WO1999056087A1

WO1999056087A1 - Encoder with improved sensing resolution

Info

Publication number: WO1999056087A1
Application number: PCT/US1999/009174
Authority: WO
Inventors: Bruce M. Schena
Original assignee: Immersion Corporation
Priority date: 1998-04-30
Filing date: 1999-04-27
Publication date: 1999-11-04
Also published as: AU3767999A

Abstract

An encoder device providing an enhanced sensing resolution includes an emitter that emits a beam of electromagnetic energy which is received by a number of detectors, such as four. Each detector outputs a signal indicative of when the detector receives the beam. A moveable member, such as a code disk or strip, is positioned to receive the beam from the emitter, where the moveable member alternately allows and prevents the beam to be received by the detector, for example, by allowing the beam to pass through spaced apart slots in the moveable member. The detectors are placed such that they produce detection signals which are 45 degrees out of phase with one another. In a different embodiment, a reticle is positioned between the moving member and detectors having multiple slots. The out-of-phase detection signals are used to sense the motion of the moveable member. The rising and falling edges of a first pair of the detection signals can be counted while rising and falling edges of a second pair of the detection signals is counted. The count information from the pairs can be added to provide a count having twice the sensing resolution as each of the pair counts.

Description

ENCODER WITH IMPROVED SENSING RESOLUTION

BACKGROUND OF THE INVENTION

The present invention relates generally to sensor devices for sensing position, and more particularly to optical encoder sensor devices that sense position by detecting the motion of a member based on alternately allowing and preventing an emitted beam to be detected by a detector.

Optical encoder sensors are used for a variety of sensing tasks. In its most basic and common form, an optical encoder includes an emitter and a detector, where the emitter emits a beam of electromagnetic energy, such as infrared or visible light, at the detector. The detector detects the presence of the beam and outputs a signal indicating to a controller or other connected electronic device when the light is impinging on the detector. To allow the detector to sense motion, a blocking moveable member can be positioned between the emitter and detector. The blocking member includes a series of slots or holes spaced at a predetermined pitch which, when positioned between emitter and detector, allow the beam to pass through the blocking member and impinge on the detector. Motion or position is sensed by moving the blocking member so that light is alternately blocked and allowed to pass through slots. A different signal amplitude is provided by the detector when light is allowed to pass through a slot than when the light is blocked. Thus, the position of a moving component attached to the blocking member can be determined by counting the number of times light is sensed, which indicates the number of slots that have moved past the detector and thus the amount of angular or linear movement of the component. Typically, the slotted blocking member is a disc or a portion of a disc for sensing rotary motion, or a planar member with slots for sensing linear motion.

Computer interface devices are common devices using optical encoders. These devices sense motion of a manipulandum moved by a user and input signals to a computer which can be used to determine the position of the manipulandum. The computer, in turn, can control a graphical object such as a cursor in accordance with the received position. For example, a computer mouse typically uses an optical encoder to sense planar motion of the mouse in two degrees of freedom. The computer updates a position of a cursor on a display screen in accordance with the received mouse position. Other devices such as joysticks, track balls, steering wheels, etc. also commonly make use of encoders, as do a variety of other types of devices. Some computer interface devices require a high sensing resolution. A high sensing resolution allows small motions of a manipulandum to be detected and thus allows .small motions of the cursor to be implemented and displayed. One way to increase resolution of an encoder is to increase the number of slots in the moveable member, i.e. decrease the pitch and width of the slots. However, due to the limits of manufacturing processes, the slots can be provided at a practical, cost effective pitch limit of about 2 mils. To gain a higher sensing resolution beyond this limit, quadrature encoders are often used. These types of encoders include two detectors, where each detector outputs a separate signal. The detectors are arranged under the slotted blocking member such that when one detector is aligned with a first slot to receive the entire portion of the beam through the slot, the other detector is positioned so that it is slightly misaligned with a second slot so as to receive only a part of an equivalent portion of the beam through the second slot. This allows one detector to sense a threshold amount of light before the other detector when the slotted member is moved, and causes the other detector to provide a detection signal out of phase with the first detector. In a typical quadrature embodiment, the detectors provide square wave signals 90 degrees out of phase with each other.

