Tactile sensor device, system with three tactile sensor devices and method for determining a force effect

Abstract

The invention relates to a tactile sensor device 100, 200, 300 for bringing two elements into contact with (1) a positioning unit 110, 210, 310, which is configured to position a first element E1 linearly along a probing direction, wherein the positioning unit comprises: an end effector 112, 212, 312, which is connected to the first element, and a position sensor 213, which is configured to detect at least a change in the position of the end effector, and (2) a controller 120, 220, wherein the controller is configured to regulate the position of the end effector to a predefined setpoint, to determine a difference between an actual value and the predefined setpoint of the position of the end effector,to determine a change in the difference or a quantity dependent on the difference and, based on the change in the difference or the quantity dependent on the difference, to determine a force exerted by a second element on the first element connected to the end effector.

Description

The present invention enters the field of tactile sensor devices and in particular a tactile sensor device for bringing two elements into contact, a system with three tactile sensor devices for aligning two planar elements and a method for determining a force acting on a first element by the second element. In DE 10 2023 134 092 A1, a method for controlling the position of the jaws of a gripper or gripper is described, which discloses the steps of measuring the position of at least one of the jaws, calculating a friction compensation force corresponding to the sum of the friction forces acting on at least one of the jaws, calculating a position error, calculating a desired closing pressure value and / or a desired opening pressure value as the solution of an optimization problem whose input data are representative for the position error and the friction compensation force, and controlling the opening pressure and / or the closing pressure of the pneumatic actuator of each movable jaw in order to achieve the desired closing pressure value and / or the desired opening pressure value. DE 10 2015 109 008 A1 describes a method which includes the following steps: measuring a contact force between at least one probe and at least one contact connection surface for several probe override positions and determining a relationship between the contact force and the probe override position from the measured contact forces; determining a first region in the relationship which exhibits a non-linear dependence of the contact force on the probe override position, and a second region which exhibits a linear dependence of the contact force on the probe override position; and determining a process window for a connection surface investigation process based on the determined first region and the determined second region. DE 10 2009 058 607 A1 describes a method for controlling a manipulator, in particular a robot, comprising the step of detecting a contact force between the manipulator and a workpiece based on actual drive forces and drive forces of a dynamic model of the manipulator; and at least one of the following steps: a) multi-stage measurement of a workpiece position based on detected contact forces; and / or b) joining a workpiece under compliant control, wherein a joining state of the workpiece is monitored based on a detected contact force and / or an end pose of the manipulator reached under compliant control; and / or c) rigidly controlled approach to a pose; and switching to compliant control based on a detected contact force. DE 197 53 303 A1 discloses a method for controlling coordinate measuring machines, in which a probe head with a movably attached stylus is moved, the stylus being subjected to a measuring force relative to the probe head. To counteract inertial forces that occur during acceleration of the stylus, the measuring force comprises (i) a constant nominal measuring force directed normal to the surface of the workpiece to be measured and (ii) a correction measuring force that serves to at least partially compensate for inertial forces that arise from the acceleration of the stylus. A tactile sensor device is applicable in the field of precision sensor technology and drive technology at the nanometer scale. In particular, such a tactile sensor device can be used as a probing mechanism for, among other things, automated assembly machines or coordinate measuring machines, for example, for the precise alignment of two flat elements relative to each other. The aim is to determine the force exerted on the first element by the second element. Force sensors in the relevant force range, i.e., less than 1 N, are known in the art. These are usually custom-built systems with a footprint of several millimeters. Piezo scanners with a positional resolution in the nanometer range are also known in the state of the art. One solution would be to combine two such systems (stack) to create a system for the precise detection of forces. A stacked system of scanner and force sensor would require a large installation space. Furthermore, dedicated electronics would be necessary for data acquisition. In addition, such a stacked system would add mass either to the scanner (resulting in a lower resonant frequency) or to the measurement system (resulting in lower sensitivity at higher frequencies). Simultaneously, integrating objects used for probing would necessitate two interfaces, for example, a lithography