On demand adaptive control system

• US 6,961,637 B2
• Filed: 02/25/2003
• Issued: 11/01/2005
• Est. Priority Date: 02/25/2003
• Status: Active Grant

• Current Assignee: Fanuc FA America Corporation (Fanuc Corporation)
• Original Assignee: GE Fanuc Automation Americas Incorporated (General Electric Company)
• Inventors: Scherer, Jerry G.
• Primary Examiner(s): Picard, Leo
• Assistant Examiner(s): KOSOWSKI, ALEXANDER J
• Application Number:
  US10/373,929
• Publication Number:
  US 20040167659A1
• Time in Patent Office: 980 Days
• Field of Search: 700/173, 700/28, 700 32- 33, 700/175
• US Class Current: 700/173
• CPC Class Codes: G05B 19/4163 Adaptive control of feed or cutting velocity without NC B23Q15/12
• CPC Class Codes: G05B 2219/49077 Control of feed and spindle, cutting speed
• CPC Class Codes: G05B 2219/49082 Maintain constant material removal rate
• CPC Class Codes: G05B 2219/49092 Vary, change controlled parameter as function of detected power

Abstract

An adaptive control system and method for controlling the path feed rate to achieve a target spindle load during machine tool operations. The adaptive control system can provide load monitoring capability, which will actively monitor an incoming load signal from a spindle drive and determine if it exceeds warning and alarm levels. If the incoming load being monitored exceeds the set warning level, a warning output is asserted and maintained until the incoming load falls below the set warning level. If the incoming load exceeds the set alarm level, the alarm output and feed hold output are asserted and maintained until an adaptive controller reset is requested. Normal cutting operations cannot resume until the conditions that generated the alarm level are addressed. Adaptive control of machine tool operations is provided by monitoring of the incoming load and requesting feed rate changes based on a proportional integral derivative (PID) controller algorithm. The adaptive controller monitors the incoming load until an arming limit is exceeded, at which point the adaptive controller proceeds to run the PID control algorithm to calculate a new feed rate that will cause the incoming load to obtain the user requested value. An interface application allows the user to set and view registers and the input/output status of the adaptive controller. The adaptive control system can be fully integrated into the machine tool management system, or can be integrated with custom tool interfaces. The adaptive control system can also be operated using a manual interface provided to the operator with no connection to tooling data.

Claims

1. A method for adaptively controlling the volumetric removal of material from a workpiece during a machining operation by a computer-controlled tool, comprising the steps of:

determining a steady state load on a spindle drive when the tool is not in an active cutting mode;

measuring a turning load of the spindle during active cutting;

adjusting the turning load of the spindle based on the steady state load;

determining a new path feed rate for the workpiece as a function of the adjusted spindle load using a control algorithm; and

adjusting a current path feed rate based on the determined new path feed rate by asserting signals from a motion controller.

2. The method for adaptively controlling of claim 1 further comprising the steps of detecting the spindle load using a load detection mechanism and providing an analog or digital representation as a percent of a maximum spindle load.

3. The method for adaptively controlling of claim 1 further comprising the steps of detecting a spindle velocity using a speed detection mechanism and providing an analog or digital representation as a percent of maximum spindle velocity.

4. The method for adaptively controlling of claim 3 further comprising the step of filtering the spindle load detection by neglecting small changes in the spindle load.

5. The method for adaptively controlling of claim 1 further comprising the step of limiting the rate of change of the determined path feed rate by clamping the determined path feed rate such that the current path feed rate can change by only a preset amount during each successive iteration of the control algorithm.

6. The method for adaptively controlling of claim 1 further comprising the step of limiting the maximum and minimum values of the determined path feed rate.

7. The method for adaptively controlling of claim 1 wherein an adaptive control function is automatically enabled by determining if the adjusted spindle load exceeds a first preset limit.

8. The method for adaptively controlling of claim 7 wherein the adaptive control function is automatically disabled by determining if the adjusted spindle load drops below a second preset limit.

9. The method for adaptively controlling of claim 8 wherein the second preset limit is determined from the first preset limit and an offset, thereby creating a hysteresis in the automatic enabling and disabling of the adaptive control function and eliminating resonance in the activation of the adaptive control function.

10. The method for adaptively controlling of claim 1 further comprising the step of overriding a commanded turning load for the spindle by an input into the control algorithm.

11. The method for adaptively controlling of claim 1 further comprising the steps of determining when the adjusted spindle load exceeds a preset warning load level and providing a signal generated by the adaptive control function to an interface.

12. The method for adaptively controlling of claim 1 further comprising the steps of determining when the adjusted load exceeds a preset alarm load level thereby disabling the adaptive control function and asserting a signal to the motion controller to stop each axis movement immediately.

13. The method for adaptively controlling of claim 12 further comprising providing a signal from the adaptive controller to an interface.

14. The method for adaptively controlling of claim 12 further comprising the steps of presetting the alarm detection and disabling the adaptive control function through an input to the adaptive control function.

