WO2000058050A1

WO2000058050A1 - Laser inscribing system with traversing laser head

Info

Publication number: WO2000058050A1
Application number: PCT/US2000/008177
Authority: WO
Inventors: Frank Eble; James R. Huntley
Original assignee: Sig Positec Automation, Inc.
Priority date: 1999-03-26
Filing date: 2000-03-24
Publication date: 2000-10-05

Abstract

A laser inscribing system including an input/output controller (20), a motion controller in communication with the input/output controller (20), an electric motor (16a) controlled by the motion controller, a slide (14a) coupled to the electric motor, a traversing laser head (12) coupled to the slide to provide for actuation of the traversing laser head in a first dimension; a laser (13) coupled to the traversing laser head (12), the laser (13) directing a laser beam at a surface to create an inscription, where the laser is triggered by the motion controller, and a variable diffraction crystal to diffract the laser beam in a second dimension.

Description

LASER INSCRIBING SYSTEM WITH TRAVERSING LASER HEAD

BACKGROUND OF THE INVENTION

The present invention relates to a motion control apparatus. More specifically the present invention relates to a laser inscribing apparatus utilizing a traversing laser.

The inscribing, imprinting or etching of images on various surfaces, particularly glass surfaces, has become increasingly important in recent years for the identification and decoration of objects. For example, in the identification of automobiles, trucks and the like, vehicle identification numbers (VI N) or other identifying marks are inscribed on the windows of the vehicle to provide a non-removable identification (permanent mark) for the vehicle.

Traditionally, the inscription process is accomplished by mechanical or chemical means. Tools such as routers can inscribe surfaces by mechanically removing part of the surface material. Another mechanical method of inscribing a surface is sandblasting. In sandblasting a stream of high velocity particles is directed at a surface overlaid with a stencil. The high velocity particles impacting the surface areas not covered with the stencil will remove part of the surface material creating an image corresponding to the stencil. Chemical etching with a stencil is also a common method of etching surfaces in combination with a chemical etching. The chemical etchant reacts with the surface to etch an image corresponding to the stencil shape.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for inscribing a surface using a traversing laser head. The laser head is mounted on multi-axis traversing slides driven by electric motors. The electric motors are coupled to a motor control system which is further integrated to a laser control system. The laser will be pulsed in accordance with the position of the traversing laser head in a first plane and the laser pulses will further be directed in a second plane by an opto-electronic converter such as a crystal having an electrically controlled index of diffraction. The pulsing of the laser will form a pattern comprising a series of scored points similar to a dot matrix image. Position information for the traversing laser head will be provided by a motor control system and communicated to the laser control system to provide for the synchronized firing of the laser. The motor and laser control systems may be further integrated to a factory control system to seamlessly integrate the laser inscribing process into a production line. To ensure repeatability and accuracy of the laser scoring executed by the present invention, multiple microprocessors or controllers are utilized to process input/output (I/O), motion control, and laser firing. In this manner, the motion control and firing of the laser are not subject to the scan time delays of a traditional centralized industrial controller (i.e. the industrial controller is used for all control functions including motion control and I/O processing) such as a programmable logic controller (PLC). Such scan time delays are unacceptable in a laser firing and positioning system since the time delays will result in small shifts of the laser and a resultant laser score pattern that is shifted. The controller used to move and trigger the laser may be configured with specific motion profiles transmitted to a laser controller containing associated message patterns and score patterns, where upon receipt of a control command to score a specific pattern, the motion control will be fully integrated to the firing of the laser, resulting in a precise score pattern.

In one embodiment of the invention, the surface being inscribed by the present invention is glass or any other inorganic oxide. The glass may be automotive glass and the pattern to be inscribed may be a VIN, part tracking code, manufacturer identification, or any other pattern suitable for replication glass. The laser used must have an emission to which glass is not optically transparent. An eximer or CO² laser provides a beam which is highly effective for etching glass. In materials where the surface being inscribed is not transparent, a YAG laser may be used. It is understood that the selection of a laser emission source is dependent on the surface being inscribed. All surfaces which may be inscribed with a laser, including organic and inorganic materials, are considered within the scope of the present invention.

