Finger unit with two-dimensional measuring device and a sensor designed as a rocker, robot hand and method for determining gripping force

Abstract

The invention relates to a finger unit (1), in particular a fingertip, for a robot hand comprising an elastic skin (2) and a substantially rigid surface (3) arranged below the elastic skin (2), wherein a two-dimensional measuring device is arranged on the rigid surface (3) and a transmission element (4) is arranged between the elastic skin (2) and the rigid surface (3), wherein the transmission element (4) is connected to the elastic skin (2) and the two-dimensional measuring device in such a way that a deformation of the elastic skin (2) leads to a movement of the transmission element (4) and the two-dimensional measuring device can measure the movement of the transmission element (4).

Description

[0001] The invention relates to a finger unit for a robot hand and a robot hand comprising at least two finger units. Furthermore, the invention relates to a method for determining a gripping force or frictional force on a finger unit of a robot hand.

[0002] Robotic arms are finding increasing application in industry and other fields. To enable more precise functions and expand the range of applications for these robotic arms, they often feature a robotic hand modeled after a human hand. Such robotic hands can, for example, perform assembly work in the automotive industry or assist in research and development in science. These robotic hands have multiple finger units to perform tasks similar to a human hand. The applications for robotic hands are vast, and the demands placed on them are extremely high, especially when handling delicate components and / or performing precise work steps. For example, handling fragile or slippery objects requires a robotic hand to precisely control the gripping force. This precise control of gripping force necessitates appropriate sensors.

[0003] For example, the gripping force of a finger unit can be inferred from the current draw of its actuator. However, current draw provides no indication of whether the gripping force is sufficient to hold the object. Furthermore, such a method would only be feasible if each finger unit had its own separate motor control. This, in turn, would increase the electronic complexity and wiring effort. Moreover, the high electronic complexity would translate into high costs. Alternatively, the gripping force can be determined via optical measurements using one or more cameras positioned on or in the hand. However, optical measurements require enormous computational resources, and neural networks might be necessary to draw unambiguous conclusions about the gripping force and / or whether it is sufficient.Therefore, optical measurement involves not only enormous computational effort but also considerable expense. Another option for measuring gripping force is the use of tactile sensors with pressure-sensitive sensor arrays in the finger units. The disadvantages of this type of measurement are the complex electronics and high costs. Numerous sensors are required to achieve sufficiently high accuracy, and even then, the spatial resolution may be low.

[0004] DE 20 16 295 A describes a tactile feedback device for motor-driven hand and arm prostheses, which signals to the user the grip forces occurring on the fingers and the position of the fingers and their limbs relative to each other on a part of the skin surface in the form of a two-dimensional pressure pattern.

[0005] DE 10 2016 206 980 A1 describes a device and a method for handling a body, in which the body is picked up at a first position by means of a receiving device and transported to a second position. In order to optimize the manner of singulating and gripping a body by means of the receiving device, it is provided that a representation of the body is first captured by means of a non-contact object recognition system.

[0006] DE 10 2010 005 673 A1 describes a gripper for a handling device with at least one elastically deformable gripper element, which can be deformed by a force to handle an object to be handled. A sensor for measuring deformation of the gripper element is integrated into the gripper.

[0007] DE 10 2023 117 351 B3 describes a method for operating a gripping device comprising a gripping arrangement with holding elements which have a partially elastically deformable structure, for holding a product to be handled, comprising measuring a stress state of at least one of the holding elements by means of stress measuring devices; and determining an instantaneous operating state of the gripping device based on the stress state of the holding element; and controlling the gripping device based on the determined operating state.

[0008] The JP H06-182688A describes a tactile sensor device for detecting deformation of a beam section using a strain sensor.

[0009] US Patent 5,844,146 A describes a force sensor for measuring shear forces. A light source is located in a recess of a deformable component. A position detection detector is positioned next to it. When the deformable component deforms, the point of impact of the light on the position detection detector moves. Disclosure of the invention

[0010] As explained above, measuring the gripping force of a robot hand's finger units is a complex task. Known devices and methods for this measurement are electronically complex, expensive, and unsuitable for determining whether the gripping force is sufficient to hold the object. Therefore, the challenge is to provide a simpler and more cost-effective finger unit that enables gripping force measurement.

