Method for adjusting a speed of an end effector of a robot and robot

Abstract

Method for adjusting a speed of an end effector (5) of a robot (1), comprising the steps: a) providing a trajectory (7) for the end effector (5), wherein the trajectory (7) has at least one trajectory section (9, 10) with a curvature; b) providing a maximum limit acceleration of the end effector (5) for the at least one trajectory section (9, 10); c) providing an initial value for the speed for the at least one trajectory section (9, 10); d) determining an expected acceleration of the end effector (5) for the at least one trajectory section (9, 10) depending on the curvature and the initial value; e) determining a correction factor depending on the provided initial value, wherein the correction factor describes a proportionality between the expected acceleration and an actual acceleration; and f) adjusting the speed of the end effector (5) for the at least one trajectory section (9, 10) depending on the expected acceleration and the correction factor, so that the maximum limit acceleration is not exceeded.

Description

Aspects of the invention relate to a method for adapting a speed of an end effector of a robot and to a robot.It is known to manually adjust path speeds of a robot end effector. This manual adaptation is complicated and is based on empirical values of a programmer and is therefore possibly inaccurate.DE 10 2019 204 484 A1 discloses a trajectory planning unit, a valve arrangement and a method.DE 10 2017 102 749 A1 relates to automatic trajectory generation for controlling a drive system.DE 10 2016 002 904 B4 relates to a robot system.It is an object of the invention to improve an adaptation of a path speed of a robot end effector.The object is achieved by the subject matters of the independent claims. Advantageous refinements of the invention are defined by the dependent claims, the following description and the figures.One aspect of the invention relates to a method for adjusting a speed of an end effector of a robot. The method has the following steps: a) in particular providing a trajectory for the end effector, wherein the trajectory has at least one trajectory section with a curvature; b) in particular providing a maximum limit acceleration of the end effector for the at least one trajectory section; c) in particular providing an initial value for the speed to be adjusted or set for the at least one trajectory section; d) in particular determining an expected acceleration of the end effector for the at least one trajectory section depending on the provided curvature and the provided initial value; e) in particular determining a correction factor depending on the provided initial value, wherein the correction factor describes a proportionality between the expected acceleration of the end effector for the at least one trajectory section and an actual acceleration of the end effector for the at least one trajectory section of the trajectory; and f) adapting the speed of the end effector for the at least one trajectory section depending on the expected acceleration and the correction factor, so that the maximum limit acceleration is not exceeded.The speed of the end effector can be adapted in an improved manner by the method, in particular for a predefined path or trajectory. The speed can also be referred to as the web speed. If necessary, the speed of the end effector can be maximized by the method on condition that the limit acceleration is not exceeded. As a result, a task to be accomplished by the robot is carried out as quickly as possible and without exceeding the limit acceleration. The end effector denotes in particular a last element of a kinematic chain of the robot. The end effector is, for example, a tool unit, such as, for example, a welding unit, or a gripper. In particular in the case of a gripper, it is advantageous if the limiting acceleration is not exceeded, since otherwise the gripper may possibly lose a gripped object due to centrifugal forces. This is prevented, for example, by the method.It is possible for the initial value to be predefined manually. It is also possible that the initial value is specified manually only for a first trajectory section and, when the method is carried out again, a value of the adapted speed of the preceding section is used as the initial value. In particular, the initial value serves as a starting value for an optimization function. For this purpose, step e) may be carried out a plurality of times until an expected acceleration lies within a predefined range, in particular is less than the predefined maximum acceleration. For example, a minimum limit acceleration is also specified. In particular, an acceleration range is specified, wherein the acceleration to be expected is determined and is then compared with the minimum limit acceleration. If the acceleration to be expected falls below the minimum limit acceleration, the initial value is optionally increased, for example by a predefined value. For example, the acceleration to be expected is determined again depending on the increased initial value. If necessary, the newly determined acceleration to be expected is again compared with the minimum limit acceleration. This procedure is preferably repeated until the acceleration to be expected exceeds the minimum limit acceleration. Analogously, it is possible, in particular in parallel, to carry out this procedure for the maximum limiting acceleration, wherein the initial value is reduced by the predefined value. The predefined value is, for example, between 1 mm / s and 1000 mm / s, in particular between 10 mm / s and 100 mm / s. It is also possible for the predefined