Drill monitor system

• US 4,251,872 A
• Filed: 02/16/1979
• Issued: 02/17/1981
• Est. Priority Date: 02/16/1979
• Status: Expired due to Term

• Current Assignee: Honeywell Information Systems, Inc. (Honeywell International Inc.)
• Original Assignee: Honeywell Information Systems, Inc. (Honeywell International Inc.)
• Inventors: Bone, Dale H.
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US06/012,679
• Time in Patent Office: 732 Days
• Field of Search: 364/474, 364/551, 364/508, 364/475, 364/476, 364/483, 73/7, 73/579, 73/104, 73/162
• US Class Current: 700/175
• CPC Class Codes: G05B 19/4065 Monitoring tool breakage, life or condition
• CPC Class Codes: G05B 2219/37245 Breakage tool, failure
• CPC Class Codes: G05B 2219/37285 Load, current taken by motor
• CPC Class Codes: G05B 2219/37382 Voltage over or short circuit between tool and workpiece
• CPC Class Codes: G05B 2219/45129 Boring, drilling

Abstract

There is disclosed herein an apparatus for automatic monitoring of numerous high speed drill spindles on a numerically controlled drilling machine for purposes of immediate detection of the absence of drilling by a particular spindle because of a broken drill bit. The apparatus detects the absence of drilling, interrupts the automatic cycle of the drilling machine and alerts the operator. Power dissipation in each drill spindle motor is compared just prior to entry of the drill bit into the workpiece and after entry if any. If power dissipation increases above a predetermined threshhold level for all spindles, no interrupt is generated. If power dissipation does not increase in one or more spindle motors, comparator circuits alert a digital processor which interrupts automatic operation of the drilling machine and alerts the operator. Such a system eliminates the expense and error of human visual monitoring and generation of expensive scrap improperly processed before discovery of the broken bit.

Claims

1. A motor monitor system comprising:

(a) a numerically controlled machine to accomplish a task requiring repeated mechanical loading of an electric motor;

(b) sensors responsive to changes in criteria indicative of whether mechanical loading of said electric motor has occurred and for generating a first signal;

(c) a drill monitor interface responsive to said first signals for sampling said first signals at two times just prior to and again after the theoretical occurrence of the mechanical loading, and for comparing said first signals as sampled at said two times and for generating a hit/miss signal for said electric motor and for generating an interrupt request after generation of said hit/miss signal;

(d) a means for predicting mechanical loading and informing said drill monitor interface when mechanical loading of said motor should occur for sending a second signal to said drill monitor interface informing it that mechanical loading should occur just after generation of said second signal;

(e) a digital processor controlling a stop mechanism in said numerically controlled machine and electrically linked to said drill monitor interface for receiving said interrupt request and said hit/miss signal from said drill monitor interface and programmed to analyze said hit/miss signals for a miss by said electric motor and to issue a stop command to said numerically controlled machine upon detection of a miss.

3. An apparatus as defined in claim 1 or 2 wherein said sensors are a means for generating data indicating the magnitude of motor current through said electric motor.

4. An apparatus as defined in claim 1 or 2 wherein said sensors are optical pickups to monitor shaft RPM of said electric motor.

5. An apparatus as defined in claim 1 or 2 wherein said sensors are magnetic reluctance pickups to monitor shaft speed of said electric motor.

7. An apparatus as defined in claim 1 or 2 or 3 or 4 or 5 or 6 wherein said drill monitor interface further comprises:

(a) a means for processing said signals and said sensors to amplify, convert to an RMS value, and eliminate high frequency noise from said signals and block transmission of the RMS signal if said RMS signal is less than a predetermined value;

(b) a means for sampling and holding the output signal from said means for processing upon receipt of a SAMPLE signal;

(c) a first means for comparing the output of the means for sampling and holding to the most recent output of said means for processing and amplifying the difference;

(d) a second means for comparing the output of said first means for comparing to a fixed voltage reference source and for generating a hit/miss signal which indicates when the output of said first means for comparing exceeds the fixed voltage reference;

(e) a timing generation logic means responsive to the signal from said means for predicting load and electrically linked to said means for sampling, said timing generation logic for generation of said SAMPLE signal after receipt of said signal from said means for predicting load and for generating a TIMER 4 signal;

(f) a means for interfacing with said digital processor responsive to said second means for comparing and electrically linked to said timing generation logic and to the data, address and control buses and the interrupt request line of said digital processor said means for interfacing for transmitting an INTERRUPT REQ signal over said interrupt request line upon receipt and storage of said hit/miss signal and said TIMER 4 signal and for transmitting said hit/miss signals to said digital processor over said data bus when said digital processor sends a predetermined address to said means for interfacing over said address bus.

2. A drill monitor system comprising:

(a) a numerically controlled drilling machine to automatically drill at least one hole in a succession of workpieces utilizing at least one electric motor to drive a drill spindle holding a drill bit;

(b) sensors responsive to changes in criteria indicative of whether each drill bit of said numerically controlled drilling machine has or has not entered the workpiece and for generating a first signal;

(c) a drill monitor interface responsive to said sensors for processing the said first signals, sampling said first signals at a time just before and again after theoretical entry of the drill bit into a workpiece and for comparing said first signals and generating a hit/miss signal for each active drill spindle indicating whether drilling occurred and for generating an interrupt request after generation of said hit/miss signal;

(d) a means for predicting load and for informing said drill monitor interface when mechanical loading should occur said means for predicting load responsive to the mechanical position of said drill spindled of said numerically controlled drilling machine and electrically linked to said drill monitor interface for sending a spindles lowered signal to said drill monitor interface just prior to entry of said drill bit into said workpiece;

(e) a digital processor controlling a stop circuit of said numerically controlled drilling machine and electrically linked to said drill monitor interface for receiving said interrupt request and said hit/miss signals and programmed to analyze said hit/miss signals for a miss by any operating drill spindle and to issue a stop command to said numerically controlled drilling machine upon detection of a miss.

