A three-finger underactuated gripper with variable finger length

Abstract

The present application relates to the technical field of mechanical gripper hand, and particularly relates to a three-finger underactuated gripper with variable finger length, comprising a driving motor, a transmission mechanism and three three-degree-of-freedom fingers, wherein the transmission mechanism comprises a gear set and three sliding assemblies connected with the gear set, one single finger on one side of the three three-degree-of-freedom fingers is arranged opposite to two fingers on the other side and is connected with the three sliding assemblies respectively, the structure of each finger is the same, and the proximal interphalangeal joint and the middle interphalangeal joint are composed of a parallel four-bar linkage mechanism, meanwhile, the proximal interphalangeal joint and the middle interphalangeal joint are internally provided with a telescopic assembly of slider-rail structure, then the parallel gripping of the gripper and the self-adaptive telescoping of the joints can be realized through the driving of the driving motor and the transmission of the gear set, so as to adjust the contact area between the gripper and the object and realize the enveloping gripping of the gripper for objects with different sizes. The present application greatly simplifies the structure and control mode of the mechanical hand and improves the adaptability of the mechanical hand.

Description

Technical Field

[0001] This invention relates to the field of mechanical gripper technology, and more particularly to a three-finger underactuated gripper with variable finger length. Background Technology

[0002] Currently, grasping is a crucial capability for most robots in practical applications. Underactuated grippers, as actuators for grasping, have significant advantages when grasping objects with special structures, such as soft, fragile, or deformable objects. Existing underactuated manipulators are typically implemented using a linkage-driven system. While they can automatically perform grasping actions to contact objects, their rigid linkage-driven grippers lack finger-length extension capabilities. Therefore, these grippers cannot balance grasping range and contact adaptability when dealing with objects of different sizes. Small grippers, while providing good coverage, have a limited grasping range; large grippers, while capable of grasping larger objects, often have fewer contact points and poor adaptability when grasping smaller objects. The inability to adjust the grasping range also results in shortcomings in adaptability to the objects being grasped. Summary of the Invention

[0003] To address the aforementioned technical problems in existing technologies, this invention proposes a variable-length, three-finger underactuated gripper. Each finger has an identical structure, and its proximal and middle finger joints are composed of parallel four-bar linkages. Furthermore, the proximal and middle finger joints incorporate telescopic components with a slider-rail structure, enabling parallel gripping and adaptive extension / retraction of the joints. This adjusts the contact area between the gripper and the object, allowing for envelope gripping of objects of different sizes. The specific technical solution is as follows: A variable-length, three-finger underactuated gripper includes: a finger base, on which a drive motor, a transmission mechanism, and three three-degree-of-freedom fingers are mounted. The transmission mechanism includes a gear set and three sliding components meshing with it. A single finger on one side of the three three-degree-of-freedom fingers is offset from two fingers on the other side. Each finger has the same structure, including: a proximal joint, a middle joint, a distal joint, a main drive link, and an upper link. The proximal joint, middle joint, and distal joint are sequentially and movably connected. The upper end of the main drive link is movably connected to the lower end of the upper link. The lower end of the drive linkage meshes with a gear set, and the upper end of the upper linkage is connected to the movable connection between the middle finger joint and the distal finger joint. The proximal finger joint and the middle finger joint are respectively provided with a proximal finger telescopic component and a middle finger telescopic component, which are superimposed and connected. The proximal finger telescopic component is movably connected to the base slider in the sliding component. The drive motor drives the base slider of the sliding component to move while rotating the main drive linkage through the gear set, thereby driving the proximal finger telescopic component and the middle finger telescopic component to extend and retract, thereby driving the three three-degree-of-freedom fingers on both sides to flex and move horizontally to perform a grasping operation.

[0004] Furthermore, the distal interphalangeal joint includes: a fingertip link, and a distal interphalangeal joint slider is connected to the front of the fingertip link via a compression spring, the distal interphalangeal joint slider being slidably disposed under the constraint of the compression spring.

