Patent ID: 12226867

DETAILED DESCRIPTION OF THE DRAWINGS

FIG.1shows a device head10, the position and/or orientation of which in a measuring environment11is to be determined with an accuracy in the millimeter range. The term “device head” includes all processing heads, assembly heads and measuring heads intended for carrying out processing, assembly or measuring tasks. The device head10may for example be formed as a grinding head, welding head, drilling head or detector head.

In the exemplary embodiment, the device head10is connected to a robot arm12which is mounted on a work platform13. The robot arm12is designed as a multi-axis robot arm with multiple axes of rotation and the work platform13can be adjusted in one plane via motor-driven wheels that are mounted on two axes. The robot arm12consists of multiple rigid members that are connected by swivel joints or sliding joints, the swivel or sliding joints being able to be adjusted by controlled drives. The number of swivel or sliding joints required depends on the type of device head10and the planned application.

By combining the robot arm12with the work platform13, the spatial area of the device head10can be increased in size. The work platform13makes it possible to position the device head10mounted on the robot arm12at least approximately in the measuring environment11, the approximate positioning taking place in two dimensions in the plane. Instead of the motor-adjustable work platform13, the robot arm12may be mounted on a manually adjustable work platform. A motor-adjustable work platform13allows the device head10to be positioned without an operator, whereas a manually adjustable work platform13has to be adjusted by the operator. Instead of the adjustable work platform13, the robot arm12may be connected to a standing foot that allows the robot arm12to stand securely; the standing foot can be adjusted by the operator in order to increase the size of the spatial area. In principle, the device head10can also be used without a robot arm and/or work platform. The number of degrees of freedom of the device head10can vary greatly and is dependent on the type of device head10and the planned application. The device head10may be adjustable in one or more directions of translation, in one or more directions of rotation or in a combination of directions of translation and directions of rotation.

The position and/or orientation of the device head10is determined by means of an on-board sensor device14and then set more precisely by means of an apparatus15for setting more precisely the position and/or orientation of the device head10. The apparatus15comprises a distance measuring device16and a control device17, which is connected in a communicating manner to the on-board sensor device14and to the distance measuring device16. The on-board sensor device14is used to determine the position and/or orientation of the device head10; a LiDAR sensor device may be used for example as the on-board sensor device14. The distance measuring device16comprises a number of M, M≥1 distance measuring sensors18, the measuring directions of which differ from one another. In the exemplary embodiment, the distance measuring device16has three distance measuring sensors18, which are arranged at right angles to one another. The distance measuring device16is connected to the device head10and serves to set more precisely the position and/or orientation of the device head10that was determined by means of the on-board sensor device14.

In order to set the position and/or orientation of the device head10more precisely, the device head10is arranged in different measuring positions, in which the distance measuring sensors18of the distance measuring device16carry out a distance measurement. The movement of the device head10from one measuring position into a new measuring position is recorded by a further on-board sensor device19, which is connected to the device head10, in the form of movement data; the further on-board sensor device19is formed for example as an acceleration sensor.

The measuring environment11is mapped in a geometry model21which is shown inFIG.2. The geometry model21depicts the objects of the measuring environment11that form boundary surfaces and allows the distances between the device head10and the boundary surfaces to be estimated. The distances are estimated in the directions which correspond to the measuring directions of the distance measuring sensors18. For example, a construction model of the measuring environment11produced with CAD support can be used as the geometry model21. Alternatively, the measuring environment11may be scanned by means of a laser scanner and a geometry model of the measuring environment11is created from the scan data. The geometry model21may map the measuring environment11completely or only partially. The surfaces of the measuring environment11that are used as a reflection surface or scatter surface for a distance measurement are decisive for the present application. The estimated distance values that are compared with the measured distance values are determined from the geometry model21by means of known ray tracing methods.

The method according to the invention for setting more precisely the position and/or orientation of the device head10is characterized by a sequence of a first, second, third and fourth step, which is carried out at least once, preferably multiple times (N times). The device head10is arranged in N, N≥1 different measuring positions and the sequence of the first to fourth steps is carried out in each measuring position. In the exemplary embodiment, the sequence of the first, second, third and fourth steps is carried out three times. The device head10is arranged in the measuring environment11in three measuring positions, which are referred to as the first measuring position MP1(FIG.3A), second measuring position MP2(FIG.3B) and third measuring position MP3(FIG.3C).

In the first step of the first sequence, the device head10is arranged in the measuring environment11in the first measuring position MP1(FIG.3A). The first measuring position MP1corresponds to the position and/or orientation of the device head10that is to be set more precisely by means of the apparatus15. For the first measuring position MP1, first pose data are determined, the position and/or orientation of the device head10that was determined by means of the on-board sensor device14being used as first pose data. In the second step of the first sequence, the distance measuring sensors18carry out a distance measurement and transmit their measured distance values dm_j1 for j=1 . . . M to the control device17; in the exemplary embodiment, the three distance measuring sensors18determine three measured distance values dm_11, dm_12, dm_31. For the first measuring position MP1, in the third step of the first sequence, the geometry model21is used to determine for the measured distance values dm_j1 corresponding estimated distance values de_j1 for j=1 . . . M; in the exemplary embodiment, three estimated distance values de_11, de_21, de_31 are determined. In the fourth step of the first sequence, the deviations Δj1for j=1 . . . M between the measured distance values dm_j1 and the corresponding estimated distance values de_j1 are calculated and stored as error values; in the exemplary embodiment, the first sequence produces three error values Δ11, Δ21, Δ31.

