Gripper

Abstract

Provided is a gripper in which a sensor can easily be disposed while limiting the number of components, regardless of the number of master jaws that are arranged.　The present invention provides a gripper comprising a main body, a piston, a plurality of master jaws, and a sensor, wherein: the main body has a cylinder chamber and a plurality of guide grooves; the cylinder chamber is configured to be supplied with and to discharge a fluid; the piston is configured to move back and forth along a central axis within the cylinder chamber by means of the fluid supplied to and discharged from the cylinder chamber; the guide grooves are configured to extend in a radial direction orthogonal to the central axis; the master jaws are configured such that a gripping member for gripping a workpiece can be attached thereto, and are configured to move back and forth along the guide grooves in conjunction with the piston; and the sensor is disposed along the central axis and is configured to detect the position of the piston in the direction of the central axis.

Description

Gripper

[0001] The present invention relates to a gripper configured to grip a workpiece (object to be gripped) on the front side.

[0002] Grippers for gripping workpieces are sometimes attached to the arm tips of industrial robots, etc. Some such grippers have sensors for measuring the dimensions of the workpieces. Patent Document 1 discloses a gripper that directly measures the distance between two master jaws by spanning a scale rod between the master jaws, thereby enabling the dimensions of the workpiece to be measured during transport.

[0003] Patent No. 7349446

[0004] When adopting a configuration in which a scale rod is attached to a master jaw as in Patent Document 1, if the number of master jaws increases, there may be inconveniences such as the need for parts such as scale rods for the number of master jaws, and restrictions on the configuration of the gripper due to the arrangement of the scale rods.

[0005] The present invention has been made in consideration of the above circumstances, and provides a gripper in which sensors can be easily arranged while reducing the number of parts, regardless of the number of master jaws arranged.

[0006] According to the present invention, the following inventions are provided: [1] A gripper capable of gripping a workpiece on its front side, the gripper having a main body, a piston, a plurality of master jaws, and a sensor, the main body having a cylinder chamber and a plurality of guide grooves, the cylinder chamber configured to be supplied with and discharged from a fluid, the piston configured to reciprocate within the cylinder chamber along a central axis by the fluid supplied to and discharged from the cylinder chamber, the guide groove configured to extend in a radial direction perpendicular to the central axis, a gripping member for gripping a workpiece can be attached to the master jaws, the master jaws configured to reciprocate along the guide grooves in conjunction with the piston, and the sensor arranged along the central axis and configured to detect a position of the piston in the direction of the central axis. [2] The gripper according to [1], wherein the cylinder chamber has a concave guide portion on its back side, the piston has a flange portion, a first shaft portion, and a second shaft portion, the flange portion is configured to divide the cylinder chamber into two pressure chambers, the first shaft portion is disposed on a front side of the flange portion and has a wedge plunger attached thereto that engages with the master jaw, and the second shaft portion is disposed on a back side of the flange portion and is configured to slide within the guide portion. [3] The gripper according to [2], wherein the piston has a through portion that is configured to pass through the first shaft portion, the flange portion, and the second shaft portion along the central axis, the wedge plunger is fastened to the first shaft portion of the piston by a fastener, and the sensor is integrally attached to the fastener and is disposed in the through portion. [4] The gripper according to [2] or [3], wherein the wedge plunger has an inclined surface that engages with the master jaw, and the inclined surface is at an angle of 10 to 40 degrees with respect to the central axis. [5] The gripper according to any one of [1] to [4], wherein three or more of the guide grooves and three or more of the master jaws are arranged radially from the central axis.

[0007] In the gripper of the present invention, it is possible to easily arrange sensors while reducing the number of parts, regardless of the number of master jaws arranged.

[0008] FIG. 1A is a perspective view of a gripper 1 according to an embodiment of the present invention as seen from the front side, and FIG. 1B is a perspective view of the gripper 1 as seen from the rear side. FIG. 2A is a side view of the gripper 1, FIG. 2B is a front view of the gripper 1, and FIG. 2C is a cross-sectional view taken along line A-A in FIG. 2A. FIG. 3A is a cross-sectional view taken along line B-B in FIG. 2B, and FIG. 3B is a diagram showing a state in which the piston 5 in FIG. 3A has moved to the rear side and gripped the workpiece W. FIG. 4A is a perspective view showing the arrangement of the sensor 7, and FIG. 4B is a perspective view of FIG. 4A as seen from a different angle. FIG. 5A is a perspective view showing a state in which the wedge plunger 6 and the sensor 7 are coupled, and FIG. 5B is a perspective view showing a state in which the sensor 7 has been detached from the wedge plunger 6. These figures show a schematic configuration of a wedge plunger 60 as a modified example.

