WO2019224288A1

WO2019224288A1 - Direction-dependent collision detection for a robot manipulator

Info

Publication number: WO2019224288A1
Application number: PCT/EP2019/063298
Authority: WO
Inventors: Sven Parusel; Saskia Golz
Original assignee: Franka Emika Gmbh
Priority date: 2018-05-23
Filing date: 2019-05-23
Publication date: 2019-11-28
Also published as: DE102018112370B4; DE102018112370A1

Abstract

The invention relates to a method for controlling an actuator-driven robot manipulator (1) having an end effector (3), in which the end effector (3) executes a predefined target movement and executes a task while executing the target movement, comprising the following steps: while executing the target movement, determining (S1) an external wrench K_ext introduced into the robot manipulator (1), wherein K_ext has a vector F_ext of at least one external force and/or a vector M_ext of at least one external torque; detecting (S2) an unwanted collision of the robot manipulator (1), if K_ext exceeds a predefined first threshold value in or about n axes of a predefined coordinates system with N axes, wherein n∈N; detecting (S3) an erroneous execution of the task, if K_ext exceeds a predefined second threshold value in or about m axes of the coordinates system, or if K_ext<K_des, wherein K_des is a wrench that is dependent on the task and desired, expected and/or occurring exclusively in or about the m axes, and wherein m∈N and m ∉ n, wherein the first threshold value is lower than the second threshold value; and actuating (S4) the robot manipulator (1) in an error mode, if an unwanted collision of the robot manipulator (1) and/or an erroneous execution the the task is detected.

Description

Direction-dependent collision detection for a robot manipulator

The invention relates to a method for controlling an actuator-driven

Robot manipulator with an end effector, and a device for controlling an actuator-driven robot manipulator with an end effector and a robot with such a device. The object of the invention is to better detect collisions of a robot manipulator, in particular during the execution of a task by the robot manipulator, and thereby perform the task better.

The invention results from the features of the independent claims. Advantageous developments and refinements are the subject of the dependent claims.

A first aspect of the invention relates to a method for controlling an actuator-driven robotic manipulator having an end effector, in which the end effector executes a predetermined target movement and performs a task during execution of the target movement, comprising the steps of:

during the execution of the desired movement, determination of an external power wincher K _ext introduced into the robot manipulator, wherein K _{ext has} a vector F _{ext of} at least one external force and / or a vector M _{ext of} at least one external moment,

Detection of an undesired collision of the robot manipulator when K _ext in or around n axes of a predefined coordinate system with N axes exceeds a predefined first limit value, where ne N,

- detecting exceeds a predefined second limit value of a faulty execution of the task, if K _ext in or near m axes of the coordinate system or if K _ex t <K _d it is, wherein K _of a dependent of the task and exclusively in or around the m axis occurring expected and / or desired force Winder, where K _of a vector F _{of the} at least one expected and / or desired force and / or a vector M _{of the} expected of at least one and / or has the desired torque, and wherein me N and min is established,

wherein the first threshold is less than the second threshold, and

- Driving the robot manipulator in an error mode when an undesirable

Collision of the robot manipulator and / or a faulty execution of the task is detected. In particular, an external force occurs as such in an axis, and an external moment as such about an axis. Thus, K _DES is a dependent on the task and occur exclusively in, or to the m axis of expected and / or desired force Winder, in particular the pre-defined coordinate system and the m axis, and especially its orientation, defined on the basis of prior knowledge of K _{of the} appropriately. K _des results advantageously by knowing the task and the expected during the execution of the task by interaction with an environment, acting on the robot manipulator mechanical forces and / or moments. Because the

Execution of the task required by the robot manipulator a period _of K is also advantageous time-dependent: K = K _of _the (t).

The end effector is also referred to as such when it is not aktuiert itself, that is, even has no movable or otherwise controllable actuators. The end effector can thus also simply be the distal end of the robot manipulator.

Under a desired movement is advantageously understood a kinematic data set for specifying the movement of the end effector of the robot manipulator. Advantageously, the desired movement is defined via a desired movement path, that is, by means of a sequence of desired positions of a specific reference point on the

Robot manipulator, in particular a reference point on the end effector of the robot manipulator or on the distal end of the robot manipulator, and further advantageously by means of a speed associated with this desired sequence of positions and an acceleration of the reference point. Accordingly, the term "desired movement" also includes a desired standstill of this reference point considered. Then, in this case of the desired standstill, a setpoint position that is constant over time and a setpoint speed of zero and one applies

Target acceleration of zero of the reference point.

