Method and apparatus for performing work in a three dimensional space

• US 4,639,653 A
• Filed: 04/15/1985
• Issued: 01/27/1987
• Est. Priority Date: 04/15/1985
• Status: Expired due to Fees

• Current Assignee: Applied Microbotics Corporation
• Original Assignee: Applied Microbotics Corporation
• Inventors: Klintz, Jerry A., Pilarski, James A., Anderson, Robert L.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): BERGMANN, SAUL
• Application Number:
  US06/723,552
• Time in Patent Office: 652 Days
• Field of Search: 318/599, 318/568, 318/570, 318/571
• US Class Current: 318/599
• CPC Class Codes: G05B 19/253 with speed feedback only
• CPC Class Codes: G05B 19/4141 characterised by a controller or microprocessor per axis
• CPC Class Codes: G05B 2219/33204 Optocoupler, galvanic separation, isolation
• CPC Class Codes: G05B 2219/33337 For each axis a processor, microprocessor
• CPC Class Codes: G05B 2219/34367 Interrupts, different tasks foreground, midground, background
• CPC Class Codes: G05B 2219/34466 Bad circuits, watchdog, alarm, indication
• CPC Class Codes: G05B 2219/35438 Joystick
• CPC Class Codes: G05B 2219/37103 Limit, proximity switch
• CPC Class Codes: G05B 2219/37313 Derive speed from position
• CPC Class Codes: G05B 2219/41089 Align, calibrate control so that one pulse or signal represents certain movement
• CPC Class Codes: G05B 2219/41285 Dynamic brake of ac, dc motor
• CPC Class Codes: G05B 2219/41358 Transmission, variable gear ratio
• CPC Class Codes: G05B 2219/42231 Detent, stop lock, current through motor in stop, locked, hold, blocked position
• CPC Class Codes: G05B 2219/42237 Pwm pulse width modulation, pulse to position modulation ppm
• CPC Class Codes: G05B 2219/42326 Protection servo for saturation of amplifier
• CPC Class Codes: G05B 2219/43158 Feedrate override
• CPC Class Codes: G05B 2219/49289 Large transmission ratio
• CPC Class Codes: G05B 2219/50048 Jogging
• CPC Class Codes: G05B 2219/50198 Emergency stop
• CPC Class Codes: Y10T 409/300896 with sensing of numerical information and regulation without mechanical connection between sensing means and regulated means [i.e., numerical control]

Abstract

Method and apparatus for moving a workpiece and/or a tool to various locations in a three-dimensional space to perform operations on the workpiece wherein a micro-computer numeric control system is used to provide a multi-axis motion control system using DC electric servo motors, each of which responds to its own control system to operate mechanisms which cooperate to perform the desired operations on the workpiece.

Claims

1. A method for controlling the relative movement of a workpiece and a tool in a three dimensional space so as to perform desired operations on the workpiece comprising:

providing a motor control means for moving at least one of said workpiece and tool in a direction along an x, y or z axis; and

generating a signal by concurrently performing a first set of tasks including foreground tasks, midground tasks and background tasks;

transmitting said signal to a motor control board;

generating another signal by said motor control board by concurrently performing a second set of tasks including foreground tasks, midground tasks and background tasks; and

using said another signal to operate said motor control means.

2. A method as in claim 1 and further comprising:

executing said foreground tasks of said first set of tasks at periodic time intervals.

3. A method as in claim 2 and further comprising:

generating a set of coordinates for said x axis and said y axis by said midground tasks of said first set of tasks; and

executing said generation of coordinates at periodic time intervals.

4. A method as in claim 3 wherein:

said periodic time interval for said foreground tasks is about 1 millisecond; and

said periodic time interval for said generation of coordinates is about 10 milliseconds.

5. A method as in claim 3 wherein said set of coordinates is generated by:

dividing a 360°

circle into eight sectors so that the angle trim in radians is always a fraction less than 1;

executing said midground and background tasks during each of said time intervals.

6. A method as in claim 3 and further comprising:

executing said foreground tasks of said second set of tasks at periodic time intervals.

7. A method as in claim 6 and further comprising:

executing said midground and background tasks of said second set of tasks during said periodic time interval of said foreground tasks of said second set of tasks.

8. A method as in claim 7 wherein:

said periodic time interval for said foreground tasks of said second set of tasks is about 200 microseconds.

9. A method as in claim 7 wherein said midground tasks include:

controlling the velocity mode of each of said motor control means using pulse width modulation.

10. A method as in claim 9 wherein said controlling of said velocity mode of each of said motor control means comprises:

calculating the PWM for said motor control means using the formula;

space="preserve" listing-type="equation">PWM=(Cv)×

(Vc)+PWM.0.+(Cg)×

(Vc-Va)

where;

PWM is the new pulse width required

Cv is the slope of the velocity gradient

Vc is the command velocity

PWM.0. is the PWM required to turn the motor

Cg is the velocity servo gain

Va is the actual velocity.

