DE102018200864B3 - Method and system for controlling a robot - Google Patents

Abstract

According to a method according to the invention for controlling a robot (10) in response to an external force (Fex) impressed on the robot, the robot is controlled (S50) in a first operating mode as a function of a surface (21) such that it is a tangential component (Ft) tries to follow this force perpendicular to an outwardly directed normal (s) on the surface in a point of contact of a robot-fixed reference (11) with the surface more closely than a normal component (Fn) of the force in the direction of this surface normal.

Description

The present invention relates to a method and system for controlling a robot in response to an external force impressed on the robot and to a computer program product for carrying out the method.

From the US 9,308,645 B2 is an admittance control for controlling robots known. In this case, on the basis of an external force impressed on a robot, a desired movement is determined by control engineering which would execute a virtual mass under this external force and which the robot tries to execute. In other words, the end effector of the robot behaves like the virtual mass.

This allows an advantageous hand guidance of the free (movable) Endeffektors by an operator by this on the robot manually impresses the external force.

However, if the end effector contacts a surface, it may happen, in particular due to control inaccuracies and the like, that the end effector unintentionally lifts off the surface.

The DE 10 2015 210 218 A1 relates to a method for operating a robot at a robot workstation, wherein the robot has a control device that is designed and / or set up to specify a state mode of the robot workstation or of the robot to be monitored, to monitor a state parameter of the robot workstation or of the robot corresponding to the state type, specify a threshold for the monitored state parameter of the robotic workstation or robot to manually move the robotic arm by manually applying forces to one or more of the members to displace the joints of the robotic arm and vibration to the robotic arm actuated by the control device to generate during the manually guided move when the monitored state parameter reaches the predetermined limit.

The DE 10 2015 009 151 A1 relates to a method for automatically determining an input command for a robot that is input to the robot by manually applying an external force, wherein the input command is determined on the basis of the fraction of joint forces impressed by the external force, which is a movement of the robot in only one seeks to effect for this input command specific subspace of the joint coordinate space of the robot.

One from the DE 10 2015 004 484 A1 A known robot controller for easily moving a desired axis of a robot by applying a force to a front end of the robot includes: a force measuring part that measures a force applied to the front end; an operation force calculation part that calculates an operation force for moving each axis based on the measured force; an operation command part that outputs a command to move the robot; and an operation axis specifying part that specifies an operation axis to be moved in response to the force and a movement direction of the operation axis depending on a direction of the force. When two or more operation axes are specified, the operation axis specifying part determines whether each operation axis is movable or not, depending on a status of the movement operation.

One from the DE 10 2015 004 481 A1 The known robot control apparatus comprises an operation axis adjusting unit that sets an axis that is rotationally moved in accordance with an applied force as an operation axis and sets a rotational movement direction of the operation axis; a first operating force detecting unit that obtains a first virtual force that is virtually applied to the operation axis to assume that the first virtual force is a first operating force; and an operation command unit that outputs an operation command for moving the operation axis, which is set by the operation axis adjusting unit, based on an operation force determined from the first operation force. The operation command unit obtains a target movement direction and a target movement speed of the operation axis on the basis of the first operation force and the rotational movement direction set by the operation axis adjustment unit to move the operation axis.

The DE 10 2013 218 823 A1 relates to a method for manually manipulating the pose of a manipulator arm of an industrial robot, comprising the steps of: detecting an operator applied to the manipulator arm by an operator of the industrial robot, determining as freedom of a reference coordinate system in the direction of which the operator has its greatest force directing component selected freedom, force-controlled driving the drives of the industrial robot such that an adjustment of a predetermined, associated with the manipulator arm reference point by moving the manipulator arm during a manually guided Adjusting the pose of the manipulator arm is done only in the selected freedom.

One from the DE 10 2008 062 622 A1 known command input to a controller of a manipulator comprises the steps of: detecting a first movement or force; Comparing the detected first motion or force with stored motions or forces, each associated with a command; Output of the instruction associated with this stored motion or force to the controller of the manipulator if the detected movement or force coincides with a stored movement or force.

