Tactile sensor-equipped finger of robot hand and tactile sensor-equipped robot hand using the same

Abstract

Provided is a haptic sensor finger capable of inhibiting breakage or malfunction of a robot hand caused by contact of a held object with a portion other than the palm surface of the finger portion when the robot hand is used with the haptic sensor. The haptic sensor finger (1F) of the present invention is a finger of a robot hand that holds a held object, and includes a finger portion (2) having a palm surface (21a) that contacts the held object, a back surface (21b) on the side opposite the palm surface (21a), a front end surface (21c) at the front end in the extension direction of the palm surface (21a) and the back surface (21b) and adjacent to the palm surface (21a) and the back surface (21b), and two side surfaces (21d, 21d) adjacent to the palm surface (21a) and the back surface (21b) in a direction crossing the extension direction of the palm surface (21a) and the back surface (21b), and a haptic sensor body (5) that is a thin film-shaped member attached to the outer surface of a housing (21) that constitutes the finger portion (2), and has a pressure-sensitive region (5a) that overlaps at least one of the palm surface (21a) and the front end surface (21c) and the two side surfaces (21d, 21d).

Description

Technical Field

[0001] This invention relates to fingers of a robotic hand equipped with tactile sensors, which can suppress damage and malfunctions caused by contact between the object being held and parts of the finger other than the palm surface. Background Technology

[0002] Today, robots are not only active in manufacturing, but also in a wide range of fields such as the service industry and healthcare. Among these robots, many are equipped with robotic arms so that they can carry various objects or grasp tools to perform tasks, just like humans.

[0003] In a robotic hand, gripping force is essential, but it is also necessary to measure various contact states, such as the shearing force generated on the palmar surface of the fingers gripping the object. For example, by measuring the shearing force exerted on the object by the robotic hand, the minimum gripping force required for the robotic hand to hold the object without causing it to fall can be determined.

[0004] Therefore, Patent Document 1 proposes a scheme to install a tactile sensor capable of measuring three-part force in the palmar surface of the fingers of a robotic hand.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-281403 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] However, in the example of the robotic hand illustrated in the aforementioned Patent Document 1, the two fingers are shaped like a cuboid. Since the pressure-sensitive area of ​​the tactile sensor body is only provided on one of the six faces of the cuboid, which is the palm, various problems exist.

[0010] For example, sometimes when the robotic arm 11 is lowered relative to a spherical object W placed at a predetermined position, if the object W rolls and deviates from the predetermined position, the front end face 21c of the finger 2 will touch the object W (see reference). Figure 18 At this point, the robotic arm 11 cannot check the contact between the front end face 21c of the finger 2 and the object W being held. As a result, the robotic arm 11 continues to descend as before until it reaches the position where it is holding the object W, thus adding an excessive load between the robotic arm 11 and the object W, which may lead to damage to the object W or malfunction of the robotic arm 11.

[0011] Additionally, as another example, sometimes when the two fingers 2 of the robotic hand 11 are brought close from both sides to a grasping object W with a complex shape, such as tree branches, the grasping object W will touch the side 21d of the fingers 2 before it touches the palm surfaces 21a of the fingers 2 (see reference). Figure 19 At this point, the robotic arm 11 cannot check the contact between the side 21d of the fingers 2 and the object being held, W. As a result, due to the two fingers 2 continuing to approach from both sides of the object being held, an additional load is added between the robotic arm 11 and the object being held, thus the object being held, W may still break or the robotic arm 11 may malfunction.

[0012] Therefore, the purpose of this invention is to solve the above-mentioned technical problems and to provide a finger of a robotic hand with a tactile sensor that can suppress damage and malfunction caused by contact between the object being held and a part of the finger other than the palm surface when using a robotic hand with a tactile sensor.

[0013] Technical solutions for solving technical problems

[0014] The following sections describe several methods as solutions to technical problems. These methods can be combined as needed.

[0015] The tactile sensor-equipped finger of the robotic hand of the present invention is a finger of a robotic hand for grasping an object, comprising a finger portion and a tactile sensor body. The finger portion has a palmar surface that contacts the object being grasped. Additionally, the finger portion has a back surface opposite to the palmar surface. Furthermore, the finger portion has a frontal surface adjacent to the palmar and back surfaces in the extending direction of the palmar and back surfaces. Additionally, the finger portion has two side surfaces adjacent to the palmar and back surfaces in a direction intersecting the extending directions of the palmar and back surfaces. The tactile sensor body is a thin film attached to the outer surface of the housing constituting the finger portion, having a pressure-sensitive area overlapping at least one of the palmar surface, the frontal surface, and the two side surfaces.

[0016] The robotic hand with this configuration, featuring fingers equipped with tactile sensors, extends the pressure-sensitive area to the tip and sides of the finger and incorporates the tactile sensor body, thus enabling it to detect contact between the tip and sides of the finger and the object being held. As a result, damage and malfunctions caused by contact between the object being held and parts of the finger other than the palmar surface can be suppressed.

[0017] In addition, as an aspect, preferably, the tactile sensor body is an electrostatic capacitive pressure sensor comprising a first electrode film having a first electrode pattern formed on a first substrate film, a second electrode film having a second electrode pattern formed on a second substrate film opposite to the first substrate film, and an insulator sandwiched between the first electrode film and the second electrode film.

[0018] The first substrate film side is attached to the finger.

[0019] Based on the above configuration, since the tactile sensor body is simply a structure formed by electrodes of thin film pattern stacked with an insulator, even if it is three-dimensionally attached to multiple surfaces of the outer surface of the housing that constitutes the finger, the detection function of the tactile sensor body can be fully utilized.

[0020] In addition, as an aspect, preferably, when the tensile elastic modulus of the first substrate film and the second substrate film are set to E1 and E2 respectively, and the thicknesses of the first substrate film and the second substrate film are set to t1 and t2 respectively, the relationship is E1×t1>E2×t2.

[0021] Based on the above configuration, because the first substrate film on the finger side is harder than the second substrate film on the outer side, even if the thin-film tactile sensor body is three-dimensionally attached along the outer surface of the housing constituting the finger, the size of the tactile sensor body is unlikely to change. Therefore, the detection accuracy is improved.

[0022] In addition, as an aspect, preferably, at least one of the palmar surface, the front surface, and the two side surfaces of the finger is composed of multiple surfaces and overlaps with the pressure-sensitive area.