[0009] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an independent invention.

[0010] 1 to 3, a gripper 1 according to one embodiment of the present invention will be described. The gripper 1 is configured to be attachable to the arm tip of an industrial robot, etc. The gripper 1 is configured to grip a workpiece W (see FIGS. 3A and 3B) on the front side. Here, an example of gripping a cylindrical workpiece W will be described, but the shape of the workpiece W is not limited to a cylindrical shape.

[0011] <Main body 2, piston 5> The gripper 1 includes a main body 2. The main body 2 includes a cylinder portion 2B, a front body 2A, and a rear body 2C. As shown in FIGS. 3A and 3B, the cylinder portion 2B is generally cylindrical with a bottom. A cylinder chamber 21 capable of accommodating the piston 5 is provided inside the cylinder portion 2B. The cylinder chamber 21 is configured so that a pressurized fluid (compressed fluid) for sliding the piston 5 along the central axis 100 is supplied to and discharged from the cylinder chamber 21. In addition, a concave guide portion 22 is provided on the rear side of the cylinder chamber 21.

[0012] In this embodiment, the pressure fluid used is, for example, but not limited to, compressed air of about 0.2 to 0.8 MPa. The compressed air is supplied to and discharged from the cylinder chamber 21 via multiple air supply and discharge passages (not shown) provided in the main body 2.

[0013] The piston 5 includes a flange portion 5B, a first shaft portion 5A, and a second shaft portion 5C. The flange portion 5B is configured to divide the cylinder chamber 21 into a first cylinder chamber 21A and a second cylinder chamber 21B. The first cylinder chamber 21A and the second cylinder chamber 21B each constitute a pressure chamber. When compressed air is supplied to the first cylinder chamber 21A, the piston 5 moves leftward in FIG. 3 (toward the rear side), and when compressed air is supplied to the second cylinder chamber 21B, the piston 5 moves rightward in FIG. 3 (toward the front side). In this way, the piston 5 reciprocates within the cylinder chamber 21 along the central axis 100 by compressed air that is supplied to and discharged from the first cylinder chamber 21A and the second cylinder chamber 21B as needed.

[0014] The first shaft portion 5A is disposed on the front side of the flange portion 5B. The first shaft portion 5A is configured to slide within the accommodation space 2A1 of the front body 2A. The first shaft portion 5A is configured to allow the wedge plunger 6 to be attached. On the other hand, the second shaft portion 5C is disposed on the rear side of the flange portion 5B. The second shaft portion 5C is configured to slide within the guide portion 22 of the cylinder chamber 21.

[0015] The front body 2A is connected to an opening on the front side of the cylinder portion 2B. The front body 2A has an accommodation space 2A1 formed around a central axis 100 and three guide grooves 20A to 20C extending radially from the accommodation space 2A1. The guide grooves 20A to 20C each have an inverted T-shaped cross section that matches the cross-sectional shape of the master jaws 3A to 3C.

[0016] <Master jaws 3A-3C, wedge plunger 6> The master jaws 3A-3C are configured to slide within the guide grooves 20A-20C while engaged with the guide grooves 20A-20C, respectively. The cross-sectional shapes of the master jaws 3A-3C are configured to match the cross-sectional shapes of the guide grooves 20A-20C when viewed from the radial direction. The master jaws 3A-3C are guided by the guide grooves 20A-20C in the radial direction perpendicular to the central axis 100, respectively. Here, a configuration including three guide grooves 20A-20C and three master jaws 3A-3C is described, but the number of guide grooves and master jaws may be two, or four or more.

[0017] Engagement portions 30A to 30C that engage with the wedge plunger 6 are provided on the central axis 100 side of the master jaws 3A to 3C. As shown in Figures 2C and 4B, tapered grooves with T-shaped cross sections are formed in the engagement portions 30A to 30C. In this embodiment, the tapered grooves have inclined surfaces that gradually approach the central axis 100 as they approach the front side.