The object of the present invention is to improve the operation of a robot.

This object is achieved by a method having the features of claim 1. Claims 12, 13 protect a system or computer program product for carrying out a method described herein. The subclaims relate to advantageous developments.

According to one embodiment of the present invention, in a method for controlling a robot as a function of an external force impressed on the robot, the robot is controlled in a first operating mode, in particular continuously, as a function of a surface in such a way or with the proviso in that it tries to follow more strongly a tangential component of the force perpendicular to an outwardly directed normal on the surface in a, in particular current, contact point of a robot-fixed reference with the surface, in particular follows, as a normal component of the force in the direction of this surface normal, in particular such or with the proviso that he tries not to follow the normal component of the force, at least substantially, in particular does not follow. In other words, in the first mode of operation, the robot is controlled to follow (less) the normal component than the tangential component to not even follow in one embodiment.

As a result, in one embodiment, an undesired lift-off from a contacted surface can be reduced, in one embodiment, at least substantially avoided.

Control in one embodiment may include, in particular, rules. In one embodiment, a force may also include a torque, in particular.

In one embodiment, the robot has at least three, in particular at least six, in one embodiment at least seven joints, in particular drivable or driven and / or rotary joints, in one embodiment, in particular electric, drives for adjusting the joints.

As a result, in one embodiment, the robot can be used advantageously, in particular flexibly and / or precisely.

The robotic reference in one embodiment is a distal end effector of the robot. The external force in one embodiment is manually imparted by an operator to the robot, in one embodiment to its robot-fixed reference, or is an external force impressed manually by an operator. In one embodiment, the external force is a force acting on the point of contact; it can be transformed or displaced there by a Jacobian matrix in a manner known per se (virtually).

As a result, the robot can advantageously be hand-guided in one embodiment, in an embodiment for teaching or presetting subsequently automatically traversable paths or the like.

An outward normal on a surface in a contact point ("surface normal") in one embodiment is perpendicular to a tangent plane (on) of the surface in the contact point and is directed away from the surface or toward the robot-fixed reference, for example be in a conventional manner differential geometric determined by the correspondingly oriented gradient or the correspondingly oriented cross product of two non-collinear tangent vectors (on) the surface in the contact point or be determined in turn, for example, in a conventional manner by differentiation or can be. If, for example, a surface or its contour is described by the function S (x, y, z) = 0 with the Cartesian coordinates x, y, and z, for example a spherical surface through x ² + y ² + z ² = 0, then is the surface normal n in a contact point (x, y, z) is determined by n = [∂S / ∂x, ∂S / ∂y, ∂S / ∂z] ^T , in the example by [x, y, z] ^T. In other words, in one embodiment of the robot in the first mode of operation, projection of the external force into the tangent plane (on) of the surface in the contact point is stronger than a projection of the external force towards the outward surface normal, or attempts to do so (correspondingly) controlled, in one embodiment, it follows the projection of the external force in the direction of the outward surface normal in the first mode of operation, at least substantially, not at all or tries this or is controlled accordingly.

In one embodiment, the robot is controlled in a second operating mode, in particular continuously, such or with the proviso that it tries to follow the normal component of the external force stronger, in particular following, as in the first operating mode, in particular such or with the proviso that he tries to follow the force regardless of its direction, in particular follows. In other words, in the second operation mode, the robot is controlled to follow the external force directionally (lightly).

As a result, in one embodiment, the robot-fixed reference in the second operating mode intentionally moved away from the surface and / or advantageously moved freely in space.

In one embodiment, depending on the normal component of the force, the force is switched from the first to the second operating mode, in one embodiment, if an amount of the normal component exceeds a predetermined threshold.

As a result, in one embodiment, an operator may simply terminate the first mode of operation, particularly to move the robot-fixed reference away from the surface by pulling sufficiently away from the surface.

Additionally or alternatively, it is also possible to switch over from the first to the second operating mode depending on a user input, for example an operator actuating a corresponding physical or software switch or the like.