[0011] The problem is solved by a finger unit, in particular a fingertip, for a robot hand comprising an elastic skin and a substantially rigid surface arranged below the elastic skin, wherein a two-dimensional measuring device is arranged on the rigid surface and a transmission element is arranged between the elastic skin and the rigid surface, wherein the transmission element is connected to the elastic skin and the two-dimensional measuring device in such a way that a deformation of the elastic skin leads to a movement, in particular tilting, of the transmission element and the two-dimensional measuring device can measure the movement of the transmission element.

[0012] The finger unit according to the invention comprises an elastic skin and a substantially rigid surface arranged beneath the elastic skin. A two-dimensional measuring device is arranged on the rigid surface, wherein the two-dimensional measuring device is capable of measuring, in particular, deformations or movements of the elastic skin in two dimensions. Furthermore, the finger unit comprises a transmission element, wherein the transmission element is arranged between the elastic skin and the rigid surface such that a deformation of the elastic skin leads to a movement of the transmission element, in particular relative to the rigid surface and / or the two-dimensional measuring device, and the two-dimensional measuring device is capable of measuring the movement of the transmission element. The transmission element can tilt and / or be displaced as a result of the deformation of the elastic skin, in particular in a direction parallel to the rigid surface.The elastic skin can move, and this movement is transmitted via the transmission element to the two-dimensional measuring device. For this purpose, the transmission element is connected to both the elastic skin and the two-dimensional measuring device. This setup enables a simple and, in particular, cost-effective measurement of gripping forces and / or frictional forces on the finger unit. Advantageously, the two-dimensional measuring device can first measure the deformation of the elastic skin and then determine a frictional force and / or gripping force based on this deformation. Furthermore, an advantage of the invention is that the two-dimensional measuring device can provide direct feedback on whether the frictional forces of the finger unit are sufficiently high to hold the object. For example, the slippage of an object across the deformation of the elastic skin of the finger unit can be detected.

[0013] In an advantageous embodiment of the invention, the two-dimensional measuring device is arranged between the elastic skin and the rigid surface, with the transmission element preferably arranged such that movement, in particular tilting, of the transmission element is only possible relative to the rigid surface and / or the two-dimensional measuring device. Preferably, the two-dimensional measuring device has a fixed point, particularly a substantially central one, about which the transmission element can be tilted. Thus, a particularly simple measuring device can be used, since no relative displacement between the transmission element and the two-dimensional measuring device is possible.

[0014] According to the invention, the two-dimensional measuring device comprises two sensors, in particular two potentiometers. A significant advantage of this design is that even a displacement of the elastic skin can be measured using just two simple sensors. The sensors are preferably arranged such that the two-dimensional measuring device can measure the two dimensions in which the elastic skin can move. Preferably, the two-dimensional measuring device can measure a movement or force of the elastic skin essentially parallel to the rigid surface. Advantageously, the sensors are designed as potentiometers, which is a particularly cost-effective and simple device.Preferably, the resistance value of the potentiometer depends on movement, in particular tilting, of the transmission element, wherein the movement, in particular tilting, is initiated, for example, by the force on the elastic skin and / or the movement of the elastic skin.

[0015] Preferably, the finger unit has a shaft area and a tip area, wherein in the shaft area the elastic skin extends substantially parallel to the rigid surface, and in the tip area the elastic skin is arranged in a cup-like shape and extends towards the rigid surface. In the tip area, the elastic skin can be firmly connected to the rigid surface. The two-dimensional measuring device is more preferably arranged in the shaft area.

[0016] In a further advantageous embodiment of the invention, the two potentiometers comprise a wiper and a resistive layer, preferably arranged on a resistive layer. The use of a resistive layer is particularly advantageous for enabling simple and cost-effective measurement.

[0017] According to the invention, the transmission element of the two-dimensional measuring device has a coupling element for each sensor. The coupling elements are arranged such that a movement, in particular a tilting motion, of the transmission element is transmitted to the respective sensor by means of the coupling elements. The transmission element is preferably connected to each sensor by means of a coupling element, whereby the movement, in particular a tilting motion, of the transmission element can advantageously be transmitted to the respective sensors by the coupling elements. Such an arrangement and transmission of the movement and / or forces on the elastic skin to the two-dimensional measuring device represents a particularly simple and cost-effective device. Force transmission can thus be achieved with simple mechanical connections.

