Abnormal state detecting apparatus of a machine tool

• US 5,142,210 A
• Filed: 01/04/1991
• Issued: 08/25/1992
• Est. Priority Date: 01/17/1990
• Status: Expired due to Term

• Current Assignee: Okuma Machinery Works Ltd.
• Original Assignee: Okuma Machinery Works Ltd.
• Inventors: Eguchi, Satoshi, Kojima, Takayoshi, Asano, Takayasu
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): BERGMANN, SAUL
• Application Number:
  US07/638,174
• Time in Patent Office: 599 Days
• Field of Search: 318/566, 318/563, 318/572, 318/475, 318/275, 364/474.12, 82/132, 82/141, 409/134
• US Class Current: 318/566
• CPC Class Codes: G05B 19/4062 Monitoring servoloop, e.g. overload of servomotor, loss of feedback or reference

Abstract

An abnormal state detecting apparatus of a machine tool having a servomotor. The apparatus is provided with a device for detecting an abnormal acceleration and an abnormal torque of the servomotor and a device for detecting an abnormal operation state of the servomotor from the directions of the detected acceleration and torque. When the torque, acceleration and operation state are all abnormal, the machine tool is judged to be in an abnormal state and the servomotor is controlled, thereby protecting the machine tool from an impact in an abnormal operation state.

Claims

1. An abnormal state detecting apparatus for protecting a machine tool which is driven by a servomotor from an impact in an abnormal operation state, said apparatus comprising:

(a) circuit means for outputting a torque signal corresponding to the load applied to a servomotor, said circuit means including at least a rotational position detector for detecting the rotational position of the servomotor, a position signal/speed signal converter for receiving a rotational position signal output from said rotational position detector and converting said position signal to a speed signal, a speed command processor for generating a speed command signal by comparing a rotational position command signal output from a position command processor with said rotational position signal and a torque command processor for generating a torque command signal by comparing said speed command signal with said speed signal, said torque command signal being amplified so as to drive the servomotor;

(b) a data setting circuit having selected reference data on a torque value and an acceleration value which can be selected and outputting a reference torque signal and a reference acceleration signal which correspond to the selected reference data on said torque value and acceleration value, respectively;

(c) a speed/acceleration converter for converting said speed signal output from said position signal/speed signal converter into an acceleration signal;

(d) an acceleration comparator for comparing said acceleration signal output from said speed/acceleration converter with said reference acceleration signal output from said data setting circuit and outputting an abnormal acceleration detection signal when the rat of speed change of the servomotor exceeds the acceleration value which corresponds to said reference acceleration signal;

(e) a torque comparator for comparing said torque command signal output from said torque command processor with said reference torque signal output from said data setting circuit and outputting an abnormal torque detection signal when the torque of the servomotor exceeds the torque value which corresponds to said reference torque signal;

(f) an operation state judging circuit for detecting the acceleration or deceleration of the servomotor from said acceleration signal and the increase or decrease of the torque of the servomotor from said torque command signal and outputting an abnormal operation state detection signal when an acceleration and a decrease of the torque of the servomotor are simultaneously generated or when a deceleration and an increase of the torque of the servomotor are simultaneously generated; and

(g) an abnormal state detecting circuit for outputting an abnormal state detection signal when said abnormal acceleration detection signal output from said acceleration comparator, said abnormal torque detection signal output from said torque comparator and said abnormal operation state detection signal output from said operation state judging circuit are simultaneously input.

2. An abnormal state detecting apparatus according to claim 1, further comprising a control circuit for controlling the driving of the servomotor when said abnormal state detection signal is input to said control circuit from said abnormal state detecting circuit.

3. An abnormal state detecting apparatus according to claim 1, further comprising a switching circuit for turning OFF said torque command signal when said abnormal state detection signal is input to said control circuit from said abnormal state detecting circuit.

4. An abnormal state detecting apparatus according to claim 1, further comprising a braking circuit for applying a torque in the reverse direction to said servomotor when said abnormal state detection signal is input to said braking circuit from said abnormal state detecting circuit.

5. An abnormal state detecting apparatus for protecting a machine tool which is driven by a servomotor from an impact in an abnormal operation state, said apparatus comprising:

(a) circuit means for outputting a torque signal corresponding to the load applied to a servomotor, said circuit means including at least a rotational position detector for detecting the rotational position of the servomotor and outputting a rotational position signal, a speed detector for detecting the rotational speed of the servomotor and outputting a speed signal, a speed command processor for generating a speed command signal by comparing a rotational position command signal output from a position command processor with said rotational position signal and a torque command processor for generating a torque command signal by comparing said speed command signal with said speed signal, said torque command signal being amplified so as to drive the servomotor;