External forces and moments are understood here as meaning those which do not arise through the drives which are connected to the robot manipulator. Preferably, the joints of the robot manipulator as drives on electric motors for generating moments between the robot members, which are each rotatably connected to each other by the joint. These moments, which can be equivalently converted into a force by dividing a corresponding radius to be considered, are, in contrast to the external forces and moments mentioned above, understood as internal forces and moments. The comparison of K _ext with _the K and K _ext of, preferably, with the first and second component-wise limit of vector generally K _ext and of the vectorial in general K, so scalars are compared with each _{of the} scalars. Alternatively, scalar vector norms || K _ext || are preferred and || K _of || formed and compared with each other and with the first and the second limit. The vector standard is preferably the 2-norm, ie || K _ext | | 2 and || K _of | 2, which as a time integral of the squared vector components forms an energy-equal standard, or alternatively preferably uses as the vector standard the "norm, that is || K _ext || ~ and || K _of || ~, which has the largest value indicates all vector components over time. In the case of using the "-norm and / or the 2-norm, the comparisons become advantageous for the m axes and the n axes after separation of the vectorial quantities in the

Components of the m axes and made into the components of the n axes.

Preferably, the determination of the external power winch K _ext by means of sensors, in particular by means of force sensors and / or torque sensors. In particular, the moment sensors are preferably already installed in joints of the robot manipulator together with the motor located in the respective joint. Furthermore, force sensors are preferably arranged on a structural component of a robot member, wherein this type of force sensors determines a tension or a force in the respective robot member via the material expansion of the robot member and the known material constants, in particular of the modulus of elasticity. Further preferably, electrical current sensors are used, which measure the electric current through an electric motor of the robot manipulator, in order to conclude from changes in the electric current to an abnormal change in torque at the motor and thus to an external force or external moment , In this case, the motors themselves serve as torque sensors.

Detecting an undesired collision of the robotic manipulator consists, in particular, in detecting an undesired collision of the robot

Robot manipulator with an object of the environment, with an object picked up at the end effector, or by a collision of the robot manipulator with itself, for example between two members of the robot manipulator, or with a

Robot base to which the robot manipulator is connected and which serves as a support for the robot manipulator. In particular, the external force winder K _{ext is} a vector which combines the detected forces F _ext as a column vector and the detected moments M _ext as a column vector and records them together in a preferably six-dimensional column vector, since both F _ext and M _ext, in particular in a Cartesian coordinate system recorded three entries for three mutually orthogonal spatial directions. In particular, if only external forces are determined, the components of this vector contain a zero in all entries for the external moments. Preferably, and in the most general case, therefore, for the external force winder K _eXt = [F _eXt ^T , M _ext ^T ] ^T , where the superscript "T" in the form of "(-)" indicates the transposed operator through which Row vector becomes column vector and vice versa.

The predefined coordinate system has in particular N axes. These N axes are preferably such that an indication of a coordinate by means of the predefined coordinate system requires the specification of only one value on each individual axis of the coordinate system and also allows what is the case in particular for orthogonal axes. Especially for complex load cases with several force directions of an expected and / or desired force Winders K _of at execution of the task is alternatively preferably an overdetermined predefined coordinate system used, so that the m axis, occurs in or near that of the expected and / or desired force Winder K _of , not necessarily orthogonal to each other and preferably form an angle of <90 ° to each other and thus more than six spatial directions (that is, more than three spatial directions in ignoring signs) by the m axes can be considered.

The external force winder is determined in a Winder coordinate system, which is generally independent of the predefined coordinate system in which the n axes and the m axes are defined. If both coordinate systems differ in particular in the location of their origin or also in their orientation, or even in their type, for example if the Winder coordinate system defines rotation coordinates with radius r and vectorial angle a and the predefined coordinate system is a Cartesian coordinate system, in particular the external force winder by coordinate system transformation from the Winder coordinate system in the

predefined coordinate system transformed in order to specify in the predefined coordinate system, a respective component of the external power winders in a respective axis of the predefined coordinate system. The coordinate system transformation consists in particular of an image, preferably comprising a rotation matrix and a displacement vector to account for different origins of the respective coordinate systems.

