An adaptive underactuated robot gripper with integrated tactile sensing and its control method

Abstract

This invention discloses an adaptive underactuated robot gripper with integrated tactile sensing and its control method. The gripper comprises a gripper housing, a drive module, finger modules, and a control system. The drive module includes a servo motor, a slider, and a linkage group. The linkage group includes a proximal finger link, a distal finger link, and a drive link. Two sets of finger modules are configured, each corresponding to a link group. Each finger module includes a first finger and a second finger. The control system includes a control unit, a rotary encoder, and an array of tactile sensors. This invention's adaptive underactuated robot gripper employs an adaptive linkage structure and incorporates an array of tactile sensors, a safety latching structure, and a torque detection mechanism based on motor feedback, providing excellent gripping adaptability and contact force detection capabilities.

Description

Technical Field

[0001] This invention relates to the field of robot end effector technology, and more specifically to an adaptive underactuated robot gripper with integrated tactile sensing. Background Technology

[0002] Robot grippers are important end effectors for robots to perform grasping tasks. Existing industrial robot grippers typically adopt a parallel gripping structure. This type of gripper is simple in structure, highly stable, and low in manufacturing cost. However, it is usually specially designed for specific workpieces, with limited structural freedom and poor adaptability to objects of different shapes and sizes.

[0003] Adaptive underactuated grippers can adaptively switch gripping modes based on the geometry of the target object, achieving parallel gripping or envelope gripping, thereby improving gripping adaptability. However, existing adaptive grippers generally lack the ability to accurately sense gripping force. When grippers grasp fragile objects or in scenarios requiring precise force control, relying solely on motor current or position feedback is insufficient to accurately control the contact force, easily causing damage to the object or unreliable gripping.

[0004] In addition, most existing gripper safety protection mechanisms are based on motor current limitations, resulting in large response delays and an inability to accurately reflect the actual contact state between the fingertips and the object. This makes it difficult to provide timely and reliable safety protection in the event of sudden changes or abnormalities in gripping force.

[0005] Therefore, a robotic gripper is needed that simultaneously possesses adaptive grasping capabilities, precise tactile perception, and real-time safety protection. Summary of the Invention

[0006] In view of this, the present invention provides, on the one hand, an adaptive underactuated robot gripper with integrated tactile perception. The gripper adopts an adaptive linkage structure and is equipped with an array of tactile sensors and a safety latching structure, which has good grasping adaptation capability and contact force detection capability. On the other hand, the present invention provides a corresponding control method for the gripper, which realizes safety protection based on pressure threshold through matching control logic, and can solve the problems of large sensing blind spots, slow protection response and low integration of existing similar products.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An adaptive underactuated robotic gripper with integrated tactile sensing, comprising:

[0009] The gripper housing has a mounting cavity inside, and the mounting cavity has assembly openings on both sides at its upper end.

[0010] The drive module includes a servo motor, a slider, and a linkage assembly. The servo motor is fixedly installed in the lower part of the mounting cavity. The slider is slidably disposed at the output end of the servo motor. There are two linkage assemblies, symmetrically arranged on opposite sides of the slider. Each linkage assembly includes a proximal link, a distal link, and a drive link. The distal link passes through the assembly opening and is rotatably connected to the gripper housing. The two ends of the distal link are respectively hinged to the lower end of the proximal link and the upper end of the drive link. The lower end of the drive link is hinged to the side wall of the slider. An elastic damping element is provided at the hinge point between the proximal link and the distal link.

[0011] The finger module consists of two sets, each corresponding to a link group. Each finger module includes a first finger rod and a second finger rod. The lower end of the second finger rod is hinged to the upper end of the proximal finger link. The upper claw surface of the second finger rod is provided with an elastic sleeve. One end of the first finger rod is rotatably mounted in the top of the mounting cavity. The other end of the first finger rod is hinged to the lower end of the second finger rod. The first finger rod, the second finger rod, and the proximal finger link are arranged radially with the lower end of the first finger rod as the center.