In the operation of the present invention, the laser traversing head is moved to generally the desired position in the y plane using the belt driven slides. The laser traversing head is then moved in only the x plane to traverse the area to be scored. As the laser traversing head is moved in the x-plane, the movement of the laser beam in the y-plane is provided by the opto-electronic crystal. Thus, as the laser head is traversed by a belt driven slide in one plane the crystal is modulated with a charge or RF signal to vary the laser beam position in an additional plane. A two dimensional character can then be easily inscribed onto a surface. In alternate embodiments of the present invention, the traversing laser head is configured to move in three planes. While Cartesian coordinates have been discussed above, any other coordinate system may be used to describe the traverse of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an illustration of the laser control system of the present invention;

Figures 2a and 2b are illustrations of the end products of a sandblasted surface and a laser inscribed surface; Figure 3 is a connection diagram of the stepper motor drive of the present invention;

Figures 4a and 4b are block diagrams of a prior art motion control system and the motion control and laser control system of the present invention;

Figure 5 is a perspective drawing of the laser control system of the present invention;

Figure 6 is a cross-sectional diagram of the laser of the present invention;

Figure 7 is a diagrammatic illustration of the laser operation of the present invention; and

Figure 8 is a diagrammatic illustration of the AOD operation of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the present invention is merely exemplary in nature and is in no way intended to limit the invention or its uses. Moreover, the following description, while depicting control system designed to operate with stepper motors, is intended to adequately teach one skilled in the art to make and use a control system for a variety of motor technologies, including, but not limited to, DC brushless motors, AC motors, and any other type of servo motors.

Referring to Figure 1 , the laser traversing system is shown generally as 10. A traversing laser head 12 having a laser 13 is coupled to two traversing slides 14a and 14b to position the laser head 12 over a surface 15 to be scored. The surface 15 is preferably a sheet of glass moving along a conveyor belt. The traversing slides 14a and 14b are preferably belt driven but may also be screw driven. Stepper motors 16a and 16b are coupled to the belts of the traversing slides 14a and 14b to provide for actuation. The stepper motors 16a and 16b are preferably directly coupled to the belts to provide a stiff coupling but in alternate embodiments gear boxes such as worm gears, planetary gears or the like may be used to couple the stepper motors 16a and 16b and the belts. Stepper motor controllers or drives 18a and 18b are mounted onto the frame of the system 10. The stepper motor drives 18a and 18b provide control commands and power to the stepper motors 16a and 16b and are electronically linked to the laser controller 20 that may also be seen in Figure 5. The laser controller 20 further includes an operator interface 22 to enable an operator to program the laser controller 20. A second motor control operator interface 24 allows an operator to program and operate the motor controllers 18a an 18b. Referring to Figure 4a and 4b, a prior art motor control system and the laser motion controller of the present invention are detailed. The prior art system 40 includes a standard motor drive 42, a PLC 44, a printer 46, and an encoder 48 providing a signal to the PLC 44 and printer 46. The PLC 44 handles both the I/O control and the generation of a position command to the motor drive 42. As discussed previously, the scan time of the PLC will lead to delays in the execution of the motion control, creating time-shifted scored patterns.

The system 10 of the present invention shown in Figure 4b, eliminates scan time delays by separately processing I/O with an I/O processor 50 and motion with a motion processor 52 within the motor controller 18. This dual processing architecture removes scan time delays caused by I/O processing normally done in conjunction with motion control. The motion processor 52 and I/O processor 50 may comprise any known microprocessor, microcontroller, indexer chip or similar control apparatus known in the art but is not limited to such.

Stepper motors are the preferred electric motors 16 of the present invention because of their digital motion control, high ruggedness, construction simplicity, high reliability, high break-away torque, and open loop control. Steppers also provide excellent torque throughout their entire speed range, eliminating the need for a gear box. The stepper motors of the present invention may comprise permanent magnet stepper motors, variable reluctance stepper motors or hybrid stepper motors. While feedback is not required for the stepper motor an encoder, resolver, or tachometer may be provided on the motor for speed and/or position feedback to the motion controllers 18 and the laser controller 20. Other servo motor technologies such as DC brushless, AC, DC, Vector or other types of servo systems are also considered within the scope of the present invention.

In operation, the stepping motors 16a and 16b move in response to an operator command entered into the operator interface 24 or move in response to a position/motion signal from an external control system. The operator command is translated into digital or analog position and/or motion command(s) that are transferred to the drives 18a and18b. The drives 18a and 18b generate a sequence of digital input commands to the stepper motors 16a and 16b. The stepping of the motors 16a and 16b occurs in strict accordance with the digital input commands. The benefits of this operation include: step error is noncumulative, the absolute position error is independent of the number of steps taken, and the shaft position is predictable. Thus the position of the motor shaft can be determined from the digital input commands generated by the drives 18a and 18b, eliminating the need for an additional feedback device. The stepping resolution of the present invention should approach 0.1 mm/step and 0.01 mm/microstep.