[0018] On the other hand, as shown in FIG. 4A, the wedge plunger 6 is provided with engaged portions 6A to 6C configured to slidably engage with the engaging portions 30A to 30C. In this embodiment, the engaged portions 6A to 6C are configured as T-shaped tapered protrusions. However, it is also possible to configure the engaging portions 30A to 30C as T-shaped tapered protrusions and the engaged portions 6A to 6C as tapered grooves. The engaging portions 30A to 30C and the engaged portions 6A to 6C fit snugly together and slidably engage with each other.

[0019] A gripping member (in this embodiment, a roughly rectangular parallelepiped top jaw 4) for gripping the workpiece W can be attached to the master jaws 3A to 3C via fasteners (bolts, nuts, etc.). The master jaws 3A to 3C are configured to reciprocate along the guide grooves 20A to 20C in conjunction with the reciprocating movement of the piston 5 along the central axis 100. This allows the top jaw 4 to grip (see FIG. 3B) and release (see FIG. 3A) the workpiece W. The gripping member attached to the master jaws 3A to 3C is not limited to the top jaw 4, and it is possible to use an optimal gripping member depending on the shape and dimensions of the workpiece to be gripped.

[0020] The wedge plunger 6 is fastened to the piston 5 with a bolt 8 (fastener). By fixing the wedge plunger 6 to the piston 5, the piston 5 and the wedge plunger 6 operate as a single unit. The wedge plunger 6 is disposed in an accommodation space 2A1 of the front body 2A. A hexagonal cover plate 9 is attached to the opening on the front side of this accommodation space 2A1.

[0021] The rear body 2C is connected to an opening on the rear side of the cylinder portion 2B. The rear body 2C is provided with a sensor housing space 2C1 for housing the sensor 7. Each of the above-described parts of the main body 2 is a metal product that is machined from a metal material such as aluminum, but the material is not particularly limited.

[0022] 3A and 3B , the sensor 7 is disposed inside a through-hole 50 that passes through the first shaft portion 5A, the flange portion 5B, and the second shaft portion 5C of the piston 5 along the central axis 100. The sensor 7 includes a scale rod 7A and a reading unit 7B. The scale rod 7A has an elongated shape and is disposed along the central axis 100. The reading unit 7B is cylindrical and, like the scale rod 7A, is disposed along the central axis 100.

[0023] The scale rod 7A is attached to the bolt 8 as shown in Figures 5A and 5B. Specifically, the bolt 8 has a cylindrical shaft, and the scale rod 7A is fixed to the inner circumferential surface of this shaft with an adhesive or the like. On the other hand, the reading unit 7B is attached to the rear body 2C as shown in Figures 3A and 3B. The rear body 2C has a through hole formed along the central axis 100, and the reading unit 7B is fixed to the inner circumferential surface of this through hole with an adhesive or the like. The method of attaching the scale rod 7A and the reading unit 7B is not limited to adhesive, and mechanical methods such as fitting may also be used.

[0024] The through-hole 50 in which the sensor 7 is disposed, the guide portion 22, and the sensor accommodating space 2C1 are isolated from the cylinder chamber 21 by the piston 5 (and a seal member appropriately arranged around the piston 5). This prevents the pressure in the cylinder chamber 21 from reaching the sensor 7. The through-hole 50, the guide portion 22, and the sensor accommodating space 2C1 all communicate with openings on the rear side of the rear body 2C, making it possible to always maintain the same pressure as the outside (ambient air pressure).

[0025] The scale rod 7A and the reading unit 7B are arranged coaxially (in a straight line) along the central axis 100. When the scale rod 7A is inserted into the reading unit 7B and the scale rod 7A and the reading unit 7B are displaced relative to each other in the longitudinal direction of the scale rod 7A, a receiving unit provided inside the reading unit 7B measures the displacement.

[0026] As described above, the first shaft portion 5A on the front side of the piston 5 is guided by the inner wall of the accommodation space 2A1 of the front body 2A, and the second shaft portion 5C on the rear side is guided by the guide portion 22 of the cylinder chamber 21, so the piston 5 does not tilt from the central axis 100 and reciprocates straight along the central axis 100. Therefore, the coaxiality of the scale rod 7A and the reading portion 7B is not lost even during the reciprocating movement of the piston 5, and the position of the piston 5 in the direction of the central axis 100 is accurately detected. Furthermore, because the scale rod 7A is configured to be able to extend over a long distance from the front end of the wedge plunger 6 to the rear body 2C, the scale rod 7A is unlikely to tilt from the central axis 100, and even if tilt does occur, errors are unlikely to occur in the detection results.