[0023] Based on the above configuration, by setting pressure-sensitive areas in more surfaces, it is possible to measure various contact states with the object being held.

[0024] Additionally, as an aspect, preferably, the tactile sensor body has an unfolded pattern after removing portions that do not follow the outer surface of the housing constituting the fingers.

[0025] Based on the above configuration, since the part that is not needed as the body of the tactile sensor does not hinder bending, it becomes easy to bend the thin-film tactile sensor body along the outer surface of the finger.

[0026] In addition, as an aspect, preferably, the pressure-sensitive area of ​​the tactile sensor body is divided into multiple parts to match the shape of the tactile sensor body after bending.

[0027] Based on the above configuration, since the pressure-sensitive area does not exist continuously across more than two surfaces, it is possible to accurately measure the direction of the three-dimensional vector of the force to be detected.

[0028] Additionally, as an aspect, preferably, the tactile sensor body is covered by a protective layer, and a notch is formed on the tactile sensor body side of the protective layer to provide a notch portion, so as to face the non-pressure-sensitive area further outward than the pressure-sensitive area of ​​the tactile sensor body.

[0029] According to the above configuration, when the object being held comes into contact with the finger on the outside of the pressure-sensitive area, the protective layer deforms significantly due to the space created by the notch on the side of the tactile sensor body facing the non-pressure-sensitive area. As a result, since the deformation also affects the pressure-sensitive area near the non-pressure-sensitive area of ​​the tactile sensor body, it is possible to detect the contact between the object being held and the finger in the non-pressure-sensitive area.

[0030] Additionally, as an aspect, preferably, the space at the notch is filled with a buffer layer that is softer than the protective layer.

[0031] Based on the above configuration, the durability degradation of the tactile sensor body caused by the presence of a notch can be minimized.

[0032] Additionally, as an aspect, preferably, the portion of the finger that is not in contact with the tactile sensor body is covered by a protective layer that is partially or entirely extended.

[0033] Based on the above configuration, it not only protects the main body of the tactile sensor, but also expands the protection area of ​​the fingers.

[0034] Additionally, as a preferred aspect, in the configuration where the tactile sensor body has a pressure-sensitive area that overlaps across the palm and front face, the entire surface of the tactile sensor body and part or all of the two sides of the finger are continuously covered by a protective layer, wherein the protective layer has a protrusion on the palm face of the finger and in the portion covering the pressure-sensitive area of ​​the tactile sensor body that protrudes further in the thickness direction than the portion near the boundary between the palm face and the two sides of the finger.

[0035] Based on the above configuration, not only is the main body of the tactile sensor protected, but the protection area of ​​the fingers can also be expanded.

[0036] In addition, because the protective layer protrudes in the thickness direction on the palm side of the finger and in the part covering the pressure-sensitive area of ​​the tactile sensor body, the object being held can be inspected through the pressure-sensitive area before it comes into contact with the palm side of the finger and near the boundary of the two sides.

[0037] It should be noted that, compared to the previously described configuration where the notch is located on the tactile sensor body side of the protective layer, the protective layer is easier to form. For example, it can be formed by methods such as embedding molding.

[0038] In addition, the robotic hand with tactile sensors of the present invention has a plurality of fingers with tactile sensors as described in any of the above-described robotic hands, and also has a support portion for supporting the rear ends of these fingers, and a drive portion for driving the fingers to grasp or release an object to be grasped.

[0039] As an aspect, preferably, it has two fingers, which are configured with the palms facing each other, each finger is jointless, and is designed to hold the object by bringing the parallel palms close to each other.

[0040] Invention Effects

[0041] The tactile sensor-equipped fingers of the robotic hand of the present invention can suppress damage and malfunctions caused by the object being held contacting the part of the fingers other than the palm surface when using the robotic hand with tactile sensors. Attached Figure Description

[0042] Figure 1 The figure illustrates an example of a robot equipped with a robotic hand using a finger with a tactile sensor according to the first embodiment.

[0043] Figure 2 The figure illustrates an example of a robotic hand using a finger with a tactile sensor according to the first embodiment.

[0044] Figure 3 The figure shows an example of a finger with a tactile sensor in the robotic hand according to the first embodiment.

[0045] Figure 4 This figure illustrates an example of the configuration of a tactile sensor body that fits onto the finger portion according to the first embodiment.

[0046] Figure 5 This is a diagram illustrating an example of the shear force distribution detected by a tactile sensor.

[0047] Figure 6 A diagram illustrating another example of a finger with a tactile sensor in the robotic hand according to the first embodiment.

[0048] Figure 7 A diagram illustrating another example of a finger with a tactile sensor in the robotic hand according to the first embodiment.

[0049] Figure 8 To show in Figure 7 The diagram shows the unfolded pattern of the tactile sensor body used in the variation example.

[0050] Figure 9 The diagram illustrates the use of a rectangular tactile sensor body fitted to the front end and two sides of the finger.

[0051] Figure 10 The figure shows an example of a tactile sensor body that fits onto a finger portion of a palm surface composed of multiple surfaces.

[0052] Figure 11 for Figure 10The diagram shows the unfolded form of the tactile sensor body.

[0053] Figure 12 The figure shows an example of the shape of the protective layer in the finger of the robotic hand with tactile sensors according to the first embodiment.

[0054] Figure 13 The figure shows an example of the shape of the protective layer in the finger of the robotic hand with tactile sensors according to the second embodiment.

[0055] Figure 14 This figure illustrates an example of the shape of the protective layer in the finger of the robotic hand with a tactile sensor according to the third embodiment.

[0056] Figure 15 The figure shows another example of the shape of the protective layer in the finger of the robotic hand with tactile sensors according to the third embodiment.

[0057] Figure 16 This figure illustrates an example of the shape of the protective layer in the finger of the robotic hand with a tactile sensor according to the fourth embodiment.

[0058] Figure 17 A diagram illustrating the features of the protective layer in the fourth embodiment.

[0059] Figure 18 A diagram illustrating an example of a robotic arm using existing technology.

[0060] Figure 19 A diagram illustrating an example of a robotic arm using existing technology. Detailed Implementation

[0061] The following is a detailed description of a robotic hand using a finger with a tactile sensor according to the present invention, based on the embodiments shown in the accompanying drawings.

[0062] <First Implementation>

[0063] Figure 1 The side view of a robot 100 equipped with a robotic hand 1 with tactile sensors according to the first embodiment of the present invention is shown.