mask on the force sensor on the scanner, or a lithography mask on the scanner on the force measurement unit. One objective of the present invention is to provide a compact scanning system that can detect very precise forces acting on the scanning system without having to resort to additional components for the motion system itself. According to the invention, a tactile sensor device for bringing two elements into contact is proposed according to a first aspect, as defined in claim 1, namely a tactile sensor device with (1) a positioning unit configured to position a first element linearly along a probing direction, wherein the positioning unit comprises: an end effector connectable to the first element, and a position sensor configured to detect at least a change in the position of the end effector, and (2) a controller, wherein the controller is configured to regulate the position of the end effector to a predefined setpoint, and to determine a difference between an actual value and the predefined setpoint of the position of the end effector.to determine a change in the difference or a quantity dependent on the difference and, based on the change in the difference or the quantity dependent on the difference, to determine a force exerted by a second element on the first element connected to the end effector. According to a second aspect of the invention, a method is proposed as defined in claim 13, namely a method for determining a force acting on a first element by a second element, preferably using the tactile sensor device according to one of the preceding claims, comprising the steps of: (i) connecting an end effector of a positioning unit to a first element for positioning the first element, (ii) detecting a change in the position of the end effector, (iii) controlling the position of the end effector to a predefined setpoint, (iv) repeatedly determining a difference between an actual value and the predefined setpoint of the position of the end effector, (v) repeatedly determining a change in the difference or a quantity dependent on the difference, and (vi) based on the change in the difference or the quantity dependent on the difference,Determining the force exerted by a second element on the first element connected to the end effector. According to a further aspect of the invention, a computer program is proposed with programming means that cause a tactile sensor device according to claim 1 to perform the steps of the method according to claim 13 when the computer program is executed on the tactile sensor device. The computer program can be provided, stored, and / or distributed on a suitable storage medium, such as an optical storage medium or a non-volatile electronic storage medium. It can also be provided together with or as part of a hardware component. The computer program can also be provided in other ways, such as via the Internet or via wired or wireless telecommunications. The tactile sensor device according to the invention provides a compact positioning unit that can very precisely detect forces acting on the positioning unit or the element to be positioned, without requiring any additional components beyond the positioning unit itself. This means that force measurement is integrated directly into the positioning unit, thus avoiding any increase in installation space. Furthermore, no additional hardware is required compared to a pure scanning system – the additional function can be implemented entirely in software. The elimination of additional components simplifies the overall system design. The tactile sensor device is designed and configured to bring two elements into contact. The tactile sensor device is a positioning unit designed to determine a force in addition to positioning. That is, the tactile sensor device includes the positioning unit and a control unit designed to determine a force application in addition to positioning. The positioning unit is designed to position a first element linearly along a probing direction. That is, the positioning unit can move the element in a dimension corresponding to a probing direction. The probing direction is the direction in which the first element moves towards the second element. The terms "first" and "second" serve only to distinguish the elements and are not to be understood as restrictive. The position of the element can be detected directly or indirectly, i.e., via another object positioned relative to the element. The position of the element can also correspond to the position of a segment of the element. The positioning unit includes an end effector and a position sensor. The end effector is connected to the first element, in particular detachably. Furthermore, the end effector is movable, preferably linearly movable, and in particular configured with respect to the second element. The end effector (by its very nature) has a predefined non-zero spring constant, i.e., it is configured to absorb a force that does not exceed a value dependent on the predefined spring constant. In other words, the end effector includes an external spring constant, i.e., the end effector is configured to absorb a force that does not exceed a value dependent on the predefined spring constant. The position sensor is designed to detect at least a change in the position of the end effector. Preferably, the position sensor is designed to detect the absolute position of the end effector. As previously stated, the tactile sensor device has a control unit designed to determine the force applied. This control unit can also