actuated. In a similar manner reversible DC motor 114 rotates pulley 116 through reduction gear box 118. Drive belt 120 is wrapped around pulleys 90, 98, and 116 to rotate wheels 86 and 94 when motor 114 is actuated. Motors 102 and 114 receive power from batteries 122, which are housed in a battery compartment 124 mounted on chassis 80. It will be apparent that motors 102 and 114 can move vehicle 76 along a straight line when one motor is rotated in the clockwise direction and the other motor is rotated in the counterclockwise direction at the same speed. Reversing the directions of rotation moves vehicle 76 backward along a straight line. Vehicle 76 can also be made to turn corners, either left or right, by rotating motors 102 and 114 at different speeds. In fact, if motor 114 drives wheels 86 and 94 in the forward direction while motor 112 drives wheels 88 and 86 in the reverse direction at the same speed, for example, vehicle 76 can be made to rotate. Accordingly, independent but coordinated control of motors 102 and 114 permits vehicle 76 to be steered.

With continuing reference to Figure 3, housings

126 are affixed to chassis 80. Support rods 128, to which bumper 130 is affixed, slidably extend into housings 126 and are biased outward by springs (not illustrated) within housings 126. Microswitch housing 132 is fixedly mounted on chassis 80 at a position where it is engaged by bumper 130 should vehicle 76 run into a stationary object.

With continuing reference to Figure 3, data generator platform 134 is mounted on chassis 80. A pair of spaced-apart flanges 136 extend upward from the top of platform 134, with forward television camera 138 and backward television camera 140 being mounted between flanges 136. A microphone 142 is mounted on the forward television camera 138.

With reference next to both Figures 3 and 8, reel assembly 144 is mounted on support 146, which in turn is mounted on chassis 80. Arms 148 and 150 are affixed to support 146 and have openings (not illustrated) through which pipe 152 rotatably extends. Gear motor (that is, a motor with reduction gearing installed in the motor housing) 154 is mounted on support 146 and is provided with a pulley 156. A belt 158 connects pulley 156 to a pulley 160 affixed to pipe 152.

With continuing reference to Figures 3 and 3, tension control arm 162 is rotatably mounted on pipe 152 and is provided with a guide portion 164 having an opening

(not illustrated) through which optical fiber 166 movably extends. A counterweight 168 is adjustably mounted at one end of tension control arm 162. Tension control arm 162has two functions. First, it guides fiber 166 to and from reel 170, which is fixedly mounted on pipe 152. Reel 170 is preferably narrow and the core (not illustrated) of the reel is preferably hyperbolic in axial cross section, much like a deep-sea fishing reel, so that fiber 166 is wound onto reel 170 relatively uniformly even without guiding the fiber back and forth from one side of reel 170 to the other. In addition to this guidance function, the position of arm 162 varies depending upon fiber tension and, as will be discussed, such variations in position are used to drive motor 154 in order to automatically take up or dispense fiber 166 as vehicle 76 moves.

Sensor board 172 is fixedly mounted on arm 148 at a position slightly spaced apart from arm 162. The inner end (not illustrated) of fiber 166 extends through pipe 152to a rotary optical coupler 174, which is affixed to arm 148. Coupler 174 optically joins fiber 166 to optical fiber 176. Turning next to Figure 9, sensors 178, 180, and 182 are affixed to board 172 at spaced-apart positions. Arm 162 actuates sensors 178-182, which are preferably elongated as shown so that each sensor is actuated for a limited range of angular positions of arm 162. For this purpose reed switches may be used for sensors 178-182, with a magnet (not illustrated) being mounted on arm 162 in order to close the switches. Other methods for sensing the position of arm 162 may be used. For example, arm 162 may be mounted on the shaft of a potentiometer (not illustrated) so that the resistance of the potentiometer varies with the angle of arm 162.

