Method and device for controlling a drive arrangement for moving a tool, in particular a robot-guided tool

Description

[0001] The present invention relates to a method and a device for controlling a drive arrangement with at least one drive for moving a tool, in particular a robot-guided tool, as well as a system with the device and a computer program product for carrying out the method.

[0002] DE 10 2011 003 539 A1 discloses a method for referencing a drive position of an electric drive of at least one pair of tongs of a production tong. A regression line of a time-following error function is determined by means of a compensation calculation, with a closed position of the tong half being determined based on a zero crossing of this line. WO 2004 / 113001 A1 discloses a method for controlling and / or regulating a welding tong movement, wherein a first drive device presses electrode holders onto a workpiece to be welded with a predetermined pressure force. A second drive device varies the spatial position of the electrode holders. EP 1166960 A2 discloses a processing machine with the function of sensitively detecting collisions or other abnormalities.An abnormality of a load is detected when it exceeds an abnormality detection level determined based on the load measured during a previous operation. GB2355547 A discloses a control of a robot arm when a collision is detected, wherein a collision is detected by determining the deviation of the actual current in each servomotor of the arm from the logical current. If this deviation exceeds a predetermined reference value, it is decided that a collision has occurred. JP2002355782 A estimates a working force on a robot flange that brings a first part on the robot flange into contact with a second part on a worktable. A force sensor under the worktable calculates a measured value when the first and second parts come into contact.EP1477284 A1 discloses a drive control with collision detection configured to detect a collision of a driven element based on an estimated speed deviation from an actual speed.

[0003] The object of the present invention is to improve the operation of a tool, in particular a robot-guided tool.

[0004] This object is achieved by a method having the features of claim 1. Claims 11-13 protect a device or a computer program product for carrying out a method described herein, or a system with a device described herein. The subclaims relate to advantageous developments.

[0005] A preferred application is the control of a pair of pliers, in particular a robot-guided pair, in particular a gripping or welding pliers. Accordingly, in a further development, a detected contact is a contact of a pliers jaw, in particular an adjustable one, in particular with a component or another pliers jaw. The present invention is explained below in particular with reference to this preferred application, but is not limited thereto. Likewise, the tool can also comprise, in particular be, a drill, milling cutter, or the like.

[0006] In one embodiment, a tool is movable or moved by a tool drive, in particular an electric, pneumatic and / or hydraulic one. In particular, a tongs drive can adjust the tongs jaw against another tongs jaw. Additionally or alternatively, a tool is movable or moved by a multi-axis, in particular six-axis, robot. Accordingly, in one embodiment, the drive arrangement comprises one or more tool drives, in particular for adjusting the tongs jaw against another tongs jaw, and / or one or more robot drives for moving the tool; it can in particular consist of the tool drive(s) and / or robot drive(s).

[0007] Based on a detection of an exceeding of a first threshold value by the characteristic variable, a contact of the tool can advantageously be detected in one embodiment, in particular without a force and / or torque sensor and / or during or, in particular immediately, after contact, in particular during a subsequent planned application of a contact force by the tool.

[0008] In one embodiment, the characteristic variable can have a position, speed, and / or acceleration lag error, in particular be such a lag error. In this context, a lag error is understood to mean, in particular, a deviation of an actual value, in particular a detected one, from a target value, in particular a predetermined one.

[0009] In a further development, the characteristic variable comprises a position following error or a deviation between an actual and a target position or position of one or more drives of the drive arrangement. In particular, the characteristic variable can be such a position following error. These (axle or joint) positions can advantageously be detected directly and / or precisely.

[0010] Additionally or alternatively, in a further development, the parameter comprises a position following error or a deviation between an actual and a target position of the tool, in particular its one-, two-, or three-dimensional position and / or orientation relative to a reference, in particular an environmental or robot-fixed reference. In particular, the parameter can be such a position following error. These (Cartesian or workspace) positions can be detected in particular by transforming positions of the drive arrangement.