[0005] Furthermore, the proximal finger joint is also provided with an outer lower connecting rod and a relay connecting rod. The upper end of the outer lower connecting rod is movably connected to the outer end of the relay connecting rod, and the lower end of the outer lower connecting rod is movably connected to the lower end of the main drive connecting rod. The proximal finger telescopic assembly includes: a proximal finger joint telescopic connecting rod, a proximal finger joint slider, a proximal finger joint slide rail, and a proximal finger end tension spring. The lower end of the proximal finger joint telescopic connecting rod is movably connected to the base slider, and the upper end of the proximal finger joint telescopic connecting rod is movably connected to the inner end of the relay connecting rod. The proximal finger joint telescopic connecting rod has a two-section structure, with one section installed and connected to the proximal finger joint slider and the other section installed and connected to the proximal finger joint slide rail. The proximal finger end tension spring is installed on both sides of the proximal finger joint slide rail to constrain the proximal finger joint telescopic connecting rod.

[0006] Furthermore, the middle finger joint is also provided with an outer upper connecting rod. The middle finger telescopic component includes: a middle finger joint telescopic connecting rod, a middle finger joint slider, a middle finger joint slide rail, and a corresponding middle finger end tension spring. The upper end of the middle finger joint telescopic connecting rod and the upper end of the outer upper connecting rod are movably connected to the rear end of the fingertip connecting rod. The lower end of the middle finger joint telescopic connecting rod is movably connected to the inner end of the relay connecting rod, and the lower end of the outer upper connecting rod is movably connected to the outer end of the relay connecting rod.

[0007] Furthermore, all the movable connections are made by means of pins, and bearings are installed at the pin mating points.

[0008] Furthermore, the sliding assembly also includes: a base slide rail that cooperates with the base slider and a slider self-locking structure located on the outer end of the base slide rail to restrict the movement of the slider.

[0009] Furthermore, a contact surface of rubber soft material is provided on the inner surface of the proximal finger joint, middle finger joint, and distal finger joint.

[0010] Furthermore, a worm gear is connected to the output shaft of the drive motor. The worm gear meshes with a gear set, which drives the gear corresponding to a single finger on one side to rotate in reverse, and the gear corresponding to two fingers on the other side to rotate in forward.

[0011] Beneficial effects: The gripper of this invention can perform opposing grasping by driving three three-degree-of-freedom underactuated mechanical fingers with only one drive motor. It can switch between different modes according to the shape of the object, and freely switch between parallel fingertip grasping and covering grasping. Each joint of the fingers has a telescopic function, which can change the contact area of ​​the gripper by extending and retracting the joints. Each finger is composed of three joints and two parallelogram linkage mechanisms. Compared with traditional mechanical hands with switchable grasping modes, this gripper can achieve adaptive grasping and has the characteristics of underactuation and variable contact surface, resulting in superior grasping performance. Attached Figure Description

[0012] Figure 1 This is a front view of the assembly in the gripper's gripping state according to the present invention; Figure 2 This is an isometric view of the assembly in the grasping state of the gripper of the present invention; Figure 3 This is a front view of the assembly in the parallel gripping state of the gripper of the present invention; Figure 4 This is an isometric view of the assembly in the parallel gripping state of the gripper of the present invention; Figure 5 This is a front view of the assembly in the gripping state of the gripper of the present invention; Figure 6 This is an isometric view of the assembly in the gripping state of the gripper of the present invention; Figure 7 yes Figure 5 Side view; In the diagram, 1 is the second distal interphalangeal joint slider, 2 is the second fingertip connecting rod, 3 is the second outer connecting rod, 4 is the upper connecting rod of the second distal interphalangeal joint, 5 is the second middle interphalangeal joint slider, 6 is the second middle interphalangeal joint slide rail, 7 is the second middle interphalangeal joint telescopic connecting rod, 8 is the second relay connecting rod, 9 is the second proximal interphalangeal joint telescopic connecting rod, 10 is the second proximal interphalangeal joint slide rail, 11 is the second proximal interphalangeal joint slider, 12 is the second main drive connecting rod, 13 is the right base slider, 14 is the slider self-locking structure, 15 is the right base slide rail, and 16 is the gear. Group 17 is the drive motor, 18 is the left base slide rail, 19 is the left base slider, 20 is the first main drive link, 21 is the first proximal finger joint slider, 22 is the first proximal finger joint slide rail, 23 is the first proximal finger joint telescopic link, 24 is the first relay link, 25 is the first middle finger joint telescopic link, 26 is the first middle finger joint slide rail, 27 is the first middle finger joint slider, 28 is the first distal finger joint upper side link, 29 is the first outer side link, 30 is the first fingertip link, and 31 is the first distal finger joint slider. Detailed Implementation