[0018] In an advantageous embodiment of the invention, the transmission element has a substantially cylindrical shape, with the coupling elements projecting substantially perpendicularly from a lateral surface of the transmission element. The coupling elements preferably have a cylindrical or rectangular shape.

[0019] According to the invention, each sensor has a rocker arm configured to be actuated by the coupling element, wherein the rockers each have a recess, particularly a centrally located one, and wherein a coupling element is at least partially arranged in the recess of the respective sensor. The advantage lies in the fact that the rocker arm can be mechanically actuated and represents a simple and cost-effective device for measuring a gripping force on the finger unit. The movement of the elastic skin can thus be easily transmitted to the respective sensors.

[0020] In a further embodiment of the invention, the two-dimensional measuring device comprises four sensors, in particular four potentiometers, with each pair of sensors arranged redundantly to one another. The sensors preferably each have a rocker switch, the rocker switches of the redundant sensors being arranged parallel to one another. Preferably, the redundant sensors are arranged on opposite sides around the transmission element.

[0021] According to a further advantageous embodiment of the invention, the sensors of the two-dimensional measuring device are arranged orthogonally to each other on the rigid surface. This enables, in particular, measurement in one dimension of the two-dimensional measuring device at a time. A sensor can preferably measure a movement, especially a tilting, of the transmission element in one spatial direction. Preferably, the rocker arms are also arranged substantially orthogonally to each other. The two sensors can thus cover a measurable plane of movements on the elastic surface.

[0022] According to a further advantageous embodiment of the invention, the rigid surface has a recess, wherein the transmission element is at least partially arranged within this recess. The recess can represent a fixed point about which the transmission element can tilt. The recess is preferably arranged on the side of the rigid surface facing the elastic skin. Advantageously, the transmission element cannot be displaced relative to the two-dimensional measuring device by the recess. Rather, the recess can represent a fixed anchor point. The recess preferably has a round cross-sectional area. The recess can also advantageously reduce the risk of the transmission element moving excessively and thus, for example, damaging the sensors or distorting measurements.

[0023] According to a further advantageous embodiment of the invention, the finger unit has a return spring, wherein the return spring is at least partially arranged in the recess and is arranged such that it returns the transmission element to a starting position, particularly after deflection of the transmission element. The transmission element can have a starting position in which preferably no external force acts on the elastic skin, particularly apart from the weight of the elastic skin. Furthermore, the transmission element can have a deflected position. The deflected position can be any position that deviates from the starting position and is produced by an external force on the elastic skin or by movement of the elastic skin. The return spring can advantageously return the transmission element, particularly after deflection of the transmission element, to its original position.When the external force on the elastic skin is removed, it returns to its starting position. The return spring is preferably designed as a helical spring.

[0024] According to a further advantageous embodiment of the invention, the finger unit comprises, in addition to the two-dimensional measuring device, a further measuring device, wherein the further measuring device is arranged such that a movement of the elastic skin essentially perpendicular to the rigid surface and / or elastic skin is transmitted to the further measuring device by means of the transmission element and can be detected. Preferably, the further measuring device is arranged in the recess of the rigid surface. Particularly preferably, the further measuring device is arranged between the transmission element and the rigid surface, especially below the transmission element. The further measuring device can detect a movement and / or force acting on the elastic skin essentially perpendicular to the rigid surface and / or elastic skin.The transmission element can measure minute changes essentially perpendicular to the elastic skin and / or rigid surface, thus enabling the determination of force or movement. The combination of the two-dimensional measuring device and the additional measuring device can advantageously enable three-dimensional measurement.

[0025] Preferably, the transmission element can be arranged in the return spring and the recess such that the return spring can return the transmission element to its original position after a deflection substantially perpendicular to the rigid surface and / or elastic skin. The initial position is preferably the vertical position of the transmission element without any external force acting on the elastic skin or movement of the elastic skin. When the substantially perpendicular force on the elastic skin is removed, the return spring can return the transmission element to its original position.