When vehicle 76 is moving forward, in the direction of arrow A in Figure 9, with fiber 166 trailing behind vehicle 76, increased fiber tension rotates arm 162 until arm 162 lies adjacent sensor 182. At this point additional fibers should be unreeled to reduce the tension and allow vehicle 76 to proceed. If vehicle 76 thereafter stops, arm 162 will lie between sensors 180 and 182. Should vehicle 76 then begin to back up, in the direction of arrow B in Figure 9, the increased fiber slack permits arm 162 to move adjacent sensor 180. At this point fiber 166 should be wound onto reel 170 in order to take up the slack and thereby return arm 162 to its "normal" position between sensors 180 and 182. Sensor 178 is provided in order to accommodate an unusual situation which arises when vehicle 76 moves in direction B while fiber 166 is beneath the vehicle rather than trailing behind it. This may occur, for example, if vehicle 76 moves in the forward direction away from stations 78, rotates on its axis, and then backs further away from station 78. In such a situation increased cable tension moves arm 162 to sensor 178, and additional fiber 156 should be unwound.

Figure 10 illustrates a circuit for driving motor 154 to take up or play out fiber 166 in response to sensors

178-182. It will be assumed that sensors 178-182 produce a logically "high" output when they are actuated by arm 162. OR gate 184 turns ON when either sensor 178 or sensor 182 is actuated. The signal is provided to buffer 186 and then to the solenoid 188 of a relay having normally open contacts 190 and 192. Contacts 190 and 192. close when either of sensors 178 and 182 is actuated, thereby connecting battery 194 across motor 154 so that additional fiber 166 can be unwound. Buffer 196 receives the output signal from sensor 180 and drives the solenoid 198 of a relay having normally open contacts 200 and 202. When contacts 200 and 202 are closed, current flows through motor 154 in a direction that is opposite that when contacts 190 and 192 are closed. Accordingly, motor 154 is driven to take up the slack in fiber 166. In order to avoid undue complexity Figure 10 does not illustrate diodes connected across motor 154 in order to absorb inductive spikes when the circuit is opened. However it will be apparent that, for each relay, a diode could be connected across motor 154 in a forward-biased direction through normally closed contacts which are opened when the respective relay is actuated, thereby leaving a reverse-biased diode connected across motor 154 through normally closed contacts of the other relay.

Returning to. Figure 3, stationary control station 78 includes a television monitor 204 and an equipment cabinet 206 having an optical socket 208 for receiving optical connector 210 at the end of fiber 166. Cabinet 206 additionally includes a speaker opening 212, a fore-or-aft camera selector switch 214, a bumper light 216, and a joy stick 218 for steering vehicle 76 in the forward, reverse, left, or right directions at a speed which depends upon joy stick displacements.

Figure 4 illustrates the electrical and optical components at control station 78. Control data generator portion 220 consists of the previously-mentioned fore- or-aft camera selector switch 214 and joy stick 218, which includes mechanically coupled potentiometers 222 and 224. Control data encoder portion 226 is based upon an LM1871 remote control encoder/transmitter integrated circuit 228, which is available from National Semiconductor Corporation, 29O0 Semiconductor Drive, Santa Clara, California 95051. Pin 9 of circuit 228 is grounded while pin 14 is connected to power supply port 230. Pin 1 is connected via resistor 232, potentiometer 224, and capacitor 234 to ground. Pin 2 is connected via resistor 236 and potentiometer 222 to capacitor 234. Pin 3 is connected via resistors 238 and 240 to capacitor 234 when switch 214 is open, but resistor 240 is removed from the circuit when switch 214 is closed. Pin 4 is connected by resistor 242 to pin 7, which in turn is connected to ground via capacitor 244. Pin 8 is connected to capacitor 234. Pin 10 is connected via resistors 245 and 246 to ground. Pin 13 is connected to the intermediate connection point between resistors 245 and 246. Finally, pin 11 is connected to pin 14 through resistor 247.