After completion of the first sequence of the first to fourth steps, in the first step of the second sequence the device head10is moved from the first measuring position MP1into the second measuring position MP2(FIG.3B). The movement of the device head10from the first measuring position MP1into the second measuring position MP2is recorded by the further on-board sensor device19in the form of first movement data.

The second pose data of the second measuring position MP2may be determined from the first pose data of the first measuring position MP1and the first movement data. Alternatively, the second pose data of the second measuring position MP2may be determined from optimized first pose data and the first movement data. For this purpose, the error values Δ11, Δ21, Δ31of the first sequence are used to carry out a compensation calculation for the position and/or orientation of the device head10, which is referred to as error minimization, and the result of this compensation calculation gives the optimized first pose data.

In the second step of the second sequence, the distance measuring sensors18carry out a distance measurement and transmit their measured distance values dm_j2 for j=1 . . . M to the control device17; in the exemplary embodiment, the three distance measuring sensors18determine three measured distance values dm_12, dm_22, dm_32. For the second measuring position MP2in the third step of the second sequence the geometry model21is used to determine for the measured distance values dm_j2 corresponding estimated distance values de_j2 for j=1 . . . M; in the exemplary embodiment, three estimated distance values de_12, de_22, de_32 are determined. In the fourth step of the second sequence, the deviations Δj2for j=1 . . . M between the measured distance values dm_j2, j=1 . . . M and the corresponding estimated distance values de_j2, j=1 . . . M are calculated and stored as error values; in the exemplary embodiment, the second sequence produces three error values Δ12, Δ22, Δ32.

After completion of the second sequence of the first to fourth steps, in the first step of the third sequence the device head10is moved from the second measuring position MP2into the third measuring position MP3(FIG.3C). The movement of the device head10from the second measuring position MP1into the third measuring position MP3is recorded by the further on-board sensor device19in the form of second movement data.

The third pose data of the third measuring position MP3may be determined from the first pose data of the first measuring position MP1and the first and second movement data. Alternatively, the third pose data of the third measuring position MP3may be determined from optimized first pose data and the first and second movement data. For this purpose, the error values Δ11, Δ21, Δ31of the first sequence and Δ12, Δ22, Δ32of the second sequence are used to carry out a compensation calculation for the position and/or orientation of the device head10(error minimization), and the result of this compensation calculation gives the optimized first pose data.

In the second step of the third sequence, the distance measuring sensors18carry out a distance measurement and transmit their measured distance values dm_j3 for j=1 . . . M to the control device17; in the exemplary embodiment, the three distance measuring sensors18determine three measured distance values dm_13, dm_23, dm_33. For the third measuring position MP3, in the third step of the third sequence the geometry model21is used to determine for the measured distance values dm_j3 corresponding estimated distance values de_j3 for j=1 . . . M; in the exemplary embodiment, three estimated distance values de_13, de_23, de_33 are determined. In the fourth step of the third sequence, the deviations Δj3for j=1 . . . M between the measured distance values dm_j3 and the corresponding estimated distance values de_j3 are calculated and stored as error values; in the exemplary embodiment, the third sequence produces three error values Δ13, Δ23, Δ33.

After completion of the third sequence of the first, second, third and fourth steps, the control device17uses the error values of the first sequence Δ11, Δ21, Δ31, the error values of the second sequence Δ12, Δ22, Δ32and the error values of the third sequence Δ13, Δ23, Δ33to carry out a compensation calculation for the position and/or orientation of the device head10(error minimization). The compensation calculation is performed for example by means of the method of least squares. The more precisely set position and/or orientation of the device head10results from the compensation calculation.

In a further development of the method, after the Nth sequence of the first to fourth steps, the control device17determines within the compensation calculation an error measure δ, which indicates the quality or accuracy with which the position and/or orientation of the device head10is set more precisely. The error measure δ is compared with a maximum error δmax, which indicates the allowed inaccuracy. If the error measure δ is greater than the maximum error δmax, the device head10is moved from the third measuring position MP3into a new measuring position, in which the sequence of the first to fourth steps is carried out again; the new measuring position is referred to as the fourth measuring position MP4. The movement of the device head10from the third measuring position MP3into the fourth measuring position MP4is recorded in the form of third movement data by the further on-board sensor device19.

In a further development of the method according to the invention, the quality of the error values Δjithat are determined in the sequences can be evaluated by the control device17by means of suitable calculation methods, and error values of poor quality can be given a lower weighting or be disregarded in the compensation calculation (error minimization) which is carried out after the last sequence of the first to fourth steps. Strong deviations between the measured distance values and the corresponding estimated distance values may occur if the distance measuring sensors18are directed at edges in the measuring environment11, since even small angular deviations can lead to large changes in the measured distance values.