[0026] According to a further advantageous embodiment of the invention, the additional measuring device is designed as a touch probe, in particular a digital touch probe, and the touch probe has a threshold value, the touch probe only detecting when the threshold value is exceeded. A touch probe is a cost-effective and simple device for determining whether a certain event has occurred. The threshold value can preferably be a predefined gripping force, and an exceedance of this force can be detected by means of the touch probe. The threshold value can represent a trigger threshold, whereby an event occurs, for example, only when the gripping force is exceeded.

[0027] In a further advantageous embodiment of the invention, a finger unit can have several two-dimensional measuring devices. The advantage is that the gripping force or the movement of the elastic skin can be measured over a larger or even the entire length of the finger unit.

[0028] A further aspect of the invention is a robot hand comprising at least two finger units according to one of the preceding claims and an evaluation unit, wherein the evaluation unit is configured to determine the movement of the transmission element by means of the two-dimensional measuring device and to determine a gripping force or frictional force at the finger unit. The evaluation unit can process the measured values ​​of the respective finger units and determine the gripping force or frictional force at the respective finger unit.

[0029] Preferably, a connecting element can be arranged between the finger unit and the robot hand, wherein a joint is arranged, in particular, between the finger unit and the connecting element and / or between the connecting element and the robot hand. This allows the finger unit to perform more numerous and complex movements. Preferably, the connecting element can be configured as a further finger unit.

[0030] According to a further advantageous embodiment of the invention, the evaluation unit is connected to each finger unit via at least one connecting cable. Preferably, the connecting cable runs through the connecting element. The electronic complexity can be minimized by means of the simple two-dimensional measuring device, which can significantly reduce the complexity and cost of a robotic hand.

[0031] A further object of the invention is a method for determining a gripping force or frictional force on a finger unit, in particular on a fingertip, of a robot hand, wherein the finger unit has an elastic skin and a substantially rigid surface arranged below the elastic skin, wherein a two-dimensional measuring device is arranged on the rigid surface and a transmission element is arranged between the elastic skin and the rigid surface, wherein the movement of the elastic skin is transmitted to the two-dimensional measuring device by means of the transmission element and the two-dimensional measuring device detects a deformation of the elastic skin and a gripping force or frictional force is determined.

[0032] According to a further advantageous embodiment of the invention, the finger unit is connected to an evaluation unit, wherein the evaluation unit determines a force on the finger unit via the deformation of the elastic skin.

[0033] The robotic hand and the method according to the invention can achieve the same technical effects and advantages as those already described in connection with the finger unit according to the invention. The advantageous embodiments and features described in connection with the finger unit according to the invention can also be applied to the robotic hand and the method for determining a gripping force or frictional force on a finger unit, either alone or in combination.

[0034] Further details and advantages of the invention will be explained below with reference to the exemplary embodiment shown in the drawings. This shows: Fig. 1 An embodiment of a finger unit according to the invention in a side sectional view; and Fig. 2 a perspective view of the embodiment from Fig. 1 from a top-down view.

[0035] Fig. Figure 1 shows a side sectional view of an embodiment of a finger unit 1 according to the invention, in particular a fingertip, for a robot hand. The finger unit 1 can be used, in particular, to detect gripping forces or frictional forces that exist, for example, between an object to be lifted and an elastic skin 2 of the finger unit 1. Such finger units 1 are preferably used in humanoid robot hands and are preferably used to lift objects. The ability to detect or measure the frictional or gripping forces present at a finger unit 1 makes it possible, in particular, to lift fragile or slippery objects. The finger unit 1 according to the invention is a cost-effective and simple device that enables the measurement of gripping or frictional forces.In addition, the finger unit 1 can provide information about whether the existing gripping or frictional forces between the finger unit 1 and the object to be lifted are sufficiently high.