be understood as the control unit for the positioning unit, i.e., it corresponds to the control of a positioning unit with the additional steps required to determine the force applied. The control system is designed to regulate the position of the end effector to a predefined setpoint. This means that if the actual position of the end effector does not correspond to the predefined setpoint (or a range around the setpoint), the position of the end effector is adjusted until the actual position again matches the setpoint (or is within the range around the setpoint). Furthermore, the control system is designed to determine the difference between an actual value and the predefined target value of the end effector's position. Preferably, the control system is designed to monitor this difference, i.e., to determine it repeatedly. It is also preferably designed to determine any change in the difference, i.e., to determine the change in the difference over time. By repeatedly determining the difference, a change in the difference over time can be determined accordingly. Additionally or alternatively, the control system is designed to determine any change in a variable that depends on the difference. The control system is further designed to determine whether a force is exerted on the first element, connected to the end effector, by a second element based on a change in the difference or a quantity dependent on the difference. This determination can be based on the change in the difference and / or on a change in a quantity dependent on the difference. Preferably, the control system compares the change with a predefined setpoint for the change and determines that a force is exerted on the element if the change exceeds the predefined setpoint, i.e., a specific value of the change. Thus, a force determination also occurs if it is determined that a force is acting, without specifying its magnitude. The change in the difference can also be understood as the first derivative of the difference (or a quantity dependent on the difference). In an advantageous embodiment of one aspect of the invention, the control is configured to determine the change in a derivative, in particular a second derivative, of the quantity. It is further preferred that a force acting on the first element is determined when a value of the (second) derivative exceeds a threshold. In particular, a jump in the difference in the second derivative can be identified as a delta function, which makes it particularly easy to detect a force acting on it. In a further advantageous embodiment of an aspect of the invention, the positioning unit includes an actuator for positioning the end effector. The control unit is then preferably configured to actuate the actuator. More preferably, the control unit is configured to calculate a setpoint for the actuator based on the difference and output it to the actuator. Furthermore, the control unit is more preferably configured to determine a change in the setpoint and, based on this change, to determine a force acting on the first element. Preferably, the actuator is a piezoelectric actuator. More preferably, an amplifier, for example a lock-in amplifier, is used to amplify the setpoint before outputting it to the actuator. In an advantageous embodiment of the above configuration, the controller incorporates a PID controller. In this case, the controller is preferably configured to determine the setpoint of the actuator, for example, the piezo actuator, using the PID controller. This is a particularly simple configuration for the controller. In a further advantageous embodiment of one aspect of the invention, the contact between the first element and the second element is represented by a point contact. In other words, a point contact is provided between the first element and the second element, through which the first element and the second element can touch each other. Preferably, contact between the first element and the second element is only possible via the point contact. A point contact can be realized, for example, by means of a hemisphere or a needle / point. In a further advantageous embodiment of one aspect of the invention, the control is configured to periodically modulate the position of the end effector. In other words, the position of the end effector relative to the second element can be changed periodically; that is, the control is configured to periodically change the position of the end effector relative to the second element. In this case, for example, the aforementioned lock-in amplifier is preferred. In a further advantageous embodiment of one aspect of the invention, the tactile sensor device comprises at least one linear positioner, wherein the linear positioner is configured to position the positioning unit and / or the second element. The control system is then preferably further configured to regulate the position of the linear positioner to a predefined setpoint. Preferably, a control loop for the position of the end effector is closed. Additionally or alternatively, a control loop for the position of the linear positioner can also be closed. The linear positioner is designed to position the positioning unit and / or the second element linearly. Specifically, the positioning unit and / or the second element is positioned on the linear positioner and can be moved by a movement of the linear positioner. For example, the linear positioner is a stick-slip linear positioner, meaning it is designed for a thrust phase and a reset phase. The control system is