Method of calibrating highly precise robots

• US 5,220,261 A
• Filed: 02/26/1992
• Issued: 06/15/1993
• Est. Priority Date: 03/19/1991
• Status: Expired due to Fees

• Current Assignee: Bodenseewerk Gerätetechnik Gmbh
• Original Assignee: Bodenseewerk Gerätetechnik Gmbh
• Inventors: Kempas, Hagen
• Primary Examiner(s): Ip, Paul
• Application Number:
  US07/841,832
• Time in Patent Office: 475 Days
• Field of Search: 318/560-640, 318/649, 395/80-99, 901/3, 901/9, 901/10, 901/15-23, 901/30, 901/46, 901/47
• US Class Current: 318/567
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G05B 2219/40597 Measure, calculate angular momentum, gyro of rotating body at end effector

Abstract

A method of calibrating highly precise robots having a plurality of arms and axes comprises the method steps of: attaching an angular rate sensor (30) at an arm of the robot, adjusting the arm to a predetermined nominal position, generating an angular rate about an axis (40) of the robot, comparing the angular rate measured by the angular rate sensor (30) about its input axis (46, 48) with the nominal component of the angular rate generated about said axis (40), which nominal component results for the nominal position, and correcting the parameters of the robot according to the deviation of the measured angular rate and the nominal component.

Claims

1. A method of calibrating robots of the type having a plurality of arms, adjacent ones of said arms being interconnected to be rotated by servomotors about robot axes under the control of control signals comprising the steps of

(a) attaching to one of said arms of said robot an angular rate sensor for sensing angular rate of said sensor relative to inertial space about an input axis,

(b) commanding, by said command signals, a configuration of said robot wherein said one arm is supposed to assume a predetermined nominal position,

(c) generating an angular rate about one of said robot axes different from said input axis, whereby said rate sensor is supposed to sense, about said input axis, a predetermined nominal component of said generated angular rate depending on said commanded configuration of said robot,

(d) measuring by said angular rate sensor the actual angular rate about said input axis,

(e) comparing said actual angular rate measured by said angular rate sensor about said input axis with said nominal component of said generated angular rate, and

(f) applying corrections to parameters of control signals of said robot in accordance with the deviation of said actual angular rate and said nominal component of said generated angular rate to compensate for deviations of at least one robot axis from its nominal orientation.

2. A method as claimed in claim 1, wherein an outermost arm of said robot carries a tool holding fixture and said angular rate sensor is attached to said tool holding fixture.

3. A method as claimed in claim 1, wherein said commanded configuration of said robot is selected to make said nominal component of said generated angular rate zero.

5. A method as claimed in claim 1 wherein a two-axis rate gyro is used as said angular rate sensor.

4. A method of calibrating robots of the type having a plurality of arms, adjacent ones of said arms being interconnected to be rotated by sevomotors about robot axes under the control of control signals, said robot axes including alternating roll axes extending longitudinally of one of said interconnected arms and pitch axes extending transversely to said interconnected arms, an outermost one of said arms having a tool holding fixture at its end, said tool holding fixture being rotatable about an outermost robot axis, comprising the steps of

(a) attaching to said tool holding fixture an angular rate sensor for sensing angular rate relative to inertial space about an input axis, said angular rate sensor being attached nominally with said input axis orthogonal to said outermost robot axis,

(b) generating an angular rate about said outermost robot axis, whereby said rate sensor is supposed to sense, about said input axis, a zero nominal component of said generated angular rate,

(c) measuring by said angular rate sensor the actual angular rate about said input axis, and

(d) correcting control signals of said robot in accordance with said actual angular rate to compensate for deviations of said outermost robot axis from its nominal position,

(e) commanding, by said command signals, a configuration of said robot wherein said outermost arm and another of said arms are supposed to be rotatable about parallel outer and inner pitch axes,

(f) generating oppositely equal angular rates about said parallel pitch axes, whereby said rate sensor is supposed to sense, about said input axis, a zero nominal component of said generated angular rates,

(g) measuring by said angular rate sensor the actual angular rate about said input axis, and

(h) applying corrections to parameters of said control signals of said robot in accordance said actual angular rate to compensate for deviations of said outer pitch axis from its nominal position,

(i) commanding, by said command signals, a configuration of said robot wherein said outermost robot roll axis is supposed to be aligned with the next inner one of said roll axes,

(j) generating an angular rate about the next inner one of said roll axes, whereby said rate sensor is supposed to sense, about said input axis, a zero nominal component of said generated angular rate,

(k) measuring by said angular rate sensor the actual angular rate about said input axis,

(l) correcting control signals of said robot in accordance with said latter angular rate to compensate for deviations of said next inner roll axis from its nominal position, and

(m) repeating said procedure with successive pitch and roll axes.