ELECTRIC GRIP

Abstract

An electric gripper comprises a gripper body that supports a jaw guide in which at least one jaw is translationally movable between a gripping position and a release position. An electric motor is housed within the gripper body. A gear drive is designed to transmit the movement and torque of the electric motor to the at least one jaw. The gripper also includes an electric brake that can be actuated to lock the at least one jaw. The electric brake is connected in series between the electric motor and the gear drive.

Description

The present invention relates to an electric gripper for gripping and moving workpieces, in particular of the type suitable for being mounted on the wrist of a robot arm. Electric grippers are known which comprise a gripper body that forms or supports a gripper jaw guide in which at least one gripper jaw is translationally movable between a gripping position and a position for releasing a workpiece. The translational movement of the gripper jaw is driven by an electric motor housed within the gripper body. The movement and torque of the electric motor are transmitted to the gripper jaw via a gear drive or a transmission unit with gears. In some embodiments, each movable gripping jaw has a toothed section that engages with a pinion of an end shaft of the transmission. In some embodiments, the electric gripper is equipped with an electric brake that can be actuated to block the translational movement of one or more movable gripping jaws. The object of the present invention is to propose an electric gripper of the aforementioned type which is able to combine high performance, reliability and compact dimensions. The problem is solved with an electric gripper according to claim 1. The dependent claims describe preferred or advantageous embodiments of the electric gripper according to the invention. The features and advantages of the electric gripper according to the invention will become apparent from the following description of its preferred embodiments, which are merely exemplary and not limiting, with reference to the accompanying figures; these show: - Fig. 1 a perspective view of an example of an electric gripper according to the invention; - Fig. 2 an axial cross-section of the electric gripper; - Fig. 3 the internal components of the electric gripper, which are intended to transmit the movement to a gripping jaw of the gripper, in a perspective view; - Fig. 4 a top view of the components of Fig. 3; - Figs. 5 and 6 two elevations of the components of Figs. 3 and 4. In the following description, all directional terms (for example, upper, lower, upward, downward, left, right, to the left, to the right, above, below, over, under, vertical, horizontal, clockwise and counterclockwise) serve only the purpose of identification to facilitate the reader's understanding of the described embodiments and do not represent any limitations, in particular with regard to the position, orientation or use of the described embodiments. Unless otherwise specified, the terms used to describe connections (e.g., fastened, coupled, connected, and similar) are to be interpreted broadly and may include intermediate elements between a connection of elements and relative movement between elements. Therefore, these terms do not necessarily imply that two elements are directly connected and in a fixed relationship to each other. In the accompanying drawings, an electric gripper according to the invention is designated in its entirety by 1. The electric gripper 1 comprises a gripper body 10, which forms or supports a gripper jaw guide 12. At least one gripper jaw 14 is translationally movable within the gripper jaw guide 12 between a gripping position and a release position of a workpiece. In the example shown in particular in Fig. 1, the gripper jaw guide 12 forms two gripper jaw seats 12' in the shape of an inverted “T”, i.e. a dovetail, which are parallel to each other, in each of which a gripper jaw 14 is housed and is translationally movable. The gripper body 10 houses an electric motor 16. The electric motor 16 can be actuated to initiate the translational movement of at least one gripper jaw 14. In one embodiment, the electric motor 16 is of the type known as an "external rotor", i.e. with a rotor located outside the stator, which is able to provide high performance with very small / low dimensions and weight. The electric gripper 1 comprises a gear drive 18 or a transmission group 18 with gears, which is suitable for transmitting the movement and torque of the electric motor 16 to the at least one gripping jaw 14. In particular, the gear drive 18 is suitable for reducing the speed and increasing the torque between the electric motor 16 and the at least one gripping jaw 14. In one embodiment, the electric gripper 1 is further equipped with an electric brake 20 which can be actuated to cause the blocking of at least one gripping jaw 14. In one embodiment, the electric motor 16 has a motor shaft 162 which is provided with a motor gear 164. The electric brake 20 has a brake shaft 202 which is provided with a brake gear 204. The brake gear 204 is coupled to the motor gear 164. According to one aspect of the invention, the electric brake 20 is connected in series between the electric motor 16 and the gearbox 18. This technical solution ensures the highest possible precision in holding the gripping jaws 12, and consequently the workpiece, in the predetermined position when the electric brake is applied. In fact, when the workpiece is gripped, the electric motor 16 applies a torque via the contact between the teeth of the