EP3484672A1

EP3484672A1 - Redundancy resolution for a redundant manipulator

Info

Publication number: EP3484672A1
Application number: EP17740292.2A
Authority: EP
Inventors: Vito Magnanimo
Original assignee: KUKA Deutschland GmbH
Current assignee: KUKA Deutschland GmbH
Priority date: 2016-07-15
Filing date: 2017-07-12
Publication date: 2019-05-22
Also published as: DE102016212958A1; WO2018010842A1

Abstract

The invention relates to a method for controlling a redundant manipulator (10), wherein the manipulator (10) has a plurality of movement axes (A1 - A7) and the method comprises the following steps: determining a primary task for controlling the manipulator (1), wherein the primary task comprises the traveling along a movement path (30) of the manipulator (10); determining at least one secondary task for controlling the manipulator (10), wherein the secondary task comprises the reducing of the effective mass (m_u) and/or the effective inertia (I_u); calculating n alternatives of possible axis angles (α1 - α7) of the movement axes (A1 - A7) of the manipulator (10) for performing the primary task, and calculating the axis angular velocities for the n alternatives; and controlling the manipulator (10) while taking into consideration the n alternatives and the secondary task.

Description

REDUNDANT RESOLUTION FOR A REDUNDANT MANIPULATOR

Field of the invention

The invention relates to a method for controlling a redundant manipulator, as well as a manipulator system and a control device, which is set up for controlling a redundant manipulator according to the method. The method includes determining a trajectory of the manipulator and reducing the effective mass of the manipulator. Background of the invention

Manipulators are machines that can physically interact with their environment. They are used in industrial manufacturing, automation and in the home environment, for example in the field of ambient assisted living. Typical manipulators are articulated arm or industrial robots that have several freely programmable axes of motion. They serve to guide and / or edit end effectors, such as tools or workpieces.

Redundant manipulators are characterized by the fact that they have at least one degree of freedom more than is necessary for the execution of the actual task. If, for example, an end effector is to be positioned freely in space, six degrees of freedom are required for this purpose. Therefore, typical industrial robots have six freely programmable axes of motion to position an end effector freely in space. A corresponding redundant industrial robot comprises at least seven degrees of freedom, i. at least seven axes of motion. The

Motion axes can be designed as linear axes or axes of rotation. However, the number of axes of movement of a redundant manipulator depends on the application. If, for example, only one linear movement in one direction is to be carried out by means of the manipulator, a movement axis for carrying out the actual task is sufficient. Correspondingly, a manipulator which should only execute a linear movement in one direction, which has two linear axes, would be a redundant manipulator.

To perform a given task, the manipulator moves trajectories. The planning of the trajectory is typically of one Assumed control device which is adapted to control the manipulator. For this purpose, axis angles (or axis positions) and / or axis angular velocities are specified for each movement axis. In order to plan a trajectory, at least the starting point and the end point of the trajectory must be known. The actual trajectory (trajectory) is calculated by the control device. Subsequently, the control device sends corresponding control commands to the manipulator to start the previously calculated trajectory by means of the manipulator. In accordance with the control commands, the manipulator then assumes the commanded axis angle (or axis position) for the respective movement axis. For non-redundant manipulators, the axis angle for each of the

Motion axes clearly determinable when a trajectory is to be traversed by means of the manipulator. In the case of redundant manipulators, there are several solutions or axis angle combinations or configurations in order to start the planned trajectory. The redundancy resolution in conventional redundant manipulator path planning methods often results in undesirable non-fluid motions.

A current trend in the field of manipulators are human-robot collaboration systems (MRK systems). These enable the collaboration between humans and humans through the use of modern safety technology

Manipulators / robots. In MRK systems, e.g. The high performance of a manipulator combined with the sensory abilities of a human being. Possible applications can be found, for example, in industrial production, such as in automobile production or ambient assisted living. Typical applications are lifting and mounting devices in which a

Workpiece is lifted by the manipulator and then accurately positioned by a human. In addition to the resulting Rationalisierungspotenzialen such applications are advantageous because, for example, the ergonomics of a

Workplace and / or the stamina of a person can be increased.