[0013] To make the objectives, technical solutions, and technical effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0014] like Figures 1 to 7 As shown in this embodiment, a variable-length, three-finger underactuated gripper includes: a finger base, on which a drive motor 17, a transmission mechanism, and three three-degree-of-freedom fingers are mounted. The drive motor 17 performs parallel gripping and enveloping gripping operations on the three three-degree-of-freedom fingers through the transmission mechanism. A single finger on one side of the three three-degree-of-freedom fingers is staggered and positioned between two fingers on the other side. The transmission mechanism includes a gear set 16 and three sliding components. Each sliding component includes: a cooperating base slider and a base slide rail, and a slider self-locking structure 14 (mechanical stop) located on the outer end of the base slide rail to restrict the movement of the slider. The base slider is connected to the gear set 16 via gear meshing. The gear set 16 is also directly meshed and driven by the three-degree-of-freedom fingers. The drive motor 17, through the gear set 16, can drive the three three-degree-of-freedom fingers on both sides to perform flexion and horizontal movement.

[0015] The three three-degree-of-freedom fingers have the same structure, and each finger includes: a proximal interphalangeal joint, a middle interphalangeal joint, a distal interphalangeal joint, a main drive link, and an upper side link.

[0016] The distal interphalangeal joint includes a fingertip link, with a distal interphalangeal joint slider and a compression spring at the front of the fingertip link. The distal interphalangeal joint slider can slide under the constraint of the compression spring and has a telescopic function. This function is mainly for grasping thin objects and does not participate in the covering grasping. In the actual grasping of thin objects, this telescopic joint ensures that the fingertip is always in close contact with the object's placement surface, making it easy to scoop up thin objects from the placement surface and perform various grasping operations, making the grasping method more diverse and effective.

[0017] The main drive link and the upper link are movably connected, wherein the lower end of the main drive link is meshed with the gear set 16, and the upper end of the upper link is movably connected with the fingertip link.

[0018] The proximal finger joint includes: a proximal finger telescopic component, an outer lower connecting rod, and a relay connecting rod 8. The upper end of the outer lower connecting rod is movably connected to the outer end of the relay connecting rod 8, and the lower end of the outer lower connecting rod is coaxially rotatably connected to the bottom end of the main drive connecting rod. The proximal finger telescopic component includes: a proximal finger joint telescopic connecting rod, a proximal finger joint slider, a proximal finger joint slide rail, and a tension spring. The lower end of the proximal finger joint telescopic connecting rod is movably connected to the base slider, and the upper end of the proximal finger joint telescopic connecting rod is movably connected to the inner end of the relay connecting rod 8. A portion of the proximal finger joint telescopic connecting rod is connected to the proximal finger joint slider, and another portion is connected to the proximal finger joint slide rail. These two portions are combined and constrained by the tension spring. When no external force is applied, the tension spring is in an unstretched state, and the proximal finger telescopic component is at its original length. When the proximal finger telescopic component is subjected to force, the tension spring gradually stretches as the proximal finger telescopic component is compressed, achieving a variable finger length effect. Specifically, two tension springs are symmetrically installed on both sides of the proximal finger joint slide rail to ensure that the resultant force is always along the guide rail direction and the resultant torque is zero, thus ensuring that the proximal finger joint slider can move smoothly. It is worth noting that the tension springs on both sides of each finger joint are configured completely independently to give full play to the underactuated characteristics. This design can further reduce gripping resistance and improve gripping effect.

