WO2012069129A1 - Method and control element for controlling a robot arrangement - Google Patents

Abstract

The invention relates to a method for the computer-aided control of a robot arrangement comprising at least two robots (1, 2), wherein said method comprises the following steps: determining at least one process section point (q_1,E, q_2,E); determining a process section time (T) for the process section point; specifying a section time (T) for at least one robot (1) of the robot arrangement based on the process section time (T); and optimizing a working process (q₁(s(t)) of said robot (1) on the basis of the specified section time (Τ₁+ΔΤ).

Description

 description

Method and control means for controlling a robot arrangement

The present invention relates to a method and a control means for

computer-aided control of a robot assembly having at least two

Robots.

In robot arrangements with two or more robots, a distinction can be made between coordinated and cooperative processes: while with cooperative ones

Processes that synchronously act as robotic axes of a virtual hyperrobot, for example, to jointly move a payload held by the robots, perform robotic tasks a priori independently of other robots in coordinated robotic operation.

In order to avoid collisions, processes are subdivided according to in-house practice into process sections, which must first have been processed by all collision-prone robots before they can start a subsequent process section. If, for example, two robots alternately move payloads in the same workspace, such process sections can be specified by the exit of a robot from this workspace so that the respective other robot may only enter the - now free - working space in a subsequent process section. However, workflows, particularly motions, of individual robots are typically timed, ie, such that the robot executes the workflow in the minimum possible time, such as constraints on motive forces and moments, joint velocities and accelerations, and / or Cartesian velocities of reference points such as the TCP. In the case of the coordinated process described above, which is clocked in process sections, this leads to the faster robot (s), which process the respective process section in minimal minimal time, waiting for the slowest robot at the end of the process section and thus at its optimum time Work unnecessarily consumed much energy. DE 196 25 637 A1 proposes for collision avoidance in multi-robot operation to project collision areas into the space of the joint joint coordinates and to plan there time-optimal collision-free trajectories. The end time of the faster robot is scaled to the end time of the slower robot to synchronously reach the same point in the joint coordinate space.

The object of the present invention is to improve the control of robot arrangements with at least two robots.

This object is achieved by a method having the features of claim 1. Claim 9 provides a control means, claim 1 1 a computer program product, in particular a machine-readable medium or a storage medium, for performing a method according to the invention under protection, wherein an agent in the context of the present invention equally hard and / or software technology can be formed, ie in particular corresponding processing, computing, storage and / or data transmission facilities and / or programs,

Program modules, and the like may include. Advantageous developments are the subject of the dependent claims.

The present invention is based on the idea of a time difference between a time that is the slowest robot of a robot assembly for

Processing of a process section needed, and the time that would require a faster robot of the robot assembly in time-optimized operation to use, to optimize the workflow of the faster robot, especially in terms of its energy consumption. In contrast to a mere scaling of the minimum end time of the faster robot to that of the slower robot, optimization here can result in significant energy savings. In general, a method according to the invention first comprises determining one or more process section points. In this case, an overall process which the robot arrangement is to carry out is preferably subdivided into two or more subprocesses or process sections. These can result, in particular, in the context of a collision avoidance, for example by the requirement that only one robot may always act in a common, preferably variable, workspace. Additionally or alternatively, process section points may also Synchronization points at which two or more robots at the same time have to assume a certain configuration, such as to hand over a payload or edit a fixed by a robot workpiece by a tool that another robot leads. Process section points may change

For example, from the funding of a conveyor yield, with the

 Robot arrangement interacts. For a more compact representation, an overall process without further subdivision can also represent a process section in the sense of the present invention whose single process section point then forms the end of the overall process.

In general, a process section point in the sense of the present invention is understood to mean in particular a point which describes a state of two or more robots of the robot arrangement, in particular poses of the robots, for example poses at the end of a machining process or a process

Transfer movement. Is a workflow of a robot i the robot assembly by the course of its joint coordinates q, over a

Process state parameter s ₀ <s <s _E described, the overall process

Accordingly, by the joint coordinates q (s) = [qi (s), q ₂ (s), ...], the robot of the robot assembly, so a process section point can be specified for example by values of the process state parameter s or the associated joint coordinates or robot poses. Process point points may be manually, such as by clicking in a graphical representation of the process or input during a teaching of the process, and / or automatically, such as in

predetermined intervals of the process state parameter to be determined.

