EP3310536A1

EP3310536A1 - Improving the temperature drift compensation by calibrating on the component and teaching the parameter sets

Info

Publication number: EP3310536A1
Application number: EP16731036.6A
Authority: EP
Inventors: Michael Groll; Markus Hager; Sebastian Kaderk; Robert Miller; Ralf Mittmann; Thomas Purrucker
Original assignee: KUKA Roboter GmbH
Current assignee: KUKA Deutschland GmbH
Priority date: 2015-06-22
Filing date: 2016-06-20
Publication date: 2018-04-25
Also published as: DE102015211405A1; WO2016206797A1; CN107771118A

Abstract

The invention relates to a method for controlling a manipulator. Said method consisting of providing a temperature-dependent calibration, using said calibration a correction parameter set is calculated which is based on determined reference point residual drift values. Subsequently, the manipulator is controlled by taking into account the correction parameter set.

Description

Improvement of the temperature drift compensation by

Calibration on the component and teaching the parameter sets l. Technical part

The present invention relates to a method for controlling a manipulator and a corresponding robot system. 2. Technical background

Robots, and in particular industrial robots, are automatically controlled, freely programmable multipurpose manipulators. They are designed for use in industrial environments and can thus be used in different areas of a production plant. For example, an industrial robot can be used to measure one or more measuring points of a component in a processing station or surveying station, or to run a specific path program on a workpiece while processing the workpiece or component by means of, for example, a folding tool.

Before use, the industrial robot usually needs to be calibrated to obtain a complete kinematic model of the robot. For this purpose, different parameters of the robot mechanics must be determined in order to finally obtain a complete robot model. In addition, the robot must be aligned with respect to the component to be measured or machined: In this case, a reference from the coordinate system of the robot to the coordinate system of the

Workstation or the component are manufactured. For this example, reference points can be approached, which represent a fixed point in space. A reference point may e.g. be read optically, or manually from one

Robots are approached. Because the position of a reference point in the

World coordinate system is defined by detecting the reference point, for example, the exact position of an end effector of the robot using

corresponding transformations between the robot coordinate system and the world coordinate system are determined.

CONFIRMATION COPY By friction in the mechanical elements of a robot and by the

Waste heat of electrical components changes the temperature of the

Robot mechanics. This can lead to a change in size of the individual elements, as well as a change in the viscosity of liquids and changes in the

Elasticity of elements, such as the transmission, bring with it. If the parameters of the robot model are not updated cyclically, there is a so-called drift in the positioning of the robot, which superimposes the repetition and absolute accuracy of the robot. This drift is stuck on a

Reference body, or reference body, with known or measured positions measurable.

From an in-house method is known to determine an optimized model parameter set during calibration. The model parameter set or the parameterizable mathematical robot model is used for the control of the manipulator. In order to determine the optimized model parameter set, deviations of the positioning of the robot on a temperature-stable calibration body are measured. The optimization then takes place by minimizing the residual error of the positioning. As the effect of temperature drift on

Different poses will affect each other differently, it will try over

Extreme poses of the manipulator as widely varying as possible and a large one

Axis position covering axle area to determine. However, only the effects resulting from the measurements on the calibration body are compensated for.

However, effects that are caused by the temperature change of the kinematics can not be mapped by the robot poses on the calibration body and are therefore not compensated.

During a typical measuring cycle, a component is introduced into a measuring cell, measured and then discharged again. This heats the robot. Consequently, the parameters of the robot model determined at the beginning of the cycle are becoming increasingly poorer in the actual positioning of the robot during the course of the cycle. Consequently, a higher residual drift at the measured points is to be expected late in the cycle. The validity of the optimized parameter set for the entire workspace is based on the assumption that a selection of extreme poses shows all temperature effects. However, this approach involves the risk that parts of the working space are not covered or that temperature-dependent effects are generally not taken into account. This leads to a visible residual drift at the component points. This residual drift on the component is composed of uncompensated, temperature-dependent influences on the positioning as well as a temperature drift due to heating of the kinematics since the last calibration. The present invention is therefore based on the object to provide a method and a robot system, which minimize the disadvantages listed above - at least partially. It is a further object of the present invention to increase the precision of a robot or manipulator. These and other objects are achieved by the subject of the main claims.