preferably designed to regulate the position of the linear positioner, or in the case of two linear positioners, the position of one or both linear positioners, to a predefined setpoint. In a case where the contact between the first element and the second element is represented by a point contact, the control is particularly preferably designed to position the first element and the second element orthogonally to each other in relation to the probing direction and to create a height profile of a plane of the second element from this. According to another aspect of the invention, an incremental measuring device is proposed, comprising a tactile sensor device according to one of the embodiments described above or below and a measuring unit, wherein the tactile sensor device is provided and configured for referencing the incremental measuring device. The measuring unit comprises the first element or corresponds to the first element. Furthermore, the control system is configured to determine a distance between the first element and the second element, i.e., between the measuring unit and the second element. In a preferred embodiment of this aspect of the invention, the measuring device is an optical measuring unit. For example, in this case, the measuring unit comprises an interferometer or an optical encoder. That is, the control is configured to determine the distance between the interferometer or the optical encoder and the second element. In the case of an interferometer, the incremental measuring device comprises a mirror movable relative to the end effector. The mirror is preferably positioned at the end effector so that it is movable by the moving end effector. The interferometer is then configured to measure at least one change in the position of the mirror and thus a change in the position of the end effector. Furthermore, the control system is preferably configured to regulate the position of the mirror, and thus of the end effector, based on the measurement by the interferometer. An interferometer enables particularly precise control of the mirror and / or the end effector. According to a further aspect of the invention, a system with three tactile sensor devices, each according to one of the embodiments described above or below, is proposed for aligning two planar elements. This allows two planar elements to be aligned relative to each other. Preferably, three point contacts are provided, wherein the point contacts are located close to the end effector of the associated tactile sensor device. "Close" here means that the point contacts are each located within a radius of 20% of the distance to the nearest point contact of the associated end effector. Features of advantageous embodiments of the invention are defined in particular in the dependent claims, with further advantageous features, embodiments and configurations also being apparent to the person skilled in the art from the above explanation and the following discussion. The present invention will now be further illustrated and explained with reference to exemplary embodiments shown in the figures. Fig. 1 shows a schematic representation illustrating a first embodiment of the tactile sensor device, Fig. 2 a schematic representation illustrating a second embodiment of the tactile sensor device, Fig. 3 a schematic representation illustrating a setup for measuring the force sensitivity of the tactile sensor device, Fig. 4 a schematic representation illustrating measurement results using the setup from Fig. 3, Fig. 5 a schematic representation illustrating a third embodiment of the tactile sensor device, and Fig. 6 a schematic flowchart of an embodiment of the force determination method according to the invention. In the accompanying drawings and the explanations relating to these drawings, corresponding or related elements are marked with corresponding or similar reference symbols, where appropriate, even if they are found in different embodiments. Fig. 1 shows a schematic representation to illustrate a first embodiment of the tactile sensor device. The tactile sensor device 100 is designed and configured to bring two elements E1 and E2 into contact. The tactile sensor device 100 comprises a positioning unit 110 and a control unit 120. The positioning unit 110 is designed to position the first element E1 linearly. The positioning unit 110 has an end effector 112 and a position sensor. The end effector 112 is connected to the first element E1, in particular by a detachable connection. Specifically, the first element E1 is positioned on the end effector. The end effector 112 is movable relative to the second element E2. Furthermore, the end effector 112 (naturally) has a predefined spring constant ksy, which is not equal to zero. The position sensor is designed to detect at least a change in the position of the end effector 112. The control unit 120 is designed to regulate the position of the end effector 112 to a predefined setpoint psoll. Furthermore, the control unit 120 is designed to determine the difference between an actual value pist and the predefined setpoint psoll of the position of the end effector 112, to determine any change in this difference or in a quantity dependent on the difference, and, based on this change, to determine the force exerted by the second element E2 on the first element E1 connected to the end effector 112. In particular, the control 120 is designed to determine a second derivative as a change, whereby a force is applied to the first element E1 when a value of the second derivative exceeds