SENSORLESS PRESSURE CHANGE DETECTION FOR SERVO GUN
First Claim
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1. A method for detecting pressure changes at servo gun tips of a robotic welding system having a servo gun with a movable tip and an opposed fixed tip configured to weld a part comprising the steps of:
- storing benchmark values for a spring constant, a pressure estimator, an efficiency and an inertia/friction during noload operation;
operating the servo gun to apply a first calibrated force at the gun tips and measuring a resulting first deflection value at the gun tips;
operating the servo gun to apply a second calibrated force at the gun tips and measuring a resulting second deflection value at the gun tips;
using the measured first and second deflection values and the pressure estimator to calculate current values for the spring constant, a first gun tip pressure, a second gun tip pressure, the efficiency and the inertia/friction during noload operation;
comparing each of the current values with a corresponding one of the benchmark values; and
generating an error indication for any of the current values that differs from the corresponding benchmark value by a predetermined amount.
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Abstract
A method and an apparatus detects pressure changes at servo gun tips of a robotic welding system having a servo gun with a movable tip and an opposed fixed tip configured to weld a part. The method and apparatus observe a tip deflection value and convert the value to a current pressure value using a pressure estimator. The current pressure value is compared to a benchmark pressure value to detect any difference.
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Citations
20 Claims
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1. A method for detecting pressure changes at servo gun tips of a robotic welding system having a servo gun with a movable tip and an opposed fixed tip configured to weld a part comprising the steps of:
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storing benchmark values for a spring constant, a pressure estimator, an efficiency and an inertia/friction during noload operation; operating the servo gun to apply a first calibrated force at the gun tips and measuring a resulting first deflection value at the gun tips; operating the servo gun to apply a second calibrated force at the gun tips and measuring a resulting second deflection value at the gun tips; using the measured first and second deflection values and the pressure estimator to calculate current values for the spring constant, a first gun tip pressure, a second gun tip pressure, the efficiency and the inertia/friction during noload operation; comparing each of the current values with a corresponding one of the benchmark values; and generating an error indication for any of the current values that differs from the corresponding benchmark value by a predetermined amount.
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2. The method according to claim 1 including selecting a standard force value;
- calculating a motor torque command based upon the standard force value and a motor torque constant for a motor to actuate the servo gun with a corresponding calibrated torque value;
determining a calculated force value from the calibrated torque value and a pressure calibration table.
- calculating a motor torque command based upon the standard force value and a motor torque constant for a motor to actuate the servo gun with a corresponding calibrated torque value;
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3. The method according to claim 2 including forming the pressure estimator by plotting two points of calibrated pressure values and corresponding measured deflection values of the gun tips, drawing a line between the points, and converting the line to an equation for determining a new calibrated force value from a new measured deflection value.
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4. The method according to claim 1 including if the spring constant current value is different from the spring constant benchmark value generating an error indication.
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5. The method according to claim 1 including if the first pressure current value is different from the first pressure benchmark value generating an error indication.
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6. The method according to claim 5 including only generating the error indication if the difference is greater than ten percent.
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7. The method according to claim 1 including if the second pressure current value is different from the second pressure benchmark value generating an error indication.
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8. The method according to claim 7 including only generating the error indication if the difference is greater than ten percent.
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9. The method according to claim 1 including if the efficiency current value is different from the efficiency benchmark value generating an error indication.
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10. The method according to claim 9 including only generating the error indication if the difference is less than or greater than a predetermined range of a ratio of the efficiency current value to the efficiency benchmark value.
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11. The method according to claim 10 wherein the range is 65% to 135%.
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12. The method according to claim 1 including only generating the error indication if the Inertia/friction current value is different from the inertia/friction benchmark value.
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13. The method according to claim 12 including only generating the error indication if the difference is greater than thirty percent.
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14. The method according to claim 1 including performing tip wear measurements on the gun tips and only performing the steps if the tip wear measurements meet predetermined wear schedule conditions.
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15. The method according to claim 1 including generating the error indication from a computer controlling the servo gun in response to any of the current values differing from a corresponding one of the benchmark values.
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16. An apparatus for detecting pressure changes in a robotic welding system comprising:
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a servo gun with a movable tip opposed by a fixed tip; a motor coupled to the movable tip for moving the movable tip toward and away from the fixed tip; a computer connected to the motor for actuating the motor to move the movable tip; and a pressure test computer program executed by the computer causing the motor to move the movable tip to apply a first pressure at the fixed tip, the motor then move the movable tip to apply a second pressure at the fixed tip, the computer to store tip deflection values for the first and second pressures, the computer to calculate and store values for a spring constant, a pressure force estimator, efficiency and inertia/friction during noload operation from the stored deflection values, and if the pressure test is a first pressure test, designate the stored values as benchmark values.
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17. The apparatus according to claim 15 wherein if the pressure test is not the first pressure test, designate the stored values as current values.
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18. The apparatus according to claim 17 wherein the computer executes the pressure test computer program to generate an error indication in response to any of the current values differing from a corresponding one of the benchmark values.
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19. A method for detecting pressure changes at servo gun tips of a robotic welding system having a servo gun with a movable tip and an opposed fixed tip configured to weld a part comprising the steps of:
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closing the movable tip against the fixed tip to apply a pressure at the tips; measure a deflection value of the fixed tip from a reference point corresponding to zero pressure at the tips; converting the deflection value to a calibrated pressure value using a pressure estimator; comparing the calibrated pressure value to a benchmark pressure value; and generating an error indication if a difference between the compared values exceeds a predetermined amount.
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20. The method according to claim 19 including generating the pressure estimator by plotting two points of calibrated pressure values and corresponding measured deflection values of the tips, drawing a line between the points, and converting the line to an equation for determining a new calibrated force value from a new measured deflection value.
Specification