Figure 5A illustrates an example of the output waveform at pin 11 of circuit 228. This waveform may be characterized as a pulse-space modulated signal which encodes information concerning three channels. Referring to the left-hand portion of Figure 5A, it will be noted that modulation pulses having a fixed duration t_m precede spaces having variable duration. The duration t_m is typically 0.5 milliseconds. The left-most pulse illustrated in Figure 5A precedes a relatively long synchronization interval. This interval in addition to the preceding modulation pulse establishes a synchronization time t_s, typically about 6.5 milliseconds. The next fixed modulation pulse precedes an interval having a duration which encodes information for control data channel 1. The channel time t_CH1 is determined by the resistor 232, potentiometer 224, and capacitor 234 in Figure 4. Thethird fixed modulation pulse in Figure 5A precedes an interval having a duration which encodes information for control data channel 2. The channel time t_CH2 is determined by resistor 236, potentiometer 222, and capacitor 234 in Figure 4. The fourth fixed modulation pulse in Figure 5A precedes an interval having a duration which encodes information for control data channel 3. The channel time t_CH3 is determined by resistor 238, by whether switch 214 shorts resistor 240, and by capacitor 234 in Figure 4. Following t_CH3 is a fixed modulation pulse which precedes another synchronization interval. The frame time t_F, which is fixed, is determined principally by resistor 242 and capacitor 244 in Figure 4. Since frame time t_F, is fixed and channel times t_CH1, t_CH2, and t_CH3 are variable, it will be apparent that the synchronization time t_S is also variable. However, t_S is greater than the maximum permissible channel time.

The LM1871 IC can be wired to provide up to six time division multiplexed channels. While the wiring in Figure 4 only produces three channels per frame, it will be apparent that additional control channels could be added. The recapitulate, in Figure 4 the channel times t_CH1 and t_CH2 vary in dependence on potentiometers 222 and 224 in joy stick 218. As will be seen channels 1 and 2 are used to control the motion of vehicle 76. The channel time t_CH3 may have one of two discrete values, depending upon whether switch 214 is open or closed. As will be seen, channel 3 is used to select one of television cameras 140 or 142. With continuing reference to Figure 4, control data encoder portion 226 also includes an electrically controlled switch 248 which is closed when the output at pin 11 is digitally "high," and an oscillator 249. Oscillator 249 provides an 11 MHz carrier which is modulated by the pulse train from pin 11 of IC 228 using on-off keying. The output is provided to optical transmitter portion 251, which includes amplifier 252 and LED 254. Amplifier 252 drives LED 254 to flash ON and OFF in accordance with a pulse train as in Figure 5A, with the light during the ON intervals varying in intensity at an 11 MHz rate (if desired the output of oscillator 249 can be biassed to avoid zero-crossings, as by summing an 11 MHz sine wave and a DC potential that is half of the peak-to-peak voltage of the sine wave). These flashes enter the end of optical fiber 256, which conveys them to combiner/splitter 258. From combiner/splitter 258 the optical signal travels via optical fiber 260 to socket 208 and is subsequently transmitted via fiber 166 to vehicle 76 (Figure 3).

Turning next to Figure 6, which illustrates a schematic block diagram of optical and electrical components at vehicle 76, the control data generated at stationary control station 78 as previously described is conveyed via fiber 166, optical coupler 174, and fiber 176 is combiner/splitter 262 . The incoming signal is conveyed by optical fiber 264 to optical receiver portion 266, which consists of a photodiode 267 to convert the light to electricity and an amplifier 268. Control data decoder portion 272 demodulates and decodes the signal received from amplifier 268 and recovers the three control data channels. Portion 272 includes a bandpass filter 269 whichis tuned to 11 MHz (the frequency of oscillator 249 in Figure 4) and a frequency-to-voltage converter 270. It will be apparent that the output of converter 270 corresponds to the output of pin 11 of IC 228 (Figure 4). If desired a Schmidt trigger (not illustrated) may be inserted at the output of converter 270 to ensure that the pulse train has sharp edges. Portion 272 also includes a retriggerable monostable device 274, a three-stage serial- to-parallel shift register 276, and an inverter 278 connected between the output of monostable 274 and the data input of shift register 276. Conductor 280 connects the input of monostable device 274 to the clock input of shift register-276.