[0064] (1) Robot body

[0065] like Figure 1As shown, the robot body 100 is a horizontal articulated robot (SCARA robot) with a base 110 and an arm 120 rotatably connected to the base 110. The arm 120 has a first arm 130 rotatably connected to the base 110 via a joint mechanism, a second arm 140 rotatably connected to the first arm 130 via a joint mechanism, and a working head 150 disposed at the front end of the second arm 140. Furthermore, a robotic hand 1 using fingers equipped with tactile sensors is mounted at the lower end of the working head 150. The working head 150 enables the robotic hand 1 to rotate around a vertical axis and to move vertically.

[0066] (2) Robotic arm 1

[0067] The following is a detailed description of such a robotic arm 1.

[0068] The robotic hand 1 using the finger with a tactile sensor according to this embodiment is as follows: Figure 2 As shown, the robot arm 1 has two fingers 1F equipped with tactile sensors. Each finger 1F has a finger portion 2 and a tactile sensor body 5 attached to the outer surface of the housing 21 constituting the finger portion 2. It also has a support portion 3 supporting the rear ends of the two finger portions 2 and a drive portion 4 for driving the finger portions 2. The drive portion 4 allows the two finger portions 2 to move in directions of approaching each other and directions of separation. Thus, the robot arm 1 can grasp or release the grasped object W. Furthermore, the entire robot arm 1 can also move up and down and rotate as needed.

[0069] It should be noted that the object W to be held is not particularly limited. For example, it can include various industrial products, crops, items of various sizes / shapes, items whose exact shape is not known, etc.

[0070] (3) Finger part 2

[0071] Figure 3 The figure shows an example of a finger 1F with a tactile sensor of the robotic hand 1 according to the first embodiment. Figure 3 (a) is a diagram obtained by observing the finger 1F with a tactile sensor from the palmar surface 21a side of the finger 2. Figure 3 (b) is Figure 3 AA line profile of (a).

[0072] Each finger 2 is constructed from a generally rectangular shell 21, which has a palm surface 21a that contacts the object being held (as a robotic hand gripping the object W), a back surface 21b opposite to the palm surface 21a, a front end surface 21c adjacent to the palm surface 21a and back surface 21b in the extending direction X of the palm surface 21a and back surface 21b, and two side surfaces 21d, 21d adjacent to the palm surface 21a and back surface 21b in the direction Y intersecting the extending direction X of the palm surface 21a and back surface 21b. The shell 21 is made of resin or metal.

[0073] In addition, each finger part 2 in Figure 2 and Figure 3 In the example shown, there are no joints. Therefore, the fingers 1F with tactile sensors grasp the object W by bringing their parallel palm surfaces 21a close to each other.

[0074] (4) Touch sensor body 5

[0075] The tactile sensor body 5, as shown Figure 3 As shown, this is a thin film attached to the outer surface of the housing 21 that constitutes the finger portion 2. Additionally, in Figure 3 In the example shown, the tactile sensor body 5 has a pressure-sensitive area 5a that overlaps the palm surface 21a and the front surface 21c across the finger portion 2.

[0076] The tactile sensor body 5 is a triaxial force sensor that detects the pressing force (pressure) and sliding force (friction) through the pressure-sensitive area 5a. By being mounted on the finger part 2 of the robotic hand 1, it can not only measure the force of gripping the object W, but also the magnitude of actions such as "twisting", "pushing", and "stretching".

[0077] Figure 4 This figure illustrates an example of the configuration of the tactile sensor body 5 attached to the finger portion 2 according to the first embodiment. The area of ​​the finger portion 2 to which the tactile sensor 5 is attached is depicted in a partially enlarged manner, surrounded by dashed lines.

[0078] The tactile sensor body 5, for example, Figure 4 As shown, it can be configured as an electrostatic capacitive pressure sensor, which includes a first electrode film 53 on a first substrate film 51 on which a first electrode 52 is disposed, a second electrode film 56 on a second substrate film 54 opposite to the first substrate film 51 on which a second electrode 55 is disposed, and an insulator 57 sandwiched between the first electrode film 51 and the second electrode film 54.

[0079] It should be noted that the area that can be inspected by the first electrode 52 and the second electrode 55 is the pressure-sensitive region 5a. In addition, there is a non-pressure-sensitive region 5b outside the pressure-sensitive region 5a, on which a wiring pattern connected to the first electrode 52 and the second electrode 55 is formed.

[0080] In this capacitive pressure sensor, the first substrate film 51 is attached to the finger 2 by the adhesive layer 6.

[0081] Because the tactile sensor body 5 is a simple structure consisting of electrodes with thin film patterns stacked in an insulator, it can fully perform its detection function even when it is three-dimensionally attached to multiple surfaces of the outer surface of the housing that constitutes the finger.

[0082] Materials used for the first substrate film 51 and the second substrate film 54 may include rubber sheets such as urethane, epoxy resin, and silicone resin, and synthetic resin films such as polyethylene terephthalate (PET), polycarbonate (PC), and polyimide (PI).

[0083] The thicknesses of the first substrate film 51 and the second substrate film 54 are 0.03 μm to 0.5 mm. In this way, since a thin and flexible film with a total thickness of less than 1 mm is used as the substrate, it can be fitted onto the surface of the finger portion 2 of the robot arm 1 without any discomfort.

[0084] However, it is preferable that when the tensile elastic modulus of the first substrate film 51 and the second substrate film 54 are set to E1 and E2 respectively, and the thicknesses of the first substrate film 51 and the second substrate film 54 are set to t1 and t2 respectively, the relationship is set to E1×t1>E2×t2.

[0085] Based on the above configuration, since the first substrate film 51, which is on the side of the finger portion 2, is harder than the second substrate film 54, which is on the outside, it is difficult for the size of the tactile sensor body 5 to change even if the thin film-shaped tactile sensor body 5 is three-dimensionally attached along the outer surface of the housing constituting the finger portion 2. Therefore, the detection accuracy is improved.

[0086] It should be noted that the tensile modulus of elasticity mentioned in this invention refers to the value obtained by cutting the first substrate film 51 and the second substrate film 54 into the shape of dumbbell No. 1 test pieces, using a tensile tester capable of measuring minute displacements in a non-contact manner, and following the tensile test method according to JISK7127 and JISK7161, by dividing the strain generated in the first substrate film 51 and the second substrate film 54 by the tensile stress experienced by the first substrate film 51 and the second substrate film 54.