a threshold. If the end effector 112 actively moves against an external contact force, i.e., if the first element E1 and the second element E2 touch, the slope of a value y, which corresponds to the change in the difference or a quantity dependent on the difference, changes abruptly at time t0, resulting in a step function in the first derivative (dy / dt) and a delta function in the second derivative (d2y / dt2). A plot of the y-value against time t (x-axis) is shown below in Fig. 1. A total of six graphs are shown, with the left-hand graphs showing the y-value for an actively moving end effector 112 and the right-hand graphs showing the y-value for a stationary end effector 112. If the end effector 112 actively moves against an external contact force, which the end effector 112 experiences due to the spring constant ksys, the slope of the y-value changes abruptly at time t0, resulting in a step function in the first derivative (dy / dt) and a delta function in the second derivative (d²y / dt²). The contact can thus be detected via a threshold value SW in the second derivative. Fig. 2 shows a schematic representation to illustrate a second embodiment of the tactile sensor device. The tactile sensor device 200 comprises a positioning unit 210 and a control unit 220. The positioning unit 210 is designed to position an element linearly. The positioning unit 210 has an end effector 212 and a position sensor 213. The end effector 212 is designed to position the element linearly. For this purpose, the end effector 212 is designed to be movable. Furthermore, the end effector 212 (naturally) has a predefined spring constant ksy, which is not equal to zero. The position sensor 213 is designed to detect at least a change in the position of the end effector 212. In the illustrated embodiment, the end effector 212 comprises an actuator 214, preferably a piezoelectric actuator, for positioning the end effector 212 and thus the element. The actuator can be connected to the end effector 212 via a compliant guide structure ks or a lever arm. The control unit 220 is designed to regulate the position of the end effector 212 to a predefined setpoint psoll. For this purpose, a position feedback system 221 is used. Furthermore, the control unit 220 is designed to determine the difference between an actual value pist and the predefined setpoint psoll of the position of the end effector 212, to determine a change in the difference or in a quantity dependent on the difference, and to determine a force applied to the element based on the change. In particular, the control 220 is designed to determine a second derivative as a change, whereby a force is applied to the element when a value of the second derivative exceeds a threshold. In the present embodiment, the end effector 212 is driven by an actuator 214. The controller 220 is configured to calculate a setpoint for the actuator 214 based on the difference and output it to the actuator 214. In other words, the controller 220 is configured to determine a change in a quantity dependent on the difference, i.e., the setpoint of the actuator 214, and further, based on the change in the setpoint, to determine a force acting on the element. Preferably, the controller 220 is configured to periodically control the position of the end effector 212. A lock-in amplifier is then preferably provided to amplify an output signal. Furthermore, the controller 220 is preferably configured to control the position of the end effector 212 to a predefined setpoint. A closed control loop for the position of the end effector 212 is preferably used. The controller 220 has a PID controller 222 and is configured to determine the setpoint of the actuator 214 using the PID controller 222. The setpoint for the actuator 214 is then output by the controller 220 as a DAC value 223 (digital-to-analog converter). Specifically, the DAC value 223 is passed to the actuator 214 via an amplifier, for example, a lock-in amplifier when the input signal is modulated. A plot of the DAC value (y-axis) against time t (x-axis) is shown below in Fig. 2. A total of six graphs are shown, with the left-hand graphs showing the DAC value for an actively moving end effector 212 and the right-hand graphs showing the DAC value for a stationary end effector 212. If the end effector 212 actively moves against an external contact force 218, which the end effector 212 experiences due to the spring constant ksyser, the slope of the DAC value (y) changes abruptly at time t0, resulting in a step function in the first derivative (dy / dt) and a delta function in the second derivative (d2y / dt2). The contact can thus be detected via a threshold value SW in the second derivative of the DAC value. Fig. 3 shows a schematic representation illustrating a setup 500 for measuring the force sensitivity of the tactile sensor device. The sensor device can correspond to the second embodiment. Figure 3 shows an interferometer 115 and a mirror 116, wherein the mirror 116 is positioned at the end effector 212 and is movable via the end effector 212 to a linear positioner 111, on which an element, for example the second element E2, can be positioned. The interferometer 115 is configured to measure at least a change in the position of the mirror 116 and thus a change in the position of the end effector 212. In this case, the controller 220 is configured to regulate the position of the mirror 116 and thus the position of the end effector 112 based on the measurement by the interferometer 115. Furthermore, a point contact 