corresponding motor gear 164 and the teeth of the gear drives downstream in the transmission chain, which in this case include the teeth of the brake gear 204. The moment the electric brake 20 is applied and the power supply to the electric motor 16 is interrupted, the brake gear 204 remains locked in its position, maintaining the torque and eliminating backlash. If, however, the electric brake 20 were not connected in series between the electric motor 16 and the gearbox 18, for example, if it were connected in parallel with the electric motor 16 with respect to the gearbox 18, the electric motor, when the workpiece is in the handle, would apply a torque via the contact between the teeth of the motor gear 164 and the teeth of the gear drives of the gearbox 18 without the involvement of the brake gear 204. Therefore, the backlash between the motor gear 164 and the gear drives of the gearbox 18 would be eliminated, but the brake gear 204 could still move freely within the limits of the backlash between the teeth.The moment the electric brake is applied and the motor's power supply is interrupted, the brake gear would remain locked in its current position. However, it would not allow the backlash to be eliminated because the teeth of the brake gear could rebound from the initial torque, causing the kinematic chain to move until the teeth of the gearbox's gear drives engage with the brake gear, which is now locked by the electric brake. In this case, the precise positioning of the gripping jaws, and therefore the workpiece, could not be maintained at the moment the electric brake is applied. In one embodiment, the motor gear 164 is coupled to the brake gear 204 via a free-running connecting gear 22. It should be noted that the free-running connecting gear 22 does not contribute to the overall reduction ratio provided by the gearbox 18, but is used to create a distance between the electric motor 16 and the electric brake 20. This prevents the respective gears 164 and 204 from having large diameters, and consequently allows the subsequent gears of the gearbox 18's kinematic chain, which instead contribute to obtaining the required reduction ratio, to have smaller diameters compared to those they would have if the motor gear 164 and the brake gear 204 had large diameters. This also reduces the dimensions of the gripper body 10 and the weight of the electric gripper 1. In one embodiment, the electric brake 20 is suitable to exert a braking effect when it is not supplied with power, and to allow the rotation of the electric motor 16 and the gears of the transmission 18 when it is supplied with power. This allows the workpiece to be held in the grip in the event of a power outage, or enables the electric gripper to be used in an energy-saving mode. In fact, when the workpiece is held in the grip, the power supply to the electric motor 16 can be interrupted and the workpiece held, thus reducing power consumption. The gear drive 18 comprises a final stage 24. The final stage 24 comprises an end shaft 26, which is provided with a gripping jaw pinion 28. The gripping jaw pinion 28 engages in at least one toothed section 14' of the at least one gripping jaw 14. In the case of two parallel gripping jaws 14, the respective toothed sections are opposite each other, and the gripping jaw pinion 28 is inserted between the two gripping jaws 14 such that it engages both toothed sections 14' simultaneously and, as a result of its rotation, causes the translational movement of both gripping jaws 14 in opposite directions. Therefore, the translation direction of the at least one gripping jaw 14 is perpendicular to the axis of rotation of the end shaft 26. In one embodiment, an end-shaft rotary encoder 30 is operationally connected to one end of the end shaft 26, which is suitable for detecting the angular position of the end shaft 26. For example, the rotary encoder 30 is connected to the end of the end shaft 26 that is opposite the end facing the at least one gripping jaw 14. In one embodiment, the gripper jaw pinion 28 is designed such that it causes the at least one gripper jaw 14 to complete its entire stroke when the end shaft 26 rotates a maximum of 360°. This advantageously makes it possible to use an absolute encoder 30. In one embodiment, the motor shaft 162 and the end shaft 26 are arranged parallel and at least partially next to each other. The gear transmission 18 comprises a plurality of intermediate gear drives 32, 34, 36, 38 between the motor shaft 162 and the end shaft 26, which are suitable for transmitting the motion and torque from the motor shaft 162 to the end shaft 26. Each intermediate gear drive 32 to 38 is suitable to rotate around a respective gear drive shaft 32' to 38' which is parallel to the motor shaft 162 and to the end shaft 26. According to one aspect of the invention, the intermediate gear drives 32 to 38 are distributed side by side around the end shaft 26 in such a way that they occupy a gear drive volume which has a predominantly radial extent relative to the end shaft 26. In other words, the intermediate gear drives 32 to 38 are positioned around the end shaft 26 in such a way that the axial extent of the gearbox 18 is minimized and instead the radial or planar dimension of the electric gripper 1, that is, the dimension that lies parallel to the translation direction of the at least one gripping jaw 14, is used. In this way, when the electric gripper 1 is attached to the wrist of a robot arm, it is possible to limit the axial extension of the wrist-gripper arrangement in favor of the maneuvering dimensions for gripping the objects. In