The computer thus receives a detection signal (e.g. a rising or falling edge of the square wave) twice as often as when only a single detector is used, effectively quadrupling the sensing resolution and allowing much finer motion to be detected.

A problem with the existing quadrature encoders is that they do not have a high enough sensing resolution for some applications. For example, force feedback interface devices, such as a force feedback mouse, require a very high sensing resolution since the device uses velocity and position of the manipulandum in the determination of forces to be output by actuators on the device. For realistic and consistent forces to be output, a sensing resolution is needed that is greater than the typical mass-produced quadrature encoder (e.g. used in normal mice) can provide. However, to keep the costs of such interface devices viable for a consumer market, the encoders must be relatively inexpensive. To provide the desired resolution, quadrature encoders having the desired increased resolution are typically too expensive to allow the computer interface device to be viably priced in the consumer market.

SUBSTTTUTE SHEET (RULE 26) SUMMARY OF THE INVENTION

The present invention is directed to an encoder device which provides a higher resolution than typical quadrature encoders. The encoder in a preferred embodiment uses four detectors and four signals in an " octature" configuration.

More specifically, an encoder of the present invention includes an emitter that emits a beam of electromagnetic energy. A number of detectors are included to receive the emitted beam, where the detectors number greater than two. For example, four detectors are preferably provided. Each detector outputs a signal indicative of when the detector receives the beam. In one embodiment, the detector signal includes a high signal when a portion of the beam having a threshold (or greater) intensity is detected by the corresponding detector, and a low signal when intensities lower than the threshold are detected. A moveable member (such as a code disk or strip) is positioned to receive the beam from the emitter, where the moveable member alternately allows and prevents the beam to be received by the detector. The signals output from the detectors are used to sense motion of the moving member relative to the detectors.

The moveable member can be moved in a linear or rotary degree of freedom. Preferably, the moveable member is positioned between the emitter and said detector and includes spaced apart slots, where the slots allow the beam to pass through the moveable member and where portions between the slots block the beam from the detector. In an alternate embodiment, the emitter and detectors are positioned on a same side of the moving member, and the moveable member includes a reflective portion such that the beam is reflected to the detector when the reflective portion is aligned to receive the beam.

The detectors produce electrical signals which are 45 (electrical) degrees out of phase with one another. In a first embodiment of a linear encoder, four detectors are arranged linearly at a varying pitch to produce the out-of-phase signals. In a different embodiment, a reticle is positioned between the moving member and detectors spaced linearly at a constant pitch. The detectors are located in a protective housing which is substantially transparent to the frequency of the electromagnetic emitter energy and the reticle is provided on the housing. The reticle consists of groups of slots, each of the groups corresponding to one of the detectors. The slots within the group are spaced at the constant slot pitch P, while the groups are spaced from each other at a varying pitch. This arrangement causes a detection signal to be 45° out of phase with adjacent detection signals. In one preferred embodiment, the moveable member is coupled to a portion of a computer interface device that provides a position of a manipulandum to a host computer. The rising and/or falling edges of the out of phase signals are counted to provide a count indicating the amount of movement of the moving member. A method for sensing motion at a high resolution using an encoder includes emitting a beam of electromagnetic energy from an emitter and detecting the beam using four detectors, where each of the detectors receives a portion of the beam having a different intensity. A detection signal is output from each of the detectors, each of the detection signals having a different phase. Each signal is preferably 45 degrees out of phase from at least one other of the detection signals. The detection signals are used to sense the motion of a moveable member, which is positioned between the emitter and the four detectors to alternately block and let pass the beam through slots in the moveable member as the member moves. A count is kept and increased when a rising and/or a falling edge of the detection signals are sensed in the proper sequence, where the rising edge is output on a detection signal when a threshold intensity or greater intensity is detected by the detector outputting the detection signal and the falling edge is output when the intensity drops below the threshold. The rising and falling edges of a first pair of the detection signals can be counted while rising and falling edges of a second pair of the detection signals is counted. In a preferred embodiment, the first pair of signals consists of Phase A and Phase C and the second pair of signals consist of Phase B and Phase D. This grouping is advantageous as the relative phase shift between the signals is 90°, allowing the use of existing quadrature detection methods and circuits to provide edge counting information from each of the two pairs. The count information from the pairs are added to provide a count having twice the sensing resolution as each of the pair counts.