[0011] Additionally or alternatively, in a further development, the characteristic variable has a speed following error or a deviation between an actual and a target speed of one or more drives of the drive arrangement; in particular, the characteristic variable can be such a speed following error. Additionally or alternatively, in a further development, the characteristic variable has a speed following error or a deviation between an actual and a target speed of the tool, in particular its one-, two-, or three-dimensional translation and / or rotation relative to a reference, in particular one that is fixed to the environment or robot; in particular, the characteristic variable can be such a speed following error. Speeds can advantageously be detected directly and / or precisely and / or advantageously change more clearly due to contact and / or are advantageously less noisy.

[0012] Additionally or alternatively, in a further development, the characteristic variable has an acceleration following error or a deviation between an actual and a target acceleration of one or more drives of the drive arrangement; in particular, the characteristic variable can be such an acceleration following error. Additionally or alternatively, in a further development, the characteristic variable has an acceleration following error or a deviation between an actual and a target acceleration of the tool, in particular its one-, two-, or three-dimensional translatory and / or rotary acceleration relative to a reference, in particular one that is fixed to the environment or robot; in particular, the characteristic variable can be such an acceleration following error. Accelerations can advantageously be detected directly and / or precisely and / or advantageously change particularly significantly due to contact.In one embodiment, the characteristic variable can comprise a power, in particular a power consumed, and / or a change thereof, in particular a current value and / or a change thereof, of one or more drives of the drive arrangement, in particular be or indicate such a power or change.

[0013] The inventive method according to claim 1 comprises, inter alia, the steps: c) detecting an exceedance of a second threshold value that is greater than the first threshold value by the characteristic variable; and d) detecting the contact of the tool on the basis of the last or most recently detected exceedance of the first threshold value if an exceedance of the second threshold value is subsequently detected by the characteristic variable.

[0014] In other words, in step d), the contact of the tool is detected on the basis of the last exceedance of the first threshold value, if an exceedance of the second, larger threshold value is subsequently detected by the parameter.

[0015] Accordingly, the device comprises means for detecting an exceeding of a second threshold value, which is greater than the first threshold value, by the characteristic variable, wherein the means for detecting a contact of the tool on the basis of the exceeding of the first threshold value are means for detecting the contact of the tool on the basis of the last exceeding of the first threshold value, if an exceeding of the second threshold value is subsequently detected by the characteristic variable.

[0016] This advantageously allows a more sensitive and a more robust criterion to be combined. This allows contact to be detected more precisely based on the more sensitive criterion or an exceedance of the first threshold. At the same time, the more robust criterion or the need to exceed the second threshold can reduce the risk of the more sensitive criterion responding incorrectly, for example, due to noise, friction and / or inertia effects, or the like.

[0017] In particular, a time or a position is thus recorded, in particular stored, at which the characteristic (last) exceeded the first threshold value. If the characteristic subsequently also exceeds the second threshold value, it can be assumed with a very high degree of probability that the immediately preceding last exceeding of the first threshold value was caused by contact with the tool. In a further development, a time or a position at or at which the characteristic exceeds the first threshold value is recorded, in particular stored, in the manner of a shift register as a current potential contact (position), and the current or last recorded, in particular stored, potential contact (position) is recorded, in particular stored, as a current contact (position) if the characteristic subsequently also exceeds the second threshold value.

[0018] In general, in one embodiment, a point in time and / or a position of the drive arrangement, in particular a position of one or more drives of the drive arrangement, and / or a position, in particular location and / or orientation, of the tool, can be detected as a contact (position) at or at which the parameter exceeds the first threshold value or an exceeding of the first threshold value has been detected.

[0019] In one embodiment, the first and / or second threshold value is determined on the basis of a, in particular a sliding, mean or maximum value of the characteristic and / or during a planned contact-free or potentially contacting movement of the tool.

[0020] Accordingly, in one embodiment, the device comprises means for determining the first and / or second threshold value on the basis of a, in particular sliding, mean or maximum value of the characteristic variable and / or during a planned contact-free or potentially contacting movement of the tool.