value to be a percentage proportion of the initial value. This means that the initial value is optionally increased or reduced between 1% and 10%. It is also possible for the predefined value to be predefined as a function of a number of iterations. For example, the predefined value is the lower the more frequently the acceleration to be expected for the at least one trajectory section has been determined. As a result, it can be achieved more quickly that the acceleration to be expected lies within the predefined acceleration range. In particular, the corrected expected acceleration is used for the comparison. The last used initial value corresponds in particular to the speed value to be set. The described procedure achieves the effect that the speed is adapted in such a way that it is maximized and does not exceed the maximum limit acceleration in the process.The limit acceleration is, for example, manually predefined. In the case of a plurality of trajectory sections, for example, the same limiting acceleration is provided for all trajectory sections or individually for each trajectory section.Preferably, the trajectory section has a curvature not equal to 0, i.e. it does not run straight. The method is particularly advantageous for such curved trajectory sections, since there are transverse accelerations which may necessitate a reduction in the speed. The at least one trajectory section is in particular still located before the end effector at a current point in time in the current working cycle of the robot. The trajectory is provided, for example, as a linked list of points in space.For example, the curvature or a curvature value is determined by using the three segments or three points of the at least one trajectory segment. In particular, a circle is mathematically defined by three points. Its radius optionally corresponds to the radius of curvature of the at least one trajectory section. A reciprocal of the radius of curvature corresponds in particular to the curvature.For example, the corrected expected acceleration is calculated according to the following formula: a corresponds to the expected acceleration, k to the correction factor, v to the initial value of the velocity, v' to the derivative with time, T to a tangential unit vector, N to a normal unit vector, and k to the curvature.Alternatively, it is possible that the speed to be expected is determined in two steps with two correction factors k1 and k2:This procedure is advantageous in particular if, for the at least one trajectory section as the initial value for the speed, the adapted speed corresponds to a preceding execution of the method, in this case the derivative of the speed v' is equal to zero and therefore only a2 is calculated.It is possible that a unit correction factor is determined in addition to the correction factor. By means of the unit correction factor, the predicted acceleration can be converted into the same unit as the limit acceleration, for example from mm / s to m / s.In particular, the acceleration to be expected is multiplied by the correction factor, in particular in step f), and the speed is optionally adapted as a function of the corrected acceleration to be expected.The method is preferably carried out by means of a collaborative robot (HRC). Alternatively, the method can also be carried out by means of an industrial robot, which is surrounded by a grid, for example.In one exemplary embodiment, the acceleration to be expected is determined for the entire trajectory before traversing the trajectory. In particular, the acceleration to be expected is respectively determined for all sections of the trajectory, that is to say for example over an overall length of the trajectory. Before the trajectory is traversed means in particular before the trajectory is traversed during a production operation of the robot. It is possible here that the trajectory has already been traveled for training purposes, i.e. in a training operation of the robot. For example, the respective speed of the end effector is adapted for the respective trajectory section depending on the determined accelerations to be expected. By determining the accelerations to be expected for a plurality or all sections of the trajectory, the travel of the trajectory during production operation of the robot is already optimized with respect to the speed of the end effector. As a result, the robot requires less computing capacity during production operation.In one exemplary embodiment, the acceleration is determined during a traversing of the trajectory, in particular during production operation of the robot, in each case in particular only for a trajectory section situated in particular directly ahead. For example, the speed of the end effector is adjusted for the trajectory section situated directly ahead in each case. For example, the trajectory section ahead extends from one point of the linked list to the closest succeeding point. The speed is thus determined in particular in each case for a trajectory section which lies between two adjacent points of the linked list. As a result, the speed of the end effector can be adapted in a situation-appropriate and individual manner for each new travel of the trajectory in the production operation of the robot. It is thus possible to react to changes, for example in a surroundings of the robot. This is advantageous in particular for collaborative robots.To determine the correction factor, an acceleration of the end effector is determined for an already traversed trajectory section of the trajectory. The correction factor is determined as a function of the determined acceleration and the expected acceleration of the end