[0027] The sensor 7 can suitably use a detection method (for example, a differential transformer detector) that converts mechanical linear motion into an electrical signal or the like for detection. However, the detection method and shape of the sensor 7 are not limited to a specific one, and any known detection method or shape can be appropriately selected and used. The electrical signal or the like from the reading unit 7B can be sent to the control unit of the gripper 1 by wire or wirelessly.

[0028] As described above, the sensor 7 accurately detects the positions of the piston 5 and the wedge plunger 6, which moves integrally therewith, in the direction of the central axis 100. As a result, the radial positions (degree of opening / closing) of the master jaws 3A-3C, which move in conjunction with the wedge plunger 6, and the radial position (degree of opening / closing) of the top jaw 4, which moves integrally therewith, are accurately detected. This makes it possible to detect the dimensions of the workpiece W based on the detection results of the sensor 7. By providing the gripper 1 with the function of accurately detecting the dimensions of the workpiece W, it becomes possible, for example, to accurately measure the outer diameter of the workpiece W while gripping and transporting the workpiece W.

[0029] Furthermore, the scale rod 7A of the sensor 7 is attached integrally to the bolt 8 that secures the wedge plunger 6 to the piston 5, and can be easily pulled out along the central axis 100 together with the bolt 8 as shown in Fig. 5B. This makes it possible to easily replace the scale rod 7A as needed. Note that, although this embodiment employs a configuration in which the bolt 8 threads into the female thread portion of the piston 5, the present invention is not limited to this.

[0030] By adopting the configuration of the gripper 1 of this embodiment, there is no need to increase the number of sensors 7, even if four guide grooves and master jaws are arranged radially from the central axis, or even if the number is increased to five to eight.

[0031] <Operation of Gripper 1> Here, an example of a method for determining whether the dimensions of the gripped workpiece W are appropriate in the gripper 1 will be described. The gripper 1 stores in advance, in the memory of the control unit, the detection value of the sensor 7 when gripping a master workpiece formed according to the desired dimensions. That is, the amount of displacement (position in the direction of the central axis 100) of the piston 5 (or the wedge plunger 6) when gripping the master workpiece is stored. Then, the detection value of the sensor 7 when gripping the master workpiece is used as a reference value, and an allowable range of the detection value of the sensor 7 is set according to the allowable dimensional error range for the workpiece W. When the gripper 1 grips the workpiece W, if the detection value of the sensor 7 is within the allowable range, the gripped workpiece W is determined to be OK, whereas if the detection value of the sensor 7 is outside the allowable range, the gripped workpiece W is determined to be NG.

[0032] The operation of the gripper 1 described above is merely an example. For example, the gripper 1 may store a correspondence between the detection value of the sensor 7 and the spacing between the top jaws 4, and measure the dimensional values ​​of the gripped workpiece W. In particular, when gripping a workpiece W that is circular in plan view with three top jaws 4, as in the gripper 1 of this embodiment, there is an advantage in that the diameter of the workpiece W can be accurately measured based on the detection value of the sensor 7. When gripping with two jaws, it can be difficult to measure the diameter of a workpiece W that is circular in plan view. However, with the gripper 1 of this embodiment, such a problem is unlikely to occur. The three top jaws 4 suitably center the workpiece W that is circular in plan view, and stable dimensional measurement of the workpiece W is achieved that is not affected by the posture of the robot or the workpiece.

[0033] <Modification of Wedge Plunger 6> Here, a wedge plunger 60 as a modification of the wedge plunger 6 will be described using FIG. 6. Like the above-described wedge plunger 6, the wedge plunger 60 is provided with engaged portions 60A to 60C configured to slidably engage with the engaging portions 30A to 30C of the master jaws 3A to 3C. The engaged portions 60A to 60C may be, for example, T-shaped tapered protrusions or T-shaped tapered grooves. In either case, the engaged portions 60A to 60C have inclined surfaces that engage with the engaging portions 30A to 30C. In FIG. 6, the angle of this inclined surface with respect to the central axis 100 is represented by θ.

