Robot feature tracking devices and methods

• US 6,430,472 B1
• Filed: 12/20/1999
• Issued: 08/06/2002
• Est. Priority Date: 12/20/1999
• Status: Active Grant

• Current Assignee: Servo-Robot Inc.
• Original Assignee: Servo-Robot Inc.
• Inventors: Villemure, Denis, Boillot, Jean-Paul
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Marc, McDieunel, Marc, McDieunel
• Application Number:
  US09/466,927
• Time in Patent Office: 960 Days
• Field of Search: 700/245, 700/259, 700/95, 700/114, 700/254, 700/262, 700/62, 318/568.2, 318/568.13, 318/568.15, 318/568.18, 318/568.16, 318/568.11, 318/568.1, 318/577, 701/23, 901/41, 901/42, 901/47, 901/9, 901/4, 414/5, 219/121.61, 219/121.84, 219/121.11, 219/121.31, 219/121.63, 219/121.64, 219/121.82, 219/121.83, 219/125.1
• US Class Current: 700/245
• CPC Class Codes: G05B 19/056 Programming the PLC
• CPC Class Codes: G05B 2219/13102 Function is a user written program, separate from rest
• CPC Class Codes: G05B 2219/14093 Display matrix of relay, contact symbols, select and show time

Abstract

Motorized slides are inserted between the end of a robot arm and a robot tool/sensor arrangement to provide additional positioning ability. A control unit of the slides cooperates with the control unit of the sensor to maintain the tool correctly positioned over a feature while the robot arm moves following a programmed path. The control unit of the sensor has look-ahead and additional buffers from which corrected information is determined to compensate for robot teaching inaccuracies, calibration and robot arm response errors. A sensor with two distinct probing zones is used to get information about the position of the tool tip and of the feature to assist in calibrating the sensor/tool relation.

Claims

1. A motorized slide assembly for providing additional positioning ability to a tool at an end of a robot arm, comprising:

a slide arrangement having a base and a sliding element movable along a predetermined course relative to the base;

a motor mounted onto the slide arrangement;

a drive means connected to the motor for moving the sliding element along the course upon operation of the motor;

a means for fastening the base of the slide arrangement to the end of the robot arm; and

a means for fastening the tool onto the sliding element.

2. The motorized slide assembly according to claim 1, wherein:

the sliding element comprises a plate and the base comprises spaced apart, opposite lateral surfaces slideably receiving the plate.

3. The motorized slide assembly according to claim 2, wherein:

the base comprises an elongated frame having spaced apart, opposite end faces extending between the lateral surfaces;

the motor is mounted on one of the end face; and

the drive means comprises a worm screw extending between the end faces and coupled to the motor, and a toothed member projecting from the plate and meshed with the worm screw.

4. The motorized slide assembly according to claim 1, wherein:

the motor is provided with an encoder.

5. The motorized slide assembly according to claim 1, wherein the means for fastening the base of the slide arrangement onto the end of the robot arm comprises a mounting surface provided by the base, adapted to receive the end of the robot arm.

6. The motorized slide assembly according to claim 1, wherein the means for fastening the tool to the sliding element comprises a clamp projecting from the sliding element opposite the base of the sliding arrangement.

7. The motorized slide assembly according to claim 6, wherein the clamp has a mounting surface opposite the sliding element, adapted to receive a sensor.

8. The motorized slide assembly according to claim 1, further comprising:

an additional slide arrangement having a base and a sliding element movable along a predetermined course relative to the base, the base of the additional slide arrangement being connected to the sliding element of the slide arrangement so that the course of the sliding element of the additional slide arrangement is substantially perpendicular to the course of the sliding element of the slide arrangement, the sliding element of the additional slide arrangement being provided with the means for fastening the tool to the sliding element;

a motor mounted onto the additional slide arrangement; and

a drive means connected to the motor mounted onto the additional slide arrangement, for moving the sliding element of the additional slide arrangement along the course upon operation of the motor.

9. The motorized slide assembly according to claim 8, further comprising a block assembling the slide arrangements.

10. A motorized slide system for providing additional positioning ability to a tool at an end of a robot arm, comprising:

a motorized slide assembly including;

a slide arrangement having a base and at least one sliding element movable along a predetermined course relative to the base;

at least one motor mounted onto the slide arrangement;

at least one drive means connected to said at least one motor for moving said at least one sliding element along the course upon operation of said at least one motor;

a means for fastening the base of the slide arrangement to the end of the robot arm;

a means for fastening the tool onto said at least one sliding element; and

at least one encoder operatively coupled to said at least one motor to provide motor positional information; and

a control unit for the motorized slide assembly, including;

a communication interface for receiving sensor related data;

a I/O interface for receiving and transmitting synchronization signals;

a CPU for controlling positions of said at least one sliding element;

a memory;

a servo-amplifier circuit for powering said at least one motor;

a slides control for controlling said servo-amplifier circuit in response to the CPU and the motor positional information provided by said at least one encoder; and

a bus circuit interconnecting the communication interface, the I/O interface, the CPU, the memory and the slides control together.

11. A compensation method for compensating errors made by a control unit of a robot sensor when evaluating a relation between a position of a robot guided tool behind the sensor and a position of a feature to be followed by the guided tool, comprising the steps of:

recording position data generated by the sensor during a dry pass of the guided tool over the feature, the position data representing consecutive positions of the feature detected by the sensor; and

subtracting the recorded position data from joint position errors computed by the control unit during a feature tracking operation where the guided tool is operated to process the feature.