Here, MRK systems assume that the person who collaborates with the manipulator is not himself endangered by the manipulator. In particular, machine safety of Category 3 according to ISO 13849 is to be achieved in MRK systems. In this case, an MRI system is considered safe. In order to exclude a threat to humans, the speed of the manipulator is often throttled, so that in collisions between humans and manipulators no Injury or serious injury to a human being. However, this greatly limits the scope and, above all, the efficiency. In order to be able to achieve high speeds and / or short cycle times, extensive security measures are necessary. The object of the present invention is to at least partially eliminate the aforementioned disadvantages and to provide a method for controlling a manipulator (or a manipulator system and / or a control device), which enables efficient movement sequences and at the same time minimizes a potential hazard by the manipulator. Detailed description of the invention

The object is achieved at least in part by a method according to claim 1, by a control device according to claim 9, a computer-readable medium according to claim 10 and by a manipulator system according to claim 11.

In particular, the object is achieved by a method for controlling a redundant manipulator, wherein the manipulator has a plurality of axes of movement and the method comprises the following steps:

Determining a primary task for controlling the manipulator, the primary task comprising traversing a trajectory of the manipulator, in particular a trajectory of the tool center point of the manipulator;

Determining at least one secondary task for controlling the

Manipulator, wherein the secondary task comprises a reduction of the effective mass and / or the effective inertia, in particular the effective mass and / or the effective inertia of an end effector of the manipulator;

Calculate n alternatives possible axis angles α of the axes of motion of the manipulator to fulfill the primary task, and calculate the

Axis angular velocities for the n alternatives; and

Controlling the manipulator taking into account the n alternatives and the secondary task.

The primary task involves tracing a trajectory. The trajectory can either be predetermined or planned by a control device.

Specified trajectories are, for example, when a trajectory has been "taught" by manually manipulating or guiding the manipulator, and the trajectory recorded trajectory recorded. The recorded

Trajectory can then be traversed again.

If the trajectory, however, be planned, it is sufficient, a

Specify starting point and an end point. The starting point can correspond to the current position of the Manipulator or the Tool Center Point (TCP) of the manipulator so that only one desired end point has to be specified. The TCP describes the tool position / workpiece position of a manipulator and is an imaginary reference point of the tool / workpiece. Starting from the planned or predetermined trajectory, which is typically present in Cartesian coordinates, the axis angles of the axes of motion are then calculated.

This calculation can be done by means of inverse kinematics. The inverse kinematics allows for a manipulator to determine the axle angle of the

Motion axes based on the pose (position and orientation) of the end effector (or Tool Center Point). In inverse kinematics, the last term of the kinematic chain, i. the end effector, moved and brought into the desired pose. The other links of the kinematic chain, ie the axes of movement of the manipulator, must then assume an associated pose according to their degrees of freedom. This can be compared with the human arm, which forms a kinematic chain with its joints: If one puts the hand in a certain pose, for example, if an object is grasped, the wrist, elbow and shoulder automatically assume a certain position as well. Exactly these positions (or axis angle) must be determined via the inverse kinematics.

In the case of redundant manipulators, the associated poses of the axes of motion are not uniquely determined. There are therefore several alternatives n. These

Alternatives can be used to accomplish a secondary task. In the example of the human arm, may correspond to the elbow in

different poses can be arranged when an object is grasped. These different positions of the elbow can be used to accomplish a secondary task, such as a comfortable gripping position. According to the invention, the secondary task comprises a reduction of the effective

Mass and / or effective inertia. Effective mass / effective inertia is a directional measure of the kinetic energy that a manipulator has in a defined direction, typically the direction of movement given by the trajectory. The lower the effective mass and / or the effective Inertia in the direction of movement of the manipulator, or the end effector, the lower the risk potential that emanates from the manipulator in the event of a collision. For example, in order to achieve a certain pose, it is advantageous to move as small masses as possible in order to reduce the effective mass and / or the effective inertia. Typically, it is therefore preferable to move distal axes of movement of the manipulator, since the movement of distal axes of motion of the

Moving less mass causes, as the movement of the proximal

Axes of motion.

The manipulation of the manipulator is typically carried out by means of a control device which is assigned to the manipulator. A controller may include hardware and / or software.