15. The method for adaptively controlling of claim 3 further comprising the steps of detecting when the spindle drive velocity drops below a preset value and providing a signal from the adaptive controller to an interface.

16. The method for adaptively controlling of claim 15 further comprising the step of providing an alternate value for at least one of a plurality of control system gains when the spindle drive velocity drops below a preset value.

17. The method for adaptively controlling of claim 1 further comprising the steps of determining when a calculated feedrate override drops below a preset minimum feedrate override level thereby disabling the adaptive control function, and asserting a signal to the motion controller to stop each axis movement immediately.

18. A system for on demand adaptive control of machining operations by a computer-controlled tool on a workpiece, comprising:

a spindle drive that controls a spindle motor for the tool and outputs a signal that is representative of the spindle load;

an adaptive controller for monitoring the spindle load and determining a path feedrate for the workpiece in relation to the tool;

a demand switch for automatically enabling the adaptive control based on the spindle load; and

a motion controller for adjusting the path feedrate in response to an output signal from the adaptive controller.

19. The system for on demand adaptive control of claim 18 further comprising a plurality of axis motors, each axis motor controlling feedrate motion of the workpiece based on axis control signals received from the motion controller.

20. The system for on demand adaptive control of claim 18 wherein the motion controller includes a spindle control component and an axis control component.

21. The system for on demand adaptive control of claim 18 wherein the adaptive controller includes control logic that controls the machining operations with a closed loop, negative feedback control algorithm.

22. The system for on demand adaptive control of claim 21 wherein the control logic includes a proportional/differential/integral (PID) algorithm.

23. The system for on demand adaptive control of claim 22 wherein a differential between a set point and a process variable is provided as an input to the PID algorithm to determine a control variable supplied to the motion controller to adjust the path feedrate.

24. The system for on demand adaptive control of claim 23 wherein the set point is a commanded load to be held by the spindle drive.

25. The system for on demand adaptive control of claim 23 wherein the process variable is based on a scaled spindle load.

26. The system for on demand adaptive control of claim 18 wherein the adaptive control is deactivated when the spindle load exceeds a preset limit.

27. The system for on demand adaptive control of claim 18 wherein the adaptive control is deactivated when the spindle load decreases below a preset limit and an offset value and activated when the spindle load increases above the preset limit and offset.

28. The system for on demand adaptive control of claim 23 wherein the adaptive control logic includes a dead band module that suppresses the input to the PID algorithm when the differential is lower than a threshold value.

29. The system for on demand adaptive control of claim 23 wherein the adaptive control logic includes a slew control module that limits the value of the control variable that is supplied to the motion controller if the control variable changes by an amount greater than a slew amount between successive iterations of the control logic.

30. The system for on demand adaptive control of claim 23 wherein the adaptive control logic includes a clamp module that limits the maximum value of the control variable if the control variable exceeds an upper limit and limits the minimum value of the control variable if the control variable drops below a lower limit.

31. The system for on demand adaptive control of claim 23 wherein the adaptive control logic includes a scaling module to scale the control variable to match the path feedrate command input of the motion controller.

32. A system for on demand adaptive control of machining operations by a computer-controlled tool on a workpiece, comprising:

a spindle drive that controls a spindle motor for the tool and outputs a signal that is representative of the spindle load;

an adaptive controller for monitoring the spindle load and determining a path feedrate for the workpiece in relation to the tool;

a demand switch for automatically enabling the adaptive control based on the spindle load;

a motion controller for adjusting the path feedrate in response to an output signal from the adaptive controller; and

an interface for setup and monitoring of the adaptive controller.

33. The system for on demand adaptive control of claim 32 wherein the interface comprises a load monitor module, an adaptive monitor module, a control monitor module and a communications monitor module.

34. The system for on demand adaptive control of claim 33 wherein the load monitor module displays an operating condition of the spindle motor.

35. The system for on demand adaptive control of claim 33 wherein the adaptive control module displays a status of the demand switch and an operational condition of the motion controller.

36. The system for on demand adaptive control of claim 33 wherein the control monitor module displays an image of the motion controller'"'"'s inputs and outputs.

37. The system for on demand adaptive control of claim 33 wherein the communications monitor module displays a total number of packets transmitted between the interface and the motion controller.

38. The system for on demand adaptive control of claim 32 wherein the interface provides a display screen for an operator to setup characteristics of a proportional/integral/derivative (PID) control algorithm in a control logic module of the adaptive controller.

39. The system for on demand adaptive control of claim 32 wherein the adaptive controller and motion controller are fully integrated to provide both interface information and tooling information.

40. The system for on demand adaptive control of claim 32 wherein the adaptive controller and motion controller are partially integrated so that the adaptive controller can operate with custom tool interfaces.

41. The system for on demand adaptive control of claim 32 wherein the adaptive controller and motion controller are not integrated and the interface to select target and limit values for the motion controller is provided through physical input devices on the adaptive controller.