[0019] The middle finger joint and the proximal finger joint share a relay link 8. The middle finger joint also includes a middle finger telescopic component and an outer upper link. The structure of the middle finger telescopic component is the same as that of the proximal finger telescopic component, including a middle finger joint telescopic link, a middle finger joint slider, a middle finger joint slide rail, and a tension spring. The upper ends of the middle finger joint telescopic link and the outer upper link are movably connected to the rear end of the fingertip link. The lower end of the middle finger joint telescopic link is movably connected to the inner end of the relay link 8, and the lower end of the outer upper link is movably connected to the outer end of the relay link 8.

[0020] The above-mentioned linkage and telescopic component work together to form a parallel four-bar linkage mechanism. It can be seen that the connection between the proximal and middle finger joints is formed by the superposition of two parallel four-bar linkage mechanisms to achieve parallel gripping of the gripper.

[0021] To facilitate the configuration of the relative position of the fingers and the realization of the grasping function, this invention introduces tension springs and mechanical stops as constraints. The built-in telescopic components realize the adaptive extension and retraction of the finger joints, thereby adjusting the contact area between the gripper and the object. This enables the gripper to cover and grasp objects of different sizes, and has the characteristics of variable contact surface, thus improving the gripping adaptability.

[0022] Each joint of the aforementioned linkage is connected by a pin, and a bearing is installed at the pin mating point.

[0023] Furthermore, rubber soft material is installed on the inner surface of the proximal, middle, and distal interphalangeal joints, i.e., the middle and tip of the fingers, which increases the surface friction coefficient and allows for gripping operations of different intensities based on force feedback, making the overall gripping more flexible.

[0024] A worm gear is connected to the output shaft of the drive motor 17. The worm gear meshes with the gear set 16. The drive motor 17 drives the gear set 16 through the worm gear to drive the gear corresponding to a single finger on one side to rotate in reverse, and the gear corresponding to two fingers on the other side to rotate in forward. The gears drive the main drive linkage, which drives the three fingers to grasp in opposite directions through the finger joints formed by the superimposed parallelogram linkage mechanism. The worm gear structure itself has a self-locking function, which allows the gripper to hold when it moves to a specific position, increasing the reliability of the gripping while reducing energy consumption.

[0025] The present invention uses retractable links and mechanical stops to constrain the fingers, allowing the force on the fingertips to be transmitted to a parallel four-bar linkage for parallel gripping. When a wrapping grip is to be performed, the length of the retractable links changes, the shape of the parallel four-bar linkage changes, and the underactuated structure can fully utilize its gripping characteristics to achieve a stable wrapping gripping effect.

[0026] More specifically, in Figure 1 and Figure 2 The crawling mode shown and in Figure 3 and Figure 4 In the parallel gripping mode shown, the first active link 12 and the second active link 20 are in their initial positions. The tension springs in the second middle finger joint slide rail 6, the second proximal finger joint slide rail 10, the first proximal finger joint slide rail 22, and the first middle finger joint slide rail 26 are in a taut state. The second middle finger joint telescopic link 7, the second proximal finger joint telescopic link 9, the first proximal finger joint telescopic link 23, and the first middle finger joint telescopic link 25 are kept coupled by the tension springs. At this time, the visible gripper has only one degree of freedom. The proximal finger joint is composed of a parallel four-bar linkage formed by the second outer link 3, the second relay link 8, and the second proximal finger joint telescopic link 9. Therefore, the middle finger joint and the distal finger joint always remain parallel, which ensures that the gripper is in the parallel gripping mode before it touches the obstacle.