[0021] The threshold value can, in particular, have a predetermined offset relative to the mean or maximum value of the characteristic. In one embodiment, a moving mean or maximum value is determined by determining a mean or maximum value for a section of a characteristic, in particular a temporal or incremental, progression preceding a current state and moving in tandem with the current state.

[0022] In a further development, during a planned, contact-free movement of the tool, in particular in a reference phase, an average or maximum value of the characteristic is determined, which results, for example, from inertia, friction, noise, or the like. This value, in particular increased by a predetermined offset, can then be used as a threshold value, in particular a first threshold value, since it can be assumed that exceeding this value, in particular increased by the predetermined offset, during a planned, potentially contact-inducing movement of the tool or detection phase following the reference phase results from contact with the tool.

[0023] In a further development, the first threshold value is determined based on a, in particular, moving, average, in particular by filtering the parameter. This average fluctuates around the average, for example, due to inertia, friction, noise, or the like. This average, in particular increased by a predetermined offset, can then be used as the first threshold value, since contact with the tool leads to an exceedance of this value, in particular increased by the predetermined offset.

[0024] In a further development, the second threshold value can be determined in the same way, in particular by increasing the mean or maximum value by a larger offset in order to provide a more robust criterion that verifies the more sensitive criterion and thus reduces the risk of a contact being falsely detected by the more sensitive criterion.

[0025] In a further development, the first and / or second threshold value is determined or specified in advance as a fixed value or independently of the mean and / or maximum value.

[0026] A detected contact position can be used in particular to determine and / or specify a contact force of the tool: if the tool is moved further in the contact direction after a contact, it imposes an increasing contact force F on its contact partner, which depends on its stiffness c and a movement-related deviation xx 0 of its actual position x from its contact position x 0 (F = c·(xx 0 )).

[0027] Therefore, in one embodiment, a contact force of the tool is determined and / or specified based on a deviation of an actual position from a contact position at which contact was detected. Accordingly, in one embodiment, the device comprises means for determining and / or specifying a contact force of the tool based on a deviation of an actual position from a contact position at which contact was detected.

[0028] If the contact is detected based on the characteristic variable, the tool already exerts a certain contact force, which causes the following error or the power (change) of the drive arrangement. According to one aspect of the present invention, this contact force, which is already in effect when the contact is detected, is taken into account when determining or specifying the contact force of the tool, in particular as a constant offset. Accordingly, in one embodiment, the contact force is determined or specified based on a contact force offset in the contact position that is different from zero, or the means for determining and / or specifying a contact force of the tool is configured for this purpose.

[0029] In a further development, a contact force characteristic curve is calibrated in advance, on the basis of which the contact force of the tool is determined or specified, wherein the contact force characteristic curve has the contact force offset explained above. For calibration, in one embodiment, a contact position is detected in the manner described here, the tool is then moved to various actual positions, and in each case the deviation of the actual position from the contact position and, in particular by means of a force measuring device, an associated contact force of the tool are detected. The contact force offset can be determined in particular when detecting the contact or by extrapolating a compensation curve through pairs of deviations of the actual position from the contact position and contact forces detected in the process.

[0030] In one embodiment, the tool is moved during the process, in particular in a position- and / or speed-controlled manner, in particular at a constant target speed.

[0031] According to one aspect of the present invention, a system comprises a tool as described herein, a drive assembly as described herein for moving the tool, and a device as described herein for controlling the drive assembly. According to one aspect of the present invention, a computer program product comprises program code for carrying out a method as described herein, stored on a computer-readable medium.

[0032] A means within the meaning of the present invention can be designed in hardware and / or software, in particular a processing unit, in particular a microprocessor unit (CPU), which is preferably connected to a memory and / or bus system in terms of data or signals, and / or can have one or more programs or program modules. The CPU can be designed to process instructions implemented as a program stored in a memory system, to detect input signals from a data bus and / or to output signals to a data bus. A memory system can have one or more, in particular different, storage media, in particular optical, magnetic, solid-state and / or other non-volatile media. The program can be designed in such a way that it embodies the methods described here orcapable of executing, so that the CPU can execute the steps of such methods and thus in particular can control the drive arrangement.