[0087] In addition to the examples shown in the figures below, the patterns of the first electrode 52 and the second electrode 55 of the electrostatic capacitive varistor can also use known patterns.

[0088] <Figure Case 1>

[0089] The first electrode 52 and the second electrode 55 can be exemplified by a pattern consisting of linear patterns that extend in the same direction when viewed from above (not shown). By assuming that the first electrode 52 and the second electrode 55 are composed of linear patterns extending in the same direction, when a force is applied from a direction intersecting the direction of the extension of the second electrode 55, the second electrode 55 deforms in response to the magnitude of the force, and the distance between it and the first electrode 52 changes. The magnitude of the force can be measured by examining the electrical signal when the electrostatic capacitance between the first electrode 52 and the second electrode 55 changes.

[0090] For example, the first electrode 52 is composed of three linear patterns extending in one direction (designated as left end, center, and right end), and the second electrode 55 is also composed of two linear patterns extending in the same direction as the first electrode 52 (designated as left side and right side). These patterns are formed at the gaps between the left-end pattern and the center pattern of the first electrode 52, and at the gaps between the center pattern and the right-end pattern of the first electrode 52. In this configuration, when a force is applied from left to right in a direction intersecting the direction of extension of the second electrode 55, the two linear patterns of the second electrode 55 deform (move parallel) in the direction of the applied force, corresponding to the magnitude of the force. The distance between the left-side pattern and the center pattern of the first electrode 52 becomes closer to the left-side pattern and farther from the right-side pattern. Furthermore, the left-end pattern of the first electrode 52 becomes farther from the left-side pattern of the second electrode 55, and the right-end pattern of the first electrode 52 becomes closer to the right-side pattern of the second electrode 55. The variation in the distance between these linear patterns is proportional to the magnitude of the applied force.

[0091] That is, because the overlapping area of ​​the multiple capacitors formed by the opposing overlap of the first electrode 52 and the second electrode 55 increases or decreases due to the shearing force acting on the surface of the tactile sensor body 5, the ratio of electrostatic capacitance changes. Therefore, by measuring the change of these multiple electrostatic capacitances, the pressing pressure and shearing force can be detected.

[0092] Therefore, by examining the changes in electrostatic capacitance between the individual linear patterns that accompany the changes in the distance between these linear patterns in the layers, it is possible to determine the magnitude of the applied force.

[0093] This example illustrates a case where the first electrode 52 has three linear patterns and the second electrode 55 has two linear patterns, but they can also have only one or more linear patterns. Furthermore, the number of linear patterns in the first electrode 52 and the second electrode 55 can also be the same.

[0094] In addition, the linear patterns of the first electrode 52 and the second electrode 55 can be rectangles of roughly the same long strip shape, or they can have different widths and lengths, or they can be patterns with varying widths.

[0095] Furthermore, it can be not limited to rectangular shapes, but can also be polygonal shapes, arc shapes, or other curved patterns. Additionally, it can be shapes derived from combinations of these, such as wave shapes. It should be noted that while squares, circles, and similar shapes are generally not considered linear patterns, in this invention, any manner in which the function and purpose of the invention are presented is also considered a type of linear pattern.

[0096] Furthermore, in Example 1 of this figure, where the first electrode 52 and the second electrode 55 are composed of linear patterns extending in the same direction, since a force (pressing pressure) is applied to the surface of the tactile sensor body 5 in the normal direction, the distance between the first electrode 52 and the second electrode 55 is close, thus increasing the electrostatic capacitance of the multiple capacitors formed by the overlapping of the first electrode 52 and the second electrode 55. The magnitude of the pressing pressure can be measured by measuring this change in electrostatic capacitance.

[0097] <Figure Case 2>

[0098] Furthermore, the first electrode 52 consists of two layers sandwiching an insulator, comprising a lower first electrode and an upper first electrode, and the second electrode 55 can also consist of two layers sandwiching an insulator, comprising a lower second electrode and an upper second electrode (not shown). In this case, it is preferable to configure the first electrode 52 as a lower first electrode with a linear pattern extending in the X direction and an upper first electrode with a linear pattern extending in the Y direction, and the second electrode 55 as a lower second electrode with a linear pattern extending in the same X direction as the lower first electrode and an upper second electrode with a linear pattern extending in the same Y direction as the upper first electrode.

[0099] It should be noted that the example is not limited to forming the two layers of the second electrode 55 on the upper part of the two layers of the first electrode 52. The layers of the first electrode 52 and the second electrode 55 can also be formed in different ways.

[0100] In this way, it is possible to separately examine the change in the ratio of the electrostatic capacitance between the lower first electrode and the lower second electrode extending along the same X direction, and the change in the ratio of the electrostatic capacitance between the upper first electrode and the upper second electrode extending along the same Y direction.

[0101] The result has the following advantages: even when the direction of the applied shear force is oblique when viewed from above, and when there are force components in the X and Y directions (when the direction of the shear force is parallel to or not perpendicular to the direction of any linear pattern in the upper first electrode pattern or the upper second electrode pattern), it is possible to measure the force components in the X and Y directions separately.

[0102] Furthermore, in Example 2 of Figure 1, where the first electrode 52 consists of two layers of insulator formed by a lower first electrode and an upper first electrode, and the second electrode 55 consists of two layers of insulator formed by a lower second electrode and an upper second electrode, when a force (pressing pressure) in the normal direction is applied to the surface of the tactile sensor body 5, the electrostatic capacitance of the multiple capacitors formed by the overlapping of the lower and upper first electrodes increases because the distances between the lower and lower second electrodes and between the upper first and upper second electrodes are close. The magnitude of the pressing pressure can be measured by measuring these changes in electrostatic capacitance.

[0103] <Figure Case 3>

[0104] Furthermore, when an electrostatic capacitive piezoresistive sensor group is formed by arranging multiple electrostatic capacitive piezoresistive sensors in a matrix as shown in Example 1 above, it is also possible to measure the planar distribution of force in the direction of the angle intersecting with the direction of each electrostatic capacitive piezoresistive sensor. That is, because each electrostatic capacitive piezoresistive sensor can measure the force in the direction of the angle intersecting with the electrostatic capacitive piezoresistive sensor at each location, even if the magnitude of the force varies depending on the location, it is possible to measure the magnitude of the force in each location when multiple electrostatic capacitive piezoresistive sensors are arranged in a matrix.