As a result, the m axes differ from the n axes in that a force winder K _des dependent on the task is expected and / or desired in or around the m axes. This is expressed by the terms m ^ N and mi n, which say that the predefined coordinate system has in particular N axes whose

Orientation in space and in particular the selection of the m axes according to the direction and orientation of the power wind K _{of be} defined. Furthermore, the terms m ^ N and mi n mean that an axis can fall below either the m axes or below the n axes, but can not simultaneously be an axis of the m and the n axes. In other words, for a certain axis, a component of the power wind K _{of is} expected or not.

This expected and / or desired force Winder K _des in particular by a desired contact with the environment of the robot manipulator with an object from the environment to the state, for example, when editing an object by the end effector, when gripping an object by the end effector, when

Machining a workpiece through the end effector, for example, welding, drilling, milling, painting, or the like. By such activities arises according to the Newton's law "Actio is equal to Reactio" a force on in particular the end effector, which should not be regarded as an undesirable collision. Therefore, this expected and / or desired force Winder K is _the taken into account as described above, in particular a desired force Winder K _of preferably from a force control of the robot manipulator is determined, and an expected force Winder K _{of the} preferred estimation a contact force of a manipulation object is determined. Again applies to the expected and / or desired force Winder K _of the

Vector property analogous to the external force Winder K _ext, where K _of the expected and / or desired forces F _of as a column vector and the expected and / or desired moments M _{of the} combined as a column vector and recorded together in a six-dimensional column vector, since both F _of and M _{of the} detected three successive entries for three orthogonally related directions in space, in particular in a Cartesian coordinate system. If, in particular, only expected and / or desired forces are determined, then the components of this vector contain a zero in all entries for the external moments. Preferably, and in the most general case, therefore, for the expected and / or desired force winder K _d es = [F _d es ^T , M _de s ^T ] ^T , where the superscript "T" in the form of "(-)" indicates the transposed operator through which a row vector becomes the column vector and vice versa.

The axes are preferably to be considered separately in their respective direction for the comparison of the determined force winders with the respective limit value, that is to say that in a Cartesian coordinate system, a distinction is made in particular between a positive and a negative axis, for example a direction "+ x" and an order 180 ° rotated on the other hand running direction "-x". Advantageously, a first limit value can thus be defined in a first direction of a Cartesian coordinate system, and a further first limit value can be defined with differing values for the negative direction of the first direction. This is particularly preferred

Distinction according to the sign of the direction made only in the m axes, whereas in the n axes of the force Winder K _{ext is} only compared in terms of absolute value with the first and second limit. For all directions of each axis, that is to say for both directions "+ x" and "- x", the component of the external power wind K _{ext is} compared here with a respective positive limit value. The statement that the first limit value is smaller than the second limit value is therefore always to be understood as positive limit values in comparison to absolute components of the external power wind K _ext and analogously thereto in comparison with the magnitude expected and / or desired force winder K _des .

The term "error mode" generally indicates a signal, a control command or a

Control program that defines the driving of the robot manipulator in response to detecting an unwanted collision of the robot manipulator and / or an erroneous execution of the task. Preferred embodiments of the failure mode are those listed below.

The failure mode is preferably that the execution of the task is aborted first and then a new attempt to execute the task is repeated with changed parameters. Alternatively preferably, the error mode consists in a termination of the instantaneous movement until the robot manipulator is at a standstill, that is to say in a so-called "safe stop". As an alternative, the execution of the error mode preferably consists in changing the parameters of one

Compliance control. Such a compliance control generates an artificial spring-mass-damper model of the robotic manipulator and defines this model as desired behavior which the controller of the robotic manipulator is to produce. Preferably, this change of the compliance control in the failure mode is in one lower spring force constant with correspondingly reduced damping of the spring mass damper model. Another alternatively preferred failure mode is an active avoidance of the external force Winder K _ext . In this case, a controller of the robot manipulator is actively controlled accordingly and with corresponding setpoints of position and / or speed and / or acceleration

acted so that the determined external force Winder K _{ext is} actively avoided. For this purpose, a method for determining an acting location, that is localization, of at least one external force or external moments is advantageously used. Alternatively, the execution of the failure mode is to issue a warning to a user or to another person. Generally speaking, three general options are to be considered for the failure mode, namely an active reaction, a passive reaction, or a stopping of the movement of the

Robotemanipulators on the respective limit exceeding external

Kraftwinder K _ext .