Referring next to both Figures 5A-F and 6, the operation of portion 272 will now be described. Monostable device 274 has been described as "retriggerable," which means that it is turned ON for a predetermined duration following receipt of a trigger signal even if it was already ON at the time of the trigger signal. That is, monostable device can be triggered and then re-triggered even if it has not timed-out from the first trigger signal. Figure 5B illustrates the output of monostable device 274 in response to the pulse train of Figure 5A. Monostable device 274 is triggered at the trailing edges of the modulation pulses, and it will be noted that synchronization time t_s is sufficiently long to permit device 274 to time-out once per frame. Figure 5C represents the output of inverter 278, this output being applied to the data input of shift register 276. Shift register 276 is clocked at the leading edges of the fixed modulation pulses. Referring to the right-hand sides of Figures 5A and 5C, at time t₁ the data input of shift register 276 is logically high and a "1" is clocked into the first stage of shift register 276. This is illustrated in Figure 5D. At time t₂ the data input of shift register 276 is logically low, so a digital zero enters the first stage of shift register 276 and the digital one previously in the first stage is shifted to the second stage Figure 5E illustrates the output of the second stage of the shift register 276. At time t₃ a digital zero is shifted into first stage, the digital zero previously in the first stage is shifted to the second stage, and the digital one previously in the second stage is shifted to the third stage as illustrated in Figure 5F. At time t₄ all three stages of the shift register 276 are cleared in preparation for the next frame of encoded command data.

With continuing reference to Figures 5A-F, it should be noted that, for each of the three control data channels, an output pulse appears once per frame. The duration of the pulse is equal to the modulation time t_m plus the respective channel time t_CH1 , t_CH2, or t_CH3 In short, portion 272 produces three phase-displaced, pulsewidth modulated pulse trains. Vehicle controller portion 282, which receives the decoded pulse trains for channels 1 and 2, includes left and right motor control circuits 284 and 286, which drive left and right motors 102 and 114 (see Figure 3) respectively. Circuits 284 and 286 drive their respective motors at speeds and directions determined by the pulse widths of the respective input signals. Figure 7 illustrates circuit 286 and motor 114. In this Figure, a pulse width modulated signal as in Figure 5D is applied to input terminal 288. The leading edges of the pulses of the input signal trigger one shot multivibrator 290, which turns ON for a period corresponding to a channel 1 output pulse when potentiometer 224 (see Figure 4) is at its center position. The output of multivibrator 290 is applied through buffer 191 to one input of an AND gate 292 and, through inverter 294, to one input of AND gate 296. The signal applied to terminal 288 is also provided to the other input of gate 296 and to inverter 298, which is connected to the remaining input of gate 292. Gate 296 turns ON if multivibrator 290 times-out before an input pulse returns to zero, while gate 292 turns ON if the input pulse returns to zero while multivibrator 290 is still ON. In either case, the gate 292 or 296 remains ON for a period of time that depends upon the duration of the interval between the falling edge of the pulse applied to the terminal 288 and the falling edge of the output of monostable device 290. It will be understood that this difference corresponds to how far potentiometer 224 (Figure 4) deviates from its center position; that is, how fast motor 114 is to be rotated in either the forward direction or the reverse direction. The outputs of gates 292 and 295 are transmitted to OR gate 299, the output of which controls switch 300 so as to close the switch when gate 299 is ON. Oscillator 302 provides a pulse train which is counted by counter 304 during the period when switch 300 is closed, the count being cleared at the leading edge of each pulse supplied to terminal 288. In order to ensure that the count is cleared even if there is a malfunction which results in loss of the signal applied to terminal 288, a "watchdog circuit" consisting of retriggerable monostable device 303 and OR gate 305 is connected to the clear input of counter 304. The output of device 303 becomes high if terminal 288 fails to receive a pulse within the frame period. During normal operation pulses from terminal 288 pass through gate 305 to clear counter 304; device 303 keeps a count from being locked into counter 304 if the pulses are interrupted. The content of counter 304 is converted to analog by digital/ analog converter 306, with the analog output being supplied to pulse width modulator 308. Pulse width modulator 308 produces a train of pulses having widths that are proportional to the analog voltage, with an analog voltage of zero resulting in a pulse width of zero. Switch 310 is turned ON and OFF by the output of pulse width modulator 308. Accordingly, it will be apparent that, as potentiometer 224 (see Figure 4) deviates from its center position, switch 310 is periodically closed for a time that depends upon the deviation and consequently motor 114 rotates at a rate proportional to the deviation. With continuing reference to Figure 7, it will be recalled that gate 296 turns ON if the output of multivibrator 290 falls before the output of the pulse applied to terminal 288, while gate 292 turns ON if the reverse situation occurs. The D input of flip-flop 312 is connected to terminal 288 and the clock input is connected to the output of gate 296 so that the output of flip-flop 312 becomes 1 if gate 296 turns ON. The D input of flipflop 314 is connected to terminal 288 via inverter 316, which is ON except when a pulse is present at terminal 288. The clock input of flip-flop 314 is connected to the output of gate 292 via inverters 318 and 320, which impose a slight delay to ensure that the clock input of flip-flop 314 becomes 1 after the D input becomes 1 in the event that gate 292 turns ON.