In particular, further secondary tasks may be present, wherein the further tasks in controlling the manipulator, preferably with different

Weighting, be taken into account. Consequently, the (first) secondary task may include other (second or third, etc.) conditions in addition to a reduction of the effective mass. These are, for example, the achievement of a short cycle time for traversing the trajectory according to the primary task, the compliance with certain axle angles and / or a working space and / or the energy-efficient traversing of the trajectory. Other secondary tasks can also be determined. A weighting of the secondary tasks, for example, allows a substantial reduction of the effective mass, while sufficiently short cycle times can be realized. Especially with contrary secondary tasks, the weighting can achieve at least partial fulfillment of all secondary tasks. Moreover, the primary task may be independent of the at least one secondary task, the primary task preferably having a higher priority than the at least one secondary task. The independence of the primary and secondary tasks simplifies the calculation of the axis angle and / or axis angular velocities and in particular leads to fluid movements of the manipulator, since no conflicts due to undesirable dependencies

be caused. Independence can be achieved, for example, by means of the following algorithm:

In the following let q be the vector of the axis angle ai to a ₇ of the axes of movement Ai to A7 of a manipulator with seven axes of movement, which are designed as hinges. The algorithm is general and can be applied to any redundant manipulator.

The functions ei and e ₂ determine the primary task and the secondary task whose Jacobian matrix (i = 1, 2) is generally defined as follows: dei

For the angular velocities, with respect to the first task ei, the following results: where Pi is the orthogonal mapping operator to the null space of J _x , and where Ji ^{+ is} the pseudoinverse of Ji. Consequently, the vector z can be used to solve the secondary task e ₂ without affecting or disturbing the solution of the primary task ei. That is, the primary and secondary tasks are independent. Thus, from the above equations, a formulation for e ₂ results:

Consequently, the axis angular velocities q result in q = J + e _x + P ₁ J ₂ P ₁ ⁺ (.e ₂ -MfeJ

Since the matrix Pi is hermetic and indempotent, q can also be formulated as follows: where f as / ^ =]? is defined and indicates the available area for solving the secondary task e ₂ without influencing the first task ei. Furthermore, e _{2 is defined} as e ₂ = e ₂ -J ₂ Ji e ₁ , wherein the term J ₂ Ji e _{t is} already satisfied by the first task ei.

If the first task is prioritized, it can be ensured that the

Movement path is maintained and the effective mass, taking into account the trajectory is reduced as far as possible. Furthermore, the manipulator may include at least two redundant axes of motion, wherein the method may include determining at least two secondary tasks which secondary tasks are independent of each other. For example, the solution of the first secondary task does not affect the solution of the second secondary task. This can be achieved analogously to the algorithm described above, but sets at least two redundant

Movement axes ahead. In the example of a manipulator described above, which should make it possible to freely position an end effector in space, eight axes of motion ("6 + 2" degrees of freedom) are necessary for this purpose.

Since redundant manipulators are distinguished by the fact that they have at least one more degree of freedom than is necessary for the execution of the primary task, it can generally be determined that, depending on the type of redundant manipulator, "x" degrees of freedom (or, respectively, "X" axes of motion) and for solving the one or more secondary tasks "y" degrees of freedom (or "y" redundant axes of motion) are provided. In particular, secondary tasks may be included, which are solved by means of two or more degrees of freedom, without influencing or disturbing the solution of the primary task and / or further secondary tasks.

In particular, the redundant manipulator may include "x + y" degrees of freedom, or "x + y" axes of motion, and for the solution of the primary task "x"

For example, a manipulator may include "6 + 2" degrees of freedom, with two degrees of freedom for solving a secondary task, or for solving two independent secondary tasks can be used. Other exemplary manipulators may include "6 + 3", "5 + 2" or any other combination of "x + y" degrees of freedom.

In particular, at least one further secondary task can be to maintain at least one predefined angular range for at least one axis of the

Manipulator and / or compliance with a predefined working space of the

Include manipulator. As a result, for example, areas of space that are typically occupied by people and / or other objects during assembly can be blocked for the manipulator. The specification of angular ranges allows, for example, to avoid unfavorable axis positions with low load or high load. Preferably, at least one further secondary task may comprise the minimization of the energy expended for tracing the trajectory. Thus, energy-efficient manipulator systems can be realized. Other secondary tasks, such as the reduction of cycle times or compliance with limit speeds, can also be defined.