117 is provided between the end effector 212 and the linear positioner 111, via which the end effector 212 can contact the linear positioner 111. The linear positioner 111 is designed as a stick-slip linear positioner in the embodiment shown. Fig. 4 shows a schematic representation to illustrate measurement results using the setup from Fig. 3. As previously explained, the end effector 212 regulates its target position. At the start of a measurement, contact is established via the point contact 117 between the end effector 212 and the linear positioner 111, which also regulates its own position. The end effector 212 is then retracted, thus breaking the point contact 117. The end effector 212 then moves forward, in this example at a speed of 100 µm / s, until contact with the linear positioner 111 is detected in the second derivative of the DAC value 123, and the movement of the end effector 212 is stopped. By comparing several repetitions 340 with a constant contact object position, the repeatability of the contact detection can be measured (shown above in Fig. 4, where the contact object has been removed for reference in graph 310).The plateaus 320, 330 at the beginning and end of the movement originate from a constant approach acceleration and are suppressed via a dead time so that the touch detection is not triggered falsely. Due to the high precision of the drive and the sensor technology, a distribution width of approximately 20 nm is measured (below in Fig. 4, shown as a histogram of the different final positions after stop detection measured via the interferometer 115). Fig. 5 shows a schematic representation to illustrate a third embodiment of the tactile sensor device for a further application. The tactile sensor device 300 in turn comprises a positioning unit 310 and a control unit 320, which will not be further explained in connection with Fig. 5 and can essentially correspond to one of the control units 120, 220. The positioning unit 310 comprises a linear positioner 311 and an end effector 312. A laser interferometer (head) 315 is arranged on the end effector, which emits a laser beam L in the direction of an element E, which can be understood as the second element E2. The end effector 312 has a point contact 317 to make contact with the element E. The sensor device 300 shown can, for example, be used for the absolute position determination of an element E, so that an absolute reference for the interferometer 315 can be determined, for example, for an incremental measurement. For this purpose, the end effector 312 is moved via the linear positioner 311 to a travel distance of the end effector 312 to the element E. By determining a force application, as described above, the exact position of the element E can then be determined. Fig. 6 shows a schematic flowchart of an embodiment of the method according to the invention for determining force. Method 400 is used to determine a force acting on a first element by a second element, preferably using the tactile sensor device according to one of the above embodiments. Method 400 comprises at least the following steps, whereby the steps do not necessarily have to be carried out in the described order or only once each: In a step 410, a first element is connected to an end effector of a positioning unit for positioning the first element, in particular detachably connected. In a second step 420, a change in the position of the end effector is detected. In a further step 430, the position of the end effector is regulated to a predefined setpoint. In a fourth step 440, a difference between an actual value and the predefined target value of the end effector position is repeatedly determined, and further in a fifth step 450, a change in the difference or a quantity dependent on the difference is repeatedly determined. In a sixth step 460, a force effect by a second element on the first element connected to the end effector is then determined based on the change in the difference or the quantity dependent on the difference. Even though the figures show various aspects or features of the invention in combination, it is apparent to the person skilled in the art – unless otherwise stated – that the combinations shown and discussed are not the only possible ones. In particular, corresponding units or sets of features from different embodiments can be interchanged. In implementations of the invention, individual components, e.g., a processor, can wholly or partially assume the functions of various elements mentioned in the claims. Processes or procedures can be implemented as program elements of a computer program and / or as special hardware components. The following are further considerations regarding the invention: The invention relates to a high-resolution tactile measuring method for nanopositioning systems without separate force sensors. This is particularly important for the precise alignment of two planes relative to each other. One way to achieve this is high-resolution probing using a force sensor. The fundamental idea behind the invention arose from the inventors' attempt to integrate a very compact and high-resolution force measurement system into an existing scanning motion system, or scan system for short. A high-resolution force measurement system can be implemented using a (defined) spring constant combined with high-resolution position measurement. Both required components are already integrated into a scanning motion system, which can be implemented as a piezoelectric scanner. Therefore, the most compact force