Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
1998-07-10
2001-05-01
Sheikh, Ayaz (Department: 2781)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C700S261000, C700S250000, C700S264000
Reexamination Certificate
active
06226565
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method for control of the movement of an industrial robot along a given track. The industrial robot has a plurality of movement axes (
1
-
6
). Each axis has servo equipment for control of the axis movement in accordance with reference values supplied thereto.
BACKGROUND ART
The invention relates to an industrial robot which has a plurality of movement axes, typically six axes. Such a robot has a stand which is rotatably arranged on a foot and which supports a first robot arm which is rotatable in relation to the stand. In the outer end of this arm, and rotatable in relation thereto, a second robot arm is arranged. In the following, the first arm is referred to as the lower arm and the second arm as the upper arm. At its outer end the upper arm supports a hand which is provided with a tool attachment and which is rotatable in two or three degrees of freedom relative to the upper arm. The robot is provided with servo equipment for control of the position and the orientation of the robot hand. For each one of the movement axes of the robot, servo equipment comprising a driving motor and a position sensor is provided, the latter delivering a signal which is a measure of the angle of rotation of the axis in question. The servo system of each axis is supplied with a reference value for the angle of rotation of the axis, and the driving motor of the axis brings the robot to move in the axis in question until the axis position indicated by the position sensor of the axis coincides with the reference value supplied to the servo system.
An industrial robot can be ordered to follow, at a certain speed, a track which is given in the form of a number of points in a Cartesian system of coordinates. For the robot to follow the given track, the axis angles required therefor must be calculated. For this purpose, the track is stepped with a length of step which is based on the given speed and an internal sampling time. For each step, the next position which the robot is to assume is first calculated in Cartesian coordinates. Then, the axis angles required for the robot to assume this position are calculated.
With the aid of a mathematical model for the robot, the axis torque required for driving the axes in accordance with the calculated axis angles can be calculated. A check is made whether any of the calculated axis torques exceeds the motor torques which the respective motor is capable of generating. If the available motor torque is not sufficient for carrying out the movement, the movement is adjusted, for example by reducing the speed and the acceleration, such that the available motor torque of each axis is utilized optimally while at the same time the robot still follows the track.
To prevent the mechanical structure of the robot from being overloaded, the mechanical structure must be designed such that, from the strength point of view, it endures loads caused by all conceivable combinations of individual axis movements. This requires designing the structure for a worst case which perhaps seldom occurs. This leads to the robot becoming unnecessarily slow for typical movements and causes the maximum permissible speed and load of the robot to be set unnecessarily low in order not to overload the structure. It is primarily some critical components which, for certain movements, are subjected to high loads and hence must be dimensioned for these loads.
SUMMARY OF THE INVENTION
The object of the invention is to suggest a method for control of an industrial robot along a track, which provides a possibility of reducing the dimensions of the mechanically critical parts compared with prior art robots.
According to the invention, while at the same time as the available motor torque is utilized to a maximum, mechanically critical components are to be monitored such that maximally allowed loads in the components are not exceeded. If the maximally allowed loads risk being exceeded, the movement along the track is to be modified such that the allowed loads are not exceeded.
The advantages of the invention include that it provides a possibility of dimensioning critical components more aggresively without risking mechanical overload. This gives great cost advantages. For example, a smaller wrist gives lower weight of the whole upper arm, which is of great importance for the dimensioning of the rest of the robot.
The necessary reductions of the motor torque need only occur in certain extreme combinations of axis angles. The other axis angles utilize the available motor torque in full. In this way, the robot may be designed so as to manage carrying out typical movements with a high performance. Other movements which occur more seldom are carried out with reduced motor torque so as not to exceed the critical components of the robot.
The invention also makes it possible to use loads which are larger than what is currently allowed for the robot, since there is no risk of overloading in the critical components.
REFERENCES:
patent: 4819184 (1989-04-01), Jonsson et al.
patent: 5325467 (1994-06-01), Torii et al.
patent: 5528116 (1996-06-01), Snell
patent: 5590034 (1996-12-01), Snell
patent: 5708342 (1998-01-01), Nihei et al.
patent: 5751130 (1998-05-01), Hara et al.
Elfving Staffan
Snell John-Erik
Asea Brown Boveri AB
Backer Firmin
Connolly Bove & Lodge & Hutz LLP
Sheikh Ayaz
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