Calibration system and displacement measurement device

• US 6,408,252 B1
• Filed: 01/27/2000
• Issued: 06/18/2002
• Est. Priority Date: 08/01/1997
• Status: Expired due to Term

• Current Assignee: Dynalog Incorporated
• Original Assignee: Dynalog Incorporated
• Inventors: De Smet, Pierre
• Primary Examiner(s): Bui, Bryan
• Application Number:
  US09/463,538
• Time in Patent Office: 873 Days
• Field of Search: 702/87, 702/94-95, 702/97, 702/150, 702/152, 702/153, 702/163, 700/245, 700/254, 700/258, 700/262, 901/15, 901/40, 318/568.11, 318/568.12, 318/568.13
• US Class Current: 702/94
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G05B 2219/39009 Using fixture with potentiometer, wire to end effector, estimate lenght of wire

Abstract

An improved system (20) for the calibration of a robot system. The system (20) comprising a linear displacement measurement device (32) in conjunction with a robot calibration system. The linear displacement measurement device (32) comprising an elongated member (34), a drum, a shaft, a drum displacement mechanism and a drum rotation sensor. The drum is displaced axially upon the shaft as the drum rotates when the elongated member (34) is moved. The drum rotation sensor provides accurate information regarding the distance the elongated member (34) travels. The displacement measuring device (32) is used in an iterative manner with the calibration system (20) for the purpose of the calibration of a robotic device (22).

Claims

1. A displacement measuring device for a robot having an end-point, said measuring device comprising;

a housing;

an elongate shaft mounted within said housing;

a drum having a central axis, a central throughhole extending along said central axis through said drum and capable of accepting the shaft, the drum being mounted on the shaft and the drum having a generally cylindrical outer surface;

a elongate member having a fixed width, a first end and a second end, the first end attached to the outer surface of the drum and the second end attached to the end-point, the elongate member being coilable about the drum;

displacement means for displacing the drum in a direction along said central axis relative to the coiling of the elongate member about the drum thereby preventing the elongate member from overlapping itself; and

rotation measuring means for measuring the rotation of the drum about the drum central axis, whereby the rotation of the drum is translated into the linear displacement of the elongate member and thusly the distance from the measuring device to the end-point.

2. A displacement measuring device as described in claim 1, wherein:

said drum has an inner cylindrical surface containing a threaded surface;

said shaft having a threaded exterior threadably engaging the drum inner cylindrical surface so as to displace the drum axially relative to said elongate member coiling about the drum.

3. A displacement measuring device as described in claim 1, wherein:

said rotation measuring means further comprising an optical encoder having an outwardly projecting and planar surface fixedly mounted to said shaft,

a transmitter mounted to said housing above the optical encoder first side,

a receiver mounted in said housing and aligned opposite the transmitter and aligned therewith, the optical encoder oriented between the transmitter and the receiver whereby the rotation of the drum rotates the optical encoder, thereby causing a disruption of the signal from the transmitter, which causes the receiver to generate a signal indicative of the displacement of said elongate member.

4. A displacement measuring device as described in claim 1, wherein:

said rotation measuring means is a mechanical measuring device.

5. A displacement measuring device as described in claim 1, wherein:

said elongate member is a cable.

6. A displacement measuring device as described in claim 1, wherein:

said elongate member is a filament.

7. A displacement measuring device as described in claim 1, further comprising:

a robot calibration means.

8. A calibration system for a robot having predetermined parameters and an end-point, comprising:

a housing;

an elongate shaft mounted within said housing;

a drum having a central axis, a central throughhole extending along said central axis through said drum and capable of accepting the shaft, the drum being mounted on the shaft and the drum having a generally cylindrical outer surface;

a elongate member having a fixed width, a first end and a second end, the first end attached to the outer surface of the drum and the second end attached to the end-point, the elongate member being coilable about the drum;

displacement means for displacing the drum in a direction along said central axis relative to the coiling of the elongate member about the drum thereby preventing the elongate member from overlapping itself;

rotation measuring means for measuring the rotation of the drum about the drum central axis;

a means for determining the displacement of the elongate member, and

a robot calibration means.

9. A calibration system for a robot as described in claim 8, wherein the calibration means comprises the steps of:

storing a mathematical model of said robot,

storing a minimumization limit value,

storing a calibration data structure having a predetermined number of elements, each of said data structure elements containing a nominal distance, a measured distance, an equation expressing the element as a function of the robot parameters and a minimumization value;

perform iteratively until the calculated minimumization values in said calibration data structure are within said minimumization limit value;

a. performing iteratively for each calibration data structure elements;

i. instructing said robot to move said end-point to a predetermined location,

ii. determining the measured distance, the measured distance being the linear distance displaced by said elongate member attached to said end-point;

iii. storing said measured distance in said calibration data structure;

iiii. calculating the difference between the measured distance and the nominal distance;

b. determine the minimumization value for each calibration data structure element.