With continuing reference to Figure 7, the output of flip-flop 312 is applied via a buffer 322 to the solenoid 324 of a relay having normally open contacts 326 and 328. When solenoid 324 is energized, contacts 326 and 328 are closed and energy from battery 330 flows through motor 114 at a rate determined by the duty cycle of switch 310. The output of flip-flop 314 is connected via buffer 332 to the solenoid 334 of a relay having normally open contacts 336 and 338. When solenoid 334 is energized, power is provided to motor 114 in the reverse direction, again at the rate determined by the duty cycle of switch 310. From the foregoing discussion it will be apparent that circuit 286 controls the speed of motor 114, in either the forward or reverse direction, at a rate which depends upon the dispclacement of potentiometer 224 (see Figure 4) from its center position.

Returning to Figure 6, environmental data generator portion 340 includes a microswitch 342 mounted in housing 132 (see Figure 3 ) at a position to be engaged by bumper 130 in the event that vehicle 76 runs into an object. Switch 342 is connected between ground and power supply terminal 344 by pull-up resistor 346. Accordingly, it will be apparent that inverter 348 turns ON if bumper 130 is displaced and switch 342 is closed. Environmental data generator portion 340 also includes microphone 142, forward television camera 138, and backward television camera 140 (see Figure 3).

Environmental data controller portion 350 receives the channel 3 output of shift register 276 and is responsible for selecting either camera 138 or camera 140, depending upon whether switch 214 (see Figure 4) is open or closed. Portion 350 includes latch 352, one show multivibrator 354, and switch 356. The channel 3 pulses (see Figure 5F) are provided to the inputs of latch 352 and multivibrator 354. The output of multivibrator 354 is connected to the clock input of latch 352, which stores the input signal existing at the time when multivibrator 354turns OFF. Latch 352 stores a digital one if multivibrator 354 times-out while an input pulse exists, and otherwise stores a zero. Switch 356 selects either camera 138 or 140 depending upon whether a digital zero or a digital one is stored by latch 352. In this way the position of switch 214 (see Figure 4) determines which of cameras 138 and 140 is selected.