[0012] The system includes a control unit, a rotary encoder, and an array of tactile sensors. The array of tactile sensors is fixed to the gripper surface at the upper end of the second finger and covered by an elastic sleeve. The rotary encoder is sleeved at the connection between the distal finger link and the gripper housing and rotates synchronously with the distal finger link. The rotary encoder and the array of tactile sensors are both electrically connected to the control unit.

[0013] To better implement the above technical solution, optionally, the distal link includes a front connecting plate, a rear connecting plate, and a link spacing support. The front and rear connecting plates are both arc-shaped structures and are arranged in parallel opposite directions. The link spacing support is fixedly located between the middle sections of the front and rear connecting plates. One end of the front and rear connecting plates is hinged to the lower end of the proximal link through a first connecting shaft, and the other end of the front and rear connecting plates is hinged to the upper end of the drive link through a second connecting shaft.

[0014] Optionally, the opposite sidewalls of the front and rear connecting plates are coaxially fixed with rotating bosses located between the upper ends of the connecting rod spacing strut and the drive connecting rod. The two rotating bosses can rotatably pass through the front and rear sidewalls of the gripper housing. The rotary encoder is an absolute magnetic encoder, which is located on the outside of the gripper housing and fixedly connected to the outer end of any rotating boss. The rotary encoder is connected to the control unit through an SPI bus interface and is used to measure the absolute rotation angle of the distal connecting rod.

[0015] Optionally, the elastic damping element includes a pair of front torsion springs and rear torsion springs. The front connecting plate and the rear connecting plate each have a first groove on their opposite sidewalls. The two opposite sidewalls of the proximal connecting rod each have a second groove. The front torsion spring and the rear torsion spring are both sleeved on the outer periphery of the first connecting shaft. The front torsion spring is housed in the first groove of the front connecting plate and the second groove on one side of the proximal connecting rod. The rear torsion spring is housed in the first groove of the rear connecting plate and the second groove on the other side of the proximal connecting rod. The legs of the front torsion spring and the rear torsion spring abut against the inner sidewalls of the corresponding first groove and second groove, respectively.

[0016] Optionally, the first finger includes a first front finger, a first rear finger, and a finger spacing support. The finger spacing support is fixedly disposed between the middle sections of the first front finger and the first rear finger. One end of the first front finger and the first rear finger are hinged to the lower end of the second finger through a third connecting shaft, and the other end of the first front finger and the first rear finger are hinged to the opposite sidewall of the gripper housing through a fourth connecting shaft.

[0017] Optionally, the servo motor is a direct-drive servo motor, which communicates with the control unit via an industrial bus and supports torque control mode, position control mode, speed control mode, and force-position hybrid control mode.

[0018] Optionally, the control system further includes a communication interface, which includes a Modbus RTU serial communication interface and a CAN bus interface. The Modbus RTU serial communication interface is used to communicate with a host computer or an external controller, and the CAN bus interface is used to communicate with a servo motor.

[0019] Optionally, the widths of the second finger rods in the two sets of finger modules are different. The gripping surface of the wider second finger rod is attached with three sets of arrayed tactile sensors, while the gripping surface of the narrower second finger rod is attached with one set of arrayed tactile sensors. Each set of arrayed tactile sensors includes 32 pressure-sensitive units. The arrayed tactile sensors of the wider and narrower second finger rods are respectively connected to the control unit through independent SPI bus interfaces.

[0020] A control method for an adaptive underactuated robot gripper with integrated tactile sensing.

[0021] The control unit carries and runs a real-time operating system, and performs five control tasks in parallel:

[0022] Motor control task: According to the set cycle, send control frames to the servo motor through the CAN bus based on the target position command, and receive feedback data from the servo motor;

[0023] Rotary encoder reading task: According to the set cycle, read the absolute angle data output by the rotary encoder through the SPI bus, calculate the difference between the real-time angle value and the pre-stored mechanical zero point, normalize it to the effective range, and calculate the opening and closing position of the finger. At the same time, use the absolute angle data as the position reference of the servo motor.