[0036] The in Fig. The finger unit 1 shown in Figure 1 can be divided into a shaft region 2.1 and a tip region 2.2. In the shaft region 2.1, the elastic skin 2 and the rigid surface 3 preferably extend in a substantially parallel direction. In the tip region 2.2, the elastic skin 2 preferably extends towards the rigid surface 3 in a fingertip shape, and the elastic skin 2 can be connected to the rigid surface 3 in the tip region 2.2. The tip region 2.2 can be modeled on a fingertip. The rigid surface 3 is arranged below the elastic skin 2. Furthermore, the finger unit 1 has a two-dimensional measuring device, wherein the two-dimensional measuring device can measure the movement of the elastic skin 2, the movement of which is preferably initiated by an external force.For this purpose, a transmission element 4 is arranged between the elastic skin 2 and the two-dimensional measuring device such that a deformation of the elastic skin 2 can lead to a movement, in this case a tilting, of the transmission element 4, which in turn can be detected and measured by the two-dimensional measuring device. A frictional force or a gripping force on the elastic skin 2 or the finger unit 1 can be determined by the tilting of the transmission element 4 and the measurement of this tilting by the two-dimensional measuring device.

[0037] The two-dimensional measuring device preferably has two sensors 6, which are particularly preferably designed as potentiometers. The advantage of using potentiometers lies especially in their low cost and complexity. Here, the potentiometers have a wiper 6.3 and a resistive layer 6.4, wherein the resistance value of the potentiometers changes depending on the movement of the wiper 6.3, thus allowing conclusions to be drawn about the movement of the elastic skin 2 and the frictional or gripping force present on the elastic skin 2. It is particularly preferred if the two potentiometers each have a wiper 6.3 but are arranged on a resistive layer 6.4. This allows for a more compact and simpler design of the two potentiometers.

[0038] Fig. Figure 1 further shows a connection between the transmission element 4 and the sensor 6 in the form of a coupling element 5. Each sensor 6 can be connected to the transmission element 4 via a coupling element 5 such that a tilting of the transmission element 4 is transmitted to the respective sensor 6 by means of the coupling elements 5. The transmission element 4 preferably has a cylindrical shape, with the coupling elements 5 particularly preferably extending substantially perpendicularly from the lateral surface of the transmission element.

[0039] It is further evident that the two-dimensional measuring device is arranged on the rigid surface 3. In the illustrated embodiment, the rigid surface 3 has a recess 9, wherein the transmission element 4 is arranged at least partially within this recess 9. The recess 9 is preferably arranged centrally in the two-dimensional measuring device. The recess 9 can be a fixed point for the transmission element 4, about which the transmission element 4 can tilt, particularly relative to the two-dimensional measuring device. This ensures that no relative displacement between the transmission element 4 and the two-dimensional measuring device is possible.

[0040] Furthermore, the finger unit 1 can have a return spring 7, in particular in the form of a helical spring, which is arranged such that the transmission element 4 can be moved back to a starting position, particularly after a deflection of the transmission element 4. For this purpose, the transmission element 4 is preferably arranged at least partially within the return spring 7. Thus, when the transmission element 4 tilts and after the gripping force or frictional force on the elastic skin 2 ceases, the return spring 7 can move the transmission element 4 back to a starting position. It is conceivable that the return spring 7 is arranged at least partially within the recess 9. Advantageously, this prevents the return spring 7 from slipping. In the illustrated embodiment, the transmission element 4 is in its starting position.The initial position is preferably the position of the transmission element 4 in which the transmission element 4 experiences no deflection due to the elastic skin. A deflected position, which can be detected and measured in particular by the two-dimensional measuring device, preferably describes any deviation of the transmission element 4 from the initial position, which is introduced, for example, by the gripping force or frictional force on the elastic skin 2.

[0041] Furthermore, the in Fig. Figure 1 shows an embodiment of the finger unit 1 with a further measuring device, wherein the further measuring device is arranged such that a movement of the elastic skin 2 essentially perpendicular to the rigid surface 3 and / or elastic skin 2 is transmitted to the further measuring device by means of the transmission element 4 and can be detected. The further measuring device can detect the essentially perpendicular movement. Preferably, the arrangement of the two-dimensional measuring device enables the detection and measurement of a movement of the elastic skin 2 essentially parallel to the rigid surface 3 and / or elastic skin 2. The further measuring device can measure and detect a movement essentially perpendicular to the elastic skin 2 and / or the rigid surface 3 and / or the application of an external force.In the illustrated embodiment, the further measuring device is designed as a sensing element 8, which is preferably arranged below the transmission element 4 and between the transmission element 4 and the rigid surface 3. It is also conceivable that the sensing element 8 is arranged in the recess 9. A movement of the elastic skin 2 essentially perpendicular to the elastic skin 2 and / or the rigid surface 3 can press on the sensing element 8, which can be detected and / or measured by the sensing element 8.

