GB2185593A - Improvements in and relating to robot teaching - Google Patents

Abstract

The movement of a robot R having several axes of rotation is controlled by a model manipulation arm A. The model has all the axes of rotation of the full size robot, and movement at each axis of rotation of the model is monitored by electrical sensors and signals generated are used either directly or indirectly to move the robot a corresponding amount. A speed buffer may be provided so that the robot does not move too fast if the model is moved quickly. <IMAGE>

Description

SPECIFICATION Improvements in and relating to robot teaching The present invention relates to robot teaching especiallyforawelding robot and in particulartoan improved control device for a welding robot and for use in teaching same.

Atypical welding robot comprises a five or six axis of rotation manipulation arm carrying a welding gun/torch of appropriate type, for example to perform are welding. Such robots are programmable to undertake welding duties. The positioning and path of the torch have to be taught with some accuracy to ensure correct quality of the ensuing weld. All the five or six axes of rotation ofthe manipulation arm can be controlled independently but require to be controlled interactively to achieve the desired torch position.

Two known teaching systems are employed. In the first, an operator pushes a series of buttons, which are provided in pairs for each axis of rotation, i.e. one for clockwise rotation and one for anti-clockwise rotation. Thus, for a six axis machine, six pairs of buttons are provided. With such a control system it is difficult, if not impossible, to move the arm about more than one axis at once.

In another system, a joystick control is employed which can control a maximum ofthree axes of the robot at once. A separate switch has to be operated to switch thejoystickto control the other three axes.

In order to have the welding torch move on a straight path during welding, the start and finish points are input into the computer. This is done by first moving the welding torch by means of the controlierto the start point and pressing a memory button which inputs the coordinates of the welding robot. The robottorch is then moved to the end point, by any route, and the memory button pressed again. The computer electronics then computes a straight line path between the two parts which the robot follows during welding. In a similarway a circularwelding path is computed using circular interpretation by inputting three points on the circular path, e.g. start/finish point and two intermediate points. It will be appreciated that with the known robot controlling system, movement of the robot to the desired position is slow and awkward.

None of the known systems provide the ideal way of controlling movement of the welding robot. The construction of a welding robot is such that it is heavy and needs to be driven, i.e. it cannot be manipulated by hand to make use of a selfteaching system of programming.

It is an aim of the present invention to provide a robot teaching system especially for a welding robot which overcomes the above mentioned difficulties with the known systems. It is a further aim of the present invention to provide a robot controllerwhich moves the robot to the desired positionoralongthe desired path more easilythan known systems.

Accordingly, we propose a robot controller in the form of a manipulation arm having all the axes of rotation ofthe robot to be controlled. We preferto use a miniature scaled down robotwith a model weld torch or 'tool point' at its extremity. Thus, wherethe robot hasfive orsix axes of rotation we provide the same number of axes of rotation on our controller arm. Latest generation robots have up to seven axes, and accordingly, a corresponding number of axes would be provided on our model. By means of transducers (say a potentiometer) the movement of the controller at each axes of rotation can be monitored simultaneously and the position conveyed to the programmer unit to produce the same movements at the robot.Alternatively, each axis of rotation of the model may have an on-offtype switch to indicate when any axis is moved. The switch conveniently has a centre off position, and two on positions, one for rotation clockwise and one for rotation anti-clockwise. The switch may be spring-biassed to return to the off position when the model is released to signal termination of movement ofthe robot By means of such switches signals are sent to drive each axis of the robot in the appropriate direction orto terminate the movement. The position of the robot can be moved incrementally by this means.

The system is particularly useful as a control system for a welding robot where the movementsto be performed are particularly intricate and frequently involve movements which cannot be covered by the limited range of movements afforded by a single three axis controller. Nevertheiess, the system is equally applicable to any robot which because of its design or size for example, cannot be taught byfollowthrough techniques.

By means of the described controller an operator can physically move the torch or tool point of the model and, by means of servo motors on the robot arm and an electronic control link between the model and the robot can seethe movements translated to the actual robot arm. Thus, the operator can actually control the robot arm to carry out a welding operation and the movements performed by the arm can be committed to memory for programming purposes. The invention also enables the robot to be positioned quickly and easily at the desired positions formovementbystraightlineorcircular interpretation.