It is an advantageous effect of the invention that a collision of a

Robotemanipulators can be detected more accurately. This advantageous effect occurs in particular in that in or around the m axes of the predefined

Coordinate system in which a force is expected and / or desired, the second threshold is selected to be higher than the first limit for the n axes in which no contact force is expected and / or desired. As a result, unwanted collisions are recognized rather quickly by the relatively low first limit in the n axes, whereas the forces and / or moments on the axes do not exert any deleterious influence on the axes that could lead to misdetections of unwanted collisions on the robot manipulator.

According to an advantageous embodiment of a faulty execution of the task is the power Winder K _ext determined by the expected and / or desired force Winder K _of compensated and the compensated force Winder with the second threshold value is compared, at least for the detection.

This embodiment is particularly known or predetermined

Kraftwinder K of _the performed. Accordingly, only the difference between the force Winder K _des and the force Winder K _ext is advantageously compared to the second limit value. Thereby an uncertainty, which share in the power actually Winder K _ext of the force _{of the} blast K occupies taken out, which provides a comparison with the second threshold value is advantageously more reliable results. According to a further advantageous embodiment, the external force Winder K _{ext is determined} by means of a pulse observer.

In particular, the impulse observer records those based on engine torques

estimated angular accelerations of the joints between the robot members of the robot manipulator. These can be compared with the actual angular accelerations of the joints and thus advantageously closed in case of deviations to external forces and moments.

According to a further advantageous embodiment, the predefined

Coordinate system and / or the m axes and / or the n axes time-varying and depending on the desired movement and / or the task.

Advantageous and particularly if the expected force Winder K _of its

Orientation over the course of the execution of the task changes, the m axes and / or the n axes are advantageously adapted over this.

According to a further advantageous embodiment, the first limit value and / or the second limit value are time-variant and dependent on the progress in the course of the execution of the task.

According to a further advantageous embodiment, the first and / or the second limit value are predetermined by a user and are adaptable by the user.

According to a further advantageous embodiment, the first and / or the second limit value are defined together with the task.

According to a further advantageous embodiment, the first and / or the second limit value are determined and adapted by machine learning.

By "machine learning" is preferably understood a parametric adaptation of the first limit value and / or the second limit value. The parametric

Adaptation is preferably carried out gradient-based or based on a general cost or energy function, the respective parameter or limit itself is at least square in the energy function or the cost function, so that when forming a time derivative of the cost or energy function of the value function decreases over time and thus has a convergence of the respective limit value or parameter to lower values of the cost function.

Alternatively, preferably one or more statistical functions are used for machine learning, in particular to form an expected value for the first or second limit value depending on the past first or second limit values. Furthermore, machine learning is preferably based on the use of neural networks or related trainable constructs which, in particular via superimposed and adapted sigmoid functions, map input / output behavior as input values depending on environmental parameters, and thus, in particular, environmental conditions and detects parameters of the respective task, determine a first and / or second threshold as the respective output value of the neural network. Further preferably, machine learning relies on linear regression to statistically adjust the respective linear factors of a linear equation system such that the result of the linear system of equations provides the first or second threshold.

Another aspect of the invention relates to an apparatus for controlling an actuator driven robotic manipulator having an end effector, wherein the end effector is configured to perform a predetermined desired movement and to perform a task during the execution of the desired movement, comprising: a

Force determination unit used to determine a robot manipulator

introduced external power winch K _ext is executed during the execution of the desired movement, wherein K _{ext has} a vector F _ext at least one external force and / or a vector M _ext at least one external moment, a computing unit, which is executed to an undesirable collision of the robot manipulator when K _ext in or around n axes of a predefined coordinate system with N axes exceeds a predefined first limit, where ne / V, and is designed to detect erroneous execution of the task, if K _ext in or around m axes of the coordinate system exceeds a predefined second threshold value or if K _ext <K _of, where K is _the one dependent on the object and occur exclusively in, or to the m axis of expected and / or desired force Winder, where K _of a vector F _of at least an expected and / or desired force and / or a vector M of _the at least one t is an expected and / or desired torque, and where m ^ N and mi n, wherein the first threshold is less than the second threshold, and a control unit configured to drive the robotic manipulator in an error mode when the computing unit detects an undesired collision of the robot manipulator and / or an erroneous execution of the task. According to a further advantageous embodiment, the device furthermore has a user interface for specifying the first limit value and / or the second limit value.