Then, a process section time is determined for the respective process section point. This is understood in particular as the time that the

Robot arrangement for reaching the process section point while processing the respective process section by the robot of the robot assembly required. In a preferred embodiment, this is done for two or more, especially all

Robot of the robot assembly, each determines a minimum section time that require the respective robot at least to process their respective process section. This minimum section time may preferably take into account maximum allowable driving forces and moments, joint speeds and accelerations and / or Cartesian velocities of reference points, in particular the TCP, can be achieved with a workflow planned at the optimum time. The process section time can then be determined on the basis of these minimum section times, in particular as the largest of the minimum section times.

Similarly, one process time may also be based on others

 Process factors are determined, for example, the time required for a workpiece to reach a predetermined temperature, a dyeing, sealing or

Adhesive application needed for drying, or a tool or

Spraying machine for machining a workpiece needed. In general, the respectively longest of the times, the robots, tools, workpieces and / or other processing means such as machine tools, conveyors or the like may each require minimal to achieve the process section point, as

Process period time are determined. In an advantageous development, the process period time thus determined from the minimum times can be increased by a predetermined value in order to provide a reserve for the slowest process agent and not to load it out. For this purpose, the respective minimum time of the individual process means can be increased in the same way by a predetermined, preferably individual, value.

Now, on the basis of the process section time, a section time for one or more robots of the robot arrangement is specified, preferably only for robots whose minimum section time does not determine the process section time.

In particular, the process section time itself can be specified as a section time. Similarly, it is possible to increase the section times, for example, by a predetermined value compared to the process section time, so as not to burden even the slowest process means. The section time can be specified, for example, as the total time that is available to the respective robot for processing the process section, or else as the time difference with respect to the previously determined minimum section time.

Then, a workflow is optimized for the robot (s) based on the given section time. In this case, a trajectory of the robot i, which can be described for example by specifying its joint angle q, over a path parameter s, be predetermined, for example, to guide the TCP on a given Cartesian path and thus avoid collisions, for example Weld seam to proceed or adhesive or colorant in a given

Apply application track. In this case, the web speed profile s (t), with which the robot departs this predetermined path, can be optimized. If the trajectory of the robot is not specified, for example, because only one start and one end pose for picking up and dropping a payload through the

 Boundary conditions are predetermined, while the transfer path between these poses is still freely selectable, the trajectory itself can be optimized. For example, in an optimizer, vertices or other parameters that generally describe the trajectory, such as the coefficients of splines or the like, may be used as variable optimization parameters. Additionally or alternatively, the web speed profile can also be optimized here, in particular in a single-stage process in which the trajectory over time is described.

For the purposes of the present invention, optimization is understood as meaning in particular the presetting of a workflow, for example a trajectory and / or a path velocity profile, for which one or more quality criteria achieve an extremal, in particular minimum value. Several quality criteria can be pareto-optimized together, preferably as a weighted sum. The quality criteria do not have to be global for the optimized workflow

Extremal values reach, in particular, if a determination is not possible closed or requires a high numerical effort. Accordingly, in a preferred embodiment, a workflow is optimized by having it - preferably numerically simulated - for at least two different ones

Parameter values of parameters that determine (with) the workflow, such as the interpolation points explained above, carried out and is determined as the optimal workflow of those for which the or the quality criteria have the lowest value.

Preferably, a quality criterion of the optimization is an energy quantity of the robot. This may in particular be an energy consumption of the robot or a quantity corresponding thereto, for example the integral of the square or the amount of drive power of the drives of the robot. It is clear from this that an energy quantity in the sense of the present invention does not necessarily have to have the physical dimension of an energy or work. The energy quantity to be optimized can preferably also be an energy consumption in the power supply of the robot, such as losses in converters,

Intermediate circuits or the like, include.