In one embodiment, the robot is controlled in the first operating mode in such a way or with the proviso that it tries to impose a particular force on the surface in the opposite direction to the surface normal with the robot-fixed reference, in particular imprints it. In other words, in the first mode of operation, the robot is controlled to impart a predetermined force to the surface in the opposite direction of the surface normal.

As a result, in one embodiment, the robot-fixed reference can advantageously be fixed to the surface by control technology and / or imprint a desired process force, for example for processing the surface.

In one embodiment, depending on a determined distance, in particular when falling below a predetermined minimum distance, in an embodiment in contact, between the robot-fixed reference and the surface switched to the first operating mode.

As a result, in one embodiment, an operator may simply initiate the first mode of operation by pulling the robot-fixed reference sufficiently close to the surface.

Additionally or alternatively, it is also possible to switch to the first operating mode depending on a user input, for example an operator can actuate a corresponding physical or software switch or the like.

In one embodiment, the external force is determined using a sensor on the robot-fixed reference.

As a result, they can be determined very precisely in one embodiment.

Additionally or alternatively, the external force is determined in one embodiment by means of sensors on joints of the robot, in particular based on a dynamic model of the robot.

As a result, in one embodiment, an additional sensor on the robot-fixed reference can be omitted.

In one embodiment, the surface normal is determined as a function of a contour of the surface determined in a design using a scan, a vision system, or the like.

As a result, they can be determined very precisely in one embodiment.

Additionally or alternatively, the surface normal in one embodiment is determined as a function of a contour of the surface predetermined in a design based on CAD data or the like.

As a result, in one embodiment, a time and / or equipment expenditure for determining the contour can be omitted.

In one embodiment, the contact point is determined in response to detection of an environment of the robot-fixed reference, in an embodiment using a scan, a vision system, or the like.

As a result, it can be determined very precisely in one embodiment.

Additionally or alternatively, in one embodiment, the contact point in dependence on detected positions of joints of the robot, a determined or predetermined contour of the determined robot-fixed reference and / or a determined or predetermined contour of the surface.

As a result, in one embodiment, a time and / or equipment expense for detecting the environment can be omitted.

In one embodiment, in the first and / or second operating mode, the robot is controlled by means of an admittance control, which determines control values for drives of the robot as a function of the determined external force.

As a result, in one embodiment, the robot can be guided in a particularly advantageous manner, in particular intuitively, reliably and / or precisely.

In one embodiment, in the first operating mode, the normal component of the determined external force in the direction of the surface normal is computationally reduced, in particular faded out or filtered.

As a result, the invention according to the invention weaker or non-follow the normal component, in particular by means of an admittance, particularly advantageous, in particular reliably and / or with little rake (time) effort can be realized.

According to one embodiment of the present invention, a system, in particular hardware and / or software, in particular program technology, for implementing a method described herein and / or has means for controlling the robot in response to an external force applied to the robot in the first operating mode in response to a surface such that the robot tries to follow a tangential component of the force perpendicular to the outward normal on the surface in a contact point of a robot-fixed reference with the surface stronger than a normal component of the force in the direction of this surface normal, in particular Normal component of the force not trying to follow up.