6. An apparatus as defined in claim 2 wherein said sensors are means for detecting bursts of infrared radiation from the tips of said drill bits.

8. A circuit for detecting and signaling when an electric motor fails to become mechanically loaded comprising:

(a) a sensor means for sensing changes in any criteria indicative of the presence of a mechanical load on an electric motor and for generating a first signal indicative of the status of said criteria;

(b) a means for predicting load and for generating a second signal indicating that mechanical loading of said electric motor should occur momentarily;

(c) a motor monitor interface means for receiving said first and second signals and for sampling and holding said first signal at the time of receipt of said second signal, and for comparing the characteristics of said first signal at a time after mechanical loading should have occurred to the characteristics of said first signal as held at the time of receipt of second signal and for generating a hit/miss signal indicating whether mechanical loading actually occurred.

9. A circuit for detecting and signaling when an electric motor fails to become mechanically loaded comprising:

(a) a sensor means for sensing changes in any criteria indicative of the presence of a mechanical load on an electric motor and for generating a first signal indicative of the status of said criteria;

(b) a means for predicting load and for generating a second signal indicating that mechanical loading of said electric motor should occur momentarily;

(c) a motor monitor interface means for receiving said first and second signals and for generation of a hit/miss signal indicating whether mechanical loading actually occurred comprising;

(1) a means for processing said first signal to eliminate high frequency noise and to block transmission if said first signal falls below a predetermined level;

(2) a means for sampling and holding the output of said means for processing upon receipt of said second signal;

(3) a means for comparing the characteristics of said first signal as held by said means for sampling and holding to the characteristics of said first signal at a time after mechanical loading should have occurred.

(4) a means generating a hit/miss signal responsive to the output of said means for comparing, said hit/miss signal indicating whether mechanical loading actually occurred.

10. A circuit for detecting and signaling when an electric motor fails to become mechanically loaded comprising:

(a) a motor current dropping resistor electrically connected in the power circuit of said electric motor so as to generate a voltage across said resistor proportional to the power being consumed in said motor, said voltage drop constituting a first signal;

(b) a limit switch responsive to the mechanical engagement between said electric motor and its mechanical load for generating a second signal indicating mechanical loading is about to occur;

(c) a means for receiving said first and second signals and for generating a hit/miss signal comprising;

(1) an amplifier to amplify said first signal;

(2) an RMS converter to convert the output of said amplifier to its RMS value;

(3) comparator to compare the output of said RMS converter to a fixed voltage reference source and to generate a cutoff signal when said RMS value is exceeded by said fixed voltage reference;

(4) an analog switch responsive to said cutoff signal and electrically linked to the output of said RMS converter to prevent transfer of said RMS value to the output of said analog switch upon receipt of said cutoff signal;

(5) a low pass filter for filtering noise above a predetermined cutoff frequency from the output of said analog switch;

(6) a sample/hold circuit for sampling and holding the output of said low pass filter upon receipt of a sample signal;

(7) timing generation logic for receiving said second signal from said limit switch and for generating said sample signal thereafter indicating mechanical loading is about to occur and causing said sample/hold circuit to sample and hold the output signal from said low pass filter and for generating a TIMER 4 signal at some predetermined time following generation of said sample signal;

(8) a differential amplifier to amplify the difference between the output of said low pass filter after mechanical loading has theoretically occurred and the output of said sample/hold circuit as held at the time of receipt of said sample signal;

(9) a comparator to compare the output of said differential amplifier to a fixed voltage reference and to generate a hit/miss signal which is true when the fixed voltage reference has been exceeded indicating that the power consumed in said electric motor has increased due to mechanical loading over the power consumed under no load;

(10) processor interface interrupt and control logic means for receiving said hit/miss signal and said TIMER 4 signal and for generating an interrupt request for use by a digital processor after receipt and storage of said hit/miss signal.

11. A method of detecting when mechanical loading of an electric motor did not occur comprising:

(a) sensing changes in any criteria indicating the presence of mechanical loading of said electric motor and generating a first signal indicating the status of said criteria;

(b) sensing when mechanical loading should occur and generating a second signal;

(c) comparing the most recent value of said first signal to the value of said first signal as it was at the time of receipt of said second signal;

(d) generating a hit/miss signal which is true when the comparison of step (c) indicates said first signal has changed in a manner indicating loading has occurred and false when loading has not occurred.

12. The method of claim 11 where step (a) further comprises sensing changes in the shaft speed of said electric motor.

13. The method of claim 11 where step (a) further comprises the step of sensing power dissipation in said electric motor by sensing the voltage drop across a motor current dropping resistor connected in the power supply circuit of said electric motor.

14. A method of detecting when drilling through a workpiece by a numerically controlled drilling machine does not occur comprising:

(a) sensing changes in electrical power dissipation in said electric motor and generating a first signal indicative of said power dissipation changes;

(b) sensing when a drill spindle holding a drill bit driven by said numerically controlled drilling machine approaches said workpiece and generating a second signal indicating drilling, if any, is about to commence;

(c) sampling and holding the value of said first signal as of the time of receipt of said second signal;

(d) comparing the value of said first signal after receipt of said second signal to the value of said first signal as held in step (c) above it at the time of receipt of said second signal;

(e) stopping said numerically controlled drilling machine if the comparison of step (d) above indicates said first signal has not appreciably changed indicating no drilling has occurred.