Additionally or alternatively, a quality criterion may preferably describe a load on the robot, for example maximum forces or moments occurring, in particular in joints, drives or the like. Also, a measure of vibrations of the robot, such as the amplitudes of elastic vibrations or the like, may form a quality criterion. Additional quality criteria can be taken into account additionally or alternatively. In particular, to calculate the value of one or more of the aforementioned quality criteria in a simulation for different parameter values that govern the workflow of the

In a preferred embodiment of the present invention, robot (with) determine and determine its operation is simulated by means of a dynamic model, in particular a rigid body or a flexible multi-body model. A workflow of a robot may include processing and / or transfer sections. In this case, a machining section can in particular be a tool or workpiece guide of the robot during a machining process,

For example, a robot-guided welding, gluing, painting, a machining or non-cutting machining or the like. One

In contrast, the transfer section may in particular have a predetermined start and end

Endpose of the robot, wherein a robot path between the two poses - optionally taking into account boundary conditions such as collision freedom, maximum values for driving forces and moments, speeds and / or accelerations, and the like - is freely selectable. Typically, for a processing section is a trajectory and a

Given a given application rate an adhesive or Lackierbahn with a desired adhesive or

Start paint job. Optimization is therefore not possible for such sections without affecting the process to be performed. In a preferred embodiment, therefore, the process section is provided in one or more transfer sections and / or one or more processing sections subdivide and optimize only the transfer section (s) to optimize the entire process section. As a transfer section is thus generally understood in particular a process section or a part of a process section in which a trajectory and / or a web speed profile can be varied. Usually, a controller of a robot arrangement is distributed: a global process or cell control carries out a control of the overall process, for example by specifying poses to be approached by the robots of the arrangement or trajectories to be traveled, while robot controls control the individual robots, for example paths between predetermined ( Support) interpolate poses. A method according to the invention can equally be performed by a cell control, one or more robot controls or distributed by cell control and

Robot controls are performed. It can be provided in particular that the specification of the section time for the robot of the robot assembly is carried out by a control of the robot assembly, which additionally or alternatively

Determine process section points and determine a process section time. The optimization of the workflow of a robot, in particular a simulation of its workflow for determining one or more quality criteria for different, the workflow determining parameter values, in addition to or alternatively to a determination of a minimum section time based on a time-optimal planned robot path preferably be done by the control of the respective robot , For this purpose, in a preferred embodiment, a simulation and an optimizer are implemented in the respective robot controller.

An inventive method may, at least in part, take place offline in advance and / or online during the work process. It is computerized by

at least one of the above-explained steps at least partially

automated by a computer, in particular the cell or robot control is performed. In particular, the simulation and optimization can be carried out by executing corresponding numerical methods, as can the determination of minimum section times for time-optimized work processes, the determination of a process section time and the like. Further advantages and features emerge from the subclaims and the exemplary embodiments. This shows, partially schematized:

Fig. 1: a process of a robot assembly according to an embodiment of the present invention; and FIG. 2 shows the sequence of a method according to an embodiment of the present invention

Invention.

Fig. 1 shows in the upper row from left to right successive states of a robot arrangement with two robots 1, 2 in a process which is controlled according to an embodiment of the present invention. In the lower line of FIG. 1, the progressions of different state variables, in particular joint coordinates and their time derivatives, over the time t for in the upper line

indicated process indicated.

In the process, the two robots 1, 2 alternate payloads 3 and 4, respectively, which are symbolized in FIG. 1 filled or hatched. For better understanding has in the highly simplified embodiment of the upper in Fig. 1 robot 1 of the automation cell on two hinges with parallel, vertical axes of rotation (perpendicular to Fig. 1), a rocker 1 .2 with a base 1 .1 or a Arm 1 .3 with the swingarm 1 .2 connect, and their position through the