one embodiment, each intermediate gear drive 32 to 38 comprises two gear drive gears with different diameters, which are superimposed along the respective gear drive shaft. A first gear drive gear 32a to 38a with a smaller diameter engages with a second gear drive gear 32b to 38b with a larger diameter in the intermediate gear drive immediately downstream of the transmission chain of motion from the motor shaft 162 to the end shaft 26. In this way, a gradual reduction of the gear ratio between the rotational speed of the motor shaft 162 and the rotational speed of the end shaft 26 is achieved. Therefore, the intermediate gear drives 32 to 38, which extend radially around the end shaft 26, can be alternately slightly axially offset from one another, as shown in particular in Figs. 3, 4, 5 to 6. In the example shown in the drawings, the motor gear 164 engages with the free-running connecting gear 22, which in turn engages with the brake gear 204. The brake gear 204 engages with a second gear 32b (gear with a larger diameter) of a first intermediate gear drive 32. The first gear 32a (gear with a smaller diameter) of the first intermediate gear drive 32 engages with the second gear 34b of a second intermediate gear drive 34. The first gear 34a of the second intermediate gear drive 34 engages with the second gear 36b of a third intermediate gear drive 36. The first gear 36a of the third intermediate gear drive 36 engages with the second gear 38b of a fourth intermediate gear drive 38. The first wheel 38a of the fourth intermediate gear drive 38 engages with a second wheel 40 of the end shaft 26, the first wheel 28 of which forms the gripping jaw pinion. In one embodiment, the motor gear 164 is pressed directly onto the motor shaft 162. In one embodiment, the brake shaft 202 and the end shaft 26 are supported by respective bearings. In one embodiment, each gear drive shaft 32' to 38' consists of a gear drive pin that is fixedly connected to the gripper body 10. The gear drive gears 32a, 32b to 38a, 38b rotate around the corresponding gear drive pin 32' to 38' via a bushing 42, for example a flange bushing made of a plastic with a low coefficient of friction, for example a polymer material. For example, the gear drive gears are press-fitted into the respective bushings 42. Therefore, the pins allow the gears to be radially restricted, while the flange of the bushings 42, coupled to the gripper body 10, restricts the gears axially. The material of the bushings 42 reduces friction between the gears and the contact surfaces during movement (gripper body and pins), thereby increasing the performance of the gearbox 18. In one embodiment, the gripper body 18 forms an intermediate wall 182, which separates a transmission chamber 184 and an actuation chamber 186 inside the gripper body 10. The transmission chamber 184 houses the plurality of gear drives 32 to 38 and the end shaft 26. The actuation chamber 186 houses the electric motor 16 and the electric brake 20. One end of the gear drive pins 32' to 38' is supported by the partition wall 182. The opposite end of the gear drive pins is supported by an upper part of the gripper body 10. In one embodiment, the gripper body 10 is formed by the coupling of three parts: a lower part 102, which closes the actuation chamber 186 at the bottom, an intermediate part 104, which, together with the lower part 102, forms the actuation chamber 186 and is separated at the top by the intermediate wall 182, and an upper part 106, which, together with the intermediate wall 182, forms the transmission chamber 184. The three parts 102, 104, 106 of the gripper body 10 are coupled to each other, for example by means of screws, with circumferential seals in between. In one embodiment, the electric gripper 1 is provided with a main circuit board 50 on which electronic devices for controlling the electric motor 16 and the electric brake 20 are mounted. The main circuit board 50 is housed in the gripper body 10. In one embodiment, the main circuit board 50 is housed in the actuation chamber 186 and extends perpendicular to the motor shaft 162. Therefore, the main circuit board 50 also utilizes the radial, i.e., planar, extent of the electric gripper 1 to reduce the axial dimension. In one embodiment, a magnet 52 is attached to the end of the motor shaft 162 facing the main circuit board 50. A magnetic sensor is mounted on the main circuit board 50, facing the magnet 52, and is capable of detecting changes in the magnetic field during rotation of the motor shaft. The magnetic sensor, which is connected to a control unit of the electric motor 16, allows, for example, the control of the electric motor 16 using field-oriented control (FOC). In one embodiment, connectors 60 for the electrical wiring of the electric gripper 1 are provided on a side wall 108 of the gripper body 10, for example, a side wall of the intermediate part 104 of the gripper body 10. This side wall 108 internally supports a connecting circuit board 70, which extends perpendicularly to and is connected to the main circuit board 50, on which electrical and electronic devices for managing the electrical connection of the electric gripper 1 are mounted. In the embodiments of the electric gripper according to the invention, a person skilled in the art can modify, adapt, and replace elements with other, functionally equivalent elements to meet specific requirements without departing from the scope of protection of the following claims. Each of the features described as belonging to one possible embodiment can be implemented independently of the other described embodiments.