In particular, the axis angle velocities α _x ά ₇ for the n alternatives can be calculated such that a predefined maximum speed of the manipulator is not exceeded when the manipulator is being controlled. The maximum speed may be the actual maximum speed of the manipulator or another specified speed which, for example, must not be exceeded in order to comply with safety regulations.

In the method described above, the effective mass m _{u can be determined} as a function of the direction of movement u of the end effector, and the vector q of the axis angles of the axes of motion and the matrix A _{v of} the pseudo kinetic energy of the manipulator in translational movements. The effective mass m _u is then given

1

u A "(q) u

Correspondingly, the effective inertia I _{u can be determined} as a function of the direction of movement u of the end effector and the (angular velocity) vector q of the axis axes of the axes of motion and the matrix Λω of the pseudo kinetic energy of the manipulator based on the angular velocities. The effective inertia Iu then arises

The object is further achieved by a control device which comprises at least one program memory and a processor, and which is set up to control at least one redundant manipulator according to the method described above. The controller may include hardware as well as software. In particular, the control device may be configured to control a plurality of manipulators. Furthermore, the control device may consist of several components (hardware and / or software), which together form a Form control. It is not necessary to integrate the components in just one housing.

The object is further achieved by a computer-readable medium on which program instructions are stored, which is a control device of a

Manipulator system to control a redundant manipulator according to the method described above. The computer readable medium may be an optical, magnetic or other storage medium.

Likewise, the object is achieved by a manipulator system which comprises at least one redundant manipulator and at least one control device, wherein the redundant manipulator is preferably an MRK-capable manipulator. The

Control device is set up to carry out the method described above.

Detailed description of the figures

In the following, individual aspects will be explained in more detail with reference to the figures. It shows

FIG. 1 is a schematic representation of an MRK-capable manipulator system; FIG.

Fig. 2 is a schematic representation of a manipulator system with a

redundant manipulator, and

Fig. 3 is a schematic flow diagram of a method for controlling a

Manipulator.

In particular, FIG. 1 shows a manipulator system 1, which has a redundant

Manipulator 10 and a control device 20 includes. The control device 20 is set up to control the manipulator 10.

The manipulator 10 comprises seven axes of movement Ai to A7. Thus, the

Manipulator 10 a redundant manipulator. The manipulator includes one

End effector 12, which is designed in the present illustration as a gripper. The end effector 12 is a Tool Center Point (TCP), i. an imaginary reference point, associated with, by means of the TCP, the movement path 30 of the manipulator 10 can be described. The shown TCP 15 corresponds to a gripping point of the

End effector 12. In particular, the manipulator system 1 is an MRK-enabled

Manipulator system in which a person 50 and the manipulator 10 collaborate. The illustrated axes of movement Ai to A7 are designed as rotation axes, which can assume different axial angles c to a ₇ . The respective axial angles a _x to a ₇ determine the orientation of the individual axes of movement Ai to A7, wherein the axes of movement Ai to A7 form a kinematic chain, at the end of which

End effector 12 is. About the axis angle, a pose of the manipulator 10 is determined and the end effector 12 is positioned and oriented in space.

FIG. 2 shows the manipulator system 1, wherein the redundant manipulator 10 is shown in different poses q, q '. The TCP 15 of the end effector 12 is positioned the same in the poses shown. The effective mass is dependent on the poses q, q 'and the direction of movement u, the poses q, q' being determined by the respective axis angles cu to a ₇ . In order to run a trajectory (primary task) with the TCP, for example, n different alternatives can be calculated in which the manipulator assumes a pose in which the TCP lies on the trajectory. If, according to a secondary task, the effective mass is to be reduced, a corresponding pose can be selected from the n alternatives with low effective mass.

3 shows a schematic flow diagram of a method 100 for controlling a manipulator. In a first method step 110, a primary task ei for controlling the manipulator 10 is determined, wherein the primary task ei includes traversing a movement path 30 of the manipulator 10. The trajectory can be predetermined or planned by a control unit. In particular, a predetermined and / or planned trajectory can be optimized.

In a second method step 120, at least one secondary task e ₂ for controlling the manipulator is determined, wherein the secondary task e ₂ comprises a reduction of the effective mass and / or the effective inertia. The reduction does not have to be aimed at achieving an absolute minimum, but can, for example, be based on adherence to defined upper limits of the effective

Mass / inertia be limited.