The encoder of the present invention advantageously provides a high sensing resolution for a low cost. The use of four detectors (or other number greater than two) and providing four signals out of phase with each other allows a greater amount of detections or counts for a given distance that the moveable member moves, thus allowing the encoder to sense very fine movements. Such fine detection is essential for such devices as force feedback peripherals that require position and velocity data to determine output forces as well as for positioning graphical objects on a computer display. Furthermore, the sensor is compatible with much of the existing electronic components used in processing encoder signals, allowing the encoder to utilized at a very low cost.

These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawing. BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a side elevational view of an encoder of the present invention;

FIGURE 2 is a top plan view of a first embodiment of the encoder of Figure 1;

FIGURES 3a and 3b are top plan views of a second embodiment of the encoder of

Figure 1;

FIGURE 4 is a diagram illustrating detection signals output by the encoder of Figure 1;

FIGURE 5 is a side elevation view of an embodiment of the encoder of the present invention including a reticle;

FIGURE 6 is a perspective view of the encoder embodiment of Fig. 5; and

FIGURE 7 is a top plan view of the slots and detectors of the encoder embodiment of Figs. 5 and 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGURE 1 is a side elevational view of an optical encoder 10 of the present invention. Encoder 10 includes an emitter 12, a detector assembly 14, and a slotted moveable member 16.

Emitter 12 is positioned facing detector assembly 14 and emits a beam 18 of electromagnetic energy at the detector assembly 14. For example, beam 18 is of infrared light in the preferred embodiment; a suitable emitter for use in the present invention is PDI-E910 from Photonic Detectors of Simi Valley CA. Other forms of electromagnetic energy, such as visible light, etc. can also be emitted. Detector assembly 14 is positioned such that multiple detectors of the detector assembly receive the emitted beam when the beam is unblocked. When a detector of detector assembly 14 detects a threshold intensity of energy of beam 18, a signal output from the detector on one of leads 20 is changed to indicate the detection of the beam. For example, the signal output by the detector can change from a low state to a high state, i.e. the signal has a zero voltage amplitude when intensities under the threshold are detected. When energy over the threshold intensity is sensed, a high signal of 1 volt amplitude (or any suitable amplitude above zero) can be output. Emitter 12 and detector assembly 14 are preferably grounded, i.e. rigidly coupled to a ground or reference surface or member.

Moveable member 16 is positioned between the emitter 12 and detector assembly 14. Member 16 can move relative to the emitter 12 and detector assembly 14 in a linear or rotary fashion. Member 16 can move in a linear degree of freedom as described with reference to Fig. 2. Alternatively, the member 16 can move in a rotary degree of freedom as described with reference to Fig. 3. Preferably, the moveable member 16 is coupled to a member or component having a position which is desired to be sensed in a device. For example, the member 16 can be coupled to a roller on a mouse that is moved when the mouse moves, so that the motion/position of the member 16 indicates the position of the mouse. Or, a member of a mechanical linkage can be coupled to the member 16 so that the position of the mechanical member in a degree of freedom can be determined based on the sensed motion of the member 16. Moveable member 16 preferably includes a number of slots that allow beam 18 to pass through, as described in greater detail below.

Encoder 10 is a relative sensor, which means herein that relative motion of the slotted member 16 is preferably sensed. For example, the detector assembly can detect the number of slots on the member 16 that have moved through its detection range since a prior position of the member 16, i.e. the relative position of the slotted member 16 with reference to a previous

SUBSTΓΓUTE SHEET (RULE 26) position of the member 16. In the preferred embodiment, the detector assembly cannot detect the absolute position of member 16 in its degree of freedom.

In other embodiments of encoders, the emitter and detector assembly are positioned on the same side of moveable member 16. Instead of slots being provided in the member 16, strips or areas of reflective material can be provided separated by non-reflective regions. Thus, the emitted beam 18 can impinge on the strips and reflect off the strips to the detector which is placed near the emitter and which detects the beam. The emitted beam 18 does not get reflected to the detector assembly when it impinges on the nonreflecting regions of the member 16, such as portions between the reflective strips. This allows the detector to detect the movement of reflecting portions as the member 16 is moved in its degree of freedom similarly to the embodiment with slots described below.