With continuing reference to Figure 6, environmental data modulator portion 358 includes FSK modulator 360, amplitude modulator 362, and summing amplifier 364. FSK modulator 360 produces a 24 MHz output if switch 342 is open and a 25 MHz output if switch 342 is closed. Amplitude modulator 362 provides a 10 MHz carrier which is modulated by the output of microphone 142. Cameras 138 and 140 produce standard video signals, which have a bandwidth of approximately 4 MHz. The baseband television signal selected by switch 356, along with the modulated signals from modulators 360 and 362, are provided to respective inputs of summing amplifier 364. It should be noted that the environmental data signals are frequency division multiplexed and are assigned frequency channels that are different from the frequency channel of the command data. That is, in addition to being frequency division multiplexed with respect to each other, the environmental data signals as a group are frequency division multiplexed with respect to the command data. The summed output from amplifier 364 is provided to optical transmitter portion 365, consisting of amplifier 366 and LED 368. LED 368 produces light having an instantaneous intensity substantially proportional to the instantaneous value of the output of amplifier 366. The result is that LED 368 emits light which varies in intensity at 24 or 25 MHz (as a result of switch 342 and FSK modulator 360), light that varies in intensity at 10 MHz (the amplitude of the 10 MHz variations being dependent on microphone 142), and light that varies in intensity according to the baseband television signal from camera 138 or camera 140. The lightproduced by LED 368 may have the same wavelength as the light produced by LED 254 (Figure 4). The optical signal enters the end of optical fiber 370 and is routed to fiber 176 by combiner/splitter 262. Returning to Figure 4, the optical data signals conveyed by fiber 260 to combiner/splitter 258 are distributed equally to optical fibers 256 and 372. The light from LED 368 (Figure 6) does not interfere with the light emitted to fiber 256 by LED 254, which continues flashing in response to the output provided by IC 228, switch 248, and oscillator 249 of circuit 228; LED 254 simply ignores the incoming optical signals. The portion of the optical signal distributed to fiber 372 is routed to optical receiver portion 374, which consists of photodiode 376 and amplifier 378. Portion 374 converts the optical signal to its electrical equivalent, so that the output of amplifier 378 corresponds to the sum of the outputs of modulator 360, modulator 362, and switch 356 in Figure 6. Environmental data demodulator portion 380 consists of filters 382-386, FSK demodulator 388, and AM demodulator 390. The baseband television signal is routed to monitor 204 of environmental data display portion 391 through lowpass filter 386. The amplitude modulated audio signal is routed to amplitude demodulator 390 through bandpass filter 384, which is tuned to 10 MHz. Demodulator 390 detects the audio signal, which is amplified by amplifier 392 and then delivered to speaker 394 mounted behind the opening 212 in Figure 3. Highpass filter 382 passes signals having a frequency, greater than 20 MHz, and the signals are subsequently demodulated by FSK demodulator 388. Driver amplifier 396 then illuminates bumper light 216 if switch 342 (see Figure 6) is closed.

From the foregoing discussion it will be apparent that the fiber optics communication link of the present invention employs a single fiber to convey control data from a stationary control station to a remote vehicle and to convey environmental data collected at the remotevehicle back to the stationary control station. The optical signals traveling in opposite directions along the fiber may occur at the same time and at the same optical wavelength, since frequency division multiplexing is electrically imposed so that noise generated in the optical domain due to reflections at discontinuities in the optical path can be eliminated by filters in the electrical domain. At the control station, the control data is encoded and modulated to provide a plurality of time multiplexed control channels within a frequency channel. The control data, which is demodulated and decoded for use at the vehicle, preferably includes data for steering the vehicle and data for selecting or otherwise controlling (as, for example, by aiming a camera or extending a probe) environmental transducers carried by the vehicle. Additional command channels can easily be added, so that a robot arm, for example, may be included on the vehicle. The environmental transducers at the vehicle may include television cameras, microphones, switches, and virtually any other type of transducer which produces an analog or digital output. The environmental data signals may be time division multiplexed rather than frequency division multiplexed prior to transmission back to the control station, but light headed in one direction should have a frequency channel (which may be baseband) different from the frequency channel of light headed in the other direction.

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)

(51) International Patent Classification ^• (11) International Publication Number: WO 88/ 01 G08C 23/00, H04B 9/00 A3 (43) International Publication Date: 11 February 1988 (11.0

(21) International Application Number: PCT/US87/01682 (81) Designated States: AT (European patent), BE (E pean patent), CH (European patent), DE (Euro

(22) International Filing Date: 13 July 1987 (13.07.87) patent), FR (European patent), GB (European tent), IT (European patent), JP, KR, LU (Euro patent), NL (European patent), SE (European

(31) Priority Application Number: 893,760 tent).