• Mittel zum Steuern des Roboters in einem zweiten Betriebsmodus derart, dass er der Normalkomponente der Kraft stärker zu folgen versucht als in dem ersten Betriebsmodus, insbesondere derart, dass er der externen Kraft unabhängig von ihrer Richtung zu folgen versucht;
• Mittel zum Umschalten von dem ersten in den zweiten Betriebsmodus in Abhängigkeit von der Normalkomponente der Kraft;
• Mittel zum Steuern des Roboters in dem ersten Betriebsmodus derart, dass er mit der roboterfesten Referenz eine vorgegebene Kraft gegensinnig zur Oberflächennormale auf die Oberfläche aufzuprägen versucht;
• Mittel zum Umschalten in den ersten Betriebsmodus in Abhängigkeit von einem ermittelten Abstand, insbesondere Kontakt, zwischen der roboterfesten Referenz und der Oberfläche und/oder in Abhängigkeit von einer Benutzereingabe;
• einen Sensor an der roboterfesten Referenz und/oder Sensoren an Gelenken des Roboters zum Ermitteln der externen Kraft;
• Mittel zum Ermitteln der Oberflächennormale in Abhängigkeit von einer ermittelten oder vorgegebenen Kontur der Oberfläche;
• Mittel zum Ermitteln des Kontaktpunkts in Abhängigkeit von erfassten Stellungen von Gelenken des Roboters, einer ermittelten oder vorgegebenen Kontur der roboterfesten Referenz und/oder Oberfläche und/oder einer Erfassung einer Umgebung der roboterfesten Referenz;
• Mittel zum Steuern des Roboters in dem ersten und/oder zweiten Betriebsmodus mithilfe einer Admittanzregelung, die Steuerwerte für Antriebe des Roboters in Abhängigkeit von der ermittelten externen Kraft ermittelt; und/oder
• Mittel zum rechentechnischen Reduzieren, insbesondere Ausblenden, der Normalkomponente in dem ersten Betriebsmodus.

In one embodiment, the system or its agent has:

• Means for controlling the robot in a second mode of operation such that it tries to follow the normal component of the force more strongly than in the first mode of operation, in particular so as to try to follow the external force regardless of its direction;
• Means for switching from the first to the second operating mode as a function of the normal component of the force;
• Means for controlling the robot in the first mode of operation so as to impose a predetermined force against the surface normal to the surface with the robot-fixed reference;
• Means for switching to the first operating mode as a function of a determined distance, in particular contact, between the robot-fixed reference and the surface and / or in dependence on a user input;
• a sensor on the robot-fixed reference and / or sensors on joints of the robot for determining the external force;
• Means for determining the surface normal as a function of a determined or predetermined contour of the surface;
• Means for determining the point of contact in dependence on detected positions of joints of the robot, a determined or predetermined contour of the robot-fixed reference and / or surface and / or detection of an environment of the robot-fixed reference;
• Means for controlling the robot in the first and / or second operating mode by means of an admittance control, which determines control values for drives of the robot in dependence on the determined external force; and or
• Means for computationally reducing, in particular hiding, the normal component in the first operating mode.

A means in the sense of the present invention may be designed in terms of hardware and / or software, in particular a data or signal-connected, preferably digital, processing, in particular microprocessor unit (CPU) and / or a memory and / or bus system or multiple programs or program modules. The CPU may be configured to execute instructions implemented as a program stored in a memory system, to capture input signals from a data bus, and / or to output signals to a data bus. A storage system may comprise one or more, in particular different, storage media, in particular optical, magnetic, solid state and / or other non-volatile media. The program may be such that it is capable of embodying or executing the methods described herein, so that the CPU may perform the steps of such methods, and thus, in particular, control the robot. In one embodiment, a computer program product may comprise, in particular, a nonvolatile storage medium for storing a program or a program stored thereon, In particular, an execution of this program causes a system or a controller, in particular a computer, to execute a method described here or one or more of its steps.

In one embodiment, one or more, in particular all, steps of the method are completely or partially automated, in particular by the system or its (e) means.

In one embodiment, the system includes the robot and / or its controller.

With particular advantage, the present method for teaching or predetermining robot tracks, in particular by means of manual guiding of the robot, in particular the robot-fixed reference, can be used. Accordingly, in one embodiment in the first operating mode - at least temporarily - a pose of the robot, in particular the robot-fixed reference, stored and subsequently given a robot path in a development on the basis of the stored poses.

• 1: ein System nach einer Ausführung der vorliegenden Erfindung; und
• 2: ein Verfahren zum Steuern eines Roboters des Systems nach einer Ausführung der vorliegenden Erfindung.