effector for the at least one trajectory section or for the already traversed trajectory section. The already traveled trajectory section is, for example, the same trajectory section of a preceding travel or the directly preceding trajectory section which is different therefrom. In the case of a regulation of the speed of the end effector, the acceleration of the end effector is determined as a function of the already traveled-on, i.e. past, trajectory sections. In the case of a control of the speed of the end effector, the acceleration is determined as a function of an already completely traversed trajectory. The determined acceleration is, for example, a measured acceleration or a calculated acceleration. This makes it possible for the correction factor to be determined in such a way that it describes the proportionality between the acceleration to be expected and the actual acceleration. As a result, the acceleration to be expected can be corrected in an improved manner, so that the speed is adapted in an improved manner.In one exemplary embodiment, control commands for angle changes of joints of the robot for traversing the trajectory are provided. The acceleration for the already traversed trajectory section is determined as a function of the angle changes provided, in particular the acceleration is calculated as a function of the angle changes. For example, the actual acceleration can be determined without an acceleration sensor.In one exemplary embodiment, the robot has an acceleration sensor at least temporarily. Depending on acceleration data of the acceleration sensor, the acceleration is determined for the already traveled trajectory section. In particular, in the case of control, the robot has the acceleration sensor only during a teaching operation. In this case, the acceleration sensor for the production operation of the robot is removed again. In the case of a regulation, the robot has the acceleration sensor permanently. In the case of control, resources can be saved by removing the acceleration sensor. By remaining the acceleration sensor in the case of the regulation, it is possible to react to changes in the environment of the robot in an improved manner. For example, it is possible for the acceleration sensor to have two sensor units, so that the acceleration can be measured even better at two different points of the robot, in particular of the end effector. By using the acceleration sensor, computing power of the robot can be saved if necessary and the actual acceleration of the end effector can be determined precisely.Alternatively or additionally, it is possible for the speed to be adapted as a function of the acceleration data of the acceleration sensor, in particular if the acceleration is determined for the entire trajectory before the trajectory is traveled.In one exemplary embodiment, the trajectory is generated by training before the provision and subsequently provided. The training of the trajectory is effected in particular by manually traversing the trajectory or by using a sensor skin. These procedures are advantageous in particular for HRC robots.A further aspect of the invention relates to a robot having an evaluation unit. The evaluation unit is configured to obtain a trajectory for the end effector. The trajectory has at least one trajectory section with a curvature. The evaluation unit is configured to obtain a maximum limit acceleration of the end effector for the at least one trajectory section. The evaluation unit is furthermore configured to obtain an initial value for the speed for the at least one trajectory section. In addition, the evaluation unit is configured to determine an acceleration to be expected of the end effector for the at least one trajectory section depending on the provided curvature and the provided initial value. The evaluation unit is configured to determine a correction factor depending on the obtained initial value. The correction factor describes a proportionality between the expected acceleration of the end effector and an actual acceleration of the end effector for the at least one trajectory section of the trajectory. The evaluation unit is configured to generate commands in order to adapt the speed of the end effector for the at least one trajectory section depending on the acceleration to be expected and the correction factor such that the maximum limit acceleration is not exceeded.In one exemplary embodiment, the robot is configured to carry out a method according to the above-mentioned aspect of the invention or an exemplary embodiment thereof. In particular, the robot carries out the method.In one exemplary embodiment, the robot has an acceleration sensor for determining the actual acceleration. The acceleration sensor is in particular an acceleration sensor permanently integrated into the robot. In an alternative exemplary embodiment, the acceleration sensor is to be removed again. It is also possible for the robot to have an integrated acceleration sensor and an acceleration sensor to be removed.In one embodiment, the robot is a collaborative robot (HRC robot). The production operation of the robot will take place in particular with maximum possible acceleration, i.e. for example in the shortest processing time. Here, the robot has, for example, information that no human is present in a work area of the robot. Alternatively, an HRC capability of the robot for production operation may be disabled as appropriate. For example, when the robot is in an HR mode in which the HR capability is activated and the robot has the information that a human is in the work area, corresponding movement restrictions are imposed on the robot, so that a