Abstract:
Disclosed is a calibration method for compensating an offset occurring when parts in an industrial robot are exchanged with now ones. A signal generation part is attached to a moving part of the robot. While the moving part is moving, a signal detection part detects the movement of the signal generation part with a sensor therein, and calibration data are generated on the basis of the detected signals. Preset calibration data are amended using a difference between the generated calibration data and the preset calibration data, so that the offset is compensated.

Description:
This application is a divisional of application Ser. No. 09/143,649, filed Aug. 31, 1998, now U.S. Pat. No. 6,035,695. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a calibration method using a sensor, and more particularly, to a calibration method for compensating an offset occurring when a driving element such as a motor and a belt in a transmission part attached to a body of the robot or a sensor for sensing the movement of a shaft of an arm in the robot is exchanged with a new one. 
     2. Prior Art 
     When a mechanical appliance requiring a precise position control such as an industrial robot undergoes a troubleshooting on a part or entire parts thereof, or it is disassembled and assembled in order to exchange parts therein with new ones, an offset may occur which is a variation of the initial position of a moving part such as an arm in the robot from a preset position thereof. Such an offset results in the reduced accuracy of the position control on the basis of the preset calibration data. Therefore, a new calibration should be necessarily performed so that the preset calibration data are amended, in order to compensating the offset after the parts are exchanged with new ones. 
     In conventional art, if the offset has to be compensated after the parts in a robot body such as a motor are exchanged, the calibration has been performed by utilizing a jig for exclusive use in calibration, or on the basis of marks signed on the robot body. 
     The calibration using the calibration jig is performed according to the following steps. 
     (1) detaching a working tool attached to the robot body. 
     (2) attaching a calibration tool. 
     (3) performing calibration using the calibration tool. 
     (4) amending calibration data or compensating an offset with the performed calibration results. 
     (5) detaching the calibration tool. 
     (6) attaching the working tool again. 
     Such a calibration method using the calibration jig requires a high preciseness of the calibration jig. Further, the working tool and the calibration tool must be exchanged with each other two times, so the calibration process is very troublesome and much time is consumed, which may cause a lowering of productivity. 
     Meanwhile, the calibration using the marks inscribed on the robot body is performed according to the following steps. 
     (1) moving every part of the body to the marked positions. 
     (2) amending the calibration data or compensating the offset using the present position of the robot. 
     Such a method does not bring about the troublesome job of exchanging the tools as the case of utilizing the calibration jig, however, that method is not preferable since the preciseness of the calibration is low. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed to overcome the above-described problems in the prior art, and accordingly it is the object of the present invention to provide a calibration method of a robot, which can amend the offset simply and precisely without the troublesome job of exchanging the tools in order to use a calibration jig. 
     To achieve the above object, the present invention provides a calibration method of an industrial robot, comprising the steps of: preparing a signal generation part attached on a moving part of the robot, the signal generation part for providing a signal about a position of the moving part, and a signal detection part for detecting the signal from the signal generation part; moving the moving part; generating calibration data on the basis of the position of the moving part detected by the signal detection part; calculating a difference between the generated calibration data and preset calibration data; and amending the preset calibration data on the basis of the difference so that an offset is compensated. 
     Here, the step of moving the moving part comprises the steps of, rotating the moving part in one rotational direction, stopping the moving part when a variation of the signal detected by the signal detection part is checked, and rotating the moving part in a reverse rotational direction. Furthermore, in the step of generating the calibration data, the calibration data are generated on the basis of the position of the moving part at a time point that the variation of the signal detected by the signal detection part is checked during the step of rotating the moving part in the reverse rotational direction. 
     Preferably, the moving part is rotated at a high rotational velocity during a rotation thereof in the one rotational direction, and at a low rotational velocity during a rotation thereof in the reverse rotational direction. 
     According to the present invention, the calibration can be performed in a short period of time without the inconvenience of exchanging a calibration jig. Furthermore, the preciseness of calibration is high. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a robot control system for realizing a calibration method according to the present invention; and 
     FIG. 2 is a flow chart of the calibration method according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1 is a block diagram of a robot control system for realizing a calibration method according to the present invention. The robot  10  has a motor  11 , a transmission part  12 , an arm  13 , a signal generation part  14 , and a signal detection part  15 . 