Advantages and preferred developments of the proposed device result from an analogous and analogous transmission of the statements made above in connection with the proposed method.

Another aspect of the invention relates to a robot with a device as described above and below.

Further advantages, features and details will become apparent from the following description in which - where appropriate, with reference to the drawings - at least one embodiment is described in detail. The same, similar and / or functionally identical parts are provided with the same reference numerals.

Show it:

Fig. 1 shows a method for controlling an actuator-driven

Robot manipulator according to an embodiment of the invention, and

2 shows a robot with a device for controlling an actuator

driven robotic manipulator according to another

Embodiment of the invention.

The illustrations in the figures are schematic and not to scale.

Fig. 1 shows a method for controlling an actuator-driven

Robot manipulator 1 with an end effector 3, in which the end effector 3 executes a predetermined desired movement and executes a task during the execution of the desired movement. In a first step, during the execution of the desired movement, a determination S1 of an external power wincher K _ext introduced into the robot manipulator 1 takes place, wherein K _{ext has} a vector F _{ext of} at least one external force and / or a vector M _{ext of} at least one external moment. The external force Winder K _ext is determined by means of a force and torque sensor. In a further step, a detection S2 of an undesired collision of the Robot manipulator 1, if K _ext in or around n axes of a predefined

Coordinate system with N axes exceeds a predefined first limit, where ne / V. Further, a detecting occurs S3 a faulty execution of the task, if K _ext exceeds a predefined second limit value in or near m axes of the coordinate system or if K _ext <K _of, where K _of a dependent of the task and exclusively in or around the m Axes expected expected and / or desired Kraftwinder is, and where m ^ N and mi n applies. The first limit value is smaller than the second limit value. In the final step, a drive S4 of the robot manipulator 1 takes place in an error mode when an unwanted collision of the robot manipulator 1 and / or an erroneous execution of the task is detected. In addition, the predefined coordinate system, along with the m axes and the n axes, is time-variant and dependent upon an execution progress task. The first and / or the second limit value are further specified by a user and can be adapted by the user during the execution of the task.

2 shows a robot 200 having a device 100 for controlling an actuator-driven robot manipulator 1 with an end effector 3, wherein the end effector 3 is designed to execute a predetermined target movement and to execute a task during the execution of the target movement. The end effector 3 in this case has a drill chuck and a drill clamped therein. The device 100 has a force determination unit 5, which is used to determine one in the

Robot manipulator 1 introduced external power windlass K _ext is executed during the execution of the desired movement, where K _{ext has} a vector F _ext at least one external force and / or a vector M _ext at least one external moment. Furthermore, the device 100 has a computing unit 7 which is designed to detect an unwanted collision of the robot manipulator 1 if K _ext in or around n axes of a predefined coordinate system with N axes exceeds a predefined first limit value, where ne / V, and detecting a faulty execution of the task, if K _ext exceeds a predefined second limit value in or near m axes of the coordinate system or if K _ext <K _of, where K _of a dependent of the task and exclusively in or around the m axis occurring expected and / or desired force winder, and wherein me / and mi n, where the first limit is less than the second limit. In this case, the following N axes are considered: "x",

where | A / | = 4. As is drilled in the in z-direction, a feed takes place as the desired motion for drilling by means of the arranged to the end effector 3 drill, and from the component, is carried out a contact force in the form of an expected and / or desired force Winders K _of the axis ,, is - z "as the only m Axis defined. The other axes "x", "y", "z" are consequently n axes. However, remains from the force _{of the} blast K, i.e. K _ext <K _of enters, so a faulty execution of the task is detected as discussed above, since the drilling not carried out as planned, for example, if the slip is to be drilled component. Furthermore, the device 100 has a control unit 9, which is designed to, the

Robotemanipulator 1 in a failure mode to control when the computing unit 7 detects an undesired collision of the robot manipulator 1 and / or an erroneous execution of the task. The error mode consists here in an abort of the

Performing the task and a stoppage of the end effector.