FIGURE 2 is a top plan view of the encoder 10 viewed along the line 2-2 of Fig. 1. Moveable member 16 is provided with a number of slots 22 which permit portions of beam 18 to impinge on the detector assembly 14. Slots 22 are shown as rectangular in shape, but can alternatively be provided in other different shapes. Moveable member 16 is shown as a linear member or strip that moves in a linear degree of freedom as shown by arrow 26. The member 16 is aligned with respect to the detector assembly so that the slots 22 move such that the slots expose detectors 28 to the beam 18. In the preferred embodiment, there are four different detectors 28a, 28b, 28c, and 28d positioned on or within a housing 30 of the detector assembly. The detectors 28 are arranged in a linear fashion in the described embodiment. Any particular slot 22 passes over each detector 28 as the member 16 is moved in the direction 26 for a sufficient distance. Detectors 28 are preferably photosensitive devices which are sensitive to an intensity of light, as is well known in the art. Each detector 28 is operative to output its own detection signal which indicates whether or not a threshold amount of light is currently being detected. Alternatively, each detector 28 can output an analog signal that is processed by a separate threshold " squaring" circuit to provide the desired square wave signals as shown in Fig. 4.

As shown in Fig. 2, the detectors 28 and/or the slots 22 are arranged so that each detector 28 receives a different amount of intensity of light from beam 18 for any single position of slotted member 16. The portions between the slots may completely or partially block beam 18 from impinging on detector assembly 14. For example, with moveable member 16 at the position shown in Fig. 2, detector 28a receives 100% of the beam portion transmitted through slot 22a, detector 28b receives about 75% of the beam portion transmitted through slot 22b, detector 28c receives about 50% of the beam portion transmitted through slot 22c, and detector 28d receives about 25% of the beam portion transmitted through slot 22d. This arrangement

SUBSTΠTΠΈ SHEET (RULE 26) allows the signals from each of the detectors to be 45 degrees out of phase with the signals from adjacent detectors 28. These signals are described in greater detail with respect to Fig. 4. .

In the embodiment of Figure 2, either detectors 28 or slots 22 are spaced at a varying pitch to provide the 45-degree out of phase signals shown in Fig. 4. Preferably, the detectors 28 are spaced at the varying pitch V while slots 22 are spaced at a constant pitch P. In a preferred embodiment, the distance from the center of detector 28a to the center of detector 28b is equal to an integral number of slot pitches P, plus 1/8 of a slot pitch P. The distance from the center of detector 28a to the center of detector 28c is an integral number of slot pitches P, plus ^lA of a slot pitch P. Finally, the distance from the center of detector 28a to the center of detector 28d is an integral number of slot pitches P, plus 3/8 of a slot pitch P. In sum:

Detector 28a - provides 0 ° phase shifted signal (i.e. reference signal) Detector 28b - located P(N+l/8) from Detector 28a, provides 45 ° phase shifted signal Detector 28c - located P(N+l/4) from Detector 28a, provides 90° phase shifted signal Detector 28d - located P(N+3/8) from Detector 28a, provides 135° phase shifted signal

where P = slot pitch in the moveable member and N = an integer number (-1, 0, 1, 2...). The phase shifts are described in greater detail with respect to Fig. 4.

In still other embodiments, a different number of detectors can be used to each provide its own detector signal. For example, three, five, 12, or 16 detectors can be provided, each detector outputting its own detection signal. When a different number of detectors is used, the phase shifts and pitch of the detectors and/or slots are determined accordingly, similar to the four sensor embodiment described below. When using more than four detectors, practical limits are imposed due to the accuracy of components used. For example, if 16 detectors are used, highly precise components must detect the edge triggers of the detector signals and must avoid confusing one signal edge with a different signal edge due to noise or other variations in the signal. In yet other embodiments, additional detectors 28 can be provided for redundancy to increase accuracy. For example, eight detectors can be provided in the embodiment described below, where each of the signals A, B, C, and D is provided by four detectors sensing the passage of a slot, while the other four detectors provide complementary signals sensing the portions of the member 16 between the slots. Each complementary signal is compared with its associated slot-sensing signal to indicate the accuracy of the sensed data.