     The motor  11  generates a force for driving the robot  10 . The transmission part  12  comprises a belt, gears, etc., and transmits the driving force of the motor  11  to the arm  13 . The arm  13  is moved by the driving force transmitted by the transmission part  12 . The signal generation part  14  is attached to the arm  13 , moves together with the arm  13 . The signal generation part  14  provides an information about the position of the arm  13 . The signal detection part  15  has a sensor (not shown) for sensing the signal generation part  14 , and detects the signal generated by the signal generation part  14 . 
     The robot control system comprises a superior controller  20 , a motion controller  30 , and a motor controller  40 . 
     The superior controller  20  is a computer for controlling the operation of the robot  10 , and has a signal input part  21 , a program control part  22 , and a data storage part  23 . The signal input part  21  is an interfacing circuit for receiving the signals from the signal detection part  15 . The program control part  22  controls the robot  10  according to the signal input through the signal input part  21  on the basis of programs stored therein. Furthermore, a key input part  4  for receiving the commands of a user and a display part  25  for displaying the operational status of the robot  10  and all relevant data are connected to the superior controller  20 . 
     The motion controller  30  controls the motor controller  40  according to the commands of the superior controller  20 , and the motor controller  40  directly controls the operation of the motor  11 . In other words, when the superior controller  20  analyzes the commands of the user input through the key input part  24  and then commands the operation of the robot  10 , the motion controller  30  receives the commands and drives the motor  11  through the motor controller  40 . As the motor  11  is driven, the driving force thereof is transmitted to the arm  13  through the transmission part  12 , and the arm  13  is rotated for the desired operation of the robot  10 . 
     While the arm  13  is rotating, the signal generation part  14  attached thereto rotates with it and the signal detection part  15  detects the position of the signal generation part  14 . In such a situation, through the signal input part  21  the superior controller  20  receives the signal detected by the signal detection part  15 , and determines the position of the arm  13  and performs required control. 
     Hereinbelow, the calibration method according to the present invention will be described with reference to such a robot control system and FIG.  2 . 
     When a signal from the key input part  24  operated by a user is input to the superior controller  20 , the superior controller  20  commands the motion controller  30  to rotate the arm  13  in one rotational direction, and the motion controller  30  drives the motor  11  of the robot  10  through the motor controller  40  according to the command of the superior controller  20 . Then, the motor  11  is rotated, and the driving force thereof is transmitted to the arm  13  through the transmission part  12 , whereby the one arm  13  is rotated S 1  in the rotational direction. In such a situation, the motor  11  rotates the arm  13  preferably at a high rotational velocity. 
     While the arm  13  is rotating, the signal generation part  14  attached to the arm  13  also rotates together with the arm  13 . The superior controller  20  checks S 2  for any variation of the signal detected by the signal detection part  15  with respect to preset reference values. If no variation of the detected signal is detected, the rotation of the arm  13  is continued, and if a variation is detected, the velocity of the motor  11  is reduced gradually to stop S 3  the arm  13 . 
     Then, the motor  11  is driven reversely, preferably at a low rotational velocity so as to rotate S 4  the arm  13  in a reverse rotational direction. While the arm  13  is rotating reversely at a low rotational velocity, the superior controller  20  checks S 5  again for a variation of the signal detected by the signal detection part  15 . If no variation is detected, the arm  13  is continued to rotate reversely. 
     If a variation of the signal detected by the signal detection part is detected while the arm  13  is rotating reversely, the superior controller  20  generates S 6  calibration data using the rotational position of the arm  13  at the time point that the variation is checked, and stops the motor  11  to stop S 7  the movement of the arm  13 . 
     Then, a difference between the calibration data achieved by the above-described process and preset calibration data is calculated S 8 , and the preset calibration data are amended S 9  using the difference so that the offset is compensated. The amended calibration data are stored in the data storage part  23 . 
     As illustrated above, new calibration data can be achieved by performing the calibration for compensating the offset with the existent robot control system. 
     According to the present invention, the calibration can be performed in a short period of time without the inconvenience of exchanging tools as the conventional calibration method using a calibration jig. Furthermore, the calibration can be performed more precisely in comparison with the conventional calibration method using marks. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, wherein the spirit and scope of the present invention is limited only by the terms of the appended claims.