Further advantages and features emerge from the subclaims and the exemplary embodiments. This shows, partially schematized:

• 1 a system according to an embodiment of the present invention; and
• 2 A method of controlling a robot of the system according to an embodiment of the present invention.

1 shows a system according to an embodiment of the present invention with a robot 10 who is an end effector 11 and a robot controller 30 ,

The end effector 11 is by an operator 40 on a surface 21 a workpiece 20 Hand-guided, for example, to teach a processing path.

This will be done in a first step S10 (see. 2 ) of a method for controlling the robot 10 according to an embodiment of the present invention by means of a force-moment sensor 12 at the end effector 11 one from the operator 40 manually impressed external force F _ex determined.

In a modification, the robot controller may also use external force via sensors 12 ' at the joints of the robot. Generally, the external force F _ex in an embodiment, by transforming the difference of the axle moments τ _msr measured at the joints by means of the sensors and the, in particular, commanded, axle moments τ _{(c) md} with the (transposed) Jacobian J ^T calculated on the basis of an optionally inverse dynamic model of the robot of the end effector or its tip: $$F_{\text{ex}}=J^T\cdot \left({\tau }_{\text{msr}}-{\tau }_{\left(\text{c}\right)\text{md}}\right)$$

This is based on the consideration that the deviation between the model-based and measured axis moments results precisely from the external force, so that the external force can be determined by transforming the corresponding axis moments into the working space of the robot (end effector).

The contour of the surface 21 is known, for example, from CAD data, or is by a camera 31 determined.

In step S10 checks the robot control 30 whether (already or still) a first operating mode is selected, for example by actuation of a corresponding switch by the operator.

This is not the case ( S10 : "N"), there is a second mode of operation and the robot controller or method moves to step S40 continued.

mit der virtuellen Masse m, und die Antriebe 13 des Roboters zur Realisierung dieser Soll-Geschwindigkeit v_d ansteuert. In einer Abwandlung kann auch eine virtuelle Dämpfung vorgesehen sein.In step S40 It carries out an admittance regulation, in which it uses the external force in a manner known per se F _ex at the top of the end effector 11 determines a desired speed v _d , for example, by time integration according to $$v_{\text{d}}={\displaystyle \int \left(F_{\text{ex}}/m\right)\text{d}t}$$

with the virtual mass m, and the drives 13 of the robot for realizing this target speed v _d drives. In a modification, a virtual damping can also be provided.

und prüft, ob der Betrag |F_n| dieser Normalkomponente F_n einen vorgegebenen Grenzwert übersteigt.If the first operation mode is selected (S10: "Y"), the robot controller determines 30 in one step S20 based on the position of the joints of the robot and the contour of the surface 21 an outward surface normal n (| n | = 1) perpendicular to the surface 21 at the point of contact of the tip of the end effector 11 with the surface 21 as well as the normal component F _n the external force attacking there F _ex towards this surface normal n according to $$F_{\text{n}}=\left\{\left[\left(F_{\text{ex}}\cdot n\right)+\left|F_{\text{ex}}\cdot n\right|\right]/2\right\}\cdot n$$

and checks if the amount | F _n | this normal component F _n exceeds a predetermined limit.

Is that the case ( S20 : "Y"), it switches to the second operating mode and continues with the above step S40 continued.

Otherwise ( S20 : "N"), ie if (still) the first operating mode is selected, the robot control fades in one step S30 the normal component computationally by taking it from the external force F _ex subtracted: $$F{\text{'}}_{\text{ex}}\leftarrow \left(F_{\text{ex}}-F_{\text{n}}\right),$$

In other words, the robot controller filters in step S30 the normal component F _n the external force F _ex towards the surface normal n out.

Then she leads in one step S50 with this filtered external force analogous to step S40 the admittance control, in the embodiment approximately according to $$v_{\text{d}}={\displaystyle \int \left(F{\text{'}}_{\text{ex}}/m\right)\text{d}t}$$

Then the process returns to step S10 back.