measurement system that can be integrated into a scan system is to use the scan system itself for force measurement without limiting the fundamental functionality of the scan system. The invention is intended for use in the field of precision sensor technology and drive technology (nanometer scale). Furthermore, the invention can be used as a probing mechanism for, among other things, automated assembly machines or coordinate measuring machines. The purpose of the invention is to enable the highly precise detection of forces acting on a scanning system without requiring additional components other than the motion system itself. This allows the scanning system to remain very compact. The core concept is to use the scan system itself as a force sensor in combination with an external spring constant, thereby detecting deviations, for example, of an actuator's internal setpoint (DAC) from a movement, without any external force being applied. The scan system is either held in a constant position or moved linearly – in both cases, the control loop is preferably closed, and the actuator's setpoint is considered. If an external force acts on the scan system, its end effector moves – however, the closed control loop ensures that the (controlled) target position is maintained by adjusting the setpoint. Since the detected force is very small, it can be applied by the scan system itself and is absorbed by the external spring constant.By calibrated detection of changes in the setpoint, the acting force can be detected by the scanning system itself without interrupting the position-controlled operation. Due to the intrinsic presence of a scanning system, the system can execute a movement triggered by force detection. For example, the system can rebound to protect a sensitive sample. Furthermore, the system can follow a linear trajectory to which a periodic motion has been superimposed. This allows for periodic probing and the use of signal amplification techniques such as lock-in amplification to increase force detection accuracy. By directly integrating force detection into the scanning system, the installation space is not increased, and no additional hardware is required compared to a pure scanning system – the additional function can be implemented entirely in software. The elimination of additional components simplifies the overall system design. Furthermore, the moving mass for measurement and movement is reduced to a minimum, allowing the resonant frequency of the motion system with a payload to be very high (due to the sensor's high stiffness), and the measurement system remains highly sensitive even at high frequencies. Integrating different payloads is also very easy by selecting a suitable adapter, as the direct integration of the sensor into the motion system itself eliminates the need for an interface. In a specific embodiment, a piezoelectric scanner positioner is held in position, and the application of an external force is detected. The deviation of the measured actual position from the target position is adjusted using position feedback (FB). The control signal for the piezoelectric actuator is output by the controller as a DAC (digital-to-analog converter) value via PID control and fed to the piezoelectric actuator via an amplifier. If the scanner actively moves against an external contact force, which is coupled to the scanner's end effector via the spring constant, the slope of the DAC value changes abruptly over time, resulting in a step function in the first derivative and a delta function in the second derivative. The contact can thus be detected via a threshold value in the second derivative. In an exemplary measurement, the position of the scanner end effector is measured using a picoscale interferometer, i.e., an interferometer with picometer precision. The scanner itself regulates its target position based on an internally integrated nanosensor. At the start of the measurement, a point contact is established between the scanner end effector and a stick-slip linear positioner, which also regulates its position internally with nanometer precision. The scanner end effector is then retracted, thus breaking the point contact. Subsequently, the scanner end effector moves forward at a speed of, for example, 100 µm / s until contact with the stick-slip linear positioner is detected in the second derivative of the DAC value, and the movement of the scanner end effector is stopped. By comparing several repetitions with a constant contact object position, the repeatability of the contact detection can be measured.Due to the high precision of the drive and the sensors, a distribution width of approximately 20 nm is measured. The invention relates to a tactile sensor device for bringing two elements into contact with (1) a positioning unit configured to position a first element linearly along a probing direction, wherein the positioning unit comprises: an end effector connected to the first element, and a position sensor configured to detect at least a change in the position of the end effector, and (2) a controller configured to regulate the position of the end effector to a predefined setpoint, to determine a difference between an actual value and the predefined setpoint of the position of the end effector, to determine a change in the difference or a quantity dependent on the difference, and, based on the change in the difference or the quantity dependent on the difference, to determine a force exerted by a second element on the first element connected to the end effector.