[0027] Slide rails are installed on both sides of the finger base, which, when mounted on the slider, enable the overall translation of the finger. Figure 3 and Figure 4In the parallel gripping mode shown, the drive motor 17 drives the worm gear, outputting torque to the gear set 16. The output of the drive motor 17 is evenly distributed through the meshing of the gear set 16 and rack. The gear set 16 meshes with the right base slider 13 and the left base slider 19 via gears, ultimately achieving horizontal movement on the right base slide rail 15 and the left base slide rail 18, thus driving the entire finger reconfiguration process. Tension springs are installed on the right base slide rail 15 and the left base slide rail 18 for constraint. It is worth noting that when the right base slider 13 moves to its rightmost position, the gripper reaches its maximum opening range, and its movement is restricted by the installed slider self-locking structure 14, ensuring stability before parallel gripping.

[0028] exist Figure 5 and Figure 6 In the enveloping grasping mode shown, after the second distal joint slider 31 and the first distal joint slider 1 contact the object, the second middle finger joint telescopic link 7, the second proximal finger joint telescopic link 9, the first proximal finger joint telescopic link 23, and the first middle finger joint telescopic link 25 are forced to change length, releasing the parallel motion state. At the same time, the first main drive link 20 and the second main drive link 12 are pushed inward and bent, and the gripper enters the enveloping grasping mode. At this time, the second middle finger joint slide rail 6 and the first middle finger joint slide rail 26 are still constrained by the tension spring, and the parallel four-bar linkage composed of the second fingertip link 2, the second outer link 3, the second middle finger joint telescopic link 7, and the second relay link 8 is still in a fixed state. Therefore, the middle finger joint and the distal finger joint remain collinear. Subsequently, when the object contacts the second middle finger joint telescopic link 7 and the first middle finger joint telescopic link 25, the object will first be pushed downwards. When the object can no longer move downwards, the second middle finger joint telescopic link 7 and the first middle finger joint telescopic link 25 are forced to be compressed. The first middle finger joint slider 27, the first middle finger joint slide rail 26, the second middle finger joint slider 5, and the second middle finger joint slide rail 6 slide and press against each other. The middle finger joint bends inwards, and finally the object will contact the first proximal finger joint telescopic link 23 and the second proximal finger joint telescopic link 9, and pressure will be generated. Finally, the gripper can achieve a large-scale flexion. The six links of the first proximal finger joint telescopic link 23, the second proximal finger joint telescopic link 9, the second middle finger joint telescopic link 7, the first middle finger joint telescopic link 25, the second distal finger joint slider 1, and the first distal finger joint slider 31 will fully cover and grasp the object, ensuring the stability of the covering and grasping of slender objects. Throughout the process, the fingers on both sides move synchronously and mirror-like under the drive of gear set 16 and drive motor 17, providing conditions for parallel grasping of two fingers and underactuated enveloping grasping.

[0029] In addition, the first distal phalanx slider 31 and the second distal phalanx slider 1 can slide under the constraint of the compression spring and have a telescopic function. The slider can ensure that the fingertip is always in close contact with the object placement surface when grasping thin objects, thereby obtaining a better grasping effect.

[0030] In summary, this invention utilizes a design based on two superimposed parallel four-bar linkages to achieve a retractable finger joint. Compared to ordinary underactuated rigid linkage manipulators, driven by a single motor, the finger can be reconstructed through retractable linkages, making it more adaptable to different grasped objects. While possessing a simple mechanical structure, compared to other multi-link manipulators, the design based on two parallel four-bar linkages allows for convenient automatic switching between parallel and enveloping grasping modes. In parallel grasping mode, high-precision grasping operations can be performed, while in enveloping mode, stable grasping of heavy, irregularly shaped objects can be achieved. Ultimately, it enables multi-modal grasping and is capable of handling various grasping tasks.