(32) Priority Date: 6 August 1986 (06.08.86)

Published

(33) Priority Country: US With international search report.

Before the expiration of the time limit for amendin claims and to be republished in the event of the recei

(71) Applicant: WESTINGHOUSE ELECTRIC CORPORamendments.

ATION [US/US]; Westinghouse Building, Gateway Center, Pittsburgh, PA 15222 (US). (88) Date of publication of the international search report:

(72) Inventor: COLBAUGH, Michael, E. ; 105 Kleylein Ct., 25 February 1988 (25.02

Levelgreen, PA 15085 (US).

(74) Agents: CRAIG, G. L. et al; Westinghouse Electric Corporation, Research and Development Center, Law Department, IPS, Pittsburgh, PA 15235 (US).

(54) Title: FIBER OPTICS COMMUNICATION LINK FOR REMOTE MOBILE VEHICLE

(57) Abstract

A fiber optics communication link (20) for a remote mobile (22) vehicle employs a single strand of optical fiber ( to convey control data from a stationary control station (24) to the vehicle and to simultaneously convey environme data generated by transducers carried by the vehicle back to the control station. At the control station, the received opti signals are converted to an electrical form and demodulated to recover the environmental data. Additionally, encoded modulated optical signals corresponding to the control data are provided to the second combiner/splitter (56) for tra mission via the fiber to the first combiner/splitter (36). At the vehicle the received optical signals are converted to electri form, decoded and demodulated to recover the control data, and used to control the vehicle and transducers. Freque multiplexing is used in different directions along the single fiber in order to eliminate noise due to reflections along optical path.

FOR THE PURPOSES OF INFORMATION ONLY

Codes used to identify Statespartyto the PCT on the frontpages ofpainphletspublishinginternationalappli- cations under the PCT.

AT Austria FR France ML Mali

AU Australia GA Gabon MR Mauritania

BB Barbados GB United Kingdom MW Malawi

BE Belgium HU Hungary NL Netherlands

BG Bulgaria IT Italy NO Norway

BJ Benin JP Japan RO Romania

BR Brazil KP Democratic People's Republic SD Sudan

CF Central African Republic ofKorea SE Sweden

CG Congo KR Republic of Korea SN Senegal

CH Switzerland LI Liechtenstein SU Soviet Union

CM Cameroon LK Sri Lanka TD Chad

DE Germany, Federal Republic of LU Luxembourg TG Togo

DK Denmark MC Monaco US United States of America

FI Finland MG Madagascar

Claims

CLAIMS:

1. A communication link for conveying environmental data generated (22) at a vehicle (76) to a control station (78) and for conveying control data generated (24) at the control station to the vehicle, the vehicle having motors (102, 114) responsive to the control data for moving the vehicle, comprising a first optical combiner/splitter (36; 258) disposed at said control station and having first, second, and third light ports; a second optical combiner/splitter (56; 262) disposed at said vehicle and having first, second, and third light ports; optical fiber (26; 166) for providing a single optical path which optically connects said first light ports of said first and second combiner/splitters characterized by first electrooptic array (70, 72; 358, 365) disposed at said vehicle for transmitting said environmental data in optical form to said second light port of said second combiner/splitter, said environmental data in optical form having at least one first frequency channel, second electro-optic array (38, 42, 44; 374, 380, 391) disposed at said control station and connected to said second light port of said first combiner/ splitter for receiving and displaying environmental data, said second electro-optic array being responsive to said at least one first frequency channel; third electro-opticarray (30, 32; 226, 251) disposed at said control station for transmitting said control data in optical form simultaneous with said transmittal of said environmental data to said third light port of said first combiner/ splitter, said control data in optical form having at least one second frequency channel that is different from said first frequency channel; and fourth electro-optic array (60, 62, 64; 266, 272, 284, 286) disposed at said vehicle and connected to said third light port of said second combiner/splitter for receiving control data for said vehicle and said motors, said fourth electro-optic array being responsive to said at least one second frequency channel, said at least one first frequency channel and said at least one second frequency channel connected to frequency multiplexing circuitry to isolate said environmental data signals and. said control data signals.