FIGURE 3 a is a top plan view of an embodiment of encoder 10 similar to the embodiment of Fig. 2. In Fig. 3a, however, a slotted moveable member 16' has rotary motion about an axis A. For example, moveable member 16' can be a slotted disc or arc. Similar to the embodiment of Fig. 2, moveable member 16' includes slots 22', which are preferably oriented towards the axis A of rotation as shown. Slots 22' may be shaped like a sector or arc of a circle

8 as shown, or may be rectangular shaped as shown in FIGURE 3b. Similarly, detectors 28 can be shaped like a sector as shown in Fig. 3a, or be rectangularly shaped as shown in Fig. 3b.

Slots 22' are positioned to allow portions of beam 18 to impinge on the four detectors 22a', 22b', 22c', and 22d\ Thus, in the position shown in Fig. 3, slot 28a' is letting 100% of a threshold intensity of a beam to impinge on detector 22a' (i.e., allowing enough light to cause a threshold detection), slot 28b' lets about 75% of threshold beam intensity through, slot 28c' lets about 50%) of beam intensity through, and slot 28d' lets about 25%> of threshold beam intensity through. This arrangement causes the signals from the four detectors 28' to be 45 degrees out of phase with respect to the adjacent detector(s). These signals are described in greater detail with respect to Fig. 4.

FIGURE 4 is a graph illustrating the detector signals 50 output by the detectors 28 while the moveable member 16 or 16' is moved. Each waveform is shown in a distance d (horizontal axis) vs. amplitude A (vertical axis) relationship. Signal A is output by detector 28a, signal B is output by detector 28, signal C is output by detector 28c, and signal D is output by detector 28d (or these signals may be output by a threshold circuit that creates the signals 50 from analog outputs of the detectors 28). Each of the signals has a low amplitude when a beam having an intensity below a threshold intensity impinges on the detector, and a high amplitude when the impinging beam has an intensity over the threshold density. This results in a series of pulses, where the rising edge of each pulse indicates the point where a threshold intensity beam is first detected, and the falling edge of each pulse indicates when the intensity of the detected beam falls below the threshold due to the moveable member and the appropriate slot having moved.

The detectors are placed such that they produce electrical signals which are 45 (electrical) degrees out of phase with one another. Signal A is provided at a 0° phase (phase A), signal B is provided at a 45° phase (Phase B), signal C is provided at a 90° phase (Phase C), and signal D is provided at a 135° phase (Phase D). This allows the rising and falling edges of each of the waveforms to be provided at a different point in the motion of the moveable member 16. All of the signals A-D are sent to an electronic device that counts the rising and/or falling edges of the signals, and these counts are used to determine the relative position of the slotted member 16 from a previous sensed position. For example, graph 52 shows the rising and falling edges that occur in all four of the signals during a movement of the member 16 over one and a half periods of signal A. For each period of the signal A waveform, eight edges are detected (four rising, four falling). Thus the encoder 10 is an "octature" encoder: eight counts per period are sensed to provide a high sensing resolution. In some embodiments, only the same edges of a signal 50 are counted once the initial edge is found to provide reliability in sensing the position of member 16. For example, once a rising edge is first detected, then only rising edges of that waveform are counted. Since it is the rising and/or falling edges that are counted to determine how far the slotted member 16 has moved, the encoder of the present invention provides a greater resolution than the encoders of the prior art. In the quadrature encoders of the prior art, only signal A and signal B are provided since only two detectors are used. Using two signals, only four rising and falling edges are provided during movement of the member 16 over the same distance that provides 8 rising and falling edges in the encoder of the present invention. Therefore, the quadrature encoders cannot detect as fine a motion of the slotted member 16 as can the encoder of the present invention. The encoder 10 can provide double the effective sensing resolution of the quadrature encoders.