This is followed by the robot 10 in the first mode of operation with its end effector 11 the normal component F _n the one from the operator 40 manually impressed external force F _ex not and thus a tangential component F _t = F _ex - (F _ex · n) · n stronger contrast, or attempts to realize this control technology. In the second operating mode, however, the robot follows 10 with his end effector 11 the external force F _ex regardless of their direction or trying to implement this control technology.

Although exemplary embodiments have been explained in the foregoing description, it should be understood that a variety of modifications are possible.

So, in a variation in step S50 instead of the normal component F _n in the direction of the surface normal also the component of the external force F _ex parallel to the surface normal, ie direction-independent filtered or as a filtered external force only the tangential component explained above F _t be taken into account. Additionally or alternatively, a predetermined force f _cmd can also be imposed on the surface in a _manner opposite to the surface _normal , for example by performing in step S50 the filtered external force is added: $$F{\text{'}}_{\text{ex}}\leftarrow \left(F_{\text{ex}}-F_{\text{n}}\right)-f_{\text{cmd}}\cdot n\text{respectively}\text{,}F{\text{'}}_{\text{ex}}\leftarrow F_{\text{t}}-f_{\text{cmd}}\cdot n$$

LIST OF REFERENCE NUMBERS

10

robot

11

End effector (robot-fixed reference)

12; 12 '

sensor

13

drive

20

workpiece

21

surface

30

robot control

31

camera

40

operator

F _ex

external force

F _n

normal component

F _t

tangential

n

surface normal

Claims (13)

Method for controlling a robot (10) in response to an external force (F _ex ) impressed on the robot, the robot being controlled in a first operating mode as a function of a surface (S50) such that it corresponds to a tangential component (S50). F _t ) tries to follow this force perpendicular to an outwardly directed normal (s) on the surface in a contact point of a robot-fixed reference (11) with the surface more strongly than a normal component (F _n ) of the force in the direction of this surface normal. Method according to Claim 1 , characterized in that the robot is controlled in the first operating mode such that it does not try to follow the normal component of the force. Method according to one of the preceding claims, characterized in that the robot is controlled (S40) in a second operating mode such that it tries to follow the normal component of the force more strongly than in the first operating mode. Method according to the preceding claim, characterized in that in dependence on the normal component of the force is switched from the first to the second operating mode (S20) and / or the robot is controlled in the second operating mode such that it is the force regardless of their direction tried to follow. Method according to one of the preceding claims, characterized in that the robot is controlled in the first operating mode such is that he tried with the robot-fixed reference to impose a predetermined force in the opposite direction to the surface normal to the surface. Method according to one of the preceding claims, characterized in that in dependence on a determined distance, in particular contact, between the robot-fixed reference and the surface and / or in response to a user input in the first operating mode is switched. Method according to one of the preceding claims, characterized in that the external force by means of a sensor (12) on the robot-fixed reference and / or sensors (12 ') is determined at joints of the robot. Method according to one of the preceding claims, characterized in that the surface normal is determined as a function of a determined or predetermined contour of the surface. Method according to one of the preceding claims, characterized in that the contact point in dependence on detected positions of joints of the robot, a determined or predetermined contour of the robot-fixed reference and / or surface and / or detection of an environment of the robot-fixed reference is determined. Method according to one of the preceding claims, characterized in that the robot is controlled in the first and / or second operating mode by means of an admittance control, which determines control values for drives (13) of the robot in dependence on the determined external force. Method according to one of the preceding claims, characterized in that in the first mode of operation, the normal component is computationally reduced, in particular hidden. A system adapted to perform a method according to any one of the preceding claims and comprising means (30) for controlling a robot (10) in response to an external force (F _ex ) applied to the robot in a first mode of operation in response to a surface (21) such that the robot tries to follow a tangential component (F _t ) of the force perpendicular to an outward normal (s) on the surface at a contact point of a robot fixed reference (11) with the surface more than a normal component (F _n ) the force in the direction of this surface normal. A computer program product having a program code stored on a computer-readable medium for performing a method according to any one of the preceding Claims 1 to 11 ,

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