3. Content of the invention

The present invention includes a method for controlling a manipulator. The manipulator can be differently pronounced and is controlled based on a manipulator or robot parameter set.

The method according to the invention comprises providing a calibration, which is preferably a temperature-dependent calibration. Preferably, the providing may include creating the calibration. The calibration has the following steps: Repeated start of at least one reference point, and in particular two or M reference points, until a temperature criterion of

Manipulator is satisfied, and determined, after each start, a calibration set comprising at least one comparison reference point residual drift and a manipulator parameter set.

The approach of a reference point means a detection of the reference point, which can be done, for example, optically or by touch. Of the

Reference point has a well-known position. Thus, an assignment to the world Coordinate system as well as the basic coordinate system of the measuring robot known. Preferably, the reference points are in the vicinity of the measuring points,

Processing points or component points on the component, and can also be arranged directly on the component. When determining the calibration rate, a residual drift with respect to the approached reference point is determined.

Preferably, at least two reference points are approached repeatedly, and after each approach of the two reference points, a calibration set is determined which comprises at least one comparison reference point residual drift and a manipulator parameter set. In this case, one of the reference points is preferably one

Component point, which is to be approached in the operating mode of the manipulator or robot. Further preferably, one of the reference points is not

Component point, and is also approached during normal operation or during a normal operating cycle of the robot. The calibration set preferably comprises a comparison reference point residual drift with respect to this

Reference point was determined. The comparison reference point residual drifts are used to calibrate or optimize the model parameter set. This model parameter set is then provided as a manipulator parameter set in the calibration set. Thus, each calibration set comprises a manipulator parameter set which has been created on the basis of the residual drifts in relation to at least one comparison reference point residual drift at the reference point.

Preferably, the temperature criterion is selected such that the starting and determining is repeated until the temperature of the robot is in a stable state and changes only marginally. Thus, the calibration is preferably performed while the robot is heating. In particular, after activating or switching on a robot or manipulator, the temperature of the robot changes rapidly and reaches a constant value after a certain time. During this time, preferably the calibration or

Temperature-dependent calibration performed to advantage all

to detect temperature-dependent effects.

The method according to the invention for controlling a manipulator also has a start-up of, in particular exactly one or N, reference points (s). This Start-up is in normal operation of the manipulator, or also

Operating mode, performed, and not during calibration. Furthermore, the method comprises determining a current reference point residual drift. Consequently, in the productive mode, the instantaneous reference point residual drift with respect to the

5 approached reference point determined. Preferably, the number of

Reference points N smaller than the number of reference points M. Thus, a precise correction for various manipulator actions can be granted.

Furthermore, the method according to the invention comprises calculating a

l o Correction parameter set based on the determined instantaneous reference point residual drift and based on at least one of the calibration sets. Thus, will

Preferably, at least the manipulator parameter set from the calibration is used to calculate the correction parameter set. It is the

Calibration set of the calibration from which the manipulator parameter set is to be used, based on the instantaneous reference point residual drift determined in the operating mode. Thus, advantageously, a suitable

Correction parameter set are determined, with a suitable value or

Manipulator parameter set can be selected from the calibration based on the determined instantaneous reference point residual drift.

0

Furthermore, the method according to the invention comprises controlling the manipulator based on the calculated correction parameter set. In this case, for example, the current robot model can be updated using the correction parameter set, or even be replaced by this. The skilled person understands that by means of

25 not only the robot model can be optimized, but also track points can be adapted from a path planning. In this case, the control preferably comprises measuring with the aid of the manipulator below

Consideration of the correction parameter includes. For example, a distance measurement can be carried out by means of the manipulator, wherein the

0 Manipulator preferably its suitable device, such. has a laser.

Furthermore, the control may also include moving the manipulator in consideration of the correction parameter. The "reference point" can thus be any point in the environment of the

Manipulator, and may for example be a component point, ie a point on a component or workpiece. The term "comparison reference point residual drift" may describe a residual drift at a reference point which is determined in the course of the calibration.A analogously, the term "instantaneous reference point residual drift" may describe a residual drift at a reference point, which is determined in the course of the operating mode , In turn, a "calibration set" may be a dataset that includes a plurality of values, such as a comparative reference point residual drift and a manipulator parameter set One, several, or all calibration sets determined during calibration may be provided in a controller of the manipulator or separately "Restdrift" itself does not have to be corrected, so it can only be a "drift".