In one preferred embodiment of the encoder 10, the detector signals 50 are paired to allow compatibility with existing quadrature encoder electronics. For example, signal A is paired with signal C and signal B is paired with signal D. The signals in a pair are thus 90 degrees out of phase, similar to the signals of prior art quadrature encoders. These pairs of signals can each be input to an existing quadrature encoder counting circuit, and the counts from the two counting circuits can be added to provide the actual octature count. For example, the counts for each of the pairs are shown in graphs 54 and 56 in Fig. 4. The A-C signal pair provides a count at rising or falling edges of signal A and signal C, as shown in graph 54, while the B-D signal pair provides a count at rising or falling edges of signal B and signal D, as shown in graph 56. If these two counts are summed at each of the corresponding eight points in a period of signal A, then an increasing count 58 is obtained at the desired higher resolution. This count 58 is provided to appropriate components in the electrical system that can process the encoder counts and determine the current position of the moveable member 16 (relative to the last received position of the member 16).

FIGURE 5 is a side elevational view of a preferred embodiment 60 of the present invention, in which detector assembly 14 includes a reticle. Detector assembly 14 is preferably an integrated package including four photodiodes on a single piece of silicon; for example, Part No. LQ-8176 from Photonic Detectors is suitable to be used as detector assembly 14. Any similar detector assembly providing more than two (preferably four or more) detectors can be used. Detectors 28 are provided within a central area of housing 30 to protect the detectors 28 from impact or damage. Beam 18 is transmitted through the material of housing 30, which is preferably transparent to the frequency of the electromagnetic emitter energy, to impinge on the detectors 28. Leads 20 are coupled to a counter circuit as described above.

A slotted reticle 70 is preferably coupled to the housing 30 and is grounded. Slotted moving member 16 is provided between reticle 70 and emitter 12, similarly to the embodiments described above. Slotted member 16 is moved in a plane parallel to the surface of the reticle 70 in either a linear or rotary degree of freedom. The slots 22 in the member 16 and in the reticle

10 70 are aligned in a predetermined arrangement that allows the detectors to output signals 45 degrees out of phase as shown in Fig. 4. This operation is described in greater detail below,

FIGURE 6 is a perspective view of the detector assembly 14 and moving member 16 of the embodiment 60 shown in Fig. 5, which is a linear encoder. Four detectors 28a, 28b, 28c, and 28d are shown positioned linearly within housing 30 as described with reference to Fig. 5. The detectors are positioned a constant width apart, i.e. with a constant pitch.

Reticle 70 is provided on the surface of the housing enclosing detectors 28. The reticle can be a separate piece (or pieces) of material located some distance from the detector(s), or it can be a layer of opaque material (e.g. aluminum) which is deposited directly upon the surface of the detector assembly housing 30 during the detector fabrication process. The reticle geometry can be produced as a separate manufacturing step (e.g. a mask layer), or as part of an existing chip masking step.

Reticle 70 includes a number of slots 72 which allow beam 18 to pass therethrough. The slots 72 are preferably provided in four different groups 74a, 74b, 74c, and 74d (only two of the groups 74a and 74b are shown in Fig. 6). Each group 74 corresponds to one of the detectors 28.

Each of the groups of slots 74 is spaced from an adjacent group of slots by a predetermined distance, where the distance between groups is different between each of the groups, i.e. the groups have a varying pitch. However, the distance between the slots 76 within a group is constant. This is shown in greater detail with reference to Fig. 7. For example, the width (x- direction) between slots 76 within a group 74 can be about 0.0584 mm, and the distances (x- direction) between the four groups 74 of slots can be about 0.7083 mm, 1.4167 mm, and 2.0666 mm, in that order. Other dimensions can be provided in other embodiments.

Moving member 16 also is provided with a number of slots 20, similarly to the embodiments described above. The slots 20 are preferably spaced with a constant pitch, since it is the irregular spacing between the groups 74 of slots on the reticle that provides the phase difference between detection signals. As an example, the slots 20 can be spaced about 0.0584 mm apart and have a width of about 0.0292 mm. Both slots 20 and slots 76 are preferably at least as long (y-direction) as the detectors 28 in the y direction.