11. A method as in claim 9 wherein said controlling of said velocity mode of each of said motor control means when said motor is near a stop lock position comprises:

calculating the PWM for said motor control means using the formula;

space="preserve" listing-type="equation">PWM=PWM.0.+(Cp)×

(De)+(Cd)×

(Va)

where;

PWM is the desired pulse width

PWM.0. is the PWM required to turn the motor

Cp is the position servo gain

De is the distance error

Cd is the coefficient of velocity damping

Va is the actual velocity.

12. A method as in claim 9 and further comprising:

using a DC servo electric motor as said motor; and

operating said DC servo electric motor at a relatively high voltage.

13. A method as in claim 12 wherein:

said relatively high voltage is about 160 volts.

14. A method as in claim 12 and further comprising:

connecting a rotatable member to said motor so that rotation of said motor rotates said rotatable member;

connecting said workpiece to said rotatable member so that rotation of said rotatable member moves said workpiece; and

establishing a relatively high speed drive ratio between about 2.4 and 3.2 to 1 between said rotatable member and said DC servo electric motor.

15. A method as in claim 14 wherein:

said ratio between about 3.2 to 1 is along said x and y axis; and

said ratio between about 2.4 to 1 is along said Z-axis.

16. A method as in claim 7 and further comprising:

using a DC servo electric motor as said motor;

connecting a rotatable member to said motor so that rotation of said motor rotates said rotatable member;

connecting said workpiece to said rotatable member so that rotation of said motor rotates said rotatable member;

using the damping characteristics of said DC servo electric motor to hold said workpiece in a locked position.

17. A method as in claim 16 and further comprising:

maintaining the electrical circuit for said DC servo electric motor closed so as to use said dampening characteristic of said DC servo electric motor.

18. A method as in claim 16 and further comprising:

placing compensating inductors around at least four chokes so that either of two pairs provides the inductive compensation to maintain said electrical circuit closed.

19. A method as in claim 18 wherein said electrical circuit comprises:

flowing current in two halves of a cycle through said electrical circuit;

flowing current in the first half of the cycle from a high voltage direct current source, through a power transistor, said DC servo electric motor in a positive direction, a choke, a power transistor and back to said high voltage direct circuit source; and

flowing current in the second half of the cycle from said high voltage direct current source, through a power transistor, said DC servo electric motor in a negative direction, a choke, a power transistor and back to said high voltage direct current source.

20. A method as in claim 19 and further comprising:

controlling the inductance in said electric circuit to about 15 mH.

21. A method as in claim 19 and further comprising:

generating a signal to be fed to said electric circuit for controlling the movement of said DC servo electric motor;

processing said signal by an opto-isolator chip; and

feeding said signal to said DC servo electric motor.

22. In apparatus for use in moving a movable element in a computer controlled mechanism wherein the movable element is connected to a rotatable member so that rotation of the rotatable member moves the movable element and wherein the rotatable member is rotated by a DC servo electric motor, the improvement comprising:

means for establishing a relatively high speed drive ratio of between about 2.4 and 3.2 to 1 between said rotatable member and said DC servo electric motor.

23. The improvement as in claim 22 wherein:

said DC servo electric motor operates at a relatively high DC voltage.

24. The improvement as in claim 23 wherein:

said relatively high DC voltage is about 160 volts.

25. The improvement as in claim 24 wherein said means for establishing a relatively high drive ratio includes:

a belt drive means.

26. The improvement as in claim 25 wherein said belt drive means comprises:

a first pulley secured to the free end of the shaft of said DC servo electric motor;

a plurality of spaced apart teeth on the periphery of said first pulley;

a second pulley secured to the free end of said rotatable member;

a plurality of spaced apart teeth on the periphery of said second pulley;

said second pulley having a diameter greater than the diameter of said first pulley;

a continuous cog belt having a plurality of spaced apart cogs on the inner surface thereof; and

said continuous cog belt being trained around said first and second pulleys so that said cogs mesh with said plurality of teeth on said first and second pulleys so as to provide a positive drive between said DC servo electric motor and said rotatable member.

27. The improvement as in claim 22 wherein:

said DC servo electric motor is controlled solely by an optical encoder.

28. The improvement as in claim 27 wherein:

said optical encoder utilizes a disk having about 500 lines per revolution.

29. The improvement as in claim 28 wherein said optical encoder includes:

a transparent disk having a plurality of radially extending lines thereon;

a first light emitting diode positioned adjacent to one side of said disk and opposite to said plurality of lines; and

a first photo transistor positioned adjacent to the other side of said disk and opposite to said plurality of lines so that light emitted by said first light emitting diode may pass through an area between adjacent lines and be picked up by said first photo transistor.