[0105] It should be noted that, regarding the electrostatic capacitive pressure sensor in this case, after the first substrate film 51 and the second substrate film 54 are completely integrated, the second electrode 55 and the first electrode 52 are formed independently.

[0106] <Figure Case 4>

[0107] Furthermore, when multiple electrostatic capacitive pressure sensors, each formed by creating multiple layers of second electrodes 55 and first electrodes 52 as shown in Example 2 above, are arranged in a matrix to form an electrostatic capacitive pressure sensor group, it is possible to measure the force components applied to each electrostatic capacitive pressure sensor in the X and Y directions, and also to measure the planar distribution of the force components in the X and Y directions. That is, because each electrostatic capacitive pressure sensor can measure the force components (force components in the X and Y directions) in the direction of the angle intersecting with the electrostatic capacitive pressure sensor at each location, even when the magnitude and direction of the force differ depending on the location, when multiple electrostatic capacitive pressure sensors are arranged in a matrix, it is possible to measure the magnitude of the force components (force components in the X and Y directions) in each location.

[0108] In this case, the electrostatic capacitive pressure sensor is similar to that in Example 3 of Figure 3, with the first substrate film 51 and the second substrate film 54 being fully integrated, and the second electrode 55 and the first electrode 52 being formed independently.

[0109] The examples 3 and 4 above are particularly suitable for robotic arm applications because they can measure planar distributions.

[0110] It should be noted that although Figures 3 and 4 above show the case of electrostatic capacitive pressure sensors arranged in a matrix, the electrostatic capacitive pressure sensors can also be arranged in a row when the finger 2 is slender.

[0111] <Figure Case 5>

[0112] Alternatively, the pattern can be configured as follows: the first electrode 52 is composed of an island-shaped pattern, and the second electrode 55, sandwiching an insulator, consists of two layers: an upper second electrode and a lower second electrode. The upper and lower second electrodes are composed of multiple intersecting line patterns when viewed from above. A portion of the island-shaped pattern of the first electrode 52 overlaps with portions of the patterns of the upper and lower second electrodes when viewed from above. The angle at which the upper and lower second electrodes intersect when viewed from above is not limited. When they are orthogonal (i.e., the angle of intersection becomes 90°), the pattern of the first electrode 52 becomes a rectangular checkerboard pattern; when they are not orthogonal, the pattern of the first electrode 52 becomes a parallelogram checkerboard pattern.

[0113] By measuring the changes in electrostatic capacitance between the first electrode 52 of the island pattern and the upper second electrode, and the changes in electrostatic capacitance between the first electrode 52 of the island pattern and the lower second electrode, the force components in the X-axis direction of the pattern direction of the upper second electrode and the force components in the Y-axis direction of the pattern direction of the lower second electrode can be measured respectively.

[0114] Furthermore, when a force component in the X-axis direction is applied from this state, the upper second electrode moves parallel to the magnitude of the force, resulting in an increase in the range within which the electrostatic capacitance value between the first electrode 52 and the upper second electrode can be detected. Therefore, by detecting this increased electrostatic capacitance value, the original force component in the X-axis direction can be measured.

[0115] Similarly, when a force component in the Y-axis direction is applied, the lower second electrode moves parallel to the magnitude of the force, resulting in an increase in the range of detectable electrostatic capacitance values ​​between the first electrode 52 and the lower second electrode. Therefore, by detecting this increased electrostatic capacitance value, the original force component in the Y-axis direction can be measured.

[0116] Furthermore, in Example 5 of this figure, when a force (pressing pressure) in the normal direction is applied to the surface of the tactile sensor body 5, the electrostatic capacitance of the multiple capacitors formed by the overlapping of the upper and lower second electrodes increases because the distance between the upper and lower second electrodes is close. By measuring this change in electrostatic capacitance, the magnitude of the pressing pressure can be measured.

[0117] The above shows several examples of the patterns of the first electrode 52 and the second electrode 55, but is not limited to these.

[0118] Regarding the materials of the first electrode 52 and the second electrode 55, in addition to 1) metal films such as gold, silver, copper, platinum, palladium, aluminum, and rhodium, examples 2) conductive paste films obtained by dispersing these metal particles in a resin binder, or organic semiconductors such as polyhexylthiophene, polydioctylfluorene, pentanebenzene, and tetrabenzoporphyrin, etc., are also possible, but there are no particular limitations.

[0119] Regarding the methods for forming the first electrode 52 and the second electrode 55, in case 1) above, a method can be used to form a pattern by etching after forming a conductive film on the entire surface by electroplating, sputtering, vacuum deposition, ion plating, etc. In case 2) above, a method can be used to directly form a pattern by printing methods such as screen printing, gravure printing, offset printing, etc.

[0120] Examples of materials that can be used as insulators 57 include rubber sheets and foam materials made from urethane, silicone resin, epoxy resin, ethylene vinyl acetate copolymer, polyethylene, polypropylene, polystyrene, butadiene, etc. Furthermore, these materials can be bonded to the first electrode film 53 and the second electrode film 55 using elastic adhesives, i.e., adhesives that remain elastic even after curing. It should be noted that insulator 57 is not limited to items obtained by sheet forming using general sheet forming methods such as extrusion molding; it can also be a coating layer formed by printing, spray plating, etc.

[0121] Furthermore, in the non-pressure-sensitive region 5b outside the pressure-sensitive region 5a of the tactile sensor body 5, wiring patterns originating from each of the first electrode 52 and the second electrode 55 are formed. These wiring patterns are as follows: Figure 3 As shown in (b), a thin-film connector 10 is laid from the tactile sensor body 5 and electrically connected to a PCB (printed substrate) 91 housed inside the housing 21 that constitutes the finger portion 2 of the robotic arm 1. Signals processed by the PCB 91 are transmitted from the PCB 91 to the robot body via a cable 92 such as a USB cable.

[0122] (5) Adhesive layer 6

[0123] In addition, the tactile sensor body 5, as Figure 4 As shown, the adhesive layer 6 is attached to the finger part 2 of the robotic hand 1.

[0124] For example, double-sided tape can be used as a material for the adhesive layer 6.

[0125] (6) Protective layer 7

[0126] In addition, the tactile sensor body 5, as Figure 4 As shown, it is covered by protective layer 7.