[0024] Tactile sensing task: According to a set period, the sampling data of all sensing units of the array-type tactile sensor are collected via the SPI bus, and the following signal processing steps are executed sequentially:

[0025] S1: Calibration phase: During the initial power-on phase, multiple frames of data are collected and averaged to serve as the baseline value for each sensing unit;

[0026] S2: Difference Calculation: Calculate the difference between the real-time acquired raw value and the baseline value, and clamp negative values ​​to zero;

[0027] S3: Digital filtering: Perform a first-order IIR low-pass filter on the difference obtained from the calculation to filter out high-frequency interference noise in the signal;

[0028] S4: Feature extraction: Calculate the total pressure of all sensing units, the maximum pressure value, the contact area, and the location of the maximum pressure;

[0029] Torque detection task: Read the torque value fed back by the servo motor according to the set cycle, and execute the feedback acquisition, filtering and zero bias compensation, friction compensation, threshold judgment and clamping and holding steps in sequence; when the estimated value of external contact torque reaches the clamping and holding threshold and continues for the preset control cycle, record the current motor position as the holding position, set the target speed and feedforward torque to zero, so that the gripper stops closing and maintains the current clamping state;

[0030] The safety protection task compares the feature values ​​extracted from the tactile perception task with the preset safety threshold. When the total pressure or peak pressure exceeds the corresponding safety threshold, the safety latch is triggered, and the servo motor is immediately controlled to stop outputting drive torque, limiting the gripper from continuing to perform clamping action.

[0031] Optionally, the release process of the safety latch flag is as follows: the host computer sends an unlock command to the control unit. After receiving the unlock command, the control unit enters a pressure relief waiting state. In this state, only the servo motor is allowed to perform the release action, and the running speed is not greater than the preset safety speed threshold. At the same time, the servo motor is prohibited from performing the clamping action to release the residual contact pressure of the gripper. When the total pressure and peak pressure are detected to drop below their respective preset release thresholds, and this state is maintained for a preset number of sampling frames, the safety latch flag is cleared, and the full stroke motion control authority of the servo motor is restored.

[0032] The beneficial effects of this invention are:

[0033] The adaptive underactuated robot gripper with integrated tactile sensing of the present invention integrates an array of tactile sensors, which can sense the contact pressure distribution of 128 units in real time, providing rich tactile information for precise force control gripping.

[0034] The adaptive underactuated robot gripper with integrated tactile sensing of the present invention has an adaptive grasping function and can adaptively switch between parallel grasping and envelope grasping modes according to the geometry and size of the target object, and has a wide range of applications.

[0035] The adaptive underactuated robot gripper with integrated tactile sensing of the present invention adopts a safety latching protection mechanism based on pressure threshold. When the tactile sensor detects that the contact force exceeds the limit, the motor is immediately locked and stopped, providing direct protection from the tactile sensing end. It has a fast response speed and high reliability.

[0036] The adaptive underactuated robot gripper with integrated tactile perception of the present invention adopts a torque detection mechanism based on motor feedback to estimate the external contact torque and lock the current position after reaching the gripping and holding threshold. It can achieve clamping stop and stable holding before the tactile safety protection is triggered, thereby improving the smoothness and reliability of gripping control.

[0037] The adaptive underactuated robot gripper with integrated tactile perception of the present invention adopts an underactuated method and uses a single servo motor to realize the adaptive gripping function of the gripper. It has a compact structure and light weight.

[0038] The adaptive underactuated robot gripper with integrated tactile sensing of the present invention supports Modbus RTU and CAN bus communication and can be easily integrated into various robot control systems. Attached Figure Description

[0039] Figure 1 This is a three-dimensional structural diagram of an adaptive underactuated robot gripper with integrated tactile sensing according to an embodiment of the present invention.

[0040] Figure 2 yes Figure 1 Exploded view of the housing of the middle gripper;

[0041] Figure 3 yes Figure 1 Frontal internal structure diagram of the gripper of a mid-adaptive underactuated robot;

[0042] Figure 4 yes Figure 3 Side view;

[0043] Figure 5 yes Figure 4 Exploded view of part of the structure;

[0044] Figure 6 yes Figure 1A 3D schematic diagram of the middle finger module and the driver module;

[0045] Figure 7 This is a structural diagram of the control system according to an embodiment of the present invention;

[0046] Figure 8 This is a flowchart of the signal processing of the tactile sensor according to an embodiment of the present invention;

[0047] Figure 9 This is a flowchart illustrating the security latching protection process according to an embodiment of the present invention;

[0048] Figure 10 This is a schematic diagram of parallel grasping according to an embodiment of the present invention;

[0049] Figure 11 This is a schematic diagram of the envelope grasping method of the present invention.