collision between the human and the robot is prevented. HRC capability means in particular that the robot shares a work area with a human.A further aspect of the invention relates to a robot having an evaluation unit, an end effector and joints. In particular, the robot has an integrated acceleration sensor and / or a removable acceleration sensor. In particular, the robot is designed to carry out a method according to the above-mentioned aspect of the invention or an exemplary embodiment thereof. In particular, the method is carried out using the robot.For situations which can arise in the method and which are not explicitly described here, provision can be made for an error message and / or a default setting and / or a predetermined initial state to be set according to the method.Features and advantages of the method according to the above-mentioned aspect of the invention and its exemplary embodiments can be transferred to the robot according to the further aspects of the invention, its exemplary embodiments, and vice versa.The invention also includes the combinations of the features of the described embodiments.An embodiment of the invention will be described below. The following shows: FIG. 1 shows an exemplary embodiment of a robot according to the invention; and FIG. 2 shows a flow diagram of an exemplary embodiment of a method according to the invention for adapting a speed of an end effector of a robot.In the figures, elements having the same function are each provided with the same reference numerals.FIG. 1 shows an exemplary embodiment of a robot 1. the robot 1 is, for example, a collaborative robot. For example, the robot 1 has an evaluation unit 2. In particular, the robot 1 has joints 3, arm elements 4 and an end effector 5. The robot 1 preferably has an acceleration sensor 6 a, 6 b. The acceleration sensor 6 ais arranged, for example, on a last joint 3. Alternatively or additionally, the acceleration sensor 6 bis arranged, for example, on the end effector 5. The end effector 5 is optionally arranged on the last joint 3.For example, the robot 1, in particular its evaluation unit 2, is designed to carry out a method for adapting a speed of the end effector 5 of the robot 1. An exemplary flow diagram of the method is shown in FIG. 2. In a step a), a trajectory 7 is provided for the end effector 5. For example, the trajectory 7 is provided as a linked list comprising points 8 in space. The trajectory 7 has, for example, at least one trajectory section 9 having a curvature. The trajectory section 9 is optionally defined or bounded by two adjacent points 8. In particular, a first trajectory section 9 is defined by three points. The curvature of the trajectory section 9 can optionally be determined by means of the three points.In a step b), in one exemplary embodiment, a maximum limit acceleration of the end effector 5 is provided for the at least one trajectory section 9, in particular provided to the evaluation unit 2. The maximum limiting acceleration is provided, for example, by a manual user input. It is also possible for a minimum limit acceleration of the end effector 5 to be additionally provided for the at least one trajectory section 9, such that an acceleration range is preferably provided. For example, the trajectory 7 has further trajectory sections 10. If necessary, the entire trajectory 7 can be represented by all trajectory sections 9, 10. In particular, a maximum and possibly minimum limiting acceleration is provided for each trajectory section 9, 10.In a step c), in one exemplary embodiment, an initial value for the speed is provided for the at least one trajectory section 9. Individual initial values are optionally provided for each of the trajectory sections 9, 10. It is possible here for the initial values to be provided all before the execution of the subsequent steps d), e) and f). Alternatively, it is possible that the initial value is provided only for a first trajectory section 9 and the respective previous value of the adapted speed is used as the initial value for all subsequent trajectory sections 10 for the respective trajectory section 9, 10 lying in front.In a step d), in one exemplary embodiment, an acceleration to be expected of the end effector 5 for the at least one trajectory section 9 is determined as a function of the provided curvature and the provided initial value.In a step e), a correction factor is determined depending on the provided initial value. The correction factor describes, in particular, a proportionality between the expected acceleration of the end effector for the at least one trajectory section 9 and an actual acceleration of the end effector 5 for the at least one trajectory section 9 of the trajectory 7. Alternatively or additionally, the actual acceleration can be determined depending on angle changes of the arm elements 4 at the joints 3. In particular, the acceleration to be expected is multiplied or divided by the correction factor in order to determine the corrected expected acceleration.If necessary, it is checked whether the corrected acceleration to be expected lies within the provided acceleration range. If the corrected acceleration to be expected is below the provided minimum limit acceleration, for example, then the initial value is optionally increased. For example, steps d) and e) are then carried out again and the corrected acceleration to be expected is determined again. If the corrected acceleration to be expected exceeds the maximum limit acceleration, for example, then the initial value is optionally reduced. In this case, too, steps d) and e) are subsequently optionally carried out again in order to determine a corrected acceleration