[0127] The protective layer 7 is a layer that protects the pressure-sensitive area of ​​the tactile sensor body 5 to which force is applied. The upper surface of the protective layer 7 becomes the contact surface with the object W being held.

[0128] Figure 12 A cross-sectional view showing an example of the shape of the protective layer 7 in the finger of the robotic hand with tactile sensors according to the first embodiment. Figure 12 (a) is a diagram obtained by observing the finger part 2 from the palmar side 21a. Figure 12 (b) is Figure 12 DD line profile of (a).

[0129] Protective layer 7 Figure 12As shown in (b), the protective layer 7 covers the tactile sensor body 5, but a notch 71 is provided on the tactile sensor body 5 side of the tactile layer 7, facing the non-pressure-sensitive area 5b further outward than the pressure-sensitive area 5a of the tactile sensor body 5. The space within this notch 71 is empty, forming an air layer.

[0130] In the non-pressure-sensitive area 5b, when the object W being held comes into contact with the finger 2, the protective layer 7 deforms significantly due to the space of the notch 71. As a result, since the deformation also affects the pressure-sensitive area 5a near the non-pressure-sensitive area 5b of the tactile sensor body 5, the contact between the object W being held and the finger 2 can be detected.

[0131] It should be noted that in the notch 71 shown in the figure, the surface in contact with the space of the protective layer 7 is composed of a lower surface parallel to the surface of the shell 21 of the finger portion 2 and a vertical wall surface, but it is not limited to this. For example, the lower surface may also be inclined relative to the surface of the shell 21 of the finger portion 2. Alternatively, the lower surface may be inclined relative to the surface of the shell 21 of the finger portion 2, and the wall surface may be removed. In addition, the surface in contact with the space of the protective layer 7 may also be composed of a curved surface.

[0132] Examples of materials that can be used for the protective layer 7 include rubber sheets and foam materials made of urethane, silicone resin, epoxy resin, ethylene vinyl acetate copolymer, polyethylene, polypropylene, polystyrene, butadiene, etc. The protective layer 7 is applied by bonding these rubber sheets or foam materials. Alternatively, it can be formed by insert molding, where the housing 21 to which the tactile sensor body 5 is bonded is placed in a molding die and liquid rubber material is injected. The thickness of the protective layer 7 is preferably 0.5 mm to 5 mm.

[0133] Furthermore, various design sheets can be bonded to the surface of the protective layer 7. In addition to patterned sheets, leather, fabric, and other materials can be bonded to create designs, depending on the purpose. Additionally, patterns can be formed on the protective layer 7 itself.

[0134] Figure 5 To show in such Figure 2 This diagram illustrates an example of the shear force distribution detected by the tactile sensor body 5 when holding an object W. One of the two fingers 1F equipped with tactile sensors is designated 1FA, and the other 1FB. The shear force when holding the object W between the palm surface 21a of the finger 2 is measured using the tactile sensor body 5 of each finger. The shear force distribution is displayed by observing the pressure-sensitive surface. It should be noted that the electrode pattern used here is the aforementioned example 5, and the object W is a cylindrical object.

[0135] Based on the detected shear force distribution, it can be determined that the object W being held was pulled away from the ground. Figure 2The paper is stretched inwards from the front.

[0136] (7-1) Variation Example 1

[0137] In the first embodiment described above, the illustration shows a case where the robot body 100, with a manipulator 1 mounted on its front end, is a horizontal articulated robot. For example, the robot body 100 could also be a vertical articulated robot or other types of robots.

[0138] (7-2) Variation Example 2

[0139] In the first embodiment described above, the illustration shows the case where the fingers 2 of the robotic arm 1 are jointless, but the fingers 2 are not limited to this. For example, each finger 2 may also have 1 to 2 joints.

[0140] Because the finger 2 has joints, the angle at which the finger 2 contacts the object W becomes more varied, and the opportunities for contact with parts other than the palm surface 21a of the finger 2 also increase. Therefore, tactile sensors are needed for these contact surfaces.

[0141] (7-3) Variation Example 3

[0142] In the first embodiment described above, the illustration shows a case where the finger portion 2 of the robotic hand 1 is a two-finger type, but the finger portion 2 is not limited to this. For example, the finger portion 2 can also be a three-finger type, a five-finger type like a human, or a multi-finger type. In the case of a multi-finger robotic hand 1, it is preferable to combine it with the joint described in Modified Example 2.

[0143] For example, three or five fingers 2 are arranged circumferentially discretely along the vertical axis of the support portion 3 that supports their rear ends. These fingers 2 are able to move in the direction close to the axis and in the direction away from the axis by using the drive portion 4 to bend the joints of each finger 2.

[0144] (7-4) Variation Example 4

[0145] In the first embodiment described above, the tactile sensor body 5 is illustrated to have a pressure-sensitive region 5a that overlaps only across the palm surface 21a and the front end surface 21c, but it is not limited to this. The pressure-sensitive region 5a may also overlap across the palm surface 21a, the front end surface 21c, and at least one of the two side surfaces 21d, 21d. For example, as Figure 6 As shown, the tactile sensor body 5 may also have a pressure-sensitive area 5a that overlaps across the palm surface 21a and two side surfaces 21d, 21d. Alternatively, the tactile sensor body 5 may also be as follows: Figure 7 The pressure-sensitive area 5a shown has an overlap of the palm surface 21a, the front end surface 21c, and two side surfaces 21d, 21d.

[0146] It should be noted that, Figure 7The unfolded pattern of the tactile sensor body 5 shown is not rectangular. For example... Figure 8 As shown, the tactile sensor body 5 of this embodiment has an unfolded pattern after removing the portion that is not along the outer surface of the housing 21 constituting the finger portion 2.

[0147] Assuming the unfolded pattern of the tactile sensor body 5 includes Figure 8 When the rectangle is represented by the dashed line, such as... Figure 9 As shown, a portion not following the outer surface of the housing 21 is formed at the boundary between the front end face 21c and the sides 21d, 21d of the finger portion 2. Because this portion hinders bending due to the rigidity of the substrate film, it is difficult to bend the thin-film tactile sensor body 5 along the outer surface of the finger portion 2. In addition, wrinkles and other protrusions are more likely to form on the outer surface of the tactile sensor body 5, making the contact between the pressure-sensitive area 5a of the tactile sensor body 5 and the object W being held unstable.