Preferably, providing the calibration includes creating the calibration. Preferably, the calibration is carried out before the production operation of the manipulator, so that the calibration already exists during the working operation or measuring operation of the manipulator. Thus, the correction parameter sets can be determined directly based on the calibration, so that the manipulator can be controlled precisely based on the correction parameter set.

Preferably, the repeated starting comprises a repeated approach of two reference points, wherein preferably one of the reference points is a component point. Thus, by means of the calibration set, the model parameters or robot parameters can be optimized efficiently with respect to the points approached in the production mode. Preferably, after each repeated start during the

Calibration for a comparison reference point residual drift a parameter set is stored and recorded in the calibration record.

Preferably, the determined calibration sets comprise two comparison reference point residual drifts and one manipulator parameter set.

Preferably, calculating the calibration set comprises the steps of: selecting a calibration set based on the determined instantaneous reference point residual drift such that the comparative reference point residual drift of the selected one Calibration set is closest to the determined instantaneous reference point residual drift, and creating the correction parameter set based on the selected calibration set. Thus, a best fit calibration set is selected so that the difference between the determined instantaneous reference point residual drift and the comparative reference point residual drift of the selected calibration set is minimal.

This ensures that the calibration set from the calibration best matches the instantaneous state of the manipulator.

Creating the correction parameter set based on the selected one

For example, the calibration set may include creating a correction parameter set based on the manipulator parameter set of the selected calibration set. Preferably, a calibration set is selected, wherein the comparison reference point residual drift from the calibration with the instantaneous reference point residual drift from the productive operation is closest, so that in the

Calibration determined manipulator parameter set best fits the current state of the manipulator and thus for the calculation of the

Correction parameter set and consequently for controlling the manipulator, such as the start or measurement of a component point, can be used. Preferably, calculating the correction parameter set comprises the steps of: selecting at least two different calibration sets based on the determined instantaneous reference point residual drift so that the comparison reference point residual drifts of the selected calibration sets are closest to the determined instantaneous reference point residual drift and creating of

Correction parameter set based on an interpolation of the selected

Calibration kits. Thus, two calibration sets are used, which best reflect the current state of the manipulator. The correction parameter set is then created based on an interpolation of these two calibration sets or based on an interpolation of the manipulator parameter sets of the selected calibration sets. It is thus possible to obtain a correction parameter set from the

Get calibration that best fits the current state of the manipulator. The person skilled in the art understands that more than two calibration sets can also be selected based on the instantaneous reference point residual drift determined in the production mode and can be used for the calculation of the correction parameter set. Thus, for example, if three calibration sets have been selected, a correction parameter set can be calculated based on a spline interpolation of the calibration sets or the corresponding manipulator parameter sets. Furthermore, the person skilled in the art understands that the method according to the invention can also be combined with other methods for the compensation of different drifts. In particular, the method according to the invention is suitable for minimizing residual drift or the effect of residual drift.

With the present invention, a calibration is thus carried out in which a great many (temperature-dependent) states of the robot are detected. By comparing a momentary reference point residual drift with a comparison reference point residual drift from the calibration, a suitable manipulator parameter set from the calibration can thus be used for the instantaneous state of the manipulator. In this case, the present invention allows the

Positioning accuracy of a robot or manipulator to improve. In this case, for example, a high accuracy of better than + 0.15 mm can be achieved.

The present invention further comprises a robot system having means for carrying out the method according to the invention. The means include in particular a robot controller. Further, the present invention includes a computer-readable medium containing instructions that, when executed by a processing system, perform steps to control a manipulator according to the inventive method for controlling a manipulator.

Fourth Embodiment (e) In the following, the present invention will be described in detail with reference to the accompanying drawings. It shows:

1 shows the sequence of the calibration according to the present invention, and Fig. 2 shows an inventive method for controlling a manipulator.

FIG. 1 schematically shows the sequence or process 10 of a (temperature-dependent) calibration according to the present invention. The process 10 begins in step n. In step 12, a reference point is approached by the manipulator. This reference point is preferably not on the component, but is provided independently of the component. In step 13, a comparison reference point residual drift with respect to the approached in step 12 reference point is determined.

In step 14, a component point is approached, i. a point on that too

measuring or to be machined component is approached by the manipulator. In the following step 15, a comparison component residual drift is determined, ie the residual drift between the manipulator and the approached component point.