[0042] Preferably, the sensing element 8 has a threshold value, and the sensing element 8 can only detect when this threshold value is exceeded. For this purpose, the sensing element 8 can be designed as a digital sensing element. Advantageously, particularly in the case of repetitive applications of the finger unit 1, a minimum gripping force or frictional force can be defined as the threshold value of the sensing element 8, whereby, for example, the respective application can only be carried out when the threshold value has been reached or exceeded. Exceeding the threshold value of the sensing element 8 can also be linked to a predefined function; for example, a signal can be transmitted to another device or unit. For this purpose, the finger unit 1 can have a connecting line 10 via which the finger unit 1 can be connected to, for example, an evaluation unit or a robot hand.

[0043] Fig. Figure 2 shows the embodiment of the finger unit 1 according to Fig. Figure 1 shows a perspective view from above. The perspective view of the finger unit 1 clearly shows the sensors 6, which in the illustrated embodiment are designed as potentiometers. The sensors 6 of the two-dimensional measuring device are preferably arranged substantially orthogonally to each other on the rigid surface 3. Advantageously, this allows a two-dimensional measurable plane to be generated, which runs substantially parallel to the elastic skin 2 and / or the rigid surface 3. It is also evident that the finger unit 1 has a semicircular cross-section.

[0044] The sensors 6 each have a rocker 6.1 designed to be actuated by the coupling element 5. To at least partially accommodate the coupling element 5, the rockers 6.1 have a recess 6.2, allowing the coupling element 5 to transmit movement of the elastic skin 2 to the rocker 6.1. Preferably, the recess 6.2 is located centrally in the rocker 6.1. This allows movement of the transmission element 4 in the respective directions to be measured equally.

[0045] The rockers 6.1 are preferably arranged on the wiper 6.3, the wiper 6.3 being arranged on the resistive layer 6.4. In the illustrated embodiment, the two sensors 6 are arranged on a resistive layer 6.4. Furthermore, the rockers 6.1 and wiper 6.3 of the sensors 6 of the two-dimensional measuring device are arranged substantially orthogonally to each other.

[0046] It is conceivable that gripping and frictional forces generate movement of the elastic skin 2. This movement of the elastic skin 2 leads to a tilting of the transmission element 4, which in turn can cause the rockers 6.1 to tilt. The tilting of the transmission element can be transmitted to the rockers 6.1, in particular via the coupling elements 5. The rockers 6.1 can tilt, and the resistance value of the respective sensor 6 can be changed by the movement of the rockers 6.1 via the wiper 6.3 on the resistive layer 6.4, and this change is measurable.

[0047] A finger unit 1 can also have several two-dimensional measuring devices, whereby the gripping or frictional forces along the finger unit 1 can be measured at several points.

[0048] Several finger units 1 can be part of a robot hand, which is suitable, for example, for picking up and repositioning objects. A robot hand can have at least two finger units 1 and an evaluation unit, the evaluation unit being configured to determine the movement of the transmission element 4 using the two-dimensional measuring device and to ascertain a gripping force or frictional force at the respective finger units 1. The evaluation unit can be connected to the respective finger units 1 by means of a connecting cable 10. Reference symbol list 1 finger unit 2 elastic skin 2.1 Shaft area 2.2 Summit area 3 rigid surface 4 transmission element 5 coupling element 6 sensors 6.1 Seesaw 6.2 Recess 6.3 Grinder 6.4 Resistance layer 7 Return spring 8 Key element 9. In-depth study 10 connecting line