12. The compensation method according to claim 11, wherein:

the control unit comprises a look-ahead buffer that stores a number of position data of the feature detected by the sensor ahead of the guided tool from a prior position of the sensor to a position of the sensor when the guided tool reaches the prior position of the sensor;

the recorded position data are stored in an additional buffer of the control unit, the recorded position data being sampled at a same sampling rate than the position data stored in the look-ahead buffer; and

the step of subtracting comprises, during the feature tracking operation;

extracting the position data of the feature stored in the look-ahead buffer corresponding to a current position of the guided tool;

extracting the position data stored in the additional buffer corresponding to a current position of the guided tool; and

subtracting the position data derived from the additional buffer and a current position data of the guided tool from the position data derived from the look-ahead buffer to produce a position correction data that compensates the position data extracted from the look-ahead buffer from teaching errors.

13. The compensation method according to claim 12, further comprising the steps of:

adding the position correction data to the current position data of the guided tool to provide a new current position data for the guided tool;

adding the new current position data for the guided tool to the position data of the feature at a current position of the sensor, to provide a look-ahead position data for the feature; and

storing the look-ahead position data in the look-ahead buffer in relation with the current position of the sensor.

14. A control unit for a robot sensor tracking a feature to be processed with a robot tool positioned behind the robot sensor, comprising:

a sensor interface having a sensor control output and a video input;

a memory connected to the sensor interface;

a CPU connected to the sensor interface and the memory; and

a communication interface connected to the CPU, the memory and the sensor interface, and having a communication port;

wherein;

the memory includes;

a look-ahead buffer that stores a number of successive feature position data computed by the CPU from signals received at the video input, as a function of tracked successive positions reached by the robot sensor during displacement over the feature; and

an additional buffer connected to the look-ahead buffer, that stores a number of the successive feature position data as a function of tracked successive positions reached by the robot tool;

and the CPU has an operating mode causing a computation of a corrected position value required to maintain the robot tool correctly positioned over the feature by subtracting a current position of the robot tool and one of the position data stored in the additional buffer related to the current position of the robot tool from one of the position data stored in the look-ahead buffer related to the current position of the robot tool, and a transmission of the corrected position value through the communication port of the communication interface.

15. The control unit according to claim 14, wherein the CPU computes a next current position of the robot tool by adding the corrected position value to the current position of the robot tool.

16. The control unit according to claim 15, wherein the current position of the robot tool corresponds to a tool center point received through the communication port of the communication interface.

17. A robot sensor assembly for simultaneously detecting a position of a feature at a given look-ahead distance in front of a tool and a position of a tip of the tool, comprising:

a sensor body;

a bracket for side attachment of the sensor body to the tool;

a first probe means attached to the sensor body and directed toward the feature in front of the tool, for providing surface range data along the feature whereby the position of the feature at the look-ahead distance in front of the tool is determinable; and

a second probe means attached to the sensor body and directed toward a target region including the tip of the tool and the feature under the tip of the tool, for providing an image of the target region whereby the position of the tip of the tool is determinable.

18. The robot sensor assembly according to claim 17, wherein:

the first probe means comprises an optical profiler module providing surface height samples forming the surface range data; and

the second probe means comprises a vision module providing the image of the target region.

19. The robot sensor assembly according to claim 18, wherein:

the optical profiler module has a first portion comprising;

a laser source;

a line generator coupled to the laser source;

mirrors optically coupled to the line generator and directing a light line derived therefrom at a tilt angle relative to a plane in which the feature extends and substantially crosswise to the feature in a measuring field in front of the tool; and

a background lighting filter arranged to filter a scattering of the light beam derived from the light line crossing the feature;

the vision module has a first portion comprising;

an orientation-adjustable mirror directed toward the target region;

a fixed mirror facing the orientation-adjustable mirror;

an adjustable disk provided with a group of optical filters selectively positionable behind the fixed mirror; and

a wedge prism behind the adjustable disk and next to the background lighting filter of the first part of the optical profiler module;

and the optical profiler and vision modules have a combined second portion comprising;

a diaphragm behind the background lighting filter and the wedge prism, with apertures facing respectively the background lighting filter and the wedge prism;

an imaging lens behind the diaphragm; and

a CCD sensor positioned behind the imaging lens and having a first sensitive area oriented so that every point within the measuring field, viewed through the imaging lens, is substantially in focus, and a second sensitive area oriented to receive light rays passing through the wedge prism and the imaging lens.

20. A sensor control unit for a robot sensor assembly according to claim 18, comprising:

a range processing circuit having an input for receiving a video signal produced by the robot sensor, and an output for producing surface range data extracted from the video signal;

a frame grabber having an input for receiving the video signal produced by the robot sensor, and an output for providing image frames stored in the frame grabber;

a main CPU having an input connected to the output of the range processing circuit, and a communication port,

a secondary CPU having an input connected to the output of the frame grabber, and a communication port;

a communication link interconnecting the communication ports of the main and the secondary CPUs; and

a communication interface connected to the communication link;

and wherein;

the secondary CPU has an operating mode causing a processing of the image frames stored in the frame grabber, a determination of the position of the tip of the tool from the image frames, and a transmission of the position of the tip of the tool to the main CPU via the communication link; and

the main CPU has a sensor/tool calibration mode causing a storage of the position of the tip of the tool received from the secondary CPU as calibration data, and a subsequent processing mode causing a comparison of the position of the tip of the tool received from the secondary CPU with a corresponding position in the calibration data, a computation of tool positioning correction values, and a transmission of the correction values through the communication interface.