In step 16, a correction parameter set is created. For this purpose, a manipulator parameter set or model parameter set is determined on the basis of at least the comparison reference point residual drift determined in step 13 and / or the comparison component residual drift determined in step 15. In the correction parameter set, this manipulator parameter set is linked to the comparison reference point residual drift determined in step 13. Subsequently, this correction parameter set is stored in a corresponding calibration database.

In the decision 17, it is checked whether the temperature of the manipulator has exceeded a predefined limit value. Alternatively, in decision 17 it can also be checked whether the temperature of the manipulator has reached a constant value. If the decision 17 is negative, a new calibration set is determined by continuing the process at step 12. If the decision 17 is positive, the calibration ends in step 18.

Thus, several calibration sets are determined with the calibration, wherein in each calibration set a comparison reference point residual drift is associated with a manipulator parameter set. Each calibration set was thereby at a determined different temperature of the manipulator. Only when the temperature of the manipulator is preferably approximately stable, the calibration is terminated.

FIG. 2 schematically shows the sequence 20 of a method according to the invention for controlling a manipulator. This method is preferably used in

Working or operating mode performed. The process begins in step 21. In step 22, a (temperature dependent) calibration is provided.

Preferably, the calibration has been performed according to the process illustrated in FIG. 1 and provides appropriate calibration sets.

In step 23, a reference point is approached by the manipulator. This reference point is identical to the reference point which was approached or measured during the calibration. In step 24, an instantaneous reference point residual drift is determined, ie the residual drift between the manipulator and the approached reference point.

In step 25, two calibration sets are selected from the calibration. The

Calibration sets are calculated by comparing the determined in step 24 instantaneous reference point residual drift and the comparison reference point residual drift of

Calibration sets of calibration selected. The comparison determines which comparison reference point residual drifts of the calibration sets of calibration are closest to the instantaneous reference point residual drift determined in step 24. Accordingly, then two calibration sets with the nearest

Comparison reference point residual drifts with regard to the instantaneous reference point residual drift selected.

In step 26, the manipulator parameter sets of the selected calibration sets associated with the two comparison reference point residual drifts are interpolated for the calibration, and a correction parameter set is calculated on the basis of the interpolation. In the following step 27, the manipulator is based on at least the

Correction parameter set controlled. Subsequently, the process ends in step 28.

Claims

claims

A method of controlling a manipulator, comprising:

a) providing a calibration, comprising the following steps:

Repeated start of at least one, in particular at least two or M, reference points (s) until a temperature criterion of the manipulator is met, and

Determining, after each start-up, a calibration set comprising at least one comparison reference point residual drift and a manipulator parameter set;

b) approaching one, in particular exactly one or N, reference points (s);

c) determining a current reference point residual drift;

d) calculating a correction parameter set based on the determined one

Instantaneous reference point residual drift and based on at least one of the calibration sets, and

e) controlling the manipulator based on the correction parameter set.

2. The method of claim 1, wherein controlling the manipulator comprises measuring with the aid of the manipulator taking into account the correction parameter set.

3. The method according to claim 1 or 2, wherein the number of reference points N from step b) is smaller than the number of reference points M from step a).

4. The method of claim 1, wherein providing the calibration comprises creating the calibration.

5. The method according to any one of the preceding claims, wherein the repeated start comprises a repeated approach of two reference points, and wherein preferably one of the reference points is a component point.

6. The method according to any one of the preceding claims, wherein the determined calibration sets comprise two comparison reference point residual drifts and a manipulator parameter set.

A method according to any one of the preceding claims, wherein the calculating comprises the steps of:

Selecting a calibration set based on the determined instantaneous reference point residual drift such that the comparative reference point residual drift of the selected calibration set is closest to the determined instantaneous reference point residual drift, and

Create the correction parameter set based on the selected calibration set.

8. A method according to any one of the preceding claims, wherein the calculating comprises the steps of:

Selecting at least two different calibration sets based on the determined instantaneous reference point residual drift such that the comparison reference point residual drifts of the selected calibration sets are closest to the determined instantaneous reference point residual drift, and

Create the correction parameter set based on an interpolation of the selected calibration sets.

9. robotic system comprising means for performing a method according to any one of claims 1-8.