Referring to Figure 3, a connection diagram of the stepper motor drive 18 is illustrated. The stepper motor drive 18 includes numerous communications inputs and outputs such as digital I/O, analog I/O, and communication interfaces. Single phase 115 or 230 Volt AC power is provided by facility power, via switchbreakers 36, and 24 Volt DC power is provided by power supply 38. The single phase 115 or 230 volt AC power is used to drive the stepper motor 16 and the 24 volt DC power is used for control logic. A portion of the I/O is connected to the drive 18 through connector 26. The connector 26 may be wired with numerous devices such as pushbuttons, switches, operator interfaces, pilot lights, relays, and other similar control devices that are all represented with the reference numeral 28 in Figure 3 connected to pins of connector 26. The LEDs 27 in Figure 3 are indicators for the signal status of the I/O of connector 26.

The drive 18 further includes a line encoder input 29 and a motor encoder input 30. The line encoder input 28 is connected to an encoder on an assembly line such that the drive 18 is able to monitor the speed of the assembly line. A motor encoder coupled to a motor 16 driven by drive 18 provides speed and position of the motor 16 in real time and coordinates the firing of the laser 13. A high speed serial output 31 , preferably a twisted pairTTL level RS 422 interface, transfers print command signals to the laser controller 20 in conjunction with an interrupt driven high speed digital output in the connector 26. A serial input 32 is included on the drive 18 to allow a programmer to download programs or data to the drive 18 and/or to transfer control information and data between the drive 18 and an external control system. The serial communication protocol may be RS232, RS 422, RS485, or any other similar serial interface, but is not limited to such. In practice, an engineer will construct a program offline on a programming device such as a personal computer where it will be compiled and downloaded onto the stepper motor drive to be burned onto an EEPROM or other nonvolatile memory storage. The stepper motor drive 18 is equipped with a microprocessor to interpret and execute the program burned onto the EEPROM. In alternate embodiments of the present invention, the EEPROM may be replaced with an alternate EEPROM to reprogram the drive 18. The operator interface 24 provides for operation and monitoring of the drives. The operator interface 24 is linked, via an RS485 connection 34, to the Drive 18. The operator interface accepts discrete, integer, and floating point inputs and also outputs discrete, integer, and floating point outputs. An operator may view drive status and enter complex commands such as speed, current limit, and position on the operator interface 24.

The laser 13 is mounted on the traversing laser head 12 and is pulsed to inscribe a surface material. An example of a laser inscribed surface is shown in Figure 2b and may be compared to a sandblasted surface shown in Figure 2a. In operation, the traversing laser head 12 is moved to the desired x, y (or z when three slides are used) position by use of the traversing slides 14. The laser controller 20, in communication with the stepper motor drives 18, is given a fire or print go command from the stepper motor drives 18, via the serial port 31 or the interrupt driven high speed digital output. In a first embodiment of the present invention, the laser controller 20 is instructed to fire by the drive 18 for each pixel. In a second embodiment, the laser controller 20 has been preprogrammed to score a particular pattern after a print go command has been received, via serial port 31 or the interrupt driven high speed digital output. In this second embodiment, the laser controller 20 will synchronize the firing of the laser 13 to create a score pattern with encoder pulses received from the stepper motor 16 with stored motion profiles corresponding to the score pattern. In this manner the firing of the laser 13 will be synchronized with the movement of the stepper motor 16.

The laser 13 depicted in Figure 6 and 7 is illustrated in cross section and in diagrammatic form. The laser 13 includes a laser tube 60 containing a medium (a mixture of carbon dioxide, helium, and nitrogen gases is contained in a cavity of parallel mirrors 62. The rear mirror 62a reflects substantially all the energy and the front mirror 62b is partially transparent to allow a laser beam to travel through the front mirror 62b. A turning mirror 70 allows the laser beam to be redirected 90 degrees to score horizontal surfaces. Inside this cavity of parallel mirrors 62, the light is reflected in the same wavelength as the desired laser beam or emissions. When the flux of photons, excited by RF energy, exceeds an energy threshold, the laser beam is obtained. Once the laser beam has been generated it is directed to an opto-electronic crystal or acoustical optical deflector (AOD) 64 which deflects the beam to score dots in different positions on the target surface. Each character scored on the surface is considered a dot matrix, in which each dot is deflected at a different angle ( A dot matrix is nothing more than the rectangular pattern of dots that make up each character.) The AOD 64 is the component that deflects the laser beam into different angles in the vertical axis to form the desired score pattern.