[0033] Further advantages and features emerge from the subclaims and the exemplary embodiments. The following, partially schematically, shows: Fig. 1: a system according to an embodiment of the present invention; Fig. 2: a method according to an embodiment of the present invention; Fig. 3: the course of a characteristic variable in the method; and Fig. 4: a contact force characteristic curve used in the method.

[0034] Fig. 1 shows a system according to an embodiment of the present invention with a tool guided by a robot 10 in the form of a welding gun with an adjustable jaw or electrode 30 and a device 20 for controlling a Fig. 1darkly filled drive arrangement for moving the tool, which includes the drives of the robot and / or a tool or pliers drive for adjusting the movable pliers jaw.

[0035] The device 20 carries out a method according to an embodiment of the present invention or is programmed to do so, which is described below with reference to Fig. 2 to 4 will be explained in more detail. The clamp is closed at a constant target speed under position and / or speed control.

[0036] In a step S10 (cf. Fig. 2 ) a characteristic value, in the example a speed lag error Δ or a motor current I of the gun drive, is recorded, the course of which over time t is shown in Fig. 3 indicated as a solid line ①.

[0037] Additionally, in step S10, during a reference phase of a planned contact-free movement of the tool, which lasts until time t 0, a maximum value of the parameter is determined as the first threshold value. The first threshold value ② is in Fig. 3 indicated by dashed lines.

[0038] Then, in a step S20, during a planned potentially contacting movement of the tool (t > t 0 ), an exceeding of the first threshold value by the characteristic variable is detected, in the exemplary embodiment at time t 4 .

[0039] This time or the position of the gun drive at this time t 4 is recorded in a step S30 as contact (position) x 0 of the tool.

[0040] In a modification, in step S10, the first threshold value is determined based on a moving average of the characteristic value by increasing the average value by a predetermined offset. This alternative first threshold value 3 is shown in Fig. 3indicated by dash-dotted lines. It is determined particularly during the planned, potentially contacting movement of the tool (t > t 0 ).

[0041] In addition, in the modification in step S10 a second threshold value 4 is determined, which is Fig. 3 is indicated as a fixed value by dash-double-dotted lines.

[0042] In the modification, in step S20, a last exceeding of the first threshold value ③ is detected by the parameter, in the embodiment of the Fig. 3 at the times t 1 , t 2 and finally t 3 . The last exceedance of the first threshold value is recorded, in particular stored, in the manner of a shift register as the current potential contact or as the current potential contact position.

[0043] In addition, in the modification in step S20, an exceeding of the second threshold value 4 by the characteristic variable is detected, in the exemplary embodiment at time t 5 .

[0044] Then, in the modification in step S30, the time of the last exceedance of the first threshold value ③ or the position of the gun drive at this time is recorded as the contact (position) of the tool, if the exceedance of the second threshold value ④ is subsequently also recorded by the parameter.

[0045] In the exemplary embodiment, the time at which the first threshold value 3 is last exceeded, before the second threshold value 4 is subsequently also exceeded by the parameter, is time t 3 . Accordingly, in the modification, this time t 3 or the position of the gun drive at this time is recorded as the contact (position) of the tool.

[0046] By comparing the initially described embodiment with the modification, it can be seen that the more sensitive criterion, namely the exceeding of the first threshold value 3, allows the contact to be detected more precisely, in particular at an earlier time t 3 compared to the time t 4 of the initially described embodiment, while at the same time, due to the combination with the more robust criterion, namely the exceeding of the second threshold value 4, the risk of false detection of a contact, for example due to noise, is reduced.

[0047] In a step S40, a contact force F of the tool is then determined and / or specified based on a deviation of an actual position x from a contact position x 0 at which the contact was detected. In this case, as in Fig. 4As indicated, the contact force F is determined or specified on the basis of a contact force characteristic curve ⑤, which has a contact force offset F 0 different from zero in the contact position x 0.