[0148] In this embodiment, since removing the portion that is not along the outer surface of the housing 21 does not hinder bending as the part that is not needed for the tactile sensor body 5, it becomes easy to bend the thin-film tactile sensor body 5 along the outer surface of the finger portion 2.

[0149] (7-5) Variation 5

[0150] In the first embodiment described above, the finger portion 2 of the robotic hand 1 is constructed from a generally rectangular shell 21, but is not limited thereto. For example, it may be possible that at least one of the palm surface 21a, the front end surface 21c, and the two side surfaces 21d, 21d is composed of multiple surfaces and overlaps with the pressure-sensitive area 5a.

[0151] Figure 10 The figure shows an example of a tactile sensor body 5 that fits onto a finger portion 2 having a palm surface 21a composed of multiple surfaces. Figure 10 (a) is a diagram showing the large area of ​​the tactile sensor body 5 viewed from the side opposite to the finger 2. Figure 10 (b) is Figure 10 BB line profile of (a). Figure 10 (c) is Figure 10 CC line profile of (a).

[0152] exist Figure 10 The example shown illustrates the shape of the tactile sensor body 5, which is a three-dimensional surface consisting of six surfaces rather than a flat surface, fitting against the palm surface 21a of the finger portion 2. Figure 11 for Figure 10The unfolded pattern of the tactile sensor body 5 shown is the shape after removing the portion that does not follow the outer surface of the housing 21 constituting the finger portion 2. It should be noted that the pressure-sensitive area 5a of the tactile sensor body 5 is divided into areas corresponding to the six faces (not shown) in a way that matches the shape of the tactile sensor body 5 after bending.

[0153] Thus, by setting pressure-sensitive areas 5a in more surfaces, it is possible to measure various contact states with the object W being held.

[0154] <Second Implementation>

[0155] Next, use Figure 13 The second embodiment of the present invention relates to a robotic arm with a tactile sensor. Figure 13 (a) is a diagram obtained by observing the finger part 2 from the palmar side 21a. Figure 13 (b) is Figure 13 EE line profile of (a).

[0156] The difference between the second embodiment and the first embodiment is that the part of the finger 2 that is not attached to the tactile sensor body 5 is covered by the protective layer 7.

[0157] That is, it not only protects the tactile sensor body 5, but also expands the protection area of ​​the finger 2. It should be noted that the expanded protection area can be the entire part of the finger 2 that is not in contact with the tactile sensor body 5, or it can be just a part of the part of the finger 2 that is not in contact with the tactile sensor body 5.

[0158] Regarding other points, since the description is repeated for the first embodiment, it is omitted. Furthermore, the variations described in the first embodiment can also be applied to the second embodiment.

[0159] <Third Implementation Method>

[0160] Next, use Figure 14 , Figure 15 The third embodiment of the present invention relates to a robotic arm with a tactile sensor. Figure 14 (a) is a diagram obtained from the palm side 21a, showing only the finger part 2 protected by the protective layer 7, which is the main body 5 of the tactile sensor. Figure 14 (b) is Figure 14 FF line profile of (a). Figure 15 (a) is a diagram obtained by viewing the finger portion 2 protected by the protective layer 7 from the palm side 21a. Figure 15 (b) is Figure 15 The GG line profile of (a).

[0161] The difference between the third embodiment and the first and second embodiments is that the space of the notch 71 of the protective layer 7 is filled by a buffer layer 8 that is softer than the protective layer 7.

[0162] By filling the space of the notch 71 with a buffer layer 8 that is softer than the protective layer 7, the concentration of stress at the edge of the pressure-sensitive region 5a can be mitigated compared to when the space is not filled with the buffer layer 8. When the concentration of stress at the edge of the pressure-sensitive region 5a continues repeatedly, the risk of wire breakage in the pressure-sensitive region 5a increases. Therefore, the durability degradation of the tactile sensor body 5 caused by the presence of the notch 71 can be minimized.

[0163] In the third embodiment, a foam material can be used as the soft material constituting the buffer layer 8. Examples of foam materials include those obtained by foaming rubber materials such as urethane or silicone resin.

[0164] It should be noted that, as a method for forming the buffer layer 8, examples include mixing foaming material with pre-vulcanized liquid rubber and injecting it into the notch 71 of the protective layer 7, or injecting pre-cured liquid of the protective layer 7 to cover the pressure-sensitive area 5a of the tactile sensor body 5 and the foam body after the foaming material has been pre-attached to the non-pressure-sensitive area 5b of the tactile sensor body 5.

[0165] Regarding other points, since the descriptions are repetitive with those of the first and second embodiments, they are omitted. Furthermore, the variations described in the first embodiment can also be applied to the third embodiment.

[0166] <Fourth Implementation>

[0167] Next, use Figure 16 An example of the shape of the protective layer in the finger of the robotic hand with a tactile sensor according to the fourth embodiment of the present invention will be described. Figure 16 (a) is a diagram obtained by viewing the finger portion 2 protected by the protective layer 7 from the palm side 21a. Figure 16 (b) is Figure 16 HH line profile of (a).

[0168] The fourth embodiment differs from the first embodiment in that the entire surface of the tactile sensor body 5 and a portion of the two side surfaces 21d, 21d of the finger portion 2 (see reference) Figure 16 ( ) or entirely (not shown) is continuously covered by the protective layer 7. Furthermore, unlike the first embodiment, the protective layer 7 has a protrusion 72 on the palmar surface 21a of the finger portion 2, covering the pressure-sensitive area 5a of the tactile sensor body 5, which protrudes further in the thickness direction than the portion near the boundary between the palmar surface 21a of the finger portion 2 and the two side surfaces 21d, 21d. It should be noted that in Figure 16 In the example shown, a protrusion 72 is also present on the front end surface 21c of the finger portion 2, which covers the pressure-sensitive area 5a of the tactile sensor body 5.

[0169] Based on the above configuration, not only is the tactile sensor body 5 protected, but the protection area of ​​the finger 2 can also be expanded. Furthermore, because the protective layer 7 protrudes in the thickness direction on the palmar surface 21a of the finger 2 and covers the pressure-sensitive area 5a of the tactile sensor body 5, the object W being held can be inspected through the pressure-sensitive area 5a with the protrusion 72 near the boundary between the palmar surface 21a and the two sides 21d, 21d, i.e., before the pressure-sensitive area 5a is absent, since the object W is in contact with the protrusion 73. (Refer to...) Figure 17 Therefore, the two fingers 2 will not continue to approach the object W from both sides, and no additional load will be added between the robot arm 11 and the object W.