Joint coordinate or the angle q-1, 1 between the base and rocker or the angle q _{1 2} between rocker and arm is described, the vector q ^

can be summarized. Your first time derivation or

Joint speed is denoted by = dqu / dt (i = 1, 2), the second time derivative or joint acceleration corresponding to dco-ij / dt. The arm 1 .3 a gripper 1.4 is fixed to hold the payload 3. The second robot has in an analogous manner an arm 2.3 attached to a base 2.1 with a gripper 2.4 for holding the payload 4, whose joint angle to the base is described by the angle q ₂ . Zero value and orientation result from the synopsis of the upper and lower lines of FIG. 1, ie the joint angles q ^ = (qi, i, qi.2) and q ₂ take for the pose shown in the left column of FIG Value 0 and are counted positive counterclockwise. The process of alternately picking up payloads 3, 4 by the robots 1, 2 and their alternating super-stacking on a stack arranged between the two robots becomes in accordance with the invention alternately

subdivided successive process sections. In a first process section [to, T], the robot 2 is transferred from a storage pose, in which it deposits a payload 4 on the stack, into a receiving pod in which it receives another payload 4 from a conveyor (not shown). In this first process section, the first robot 1 transports a payload 3 from another conveyor (not shown) onto the stack and sets it down there. In a subsequent second process section [T, 2T = t ₀ ], conversely, the robot 2 transports a payload 4 from the conveyor onto the stack, while now the robot 1 is transferred from the storage pose to the receiving pod to receive another payload 3.

This is followed by a first process section, etc. This ensures that the two robots 1, 2 do not collide with one another in the common working space above the stack. This subdivision can be done manually or automatically, for example, during the planning of the overall process.

Now, for example, in advance during process flow planning, for each process section, i.e. the above-explained first and second

Process section, each determined by a robot control of the time-optimal workflow or the time-optimal motion q, (t) for the respective robot i = 1, 2.

For the robot 2, in the exemplary embodiment, the course of its joint angle q ₂ shown in the lower line of FIG. 1 and its first or second time derivative dq ₂ / dt result, since> ₂ / dt over the time t. In the first half of the process section, the robot 2 accelerates in the first half of the process section with an acceleration limited by its maximum permissible drive torque and brakes in the second half with the same negative value

Acceleration by a corresponding counter-torque to a standstill, resulting in a corresponding, customary in the railway planning

Speed trapezoidal profile results in the embodiment of a

Velocity triangle profile degenerate and drawn in Fig. 1 by dashed lines.

This results in at least optimal workflow of the robot 2 required time, which is the same for both process sections and represents the respective mininnale section time T ₂ .

In the same way, for the robot 1, a minimum section time Ti can be determined, which in the exemplary embodiment, for example due to stronger

Drive motors and / or lesser masses and thus greater allowable accelerations, is less than the minimum section time T _{2 of} the robot. 2

The robot controller R, of the respective robot i = 1, 2 first determines, for example after teaching the recording and storage poses, the above-described minimum section time Tj, for example by simulation and numerical optimization, and transmits them to the cell controller Z (see FIG 2).

In the cell controller Z, a process section time T is determined from this as the maximum of the minimum section times Tj (T = ΜΑΧΟΊ, T ₂ ) = T ₂ ) and the difference ATj = T - Tj between this process section time T and the respective minimum

Section time Tj to the individual robot i = 1, 2 transmitted (see Fig. 2). In the individual robot controllers R 1, the respective process section is transformed into one or more transfer sections s _a and / or one or more

Processing section s _b divided, which in Fig. 1 by the sections "a" and

In the exemplary embodiment, these are two short ones

Processing sections b for receiving or storing the payload

Closing or opening the gripper, in which the workflow, in particular the movement, of the respective robot must not be changed. Between the processing sections b results in a transfer section a, in which the

Workflow, in particular the movement of the robot between the recording and storage pose is freely selectable and can be optimized. The controller Ri of the robot 1 now optimizes the operation, here the movement, of the robot in this transfer section a under the condition that it is completed after Ti + ΔTi, i. beats that time difference of

Transfer movement to (T (s _a, E) -> T (s _a , E) ⁺ ΔTi). The index "E" denotes the

End position. In the exemplary embodiment, the robot controller Ri can optimize the movement qi (t), ie the trajectory q ^ s) and the path velocity profile s (t), for the transfer section a. As a quality criterion, a characteristic value for the energy required by the robot 1, for example an integral over the square of its drive torques, is minimized under the constraint that the movement must be completed within the available time. It follows that the robot 1 first pivots his arm 1.3 to minimize the moment of inertia about the axis of rotation of the base 1.1, then pivoted the base by 180 ° and finally pivots the arm 1.3 again to reach the Ablagepose. If, on the other hand, the trajectory qi (s) for the transfer section is given to