Referring to Figure 8, the AOD 64 is controlled by RF energy. By varying the RF energy applied to the AOD 64, the index of refraction of the AOD 64 is varied. The variable refractive properties of the AOD 64 enable a laser beam to be directed in multiple directions. The RF energy or charge applied to the AOD 64 is controlled by laser controller 20. The AOD 64 in the preferred embodiment is configured to vary the laser beam in the y direction. As discussed previously, in the operation of the present invention, the traversing laser head 12 is moved in the x direction by the slide 14a across the surface to be inscribed. Thus, the positioning of the laser pulses is done in both the x and y direction to provide for the inscription of two-dimensional images or characters. An additional actuator may be included to position the traversing laser head 12 in the Z direction.

The system 10 of the present invention may be integrated to an external control system such as those used in a manufacturing plant through numerous electronic connections. As discussed previously, the system 10 is equipped with digital inputs and outputs for start and stop instructions, status, error codes and other similar types of digital information. A network connection such as CAN, DeviceNet, Interbus, Profibus DP 485 or other similar communication interface may also be included in the motor controller 18 or the laser controller 20 to allow for the transfer of large amounts information between the system 10 and an external control system. These various communication methods allow for the seamless integration of the control system 10 of the present invention with an external control system.

It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

I CLAIM

1. A laser inscribing system comprising: an input/output controller; a motion controller in communication with said input/output controller; an electric motor controlled by said motion controller; at least one slide coupled to said electric motor; a traversing laser head coupled to said at least one slide to provide for actuation of said traversing laser head in a first dimension; a laser coupled to said traversing laser head, said laser directing a laser beam at a surface to create an inscription, wherein said laser is triggered by said motion controller; and a variable diffraction crystal to diffract said laser beam in a second dimension.

2. The laser inscribing system of Claim 1 wherein said input/output controller is a microprocessor.

3. The laser inscribing system of Claim 1 wherein said electric motor is coupled to said slide with a gearbox.

4. The laser inscribing system of Claim 1 wherein said input/output controller is electronically coupled to said laser via a high speed output.

5. The laser inscribing system of Claim 1 wherein said motion controller is an indexer chip.

6. The laser inscribing system of Claim 5 wherein said indexer chip generates and stores motion profiles for said electric motor.

7. The laser inscribing system of Claim 1 wherein said electric motor is a stepper motor or servo motor.

8. The laser inscribing system of Claim 1 wherein said electric motor includes a speed and position feedback apparatus.

9. The laser inscribing system of Claim 1 wherein said slide is a belt driven slide.

10. The laser inscribing system of Claim 1 wherein said laser is a CO2 laser.

11. The laser inscribing system of Claim 1 further comprising a laser controller in communication with said motion controller.

12. The laser inscribing system of Claim 11 wherein said laser controller stores messages and images corresponding to a laser score pattern.

13. The laser inscribing system of Claim 11 wherein said laser controller receives high speed control triggers from said motion controller corresponding to said images and messages stored in said laser controller.

14. The laser inscribing system of Claim 11 wherein said laser controller receives serial data from said motion controller to select at least one of said images and messages stored in said laser controller to score on said surface.

15. A laser inscribing system comprising: an input/output controller; a motion controller in communication with said input/output controller, said input/output controller and motion controller contained in a motor drive; an electric motor controlled by said motion controller; at least one slide coupled to said electric motor; a traversing laser head coupled to said at least one slide to provide for actuation of a traversing laser head; a laser controller in communication with said motion controller and said input/output controller; a laser controlled by said laser controller, said laser coupled to said traversing laser head, said laser directing a laser beam at a surface to create an inscription, wherein said laser is triggered by said motion controller; and a variable diffraction crystal to diffract said laser beam.

16. The laser inscribing system of Claim 15 wherein said motion controller communicates with said laser controller via a high speed output.

17. The laser inscribing system of Claim 15 wherein said electric motor is a stepper motor or servo motor.

18. The laser inscribing system of Claim 15 wherein said laser beam is used to inscribe automotive glass.

19. A method of inscribing a surface comprising; providing a motion controller; providing a laser controller; moving a laser across the surface in a first dimension with an electric motor controlled by said motion controller; diffracting a laser in a second dimension with an opto-electronic diffraction apparatus controlled by said laser controller, wherein a two dimensional character may be inscribed on the surface.

20. The method of claim 19 further comprising the step of providing an I/O controller to process I/O for said motion controller.

21. The method of Claim 19 wherein said surface is automotive glass.