Thus, signalling means is required for each axis of rotation of the model/robot in orderthatchange in position of any axis is conveyed to the robot drive system. For example, when using on-offtype switches, three axes may be moved and therefore give an on signal - whilst the remaining axes where movement has not occurred give no signal. The electronics cause the corresponding axis ofthe robot to be driven (at a predetermined rate) when an on signal is received, and to stop driving when an off signal is indicated. By this means an incremented movement is produced as opposed to say a proportional movement.Such a proportional movement may be achieved, as an alternative, by transducers which monitorthe position of each axis of rotation of the model and convert these into electrical signals which can either be stored in the memory of a controlling microprocessor/computer for subsequent use or for immediate translation into signalsfor controlling the movementofthe individual axes of the robot For instance, a simple potentiometer may be utilised as the transducer. By a suitable buffer arrangement, the signals from the five or six axes ofthe model controller can be input or operated on to give the desired output movement which utilises the individual position signals interactively to control movement in several directions simultaneously.

It is felt desirable to incorporate what is termed "speed buffering" so as to avoid thefull size equipmenttravelling atthe same speed asthemodel teacher, in case the model is moved too fast. An optimum slow learning speed can be easily incorporated electronically into the robot drive commands.

Another aspect according to the invention isto have a model controllerfortheworkpiece holder/manipulator, operating on similar principles to that ofthe robot controller. Workpieces, to be operated on by robots, are typically held on a manipulatorwhichhassayoneortwo axes of rotation. Thus, by providing a model of the workpiece manipulator, the full size manipulator can be moved in a simplefasion.Typically,the manipulator is under the control of the same computerwhich controls the robot, thus, according to a refinement ofthe present invention, a model manipulator is provided in addition to a model robot so that both the robot and workpiece manipulator can be moved by the operator, say with one model in each hand.

The present invention will now be described further byway of example only, with reference to the accompanying drawing, which is a diagrammatic illustration of robot control means embodying the present invention.

Afull size robot, a welding robot in the illustrations, is shown at R. It has six axes of rotation provided by various limbs and indicated by the references 1 to 6. Respective servo controlled drive motors are provided to control movement of the limbs aboutthe respective axes (i.e. one motor for each axis). These are not described in further detail.

Anysuitabletype of drive motor is employed in which the position can be controlled.

The movement of each ofthe motors is controlled by signals from a drive motor controller B whose output signals are derived from input signals corresponding to the desired movements to be performed by the robot. The construction ofthe robot is such that its limbs cannot be moved unless driven bythe motors. The drive motorcontrollerB receives signals from a computer C which is programmed to producethe desired movements of the robot. These movements are stored in memory M to which the computer has access.

In orderto produce the desired program (i.e. the desired movements) a programming unit P is provided which inputs signals into the computer corresponding to outputsignalsfrom position transducers 7 to 12 according to one embodiment.

The position transducers are mounted on a miniature model Aofthe robot R. The model has the same axes of rotation and limb formation as the full size robot and atool-tipTwhose position is equatabletothe position of the robottool-tipT'.

Thus, by moving the tool-tip T' in the desired direction, the limbs ofthe model move in the same fashion as that required of the actual robot, and signals corresponding to those positions are generated by the transducers disposed at each axis of rotation of the miniature robot limbs. A position transducer is provided for each axis of rotation and each may comprise a graduated disc 13 and an optical viewing transducer 14 as perthe illustration.

Only one transducer is illustrated in the drawing. The disc is secured to one of the axes of rotation and the optical transducer is secured to a partfixed relative thereto. Thus,the transducer produces a signal conveniently in the form of pulses indicative ofthe angle of rotation. Bythis means as many as 64000 impulses may be generated for 360" of rotation.

Signal conditioning electronics 15 are provided to operate on the signal to ensure that the direction of rotation is taken into consideration and to enable a counter 16to be incremented ordecremented appropriately. Thus,the counters are incremented or decremented accordingly and thevalue committed to respective registers 17.

These registers may then be sampled atintervals approximate to or approximating to the required accuracy via straight line lengths in accordance with -the operating program. In the teaching mode the inputsignalsare relayed, preferablyviathe computer, to the drive motor controller Whereby the robot performs virtually instantaneously the movements input to it by the person operating the miniature robot. Thus, the operator gets feed back from the robot and moves the model in the appropriate direction so that the robotmoves along the desired path.

