Method and device for disturbance sensing, especially collision sensing, in the drive system of a numerically controlled machine tool

• US 20010012973A1
• Filed: 12/15/2000
• Published: 08/09/2001
• Est. Priority Date: 12/16/1999
• Status: Active Grant

• Current Assignee: AGI (Meadwestvaco Corporation)
• Original Assignee: AGI (Meadwestvaco Corporation)
• Inventors: Wehrli, Peter, Sargenti, Orio
• Granted Patent: US 6,920,370 B2
• Time in Patent Office: Days
• US Class Current: 700/193
• CPC Class Codes: B23Q 17/22 for indicating or measuring existing or desired position of tool or work B23Q16/005 takes precedence
• CPC Class Codes: G05B 19/4061 Avoiding collision or forbidden zones
• CPC Class Codes: G05B 2219/37622 Detect collision, blocking, stall by change, lag in position
• CPC Class Codes: G05B 2219/37624 Detect collision, blocking by measuring change of velocity or torque

Abstract

A method and device for disturbance sensing in the drive system of a numerically controlled machine tool or similar device is disclosed, in which at least one drive motor for positioning of a machine part being moved such as an advance slide or an X/Y cross-slide is coupled via one or more transmission elements in which the position of the moving machine part is measured directly on the machine part and also indirectly in at least one location in the transmission chain. Direct and indirect position measured values are compared and the measured value comparison value is used to record a disturbance with consideration of the actual operating conditions, such as machining speed and acceleration/delay, optionally moved masses and machine-specific process forces upon fulfillment of a specific criterion.

Claims

1. A method for disturbance sensing in a drive system of a numerically controlled machine tool, in which at least one drive motor for positioning a machine part is coupled via one or more transmission elements to the machine part, the method comprising the steps of:

a) measuring a position of the moving machine part directly on the machine part and also indirectly at at least one location in a transmission chain;

b) comparing the direct and indirect position measured values; and

c) using the comparison between the direct and indirect positions value to record a disturbance with consideration of the actual operating conditions on fulfillment of a prescribed criterion.

2. A method as defined in

claim 1

, wherein the indirect measurement of the position of the machine part being moved is conducted on the drive motor.

3. A method as defined in

claim 1

, wherein a difference value between the direct and indirect position measured values is used as criterion for recognition of a disturbance.

4. A method as defined in

claim 3

, wherein the difference value is compared with one or more prescribed threshold values, the one or more prescribed threshold values being determined with consideration of actual operating conditions, and wherein predetermined measures are automatically initiated on at least one of reaching and surpassing the one or more prescribed threshold values.

5. A method as defined in

claim 4

, wherein the actual operating conditions include at least one of inertial forces during acceleration of the moving machine part, process forces of work place machining and friction forces in the drive system

6. A method as defined in

claim 4

wherein a calibration procedure is performed to determine machine-specific threshold values in which machine-specific standard disturbance situations are run.

7. A method as defined in

claim 1

wherein collision sensing is performed through the use of determining a difference value between the direct and indirect position measured values and considering the actual operating conditions.

8. A method as defined in

claim 7

, wherein disengagement of at least one of advance movement of the moving machine part and reversal movement of the moving machine part is initiated directly after collision sensing.

9. A method as defined in

claim 7

wherein possible damage is evaluated after collision sensing with consideration of at least one of a determined collision direction, a collision speed and a collision depth and correction is activated to prevent damage when necessary.

10. A method as defined in

claim 7

, further including a preventive collision protection method used in combination with collision sensing.

11. A method as defined in

claim 10

, wherein the machining process is monitored by an active collision protection system and collision monitoring is initiated by difference formation of the direct and indirect position measured values only upon failure of the active collision protection system.

12. A device for disturbance sensing in a drive system of a numerically controlled machine tool in which at least one drive motor for positioning of a machine part being moved is coupled via one or more transmission elements to the machine part, the device comprising:

a) a direct measurement system connected to the machine part being moved by the least one drive motor configured to measure an actual position of the machine part being moved;

b) an indirect measurement system configured to indirectly determine a position of the moving machine part located at at least one location in a transmission chain; and

c) a control unit configured to compare determined position measured values and to determine a disturbance when the comparison of the determined position measured values fulfills a prescribed criterion.

13. A device as defined in

claim 12

, wherein the direct measurement system is a linear measurement system connected to the machine part being moved.

14. A device as defined in

claim 13

, wherein the linear measurement system is a phase grating length measurement system.

15. A device as defined in

claim 13

, wherein the linear measurement system has a stationary phase grating scale and a vertical resonator laser scanning sensor coupled to the machine part being moved.

16. A device as defined in

claim 12

, wherein the indirect measurement system is a rotation angle sensor that is one of directly and indirectly coupled to a rotor shaft of the drive motor.

17. A device as defined in

claim 12

, further comprising:

an active collision protection system used in conjunction with the device for disturbance sensing, wherein the device for disturbance sensing is activated when one of a defect and a failure of the active collision protection system occurs.

18. A device as defined in

claim 17

further comprising:

a proximity sensor connected to the moving machine part and configured for use as the active collision protection system.

19. A device as defined in

claim 17

, further comprising:

an image processing system configured for use as the active collision protection system and further configured to record the size and position of elements in a work space of the machine tool.