[0170] Regarding the degree of protrusion of the protrusion 72, for example, it is preferable to be as... Figure 16 (a) HH line profile Figure 16 In (b), a virtual surface connects the outer edge of the protective layer 7 surface parallel to the palm surface 21a of the finger portion 2 and the outer edge of the top surface of the protrusion 72. Figure 16 The angle θ between the double-dotted line in (b) and the palm surface 21a is 30° or more. If the angle θ is less than 30°, it is difficult to obtain the effect based on the protrusion 72.

[0171] The protective layer 7 with the aforementioned protrusion 72 is easier to form than the previously described configuration where the notch 71 is provided on the side of the tactile sensor body 5. For example, it can be formed by embedding molding or the like. That is, the protective layer 7 is formed by placing the housing 21 to which the tactile sensor body 5 is attached in a molding die and injecting liquid rubber material or the like. Of course, as explained in the first embodiment, the protective layer 7 can also be covered by bonding.

[0172] It should be noted that, in Figure 16 The example shown illustrates an exposed housing 21 of the finger portion 2, but this embodiment 4 is not limited to this. For example, the exposed area of ​​the housing 21 of the finger portion 2 can be relative to... Figure 16 The examples shown can be expanded or reduced, or the protective layer 7 can be used to completely cover the finger part 2.

[0173] Regarding other points, since the description is repeated for the first embodiment, it is omitted. Furthermore, the variations described in the first embodiment can also be applied to the fourth embodiment.

[0174] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. In particular, the various embodiments and modifications described in this specification can be arbitrarily combined as needed.

[0175] Explanation of reference numerals in the attached figures

[0176] 1, 11: Robotic arm; 1F: Finger with tactile sensor; 2: Finger; 21: Housing; 21a: Palm; 21b: Back; 21c: Front end; 21d: Side; 3: Support; 4: Drive unit; 5: Tactile sensor body; 5a: Pressure-sensitive area; 5b: Non-pressure-sensitive area; 51: First substrate film; 52: First electrode; 53: First electrode film; 54: Second substrate film; 55: Second electrode; 56: Second electrode film; 57: Insulator; 6: Adhesive layer; 7: Protective layer; 71: Notch; 72: Protrusion; 8: Buffer layer; 90: Film connector; 91: PCB; 92: Cable; 100: Robot body; 110: Base; 120: Arm; 130: First arm; 140: Second arm; 150: Working head.

Claims

1. A finger of a robotic hand equipped with a tactile sensor, which is a finger of a robotic hand for grasping an object, comprising: The finger portion has a palmar surface that contacts the object being held, a back surface opposite to the palmar surface, a front end face adjacent to the palmar surface and the back surface in the extending direction of the palmar surface and the back surface, and two side surfaces adjacent to the palmar surface and the back surface in a direction intersecting the extending direction of the palmar surface and the back surface; and The tactile sensor body is a thin film attached to the outer surface of the housing constituting the finger, having pressure-sensitive areas overlapping across the palm surface, the front end surface, and at least one of the two side surfaces. The tactile sensor body is an electrostatic capacitive pressure sensor. The electrostatic capacitive pressure sensor includes a first electrode film with a first electrode disposed on a first substrate film, a second electrode film with a second electrode disposed on a second substrate film opposite to the first substrate film, and an insulator sandwiched between the first electrode film and the second electrode film. The first substrate film side is attached to the finger portion. When the tensile modulus of the first substrate film and the second substrate film are set to E1 and E2 respectively, and the thicknesses of the first substrate film and the second substrate film are set to t1 and t2 respectively, The relationship is E1×t1>E2×t2.

2. The finger of the robotic hand with a tactile sensor according to claim 1, wherein, The tactile sensor body has a pressure-sensitive area that overlaps across the palm and the front face.

3. The finger of the robotic hand with a tactile sensor according to claim 1, wherein, The tactile sensor body has pressure-sensitive areas that overlap across the palm and the two sides.

4. The finger of the robotic hand with a tactile sensor according to any one of claims 1 to 3, wherein, The palmar surface, the front surface, and at least one of the two side surfaces of the finger are composed of multiple surfaces and overlap with the pressure-sensitive area.

5. The finger of the robotic hand with a tactile sensor according to any one of claims 1 to 3, wherein, The tactile sensor body has an unfolded pattern that removes portions not along the outer surface of the housing that constitute the finger.

6. The finger of the robotic hand with a tactile sensor according to any one of claims 1 to 3, wherein, The pressure-sensitive area of ​​the tactile sensor body is divided into multiple segments to match the shape of the tactile sensor body after bending.

7. The finger of the robotic hand with a tactile sensor according to any one of claims 1 to 3, wherein, The tactile sensor body is covered by a protective layer, and a notch is provided on the tactile sensor body side of the protective layer in such a way that it faces a non-pressure-sensitive area further outward than the pressure-sensitive area of ​​the tactile sensor body.

8. The finger of the robotic hand with a tactile sensor according to claim 7, wherein, The space at the notch is filled with a buffer layer that is softer than the protective layer.

9. The finger of the robotic hand with a tactile sensor according to claim 7, wherein, The portion of the finger that is not attached to the body of the tactile sensor is covered by the protective layer, which is partially or entirely extended.

10. The finger of the robotic hand with a tactile sensor according to claim 2, wherein, The entire surface of the tactile sensor body and part or all of the two sides of the finger are continuously covered by a protective layer. The protective layer has a protrusion in the thickness direction at the portion of the palm surface of the finger and covering the pressure-sensitive area of ​​the tactile sensor body that is more prominent than the portion near the boundary between the palm surface covering the finger and the two sides.

11. A robotic hand with a tactile sensor, comprising: The fingers of the robotic hand with tactile sensors according to any one of claims 1 to 10, The robotic arm with tactile sensors also has: Support portion, supporting the rear end of the finger; and A drive unit that drives the fingers to grasp or release an object being grasped.

12. The robotic arm with a tactile sensor according to claim 11, wherein, The robotic hand with tactile sensors has two fingers. These fingers are configured such that the palm faces each other. The fingers are jointless and grasp the object by bringing the parallel palm surfaces close to each other.

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