[0050] Figure label.

[0051] Gripper housing 100, gripper front housing 101, gripper rear housing 102, base plate 103, aviation connector 104;

[0052] Drive module 200, servo motor 201, lead screw 202, slider 203, drive link 204, distal link 205, front connecting plate 2051, rear connecting plate 2052, link spacing support 2053, rotating boss 2054, first connecting shaft 2055, second connecting shaft 2056, first groove 2057, proximal link 206, second groove 2061, front torsion spring 2071, rear torsion spring 2072;

[0053] Finger module 300, first finger rod 301, first front finger rod 3011, first rear finger rod 3012, finger rod spacing support rod 3013, third connecting shaft 3014, fourth connecting shaft 3015, second finger rod 302, elastic sleeve 303;

[0054] Control unit 401, rotary encoder 402, array-type tactile sensor 403;

[0055] The object being held is 500. Detailed Implementation

[0056] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Identical components are indicated by the same reference numerals.

[0057] Please see Figures 1 to 11 This invention discloses an adaptive underactuated robot gripper with integrated tactile perception, comprising a gripper housing 100, a drive module 200, a finger module 300, and a control system.

[0058] like Figure 1 and Figure 2 As shown, the gripper housing 100 has a mounting cavity, and the upper end of the mounting cavity has assembly openings on both sides. Specifically, the gripper housing 100 includes a front housing 101, a rear housing 102, and a base plate 103. The front housing 101, the rear housing 102, and the base plate 103 are connected by multiple bolts. The front housing 101 and the rear housing 102 each include an upper housing and a lower housing, which are also connected by multiple bolts to facilitate the assembly of the drive module 200. The bottom of the gripper housing 100 is provided with an aviation plug 104, which is used to connect external devices to provide power and communication.

[0059] like Figures 3-6 As shown, the drive module 200 includes a servo motor 201, a slider 203, and a linkage assembly. The servo motor 201 is fixedly installed in the lower part of the mounting cavity, and the slider 203 is slidably disposed at the output end of the servo motor 201.

[0060] In this embodiment, the servo motor 201 is an integrated servo geared motor, such as model DM-J4310-2EC, with a rated voltage of 24~48V, a rated current of 2.5A, a peak current of 7.5A, a rated torque of 3N·m, a peak torque of 7N·m, a maximum no-load speed of 200RPM, a built-in 10:1 planetary reducer, and 14 pole pairs. The servo motor 201 communicates with the control unit 401 via an industrial bus and supports torque control mode, position control mode, speed control mode, and force-position hybrid control mode.

[0061] In this embodiment, the drive module 200 further includes a lead screw 202 and a nut slider 203. The lead screw 202 is mounted on the output shaft of the servo motor 201, and the nut slider 203 is connected to the lead screw 202 via a threaded connection. The servo motor 201 drives the lead screw 202 to rotate, and the nut slider 203 moves linearly along the lead screw 202. The transmission mechanism formed by the lead screw 202 and the nut slider 203 has a self-locking function. When the servo motor 201 stops rotating or is powered off, the position of the nut slider 203 will be locked, and the gripper will maintain its current gripping state, thus achieving self-locking gripping.

[0062] like Figures 3-6 The connecting rod assembly shown consists of two sets, symmetrically arranged on opposite sides of the slider 203. Each set of connecting rods includes a proximal connecting rod 206, a distal connecting rod 205, and a drive connecting rod 204. The distal connecting rod 205 passes through the assembly opening and is rotatably connected to the gripper housing 100. The two ends of the distal connecting rod 205 are respectively hinged to the lower end of the proximal connecting rod 206 and the upper end of the drive connecting rod 204. The lower end of the drive connecting rod 204 is hinged to the side wall of the slider 203. An elastic damping element is provided at the hinge point between the proximal connecting rod 206 and the distal connecting rod 205.