Claims

Tactile sensor device (100, 200, 300) for bringing two elements (E1 and E2) into contact with a positioning unit (110, 210, 310) configured to position a first element (E1) linearly along a probing direction, the positioning unit (110, 210, 310) comprising: an end effector (112, 212) connectable to the first element (E1), and a position sensor (213) configured to detect at least one change in the position of the end effector (112, 212), and a controller (120, 220) configured to regulate the position of the end effector (112, 212) to a predefined setpoint (psoll), and to detect a difference between an actual value (pist) and the to determine the predefined target value (psoll) of the position of the end effector (112, 212),to determine a change in the difference or a quantity dependent on the difference (y) and, based on the change in the difference or the quantity dependent on the difference (y), to determine a force acting by a second element (E2) on the first element (E1) connected to the end effector. Tactile sensor device (100, 200, 300) according to claim 1, wherein the control (120, 220) is configured to determine the change of a derivative, in particular a second derivative, of the quantity (y), wherein a force is applied to the first element (E1) when a value of the second derivative exceeds a threshold value. Tactile sensor device (100, 200, 300) according to one of claims 1 and 2, wherein the positioning unit (110, 210, 310) has an actuator (214), preferably a piezo actuator, to position the end effector (112, 212), wherein the control (120, 220) is configured to control the actuator, preferably to calculate a setpoint for the actuator (214) based on the difference and output it to the actuator (214), to determine a change in the setpoint and to determine a force acting on the first element (E1) based on the change in the setpoint. Tactile sensor device (100, 200, 300) according to claim 3, wherein the controller (120, 220) has a PID controller (222) and is configured to determine the setpoint of the actuator (214) with the PID controller (222). Tactile sensor device (100, 200, 300) according to one of the preceding claims, wherein the contact between the first element (E1) and the second element (E2) is represented by a point contact (117). Tactile sensor device (100, 200, 300) according to one of the preceding claims, wherein the control (120, 220) is configured to periodically modulate the position of the end effector (112, 212). Tactile sensor device (100, 200, 300) according to one of the preceding claims, further comprising: at least one linear positioner (111), wherein the at least one linear positioner (111) is configured for positioning the positioning unit (110, 210, 310) and / or the second element (E2), wherein preferably the control (120, 220) is configured to regulate the position of the linear positioner (111) to a predefined setpoint. Tactile sensor device (100, 200, 300) according to one of the preceding claims, wherein a control loop for the position of the end effector (112, 212, 312) is closed. Tactile sensor device (100, 200, 300) according to claim 5, wherein the control (120, 220) is further designed to position the first element (E1) and the second element (E2) orthogonally to each other in relation to the probing direction and to create a height profile of a plane of the second element (E2) therefrom. Incremental measuring device with the tactile sensor device (300) according to one of claims 1 to 8 and a measuring unit for referencing the incremental measuring device, wherein the measuring unit comprises the first element, wherein the control is further configured to determine a distance between the first element (E1) and the second element (E2). Incremental measuring device according to claim 10, wherein the measuring unit is an optical measuring unit and comprises, for example, an interferometer (315) or an optical encoder. System with three tactile sensor devices (100, 200, 300) each according to one of the preceding claims for aligning two planar elements, preferably by means of three point contacts, wherein the point contacts are located locally in the vicinity of the end effector of the associated tactile sensor device (100, 200, 300). Method (400) for determining a force acting on a first element (E1) by the second element (E2), preferably using the tactile sensor device (100, 200, 300) according to one of the preceding claims, comprising the steps: connecting (410) an end effector of a positioning unit to a first element (E1) for positioning the first element (E1), detecting (420) a change in the position of the end effector, controlling (430) a position of the end effector to a predefined setpoint, repeatedly determining (440) a difference of an actual value to the predefined setpoint of the position of the end effector, repeatedly determining (450) a change in the difference or a quantity dependent on the difference (y), and based on the change in the difference or the quantity dependent on the difference (y) determining (460) a force acting by a second element (E2) on the first element (E1) connected to the end effector. Computer program with programming means that cause a tactile sensor device (100, 200, 300) according to claim 1 to perform the steps of the inventive method (400) according to claim 13 when the computer program is executed on the tactile sensor device (100, 200, 300).

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