to be expected. In particular, the increasing or the reducing of the initial value can be referred to as an adaptation of the speed.In general, in a step f), the speed of the end effector 5 for the at least one trajectory section 9 is adapted as a function of the acceleration to be expected and as a function of the correction factor, so that the maximum limit acceleration is not exceeded. In particular, the speed of the end effector 5 is determined for all further trajectory sections 10. In one exemplary embodiment, the speed for the trajectory section 9, 10 situated directly ahead is adjusted in each case only during a production operation of the robot 1. In an alternative exemplary embodiment, the speeds for all trajectory sections are determined in advance in a training operation of the robot 1.List of reference characters1 Robot 2 Evaluation unit 3 Joints 4 Arm elements 5 End effector 6 aAccelerometric sensor 6 bAccelerometric sensor 7 Trajectory 8 Points 9 Trajectory section 10 Trajectory sections

Claims

Method for adapting a speed of an end effector (5) of a robot (1), comprising the steps: a) providing a trajectory (7) for the end effector (5), wherein the trajectory (7) comprises at least one trajectory section (9, 10) having a curvature; b) providing a maximum limit acceleration of the end effector (5) for the at least one trajectory section (9, 10); c) providing an initial value for the speed for the at least one trajectory section (9, 10); d) determining an expected acceleration of the end effector (5) for the at least one trajectory section (9, 10) depending on the provided curvature and the provided initial value; e) determining a correction factor depending on the provided initial value, wherein the correction factor describes a proportionality between the expected acceleration of the end effector (5) for the at least one trajectory section (9, 10) and an actual acceleration of the end effector (5) for the at least one trajectory section (9, 10) of the trajectory (7), wherein for determining the correction factor an acceleration of the end effector (5) is determined for an already traversed trajectory section (9, 10) of the trajectory (7) and the correction factor is determined depending on the determined acceleration and the expected acceleration of the end effector (5) for the at least one trajectory section (9, 10) or for the already traversed trajectory section (9, 10); and f) adapting the speed of the end effector (5) for the at least one trajectory section (9, 10) as a function of the acceleration to be expected and of the correction factor, so that the maximum limit acceleration is not exceeded.Method according to Claim 1, wherein the acceleration to be expected is determined for the entire trajectory (7) before traversing the trajectory (7).Method according to Claim 1, wherein the acceleration to be expected is determined during a traversing of the trajectory (7) in each case for a trajectory section (9, 10) lying ahead.Method according to one of the preceding claims, wherein control commands for angle changes of joints (3) of the robot (1) are provided for traversing the trajectory (7) and the acceleration for the already traversed trajectory section (9, 10) is determined as a function of the angle changes.Method according to one of Claims 1 to 3, wherein the robot (1) has an acceleration sensor (6a, 6b), wherein the acceleration for the already traveled trajectory section (9, 10) is determined as a function of acceleration data of the acceleration sensor (6a, 6b).Method according to one of the preceding claims, wherein the trajectory (7) is generated by training and subsequently provided.Robot (1) with an evaluation unit (2), wherein the evaluation unit is configured to - obtain a trajectory (7) for the end effector (5), wherein the trajectory (7) has at least one trajectory section (9, 10) with a curvature; - obtain a maximum limit acceleration of the end effector (5) for the at least one trajectory section (9, 10); - obtain an initial value for the speed for the at least one trajectory section (9, 10); - determine an acceleration to be expected of the end effector (5) for the at least one trajectory section (9, 10) depending on the obtained curvature and the obtained initial value; determining a correction factor depending on the initial value obtained, wherein the correction factor describes a proportionality between the expected acceleration of the end effector (5) for the at least one trajectory section (9, 10) and an actual acceleration of the end effector (5) for the at least one trajectory section (9, 10) of the trajectory (7), wherein the evaluation unit is configured to determine the correction factor by determining an acceleration of the end effector (5) for an already traversed trajectory section (9, 10) of the trajectory (7) and to determine the correction factor depending on the determined acceleration and the expected acceleration of the end effector (5) for the at least one trajectory section (9, 10) or for the already traversed trajectory section (9, 10); and generating commands in order to adapt the speed of the end effector (5) for the at least one trajectory section (9, 10) depending on the acceleration to be expected and the correction factor such that the maximum limit acceleration is not exceeded.Robot (1) according to claim 7, comprising an acceleration sensor (6a, 6b) for determining the actual acceleration, wherein the acceleration sensor (6a, 6b) is an acceleration sensor (6a, 6b) permanently integrated into the robot (1).Robot (1) according to one of claims 7 or 8, wherein it is a collaborative robot (1).

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