[0031] This invention fills the gap in underactuated manipulators with multiple gripping modes under simple mechanical structures, and in particular, proposes an adaptive gripping manipulator with variable contact surface and extendable finger length.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Although the implementation process of the present invention has been described in detail above, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A three-finger underactuated gripper with variable finger length, comprising: A finger base, on which a drive motor (17), a transmission mechanism, and three three-degree-of-freedom fingers are mounted, characterized in that: the transmission mechanism includes a gear set (16) and three sliding components meshing with it; one finger on one side of the three three-degree-of-freedom fingers is staggered and facing the other two fingers; each finger has the same structure, including: a proximal joint, a middle joint, a distal joint, a main drive link, and an upper link; the proximal joint, the middle joint, and the distal joint are sequentially and movably connected; the upper end of the main drive link is movably connected to the lower end of the upper link; and the lower end of the main drive link is connected to the gear set (16). The wheel assembly (16) is meshed and connected, and the upper end of the upper connecting rod is connected to the movable connection of the middle finger joint and the distal finger joint; the proximal finger joint and the middle finger joint are respectively provided with a proximal finger telescopic component and a middle finger telescopic component, and the two are superimposed and connected, wherein the proximal finger telescopic component is movably connected to the base slider in the sliding component; the drive motor (17) is driven by the gear set (16) to move the base slider of the sliding component while rotating the main drive connecting rod, thereby driving the proximal finger telescopic component and the middle finger telescopic component to extend and retract, thereby driving the three three-degree-of-freedom fingers on both sides to flex and move horizontally to perform the grasping operation; The proximal finger joint is also provided with an outer lower connecting rod and a relay connecting rod (8). The upper end of the outer lower connecting rod is movably connected to the outer end of the relay connecting rod (8), and the lower end of the outer lower connecting rod is movably connected to the lower end of the main drive connecting rod. The proximal finger telescopic assembly includes: a proximal finger joint telescopic connecting rod, a proximal finger joint slider, a proximal finger joint slide rail, and a proximal finger end tension spring. The lower end of the proximal finger joint telescopic connecting rod is movably connected to the base slider, and the upper end of the proximal finger joint telescopic connecting rod is movably connected to the inner end of the relay connecting rod (8). The proximal finger joint telescopic connecting rod is a two-section structure. One section is installed and connected to the proximal finger joint slider, and the other section is installed and connected to the proximal finger joint slide rail. The proximal finger end tension spring is installed and configured on both sides of the proximal finger joint slide rail to constrain the proximal finger joint telescopic connecting rod.

2. A three-finger underactuated gripper with variable finger length as described in claim 1, characterized in that, The distal interphalangeal joint includes: a fingertip link, and a distal interphalangeal joint slider connected to the front of the fingertip link via a compression spring, the distal interphalangeal joint slider being slidably configured under the constraint of the compression spring.

3. A three-finger underactuated gripper with variable finger length as described in claim 2, characterized in that, The middle finger joint is also provided with an outer upper connecting rod. The middle finger telescopic component includes: a middle finger joint telescopic connecting rod, a middle finger joint slider, a middle finger joint slide rail and a corresponding middle finger end tension spring. The upper end of the middle finger joint telescopic connecting rod and the upper end of the outer upper connecting rod are movably connected to the rear end of the fingertip connecting rod. The lower end of the middle finger joint telescopic connecting rod is movably connected to the inner end of the relay connecting rod (8). The lower end of the outer upper connecting rod is movably connected to the outer end of the relay connecting rod (8).

4. A three-finger underactuated gripper with variable finger length as described in claim 1, characterized in that, All the movable connections are made by means of pins, and bearings are installed at the pin mating points.

5. A three-finger underactuated gripper with variable finger length as described in claim 1, characterized in that, The sliding assembly further includes: a base slide rail that cooperates with the base slider and a slider self-locking structure (14) located on the outer end of the base slide rail to restrict the movement of the slider.

6. A three-finger underactuated gripper with variable finger length as described in claim 1, characterized in that, A rubber soft material contact surface is provided on the inner surface of the proximal finger joint, middle finger joint, and distal finger joint.

7. A three-finger underactuated gripper with variable finger length as described in claim 1, characterized in that, The output shaft of the drive motor (17) is connected to a worm gear, which meshes with a gear set (16). The gear set (16) drives the gear corresponding to a single finger on one side to rotate in reverse, and the gear corresponding to two fingers on the other side to rotate in forward.

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