FIGURE 7 is a top plan view showing the slots 20 of moving member 16, the slots 76 of reticle 70, and the detectors 28 of Fig. 6. Slots 20 of the moving member 16 are positioned over the slots 76 of the reticle, which are shown in dashed lines. The detectors 28 (in dashed lines) are positioned below the reticle. As shown, the group 74a of slots 76 are completely aligned with slots 20 so that the beam 18 may pass through the full width of the slots 20 to the detector 28a. The area through which the beam 18 may pass through is shown as areas 80. The group 74b of slots 76 is positioned away from group 74a by a distance dl, so that only a partial

11 alignment between the slots of group 74b and the slots 20 over the group 74b occurs when the slots of group 74a are fully aligned with the slots 20. In the preferred embodiment, about 75% of the width of slots 20, shown as areas 82, is available to allow beam 18 to pass through to the detector 28b. Likewise, group 74c of slots 76 is positioned a distance d2 from the group 74b of slots. This causes a partial alignment between slots 76 of group 74c and near slots 20 such that about 50%) of the width of slots 20, shown as areas 84, is available to allow beam 18 to pass through to the detector 28c. Finally, group 74d of slots 76 is positioned a distance d3 from the group 74c of slots, causing a partial alignment between slots 76 of group 74d and near slots 20 such that about 25% of the width of slots 20, shown as areas 86, is available to allow beam 18 to pass through to detector 28d.

The slots 20 and 76 are provided with sufficient width to cause a threshold detection of beam 18 by a detector 28 only when more than 50%> of the width of slots 20 allows beam 18 to pass through to a detector (other percentages of slot width can be used in other embodiments). Thus, the position of slotted member 16 shown in Fig. 7 will cause a high signal in Signals A and B as shown in Fig. 4. As the slotted member 16 is moved in the direction of arrow 90, the group 74c of slots will align with slots 20, allowing more than 50% of the slot width to pass beam 18, and causing a high detection signal on Signal C. As the slotted member is still moved, group 74d of slots will similar align to cause a high signal on Signal D. However, as the slotted member is moved further, the group 74a of slots will only become less than 50% aligned so that the intensity of the beam 18 will drop below the detection threshold, causing Signal A to go low.

A similar procedure is followed as the slotted member is continued to be moved in direction 90: each group 74 of slots will become less than 50% aligned with slots 20 at a particular point to cause its output signal to go low. The process then repeats.

The distances dl, d2, and d3 are thus calculated to position the groups 74 of slots apart from each other to cause the 45 degree phase difference between detector output signals.

Preferably, the distances dl, d2, and d3 are determined similarly to the spacing between detectors as described above with reference to Fig. 2.

The advantage to using reticle 70 is that a higher sensing resolution can be obtained than in the embodiment of Fig. 2. If the size of each detector 28 is limited to the size of the slot 22 as shown in Fig. 2, then the slots must have a relatively large width, since the size of a detector 28 is limited by manufacturing processes. However, if the detector 28 is allowed to be the size of a group 74 of slots as in the embodiment of Figs. 5-7, then the slots 22 in member 16 (and slots 76 in the reticle) may be made with a much smaller width. The smaller the width of slots 22, the greater resolution is obtained, since very fine motions of the member 16 can then be detected. If close to the minimum cost effective pitch is used for slots 22 (typically about 2 mils), then the

12 octature embodiment of the present invention can provide a sensing resolution equivalent to providing slots with about a 0.25-mil pitch.

Detectors 28 do not have to be arranged linearly; they could be provided in a staggered, non-sequential, or radial pattern (rotary encoder), for example, depending on the application. For example, although only an embodiment showing linear motion of member 16 is shown, a similar technique can be used to detect rotary motion of member 16. In such an embodiment, the slots 76 and 20 can be arranged in a radial manner toward an axis of rotation, as described with reference to Fig. 3. The embodiment of Fig. 7 can also be provided using reflective strips for slots 20 instead of apertures, where the emitter 12 and detectors 28 are provided on the same side of member 16 and where reticle 70 with slots 76 is placed between the emitter/detectors and the member 16. Furthermore, any number of detectors greater than two can be provided in encoder 60 to enhance the sensing resolution of the encoder.

While this invention has been described in terms of several preferred embodiments, it is contemplated that alterations, permutations and equivalents thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings.

Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention. It is therefore intended that the following appended claims include all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.