[0063] like Figure 5As shown, the distal link 205 includes a front connecting plate 2051, a rear connecting plate 2052, and a link spacing support 2053. The front connecting plate 2051 and the rear connecting plate 2052 are both arc-shaped structures and are arranged in parallel opposite directions. The link spacing support 2053 is fixedly located between the middle sections of the front connecting plate 2051 and the rear connecting plate 2052. One end of the front connecting plate 2051 and the rear connecting plate 2052 is hinged to the lower end of the proximal link 206 through a first connecting shaft 2055. The other end of the front connecting plate 2051 and the rear connecting plate 2052 is hinged to the upper end of the drive link 204 of the proximal link 206 through a second connecting shaft 2056.

[0064] Specifically, the link spacing strut 2053 is connected to the front connecting plate 2051 and the rear connecting plate 2052 by two bolts spaced apart. The link spacing strut 2053 can maintain the spacing between the front connecting plate 2051 and the rear connecting plate 2052 and improve the strength of the distal link 205.

[0065] like Figure 4 and Figure 5 As shown, the front connecting plate 2051 and the rear connecting plate 2052 are coaxially fixed with rotating bosses 2054 located between the upper ends of the connecting rod spacing support 2053 and the drive connecting rod 204 on their opposite side walls. The two rotating bosses 2054 can rotatably penetrate the front and rear side walls of the gripper housing 100.

[0066] Specifically, the front connecting plate 2051 and the rear connecting plate 2052 are provided with rotating bosses 2054, and the two upper housings are provided with mounting holes that cooperate with the rotating bosses 2054. The distal connecting rod 205 rotates around the rotating bosses 2054 as the rotation center.

[0067] like Figure 1 and Figure 5 As shown, there are two sets of finger modules 300, which are arranged in a one-to-one correspondence with the connecting rod group. Each finger module 300 includes a first finger rod 301 and a second finger rod 302. The lower end of the second finger rod 302 is hinged to the upper end of the proximal finger connecting rod 206. The upper claw surface of the second finger rod 302 is provided with an elastic sleeve 303. One end of the first finger rod 301 is rotatably disposed in the top of the mounting cavity. The other end of the first finger rod 301 is hinged to the lower end of the second finger rod 302. The first finger rod 301, the second finger rod 302 and the proximal finger connecting rod 206 are arranged radially with the lower end of the first finger rod 301 as the center.

[0068] like Figure 5As shown, the first finger rod 301 includes a first front finger rod 3011, a first rear finger rod 3012, and a finger rod spacing support rod 3013. The finger rod spacing support rod 3013 is fixedly disposed between the middle sections of the first front finger rod 3011 and the first rear finger rod 3012. One end of the first front finger rod 3011 and the first rear finger rod 3012 is hinged to the lower end of the second finger rod 302 through a third connecting shaft 3014. The other end of the first front finger rod 3011 and the first rear finger rod 3012 is hinged to the opposite side wall of the housing 100 through a fourth connecting shaft 3015.

[0069] Specifically, each of the finger spacing support rods 3013 is connected to the first front finger rod 3011 and the first rear finger rod 3012 by two spaced bolts. The finger spacing support rods 3013 can maintain the spacing between the first front finger rod 3011 and the first rear finger rod 3012 and improve the strength of the first finger rod 301.

[0070] like Figure 5 As shown, the elastic damping element includes a front torsion spring 2071 and a rear torsion spring 2072 arranged in pairs. The front connecting plate 2051 and the rear connecting plate 2052 each have a first groove 2057 on their opposite sidewalls, and the proximal connecting rod 206 has a second groove 2061 on each of their opposite sidewalls. Both the front torsion spring 2071 and the rear torsion spring 2072 are sleeved on the outer periphery of the first connecting shaft 2055. The front torsion spring 2071 is housed within the first groove of the front connecting plate 2051. The rear torsion spring 2072 is housed in the first groove 2057 of the rear connecting plate 2052 and the second groove 2061 on the other side of the proximal finger link 206. The legs of the front torsion spring 2071 and the rear torsion spring 2072 respectively abut against the inner sidewalls of the corresponding first groove 2057 and second groove 2061, so that there is an elastic angle constraint between the proximal finger link 206 and the distal finger link 205.