[0048] This contact force characteristic curve and in particular the contact force offset can be calibrated by detecting a contact position as described above, then detecting several actual positions x or their deviation from the contact position x 0 , and the contact forces acting there, as in Fig. 4 indicated by filled circles, which symbolize measuring or recording points.

[0049] The device 20 forms or has means within the meaning of the present invention and is thus configured to carry out the method described here.

[0050] The scope of the invention is defined by the following claims 1-13. List of reference symbols

[0051] ①Characteristic (speed following error Δ; motor current I) ②; ③First threshold ④Second threshold ⑤Contact force characteristic curve 10Robot 20Control device 30Welding gun (tool) tTime xPosition

Claims

1. A method of controlling a drive arrangement comprising at least one drive for moving a robot-guided tool (30), wherein the tool is moved and the method comprises the steps of: a) detecting (S10) a characteristic variable (①) which has a tracking error (Δ) and / or a power (I) and / a change thereof; b) detecting (S20) an exceeding of a first threshold value (②; ③) by the characteristic variable; c) detecting (S20) an exceeding of a second threshold value (④), which is greater than the first threshold value, by the characteristic variable; and d) detecting (S30) a contact (t3; t4; x0) of the tool on the basis of the exceeding of the first threshold value; wherein a tracking error is understood to be a deviation of an actual value, in particular a detected actual value, from a target value, in particular from a specified target value, of the tool and / or of one or more drives of the drive arrangement, wherein the power is a power of one or more drives of the drive arrangement, in particular a power consumed by one or more drives of the drive arrangement, wherein, in step d), the contact of the tool is detected on the basis of the last exceeding of the first threshold value, if an exceeding of the second, larger threshold value is subsequently detected via the characteristic value, wherein a time and / or a position is detected at which the characteristic variable last exceeded the first threshold value.

2. The method according to claim 1, wherein at least one threshold value (②; ③, ④) is determined on the basis of an average value or a maximum value of the characteristic variable, in particular on the basis of a moving average value or a moving maximum value of the characteristic variable.

3. The method according to any one of the preceding claims, wherein at least one threshold value (②; ③, ④) is determined during a movement of the tool that is planned to be free of a contact or with potential contact.

4. The method according to any one of the preceding claims, wherein the characteristic variable comprises a position tracking error (Δ), a velocity tracking error (Δ) and / or an acceleration tracking error (Δ).

5. The method according to any one of the preceding claims, wherein the tracking error (Δ) comprises a deviation of an actual value of at least one drive of the drive arrangement and / or of the tool from a target value.

6. The method according to any one of the preceding claims, wherein the characteristic variable comprises a power and / or its change, in particular a current value (I) and / or its change, of at least one drive of the drive arrangement.

7. The method according to any one of the preceding claims, wherein a contact force (F) of the tool is determined and / or specified on the basis of a deviation of an actual position (x) from a contact position (x0) at which the contact has been detected.

8. The method according to the preceding claim, wherein the contact force is determined or specified on the basis of a non-zero contact force offset (F0) in the contact position (x0).

9. The method according to the preceding claim, wherein a contact force characteristic curve, on the basis of which the contact force of the tool is determined and / or specified, is calibrated, wherein the contact force characteristic curve includes the contact force offset.

10. The method according to any one of the preceding claims, wherein the tool comprises a gripper jaw, in particular an adjustable gripper jaw, in particular of a gripping device or of an electrode holder (30).

11. A device (20) for controlling a drive arrangement comprising at least one drive for moving a tool (30), in particular a robot-guided tool (30), which is set up for carrying out a method according to any one of the preceding claims.

12. A system which comprises a tool (30), in particular a robot-guided tool (30), a drive arrangement with at least one drive for moving the tool, and a device (20) according to the preceding claim.

13. A computer program product which comprises a program code which is stored on a computer-readable medium, for carrying out a method according to any one of the preceding claims 1 to 10.