In a third method step 130, n alternatives of possible axis angles ai to j of the movement axes Ai to A7 of the manipulator 10 are calculated to fulfill the primary task ei. Similarly, axis angular velocities for the n

Alternatives calculated. In a fourth method step 140, the manipulator 10 is then connected taking into account the n alternatives and the secondary

Task e ₂ controlled. LIST OF REFERENCE NUMBERS

1 manipulator system

io manipulator

12 end effector

15 Tool Center Point

20 control device

30 trajectory

50 human

IOO procedure

HO Determining the primary task

120 Determining the secondary task

130 calculation

140 taxes

A1-A7 motion axes

aa ₇ axis angle

a primary task

e2 secondary task

u direction of movement

q. q 'Vector of the axis angle

Claims

Claims 1 to 11

A method (100) for controlling a redundant manipulator (10), wherein the manipulator (10) has a plurality of axes of movement (Ai - A7) and the method (100) comprises the following steps:

Determining (110) a primary task (e for controlling the manipulator (10), wherein the primary task (e the departure of a trajectory (30) of the manipulator (10), in particular a trajectory of the tool center point (15) of the manipulator ( io);

Determining (120) at least one secondary task (e ₂ ) for controlling the manipulator (10), wherein the secondary task (e ₂ ) involves reducing the effective mass (m _u ) and / or the effective inertia (I _u ), in particular the effective mass (m _u ) and / or the effective inertia (I _u ) of an end effector (12) of the manipulator (10);

Calculating (130) n alternatives of possible axis angles (cii-a) of the axes of motion (Ai-A7) of the manipulator (10) to perform the primary task (e, and calculate the axis angular _velocities (ά _λ -ά _Ί ) for the n alternatives; and

Controlling (140) the manipulator (10) taking into account the n alternatives and the secondary task (e ₂ ).

2. Method (100) according to claim 1, wherein there are further secondary tasks (e _2a; e ₂ b), wherein the further secondary tasks (e _2a; e ₂ b) in controlling the

Manipulator (10), preferably with different weighting, are taken into account.

3. The method according to any one of the preceding claims, wherein the primary task (e is independent of the at least one secondary task and preferably has a higher priority than the at least one secondary task (e »).

4. The method according to any one of the preceding claims, wherein the manipulator (10) comprises at least two redundant axes of motion, and wherein the method (100) comprises determining (120) at least two secondary tasks (e _2), said secondary tasks (e ₂ ) are independent of each other.

5. The method according to any one of the preceding claims, wherein at least one further secondary task (e ₂ ) adherence to at least one predefined

Angular range for at least one axis (Ai -A7) of the manipulator (10) and / or compliance with a predefined working space of the manipulator (10) includes.

6. The method according to any one of the preceding claims, wherein at least one further secondary task (e ₂ ) minimizing the for the shutdown of

Movement path (30) expended energy comprises.

7. The method according to any one of the preceding claims, wherein the

Achswinkelgeschwindigkeiten (ά, -ά ₇ ) for the n alternatives are calculated such that a predefined maximum speed of the manipulator (10) when controlling the manipulator (10) is not exceeded.

8. The method according to any one of the preceding claims, wherein the effective mass (m _u ) a function of the direction of movement (u) of the end effector (15) and the vector (q) of the axis angle (α _χ - a ₇ ) and the matrix (A _v ) of the pseudo kinetic energy of the manipulator (10) at translational velocities, and is determined as follows:

1

u A _v (q) u and where the effective inertia (I _u ) is a function of the direction of movement (u) of the end effector (15) and the vector (q) of the axis angles (cii - a ₇ ) and the matrix (Λω) of the pseudo kinetic energy of the manipulator (10) based on the

Angular velocities, and is determined as follows:

/. - u ^T ^ ¹ (q) u.

9. control device (20), which comprises at least one program memory and a processor, and which is adapted to control at least one redundant manipulator (10) according to the method (100) of claims 1 to 8.

10. A computer-readable medium having stored thereon program instructions for causing a control device (20) of a manipulator system (1) to control a redundant manipulator (10) according to the method of claims 1 to 8. Ii. Manipulator system (l) comprising at least one redundant manipulator (10) and a control device (20) according to claim 9, wherein the redundant manipulator (10) is preferably an MRK-enabled manipulator.