By using a controller which embodies all the axes of movementofthe robottheoperation ofteaching the robot the required movements can be performed quickly and easily by an operator. An alternative to the above described transducer is to utilise a simple potentiometer which outputs a signal related to its position. By controlling the robot in the manner described above it can be moved quickly to any desired position. Straightline or circular interpretation may be employed to movethe robot over the desired welding path.

The position of the robot axes can also be computed in relation to elapsed time, as measured by the computers built in clock, and retained in the computers memory during the teaching operation, and if the movements are satisfactory, they are saved to memoryso that subsequent operations ofthe robotare performed according to the program saved to memory.

According to another alternative embodiment, each of position transducers described above are replaced by respective ON-OFF switches. The model has a rest position into which its limbs are biased when no operatorforce is exerted on it, and in this position, each switch of each axis is in its OFF position. On movement of the model by its tool-tip, one or more of the axes move and on movement, the switch changes over to its ON position. The switch has two ON positions, one for clockwise rotation, and one for anti-clockwise rotation. The signal from a switch is transmitted to signal processing electronics and the appropriate drive motor of the robot is given signals to move when an ON signal is generated. By the use of appropriate electronics, the drive motor ofthe robot is caused to move at a predetermined rate when an ON signal is present.By this means a speed buffer may be incorporated in the electronics sothatthe robot does not move too fast when the model is moved too fast. On release ofthe model, it returns to its rest position in which OFF signals are given. The robot remains in the last set position until a revised command is given by moving the model and generating ON signals to cause the robotto move in the desired direction. The use of ON-OFF switches enables the robotto be positioned quickly by movement of the model robot with movement of all the relevant axes. Thus, positions can be committed to memoryquicklyforthe purposes of calculating straight line or circular paths.

Suitable switches, with a central OFF position and two ON positions are mounted on each axis of rotation ofthe model. This teaching/controlling method operates in the same manner as that described in the first mentioned example with the exception that the position ofthe model is not directly equated to the position of the robot.

The control and teaching of the movement ofthe workpiece manipulator is controlled similarly to that described with reference to the robot controller, and again a position transducer or ON-OFF switch type transducers may be employed as convenient.

As will be apparent from the fore going the present invention is directed to both a method and an apparatus for controlling the movements of a robot, be it a welding robot and/or a workpiece manipulating robot.

Claims (12)

1. Arobot controller in the form of a manipulation arm having all the axes of rotation of the robot to be controlled.

2. A robot controller as claimed in claim 1 in which the manipulation arm is a scaled down model of the robot.

3. A robot controller as claimed in any one of claims 1 or2 in which the manipulation arm has a plurality of axes of rotation, corresponding to each joint, and transducers are provided to monitor movement at each axis of rotation and convey position related signals to a programmer unit to produce the same movements in the robot.

4. A robot controller as claimed in claim 3 in which the transducers comprise an ON-OFFtype switch to signal movement or no movement at the joint.

5. A robot controller as claimed in claim 4 in which the switch provides centre-off and two on positions, oneforclockwise rotation and one for anti-clockwise rotation.

6. A robot controller as claimed in claims 4 or 5 in which the robot is moved at a predetermined rate on receipt of an on signal.

7. A robot controller as ciaimed in ciaim 3 in which electrical signals from the transducers are stored in the memory of a controlling micro processor/computer for subsequent use, or immediately translated into signals controlling movement of the individual axes of the robot.

8. A robot controller as claimed in claim 7 further comprising a buffer which inputs or operates on signals from the axes of the model controller to give the desired output movement utilising the individual position signals interactively to control movement in several directions simultaneously.

9. A robot controller as claimed in any preceeding claim further comprising speed buffering to limitthespeed of movement of the robot.

10. Arobotcontrollerasclaimed in any preceeding claim in which the robot to be controlled is a welding robot.

11. A robot controller as claimed in any one of claims 1 to 9 in which the robot to be controlled is a workpiece holder/manupulator.

12. A method of controlling a robot having several axes of rotation substantially as hereinbefore described.