For example, avoiding a collision with obstacles, not shown, for this trajectory, the path velocity profile s (t) for the condition that the required energy E of the robot 1 is minimal (E = E _mjn ), optimized and in turn the energy consumption can be reduced. In principle, the energy optimization explained above can also be carried out for the robot 2. However, this leads to the already initially determined time-optimal workflow, since only with this the specified section time can be met. In general, therefore, it is provided in an advantageous embodiment to carry out the optimization only for those or those robots whose minimum section time does not determine the process section time.

The process section time does not have to correspond to the largest minimum section time. For example, in the above example, the process section time determined based on the minimum section time of the robot 2 may be one

predetermined value can be increased in order to reduce the load on the robot 2 by constantly shutting down time-optimal paths. This can, in an advantageous development only for one of the two alternating

Process sections are performed in which then, for example, the

Drive motors of the robot 2 can cool as a result of the submaximal load. LIST OF REFERENCE NUMBERS

1, 2 robots

 1.1, 2.1 basis

 1.2 swingarm

 1.3, 2.3 arm

 1.4, 2.4 grippers

 3, 4 payload

 Qu Joint Angle Base - Rocker (Robot 1) qi, 2 Joint Angle Rocker Arm (Robot 1) q2 Joint Angle Base - Arm (Robot 2) d / dt Derivative by Time t

 T process section time

a transfer section

b processing section

z cell control

 Ri, R2 robot controller

Claims

claims 1 . Method for computer-aided control of a robot arrangement with  at least two robots (1, 2), with the steps: Determining at least one process section point (q _{1 E} , q 2 _, E);  Determining a process section time (T) for the process section point; Specification of a section time (T) for at least one robot (1) of  Robot arrangement based on the process section time (T); and  Optimizing a workflow (gi (s (t)) of this robot (1) on the basis of the specified section time (ΤΊ + ΔΤ). 2. The method according to claim 1, characterized in that the workflow of a robot is optimized on the basis of the predetermined section time, wherein a quality criterion of the optimization based on an energy quantity (E) of the robot is determined. 3. The method according to any one of the preceding claims, characterized in that for optimizing a workflow this, in particular with a dynamic model of the robot, for at least two different  Parameter values of parameters is simulated, which at least partially determine the workflow. 4. Method nahe one of the preceding claims, characterized in that for optimizing the workflow of a robot based on the predetermined section time a web speed profile (s (t)) and / or a trajectory (g-i (s)) is determined. 5. The method according to any one of the preceding claims, characterized in that a transfer section (a) in a workflow (qi (s)) of a robot is determined and optimized. 6. The method according to any one of the preceding claims, characterized in that a minimum section time (T,) for at least two robots (i = 1, 2) of the robot assembly is determined, and that the process section time (T) on the basis of these minimum section times (Tj ) is determined. 7. The method according to any one of the preceding claims, characterized in that the optimization of the workflow of a robot at least partially by the control (R,) takes place. 8. The method according to any one of the preceding claims, characterized in that the specification of the section time for a robot by a controller (Z) of the robot assembly takes place. 9. control means (Z, Ri) for computer-aided control of a robot arrangement with at least two robots (1, 2), comprising: a process point point means (Z) for determining at least one process point point (qi, _E , q2, E);  a process section time means (Z, R,) for determining a  Process section time (T) for the process section point;  a section time means (Z) for specifying a section time (T) for at least one robot (1) of the robot arrangement on the basis of  Process time (T); and  an optimization means (Ri) for optimizing a workflow (gi (s (t)) of this robot on the basis of the predetermined section time, thereby  characterized in that the control means is arranged to carry out a method according to one of the preceding claims. 10. Control means according to claim 9, characterized in that one of its means at least partially in a control (Rj) of a robot of  Robot assembly and / or in a controller (Z) of the robot assembly is implemented. 1 1. Computer program product with a computer program stored thereon for carrying out a method according to one of the preceding claims 1 to 8.