[0071] In this embodiment, the parameters of the front torsion spring 2071 and the rear torsion spring 2072 are: wire diameter 1mm, working angle 180°, outer diameter 5mm, and effective number of coils 5.

[0072] Under normal conditions, the front torsion spring 2071 and the rear torsion spring 2072 together provide preload to maintain the initial relative angle between the distal link 205 and the proximal link 206. When the external force exceeds the preload torque provided by the front torsion spring 2071 and the rear torsion spring 2072, the rotating pair formed by the distal link 205 and the proximal link 206 deflects at an angle, achieving compliant yielding.

[0073] Specifically, the gripper housing 100, the first finger 301, the second finger 302, the distal finger link 205, and the proximal finger link 206 form a planar four-bar linkage. In the initial state, the front torsion spring 2071 and the rear torsion spring 2072 between the distal finger link 205 and the proximal finger link 206 do not deflect and remain collinear. At this time, the planar four-bar linkage is a parallelogram linkage system, and the second finger 302 maintains a parallel posture and moves to achieve parallel gripping. When the first finger 301 touches the object 500 and is blocked, the driving force continues to be transmitted to the second finger 302 through the distal finger link 205 and the proximal finger link 206. This overcomes the preload of the front torsion spring 2071 and the rear torsion spring 2072, breaks the parallelogram geometry, and transforms the four-bar system into a general four-bar system. The second finger 302 continues to rotate inward to achieve envelope gripping, giving the finger module 300 two modes: parallel gripping and envelope gripping, which can be adaptively switched according to the geometric shape characteristics of the target object.

[0074] like Figure 3 , Figure 5 as well as Figure 7 As shown, the control system includes a control unit 401, a rotary encoder 402, and an array-type tactile sensor 403. The array-type tactile sensor 403 is fixed to the gripping surface at the upper end of the second finger rod 302 and is covered by an elastic sleeve 303. The array-type tactile sensor 403 can obtain the contact pressure between the finger module 300 and the gripped object 500 in real time. The rotary encoder 402 is sleeved at the connection between the distal finger link 205 and the gripper housing 100 and rotates synchronously with the distal finger link 205. The rotary encoder 402 and the array-type tactile sensor 403 are both electrically connected to the control unit 401.

[0075] In this embodiment, the control system also includes a communication interface, which includes a Modbus RTU serial communication interface and a CAN bus interface. The Modbus RTU serial communication interface is used to communicate with a host computer or an external controller, and the CAN bus interface is used to communicate with the servo motor 201.

[0076] In this embodiment, the rotary encoder 402 is an absolute magnetic encoder. The rotary encoder 402 is located on the outside of the gripper housing 100 and is fixedly connected to the outer end of any rotating boss 2054. The rotary encoder 402 is connected to the control unit 401 through the SPI bus interface and is used to measure the absolute rotation angle of the distal link 205.

[0077] Specifically, the rotary encoder 402 is an absolute magnetic encoder with a resolution of at least 14 bits (such as an AS5048A), which reads the absolute rotation angle of the distal finger link 205 in real time at fixed intervals via the SPI bus. Since there is a definite kinematic mapping relationship between the angle of the distal finger link 205 and the finger's opening and closing position, the control unit 401 calculates the real-time opening and closing position of the finger by subtracting the absolute angle of the distal finger link 205 from a pre-calibrated mechanical zero point. The mechanical zero point is calibrated via user commands, and during calibration, the current absolute angle of the distal finger link 205 is saved to the Flash non-volatile memory of the control unit 401, which is automatically loaded upon power-on. Meanwhile, when the control unit 401 receives the CAN feedback frame from the servo motor 201 for the first time, it uses the absolute position provided by the magnetic encoder 402 as a reference to calculate the offset between the coordinates of the magnetic encoder 402 and the multi-turn coordinates inside the motor, and establishes a mapping relationship between the two coordinate systems. This solves the problem that the servo motor 201 does not have absolute position information after power-on, and realizes the accurate conversion between the target position command of the host computer and the motor control coordinates.