Claims

Electric gripper comprising: - a gripper body forming or supporting a gripper jaw guide; - at least one gripper jaw being translationally movable in the gripper jaw guide between a gripping position and a release position; - an electric motor housed in the gripper body and operable to cause the translational movement of the at least one gripper jaw; - a gear transmission or transmission group with gears suitable for transmitting the movement and torque of the electric motor to the at least one gripper jaw; - an electric brake operable to cause the locking of the at least one gripper jaw, the electric brake being connected in series between the electric motor and the transmission. Electric gripper according to claim 1, wherein the electric motor has a motor shaft which is provided with a motor gear, and wherein the electric brake has a brake shaft which is provided with a brake gear which is coupled to the motor gear. Electric gripper according to claim 2, wherein the motor gear is coupled to the brake gear via a free-running connecting gear. Electric gripper according to one of the preceding claims, wherein the electric brake is capable of exerting a braking effect when it is not supplied with power, and of allowing the rotation of the electric motor and the gears of the transmission when it is supplied with power. Electric gripper according to one of the preceding claims, wherein the gear drive comprises a final stage comprising an end shaft which is provided with a gripper jaw pinion which engages in at least one toothed section of the at least one gripper jaw. Electric gripper according to claim 5, wherein an end shaft rotary encoder is operationally connected to one end of the end shaft, which is suitable for detecting the angular position of the end shaft, and wherein the gripper jaw pinion is designed such that it causes the at least one gripper jaw to complete its entire stroke or travel when the end shaft rotates by a maximum of 360°, wherein the end shaft rotary encoder is an absolute rotary encoder. Electric gripper according to claim 5 or 6, wherein: - the motor shaft and the end shaft are arranged parallel and at least partially side by side, - the gear drive between the motor shaft and the end shaft comprises a plurality of intermediate gear drives suitable for transmitting the motion and torque from the motor shaft to the end shaft, - each intermediate gear drive is suitable for rotating about its own gear drive shaft which is parallel to the motor shaft and the end shaft, - the intermediate gear drives are distributed side by side around the end shaft in such a way that they occupy a gear drive volume which has a predominantly radial extent with respect to the end shaft. Electric gripper according to claim 7, wherein each intermediate gear drive comprises two gear drive gears of different diameters which overlap along the gear drive shaft, wherein the gear drive gear with the smaller diameter engages with the gear drive gear with the larger diameter of the intermediate gear drive immediately downstream along the transmission chain of the motion from the motor shaft to the end shaft. Electric gripper according to claim 7 or 8, wherein each gear drive shaft consists of a gear drive pin which is fixedly connected to the gripper body, and wherein the gear drive gears rotate about the respective pin via an interposed bushing which is made of a plastic with a low coefficient of friction. Electric gripper according to claim 9, wherein the gripper body forms an intermediate wall which separates or defines inside the gripper body a transmission chamber in which the plurality of gear drives and the end shaft are housed and an actuation chamber in which the electric motor and the electric brake are housed, wherein one end of the gear drive pins is supported by the intermediate wall. Electric gripper according to one of the preceding claims, comprising a printed circuit board on which electronic devices for controlling or regulating the electric motor and the electric brake are mounted, wherein the printed circuit board is housed in the gripper body. Electric gripper according to claims 10 and 11, wherein the circuit board is housed in the actuation chamber and extends perpendicular to the motor shaft. Electric gripper according to claim 12, wherein a magnet is attached to the end of the motor shaft facing the circuit board, and a magnetic sensor is mounted on the circuit board, which is facing the magnet and is suitable for detecting the change in the magnetic field during the rotation of the motor shaft.

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