30. The improvement as in claim 29 and further comprising:

a second light emitting diode positioned to said one side of said metal disk and opposite to said plurality of lines;

a second photo transistor positioned adjacent to said other side of said disk and opposite to said plurality of lines so that light emitted by said second light emitting diode may pass through an area between adjacent lines and be picked up by said second photo transistor; and

said second light emitting diode and said second photo transistor are spaced 90°

from said first light emitting diode and said first photo transistor.

31. Apparatus for controlling the relative movement of a workpiece and a tool in a three-dimensional space so as to perform desired operations on the workpiece comprising:

means for mounting a workpiece on a work table;

means for mounting a tool adjacent to said work table;

means for causing relative movement of one of said workpiece and said tool in a three-dimensional space along a x-axis, a y-axis or a z-axis;

said means for causing relative movement includes a DC servo electric motor associated with each of said x-axis, y-axis and z-axis;

a motor control board for each of said DC servo electric motors;

each of said motor control boards concurrently performing a set of tasks including foreground tasks, midground tasks and background tasks to generate a signal; and

means for transmitting each generated signal to an associated one of said DC servo electric motors.

33. Apparatus as in claim 31 and further comprising:

an electric circuit for using the damping characteristics of each of said DC servo electric motors to retain said means for causing relative movement in a stop hold mode.

34. Apparatus as in claim 33 wherein:

said electric circuit includes at least four chokes.

35. Apparatus as in claim 34 and further comprising:

an H style motor drive amplifier for each of said DC servo electric motors; and

one of said chokes being located in each leg of said H style motor drive amplifiers.

36. Apparatus as in claim 35 wherein said electric circuit comprises:

a 160 volt DC power source, a power transistor, a choke, a DC servo electric motor positive direction, another choke and another power transistor in a first half cycle; and

a 160 volt DC power source, a power transistor, a choke, a DC servo electric motor negative direction, another choke and another power transistor in a second half-cycle.

37. Apparatus as in claim 31 wherein:

said signal is generated in accordance with the following formula;

space="preserve" listing-type="equation">PWM=(Cv)×

(Vc)+PWM.0.+(Cg)×

(Vc-Va)

where;

PWM is the new pulse width desired

Cv is the slope of the velocity

Vc is the commanded velocity

PWM.0. is the PWM required to turn the motor

Cg is the velocity servo gain

Va is the actual velocity.

38. Apparatus as in claim 31 wherein:

said signal is generated in accordance with the following formula when said motor is near a stop lock position;

space="preserve" listing-type="equation">PWM=PWM.0.+(Cp)×

(De)+(Cd)×

(Va)

where;

PWM is the desired pulse width

PWM.0. is the PWM required to turn the motor

Cp is the position servo gain

De is the distance error

Cd is the coefficient of velocity damping

Va is the actual velocity.

39. Apparatus as in claim 31 wherein said means for causing movement comprises:

a rotatable member for each of said x-axis, y-axis and z-axis; and

means for connecting each of said rotatable members to one of said DC servo electric motors so that the ratio of rotation of said rotatable member to said DC servo electric motor is at least about 2.4 to 1.

40. Apparatus as in claim 31 wherein said means for causing movement comprises:

a rotatable member for each of said x-axis and said y-axis; and

means for connecting each of said rotatable members to one of said DC servo electric motors so that the ratio of rotation of said rotatable member to said DC servo electric motor is at least 3.2 to 1.

41. Apparatus as in claim 31 and further comprising:

an optical tachometer associated with each of said DC servo electric motors; and

each of said optical tachometers having about 500 lines per revolution.

42. Apparatus as in claim 41 and further comprising:

an optical encoder associated with each one of said optical tachometer.

43. Apparatus as in claim 31 and further comprising:

means for generating a signal by concurrently performing a first set of tasks including foreground tasks, midground tasks and background tasks and transmitting said signal to each of said motor control boards.

32. Apparatus for controlling the relative movement of a workpiece and a tool in a three dimensional space so as to perform desired operations on said workpiece comprising:

means for mounting a workpiece on a work table;

means for mounting a tool adjacent to said work table;

means for causing relative movement of one of said workpiece and said tool in a three-dimensional space along a x-axis, a y-axis or a z-axis;

said means for causing relative movement includes a DC servo electric motor associated with each of said x-axis, y-axis and z-axis;

a motor control board for each of said DC servo electric motors;

each of said motor control boards concurrently performing a set of tasks to generate a signal;

means for transmitting each generated signal to an associated one of said DC servo electric motors; and

an opto-isolator chip located between each of said motor control boards and each of said DC servo electric motors and through which said signal is transmitted.