Claims

[1] Finger unit (1), in particular fingertip, for a robot hand comprising an elastic skin (2) and a substantially rigid surface (3) arranged below the elastic skin (2), wherein a two-dimensional measuring device is arranged on the rigid surface (3) and a transmission element (4) is arranged between the elastic skin (2) and the rigid surface (3), wherein the transmission element (4) is connected to the elastic skin (2) and the two-dimensional measuring device in such a way that a deformation of the elastic skin (2) leads to a movement, in particular tilting, of the transmission element (4) and the two-dimensional measuring device can measure the movement of the transmission element (4), characterized by , that the two-dimensional measuring device comprises two sensors (6), in particular two potentiometers, the transmission element (4) of the two-dimensional measuring device has a coupling element (5) for each sensor (6), wherein the coupling elements (5) are arranged such that a movement, in particular tilting, of the transmission element (4) is transmitted to the respective sensor (6) by means of the coupling elements (5), and the sensors (6) each have a rocker (6.1) which is designed to be actuated by the coupling element (5), wherein the rockers (6.1) each have a centrally arranged recess (6.2), wherein a coupling element (5) is at least partially arranged in the recess (6.2) of the respective sensor (6). [2] Finger unit (1) according to claim 1, characterized by , that the sensors (6) of the two-dimensional measuring device are arranged orthogonally to each other on the rigid surface (3). [3] Finger unit (1) according to any one of the preceding claims, characterized bythat the rigid surface (3) has a recess (9), wherein the transmission element (4) is arranged at least partially within this recess (9). [4] Finger unit (1) according to claim 3, characterized by , that the finger unit (1) has a return spring (7), wherein the return spring (7) is at least partially arranged in the recess (9) and the return spring (7) is arranged such that the return spring (7) moves the transmission element (4) back to a starting position, in particular after a deflection of the transmission element (4). [5] Finger unit (1) according to any one of the preceding claims, characterized by, that the finger unit (1) has, in addition to the two-dimensional measuring device, a further measuring device, wherein the further measuring device is arranged such that a movement of the elastic skin (2) substantially perpendicular to the rigid surface (3) and / or elastic skin (2) is transmitted to the further measuring device by means of the transmission element (4) and can be detected. [6] Finger unit (1) according to claim 5, characterized by , that the further measuring device is designed as a sensing element (8), in particular a digital sensing element, and the sensing element (8) has a threshold value, wherein the sensing element (8) only detects the exceeding of the threshold value. [7] Robot hand comprising at least two finger units (1) according to one of the preceding claims and an evaluation unit, wherein the evaluation unit is configured to determine the movement of the transmission element (4) by means of the two-dimensional measuring device and to determine a gripping force or frictional force on the finger unit (1), characterized by , that the two-dimensional measuring device comprises two sensors (6), in particular two potentiometers, the transmission element (4) of the two-dimensional measuring device has a coupling element (5) for each sensor (6), wherein the coupling elements (5) are arranged such that a movement, in particular tilting, of the transmission element (4) is transmitted to the respective sensor (6) by means of the coupling elements (5), and the sensors (6) each have a rocker (6.1) which is designed to be actuated by the coupling element (5), wherein the rockers (6.1) each have a centrally arranged recess (6.2), wherein a coupling element (5) is at least partially arranged in the recess (6.2) of the respective sensor (6). [8] Robot hand according to claim 7, characterized by that the evaluation unit is connected to a finger unit (1) via at least one connecting line (10). [9] Method for determining a gripping force or frictional force on a finger unit (1), in particular on a fingertip, of a robot hand, wherein the finger unit (1) has an elastic skin (2) and a substantially rigid surface (3) arranged below the elastic skin (2), wherein a two-dimensional measuring device is arranged on the rigid surface (3) and a transmission element (4) is arranged between the elastic skin (2) and the rigid surface (3), wherein the movement of the elastic skin (2) is transmitted to the two-dimensional measuring device by means of the transmission element (4) and the two-dimensional measuring device detects a deformation of the elastic skin (2) and determines a gripping force or frictional force, wherein the two-dimensional measuring device comprises two sensors (6), in particular two potentiometers, The transmission element (4) of the two-dimensional measuring device has a coupling element (5) for each sensor (6), the coupling elements (5) being arranged such that a movement, in particular tilting, of the transmission element (4) is transmitted to the respective sensor (6) by means of the coupling elements (5). the sensors (6) each have a rocker (6.1) which is designed to be actuated by the coupling element (5), wherein the rockers (6.1) each have a centrally arranged recess (6.2), wherein a coupling element (5) is at least partially arranged in the recess (6.2) of the respective sensor (6). [10] Method according to claim 9, characterized by , that the finger unit (1) is connected to an evaluation unit, wherein the evaluation unit determines a force on the finger unit (1) via the deformation of the elastic skin (2).

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