(b) a data setting circuit having selected reference data on a torque value and an acceleration value which can be selected and outputting a reference torque signal and a reference acceleration signal which correspond to the selected reference data on said torque value and acceleration value, respectively;

(c) a speed/acceleration converter for converting said speed signal output from said position signal/speed signal converter into an acceleration signal;

(d) an acceleration comparator for comparing said acceleration signal output from said speed/acceleration converter with said reference acceleration signal output from said data setting circuit and outputting an abnormal acceleration detection signal when the rate of speed change of the servomotor exceeds the acceleration value which corresponds to said reference acceleration signal;

(e) a torque comparator for comparing said torque command signal output from said torque command processor with said reference torque signal output from said data setting circuit and outputting an abnormal torque detection signal when the torque of the servomotor exceeds the torque value which corresponds to said reference torque signal;

(f) an operation state judging circuit for detecting the acceleration or deceleration of the servomotor from said acceleration signal and the increase or decrease of the torque of the servomotor from said torque command signal and outputting an abnormal operation state detection signal when an acceleration and a decrease of the torque of the servomotor are simultaneously generated or when a deceleration and an increase of he torque of the servomotor are simultaneously generated; and

(g) an abnormal state detecting circuit for outputting an abnormal state detection signal when said abnormal acceleration detection signal output from said acceleration comparator, said abnormal torque detection signal output from said torque comparator and said abnormal operation state detection signal output from said operation state judging circuit are simultaneously input.

6. An abnormal state detecting apparatus according to claim 5, further comprising a control circuit for controlling the driving of the servomotor when said abnormal state detection signal is input to said control circuit form said abnormal state detecting circuit.

7. An abnormal state detecting apparatus according to claim 5, further comprising a switching circuit for turning OFF said torque command signal when said abnormal state detection signal is input to said switching circuit from said abnormal state detecting circuit.

8. An abnormal state detecting apparatus according to claim 5, further comprising a braking circuit for applying a torque in the reverse direction to said servomotor when said abnormal state detection signal is input to said braking circuit from said abnormal state detecting circuit.

9. An abnormal state detecting apparatus for protecting a machine tool which is driven by a servomotor from an impact in an abnormal operation state by utilizing a feedback control system of a servo mechanism of a machine tool, said apparatus comprising:

(a) circuit means for outputting a torque signal corresponding to the load applied to a servomotor, said circuit means including at least a rotational position detector for detecting the rotational position of the servomotor and outputting a rotational position signal, a speed detector for detecting the rotational speed of the servomotor and outputting a speed signal, a speed command processor for generating a speed command signal by comparing a rotational position command signal output from a position command processor with said rotational position signal and a torque command processor for generating a torque command signal by comparing said speed command signal with said speed signal, said torque command signal being amplified so as to drive the servomotor;

(b) a data setting circuit having selected reference data on a torque value and an acceleration value which can be selected and outputting a reference torque signal and a reference acceleration signal which correspond to the selected reference data on said torque value and acceleration value, respectively;

(c) an acceleration detector for detecting the rotational acceleration of the servomotor and outputting an acceleration signal;

(d) an acceleration comparator for comparing said acceleration signal output from said acceleration detector with said reference acceleration signal output from said data setting circuit and outputting an abnormal acceleration detection signal when the rate of speed change of the servomotor exceeds the acceleration value which corresponds to said reference acceleration signal;

(e) a torque comparator for comparing said torque command signal output from said torque command processor with said reference torque signal output from said data setting circuit and outputting an abnormal torque detection signal when the torque of the servomotor exceeds the torque reference value which corresponds to said reference torque signal;

(f) an operation state judging circuit for detecting the acceleration or deceleration of the servomotor from said acceleration detection signal and the increase or decrease of the torque of the servomotor from said torque command signal and outputting an abnormal operation state detection signal when an acceleration and a decrease of the torque of the servomotor are simultaneously generated or when a deceleration and an increase of the torque of the servomotor are simultaneously generated; and

(g) an abnormal state detecting circuit for outputting an abnormal state detecting signal when said abnormal acceleration detection signal output from said acceleration comparator, said abnormal torque detection signal output from said torque comparator and said abnormal operation state detection signal output from said operation state judging circuit are simultaneously input.

10. An abnormal state detecting apparatus according to claim 9, further comprising a control circuit for controlling the driving of the servomotor when said abnormal state detection signal is input to said control circuit form said abnormal state detecting circuit.

11. An abnormal state detecting apparatus according to claim 9, further comprising a switching circuit for turning OFF said torque command signal when said abnormal state detection signal is input to said switching circuit from said abnormal state detecting circuit.

12. An abnormal state detecting apparatus according to claim 9, further comprising a braking circuit for applying a torque in the reverse direction to said servomotor when said abnormal state detection signal is input to said braking circuit from said abnormal state detecting circuit.