[0034] The wedge plunger 60 is set to have a smaller angle θ than the wedge plunger 6. The wedge plunger 60 is set to have an angle θ of 10 to 40 degrees, and more preferably 20 to 25 degrees. The inclination angles of the engaging portions 30A to 30C of the master jaws 3A to 3C are also changed appropriately depending on the value of θ, but a description thereof will be omitted here.

[0035] In this way, by making the value of θ relatively small, the variation in the detected value of the diameter of the workpiece W is reduced. The reason for this is that the amount of radial displacement of the top jaw 4 (or master jaws 3A to 3C) is considerably smaller than the amount of displacement of the wedge plunger 6 (or piston 5) in the direction of the central axis 100.

[0036] For example, the displacement of the wedge plunger 6 is ΔP ＳＴ In this case, the displacement ΔD of the top jaw 4 is expressed as follows: ΔD = ΔP ＳＴ This can be calculated using the formula tan θ. From this, it can be said that the smaller θ is made, the higher the accuracy of the displacement amount ΔD of the top jaw 4 becomes.

[0037] As described above, by using the gripper 1, for example, it is possible to measure the dimensions of the workpiece W with high precision while it is being transported, which makes it possible to reduce the amount of inspection equipment and personnel required and shortens the manufacturing takt time. Furthermore, even when three master jaws 3A to 3C are provided, it is sufficient to provide only a single sensor 7, which reduces the number of parts and manufacturing costs.

[0038] Furthermore, since the sensor 7 is isolated in a position where it is not affected by the pressure fluid (compressed air) that operates the piston 5, malfunctions caused by pressure being applied to the sensor 7 are unlikely to occur.

[0039] <Other Embodiments> In the above-described embodiment, the wedge plunger 6 is shown to have a shape tapering toward the front, but the present invention can also be applied to a shape in which the wedge plunger 6 is tapered toward the back. Although an example of an air-driven piston 5 using air as the pressure fluid has been described, it is also possible to use a liquid such as hydraulic oil as the pressure fluid. Rather than measuring the dimensions of the workpiece W while the gripper 1 is transporting it, it is also possible to measure the dimensions of the workpiece W by using the gripper 1 as a stationary type.

[0040] 1: Gripper, 2: Main body, 3A: Master jaw, 3B: Master jaw, 3C: Master jaw, 5: Piston, 5A: First shaft portion, 5B: Flange portion, 5C: Second shaft portion, 6: Wedge plunger, 7: Sensor, 20A: Guide groove, 20B: Guide groove, 20C: Guide groove, 21: Cylinder chamber

Claims

1. A gripper capable of gripping a workpiece on its front side, the gripper having a main body, a piston, multiple master jaws, and a sensor, wherein the main body has a cylinder chamber and multiple guide grooves, the cylinder chamber is configured to receive and discharge fluid, the piston is configured to reciprocate within the cylinder chamber along a central axis by the fluid supplied to and discharged from the cylinder chamber, the guide groove is configured to extend in a radial direction perpendicular to the central axis, a gripping member for gripping the workpiece can be attached to the master jaw, and the master jaw is configured to reciprocate along the guide groove in conjunction with the piston, and the sensor is arranged along the central axis and configured to detect the position of the piston in the direction of the central axis.

2. A gripper according to claim 1, wherein the cylinder chamber has a concave guide portion on its back side, the piston has a flange portion, a first shaft portion, and a second shaft portion, the flange portion is configured to separate the cylinder chamber into two pressure chambers, the first shaft portion is located on the front side of the flange portion and has a wedge plunger attached thereto that engages with the master jaw, and the second shaft portion is located on the back side of the flange portion and is configured to slide within the guide portion.

3. A gripper according to claim 2, wherein the piston has a through-portion, the through-portion is configured to pass through the first shaft portion, the flange portion, and the second shaft portion along the central axis, the wedge plunger is fastened to the first shaft portion of the piston by a fastener, and the sensor is integrally attached to the fastener and is disposed in the through-portion.

4. A gripper according to claim 2 or 3, wherein the wedge plunger has an inclined surface that engages with the master jaw, and the angle of the inclined surface relative to the central axis is 10 to 40 degrees.

5. A gripper according to any one of claims 1 to 3, wherein three or more of the guide grooves and three or more of the master jaws are arranged radially from the central axis.

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