2. The communication link of claim 1 characterized by said at least one second frequency channel being a single second frequency channel, wherein said control data is generated by a plurality of control data generators (28; 220) which are disposed at said control station and which generate control data signals in electrical form, wherein said third electro-optic array includes control data encoder (30, 226) for encoding the data signals and for using the encoded data signals to modulate a carrier having a frequency which corresponds to said second frequency channel, and first optical transmitter (32; 251) for transforming the modulated carrier to optical form, and wherein said fourth electro-optic array includes a first optical receiver (60; 266) connected to said third light port of said second combiner/splitter for converting optical signals to electrical form, and control data decoder (62; 272) for demodulating and decoding the output of said first optical receiver.

3. The communication link of claim 2 characterized by said environmental data being generated by a plurality of environmental data generators (66; 340) whichare mounted on said vehicle and which generate environmental signals in electrical form, wherein said first electro-optic array includes an environmental data modulator (70; 358) for modulating at least one additional carrier using the environmental signals in electrical form from at least one of said environmental data generators, each at least one additional carrier having a frequency which corresponds to a respective at least one first frequency channel, and second optical transmitter (72; 365) for thereafter transforming the output of said environmental data modulator to electrical form, and wherein said second electro-optic array includes a second optical receiver (38; 374) connected to said second light port of said first combiner/splitter for converting optical signals to electrical form and an environmental data demodulator (42; 380) for demodulating the output of said second optical receiver for each at least one additional carrier.

4. The communication link of claim 3 characterized by at least one of said environmental data generators being a television camera (138, 140) which generates television signals, said at least one first frequency channel for said television signals being a baseband channel, and wherein said second electro-optic array further includes an environmental data display (44; 391) responsive to the output of said environmental data demodulator, said display including a television monitor (204) to display said television signals.

5. The communication link of claim 4 characterized by said vehicle being a wheeled vehicle (76), wherein said motors are operatively connected to the wheels, and wherein said control data generators include a manual controller (218) for generating control data signals to selectively control the rotation of said motors. 6. The communication link of claim 5 characterized by said control data generators additionally including a selector (214) to selectively control at least one of said environmental data generators.

1 . The communication link of claim 6 characterized by said manual controller including a joy stick having a pair of mechanically linked potentiometers (222, 224) and said selector comprising a switch for selecting an environmental data generator.

8. The communication link of claim 7 characterized by said fourth electro-optic array additionally including a vehicle controller (64; 284, 286) connected to said control data decoder for variably and independently controlling the rotation of each of said motors in response to the position of a respective potentiometer.

9. The communication link of claim 8 characterized by said vehicle having a moveable bumper (130), and wherein said environmental data generators include a sensor (342) for detecting movement of said bumper.

10. The communication link of claim 9 characterized by said control data modulator including circuitry (226) for pulse-spacing modulating signals from said potentiometers and said switch and circuitry (272) for generating at least three pulse-width modulated pulse trains in response to said pulse spacing modulated signals from circuitry (226). 11. The communication link of claim 10 characterized by said pulse train circuitry including a shift register (276) having a data input and a clock input, a retriggerable monostable device (274) operatively connected between said data input and said second optical receiver, and a conductor connecting said clock input to said second optical receiver.

12. The communication link of claim 10 characterized by there being a plurality of additional carriers at different frequencies, and said environmental data modulator includes circuitry (360; 362) for FSK modulating and for amplitude modulating said additional carriers. 13. The communication link of claim 2 characterized by said control data encoder including circuitry(226) for providing a plurality of different time divisions multiplexed control data channels on said second frequency channel, each of said different control data channels corresponding to a respective control data generator.

14. The communication link of claim 3 characterized by said environmental data modulator including circuitry (360, 362) for providing different environmental data channels, each corresponding to a respective environmental data generator.

15. the communication link of claim 14 characterized by said circuitry (360; 362) for providing different environmental channels including circuitry responsive to said environmental data generators for frequency division multiplexing said environmental signals.