Although the invention has been illustrated and explained in detail by preferred embodiments, the invention is not limited by the disclosed examples

and other variations can be deduced therefrom by those skilled in the art without departing from the scope of the invention. It is therefore clear that a multitude of possible variations exists. It is also to be understood that exemplified embodiments are really only examples that are not in any way intended to limit such scope, uses, or uses

Configuration of the invention are to be construed. Rather, the foregoing description and description enable the skilled artisan to practice the exemplary embodiments, and those of skill in the knowledge of the disclosed inventive concept may make various changes, for example, to the function or arrangement of particular elements recited in an exemplary embodiment. without departing from the scope of the protection by the claims and their legal equivalents, such as more extensive

Explanations in the description, is defined.

LIST OF REFERENCE NUMBERS

1 robot manipulator

3 end effector

5 force determination unit

7 arithmetic unit

9 control unit

100 device

200 robots

51 Determine

52 Detect

53 Detect

54 driving

Claims

claims

Anspruch [en] A method of controlling an actuator-driven robotic manipulator (1) having an end effector (3), wherein the end effector (3) has a predetermined one

Executes target movement and executes a task during execution of the target movement, comprising the steps of:

- During the execution of the desired movement determining (S1) one in the

Robotemanipulator (1) introduced external force winders K _ext , where K _ext a

Vector F _{ext has} at least one external force and / or vector M _{ext of} at least one external moment,

Detecting (S2) an undesired collision of the robot manipulator (1) when K _ext in or around n axes of a predefined coordinate system with N axes exceeds a predefined first limit, where ne N,

- detecting (S3) a faulty execution of the task, if K _ext exceeds a predefined second limit value in or near m axes of the coordinate system or if K _ext <K _of, where K _of a dependent of the task and exclusively in or around the m Axes expected and / or desired force winders, and where me N and min,

wherein the first threshold is less than the second threshold, and

- driving (S4) of the robot manipulator (1) in an error mode when an unwanted collision of the robot manipulator (1) and / or a faulty execution of the task is detected.

2. The method according to claim 1,

wherein, at least for detecting an erroneous execution of the task, the determined force winder K _{ext is} compensated for by the expected and / or desired force winder K _des and the compensated force winder is compared with the second limit value.

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

wherein the external force Winder K _{ext is determined} by means of a pulse observer. 4. The method according to any one of the preceding claims,

wherein the predefined coordinate system and / or the m axes and / or the n axes are time-variant and dependent on the desired movement and / or the task.

5. The method according to any one of claims 1 to 4,

wherein the first and / or the second limit value are predetermined by a user and are user-adaptable.

6. The method according to any one of claims 1 to 4,

wherein the first and / or the second limit are defined together with the task. 7. The method according to any one of claims 1 to 4,

wherein the first and / or second thresholds are determined and adjusted by machine learning.

Device (100) for controlling an actuator-driven

A robotic manipulator (1) having an end effector (3), wherein the end effector (3) is adapted to perform a predetermined target movement and to perform a task during execution of the target movement, comprising:

- A force determination unit (5) for determining a in the

Robot manipulator (1) introduced external power windlass K _ext is executed during the execution of the desired movement, wherein K _{ext has} a vector F _ext at least one external force and / or a vector M _ext at least one external moment,

a computing unit (7) designed to detect an undesired collision of the robot manipulator (1) when K _ext in or around n axes of a predefined coordinate system with N axes exceeds a predefined first limit, where ne / V, and to detect a faulty execution of the task, if K _ext exceeds a predefined second limit value in or near m axes of the coordinate system or if K _ex t <K _d it is, wherein K _of a dependent of the task and exclusively in or around the m axis occurring expected and / or desired Kraftwinder, and wherein m ^ N and min applies, wherein the first limit is less than the second threshold, and

a control unit (9) designed to control the robotic manipulator (1) in an error mode when the arithmetic unit (7) detects an undesired collision of the robotic manipulator (1) and / or an erroneous execution of the task.

The apparatus (100) of claim 8, further comprising: a user interface for specifying the first and / or the second threshold.

10. robot (200) with a device (100) according to any one of claims 8 to 9.