What is claimed is:

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Claims

C L A I M S

1. An encoder providing a high sensing resolution, the encoder comprising:

an emitter that emits a beam of electromagnetic energy;

a number of detectors receiving said beam, wherein said detectors number greater than two, each detector outputting a signal indicative of when said detector receives said beam; and

a moveable member positioned to receive said beam from said emitter, said moveable member alternately allowing said beam to be received by said detector and preventing said beam from being received by said detector;

whereby said signals output from said detectors are used to sense motion of said moveable member relative to said detectors.

2. An encoder as recited in claim 1 wherein said number of detectors is four.

3. An encoder as recited in claim 2 wherein said moveable member is moved in a linear degree of freedom.

4. An encoder as recited in claim 2 wherein said moveable member is moved in a rotary degree of freedom.

5. An encoder as recited in claim 2 wherein said moveable member is positioned between said emitter and said detector, said moveable member including spaced apart slots, wherein said slots allows said beam to pass through said moveable member and wherein portions between said slots block said beam from said detector.

6. An encoder as recited in claim 2 wherein said emitter and said detectors are positioned on a same side of said moveable member, and wherein said moveable member includes a reflective portion such that said beam of said emitter is reflected to said detector when said reflective portion receives said beam.

7. An encoder as recited in claim 2 wherein said detectors each provide a signal that is 45 degrees out of phase with a signal from a different one of said detectors.

8. An encoder as recited in claim 5 wherein each of said detectors is spaced at a varying pitch from adjacent detectors.

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9. An encoder as recited in claim 2 further comprising a reticle positioned between said emitter and said detectors, said reticle including a plurality of slots and maintaining a stationary position relative to said detectors.

10. An optical encoder providing high sensing resolution, said encoder comprising:

an emitter that emits a beam of electromagnetic energy;

a number of detectors receiving said beam, wherein said detectors number greater than two, each detector outputting a signal indicative of when said detector receives said beam;

a moveable member positioned between said emitter and said detectors, said moveable member including a plurality of slots that alternately allow said beam to be received by said detector and blocking said beam from being received by said detector when said moveable member is moved; and

a reticle positioned between said moveable member and said detectors, said reticle including a plurality of reticle slots;

11. An optical encoder as recited in claim 10 wherein said number of detectors is four.

12. An optical encoder as recited in claim 11 wherein said detectors are provided in a housing, and wherein said reticle is coupled to said housing.

13. An optical encoder as recited in claim 12 wherein at least a portion of said housing between said reticle and said detectors is transparent to said beam and allows said beam to impinge on said detectors.

14. An optical encoder as recited in claim 13 wherein at least a plurality of said slots of said reticle are spaced at a varying pitch, and wherein said slots of said moveable member are spaced at a constant pitch.

15. An optical encoder as recited in claim 14 wherein said slots of said reticle are provided in four groups, each of said groups corresponding to one of said detectors, wherein

15 slots within each of said groups are spaced at a constant pitch, and wherein said groups are spaced from said other groups at a varying pitch.

16. An optical encoder as recited in claim 11 wherein said moveable member is coupled to a portion of a computer interface device that provides a position of a manipulandum to a host computer.

17. A method for sensing motion at a high resolution using an encoder, the method comprising:

emitting a beam of electromagnetic energy from an emitter;

detecting said beam using four detectors, wherein each of said detectors receives a portion of said beam having a different intensity;

outputting a detection signal from each of said detectors, each of said detection signals having a different phase; and

using said detection signals to sense the motion of a moveable member.

18. A method as recited in claim 17 wherein said moveable member is positioned between said emitter and said four detectors to alternately block and let pass said beam through slots in said moveable member as said moveable member moves.

19. A method as recited in claim 18 wherein each of said detection signals is 45 degrees out of phase from at least one other of said detection signals.

20. A method as recited in claim 19 further comprising adding to a count when a rising or a falling edge of said detection signal is sensed, wherein said rising edge is output on a detection signal when a threshold intensity or greater intensity is detected by said detector outputting said detection signal.

21. A method as recited in claim 20 wherein said rising and falling edges of a first pair of said detection signals are counted while said rising and falling edges of a second pair of said detection signals is counted, wherein said counts of said first and second pairs are added to provide a count having twice a sensing resolution as each of said pair counts.

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