[0078] In this embodiment, the control system is also configured to perform torque detection. The control unit 401 obtains the torque value, current value or equivalent output torque value fed back by the servo motor 201 through the CAN bus, and estimates the external contact torque during the clamping process by combining the position and speed of the servo motor 201 and the preset friction compensation parameters. When the external contact torque reaches the preset torque clamping threshold, the control unit 401 records the current motor position and restricts the clamping to continue closing, so that the clamping enters the clamping and holding state.

[0079] like Figure 1 As shown, the widths of the second finger rods 302 in the two sets of finger modules 300 are different. The gripping surface of the wider second finger rod 302 is attached with three sets of arrayed tactile sensors 403, while the gripping surface of the narrower second finger rod 302 is attached with one set of arrayed tactile sensors 403. Each set of arrayed tactile sensors 403 includes 32 pressure-sensitive sensing units, arranged in an 8-row × 4-column matrix, for a total of 128 sensing units. The elastic protective sleeve 303 is fitted on the outside of the second finger rod 302, pressing the tactile sensors 403 tightly and protecting them from below. The contact pressure of the object 500 is evenly transmitted to the sensor array through the elastic protective sleeve 303.

[0080] The array-type tactile sensors 403 of the wider and narrower second finger 302 are connected to the control unit 401 via independent SPI bus interfaces. The three sensor arrays of the wider second finger 302 transmit a total of 194 bytes of data frames, while the one sensor array of the narrower second finger 302 transmits a total of 66 bytes of data frames. Each data frame is identified with 0xA5 as the frame header and 0x5A as the frame tail, used to verify data integrity.

[0081] In this embodiment, the maximum clamping distance of the grippers is about 90mm, the maximum clamping force is about 80N, and it can grip an object 500 weighing about 3kg. The grippers themselves weigh about 1kg, and the overall dimensions of the grippers are about 210mm in height, 130mm in width, and 70mm in thickness.

[0082] like Figure 8 As shown, the tactile sensor 403 in the adaptive underactuated robot gripper of this embodiment integrates tactile perception. According to a set cycle, it collects sampling data from all sensing units of the array-type tactile sensor 403 via the SPI bus and sequentially executes the following signal processing steps:

[0083] S1: Calibration phase: During the initial power-on phase, multiple frames of data are collected and averaged to serve as the baseline value for each sensing unit;

[0084] Specifically, after the system is powered on, it continuously collects 100 frames of data from each sensing unit in a contactless state, and calculates the average value of each unit as the baseline value to compensate for the zero drift and initial deviation of the array-type tactile sensor 403.

[0085] S2: Difference Calculation: Calculate the difference between the real-time acquired raw value and the baseline value, and clamp negative values ​​to zero;

[0086] Specifically, during normal operation, the difference between the raw value (raw) of each sensor unit acquired in real time in each frame and the corresponding baseline value (base) is obtained (d=raw-base). If the difference is negative, it is clamped to zero to eliminate noise interference.

[0087] S3: Digital filtering: Perform a first-order IIR low-pass filter on the difference obtained from the calculation to filter out high-frequency interference noise in the signal;

[0088] Specifically, the low-pass filtering formula is y[n]=y[n-1]+(d[n]-y[n-1])>>β, where β is the shift amount of the filtering coefficient. In this embodiment, β=2, corresponding to a smoothing coefficient of about 0.25. y[n] is the output smoothing value after the nth filtering, y[n-1]=the output value of the previous filtering, and d[n] is the original difference input signal acquired in the nth sampling, effectively filtering out the high-frequency noise of sensor 403.

[0089] S4: Feature extraction: Calculate the total pressure of all sensing units, the maximum pressure value, the contact area, and the location of the maximum pressure;

[0090] - Total Pressure (sum): The sum of all unit filter values, reflecting the total contact force;

[0091] -Maximum pressure value (max): The maximum filtered value among all units, reflecting the peak contact force;

[0092] -Contact area (area): The number of cells whose filter value exceeds the cell trigger threshold, reflecting the size of the contact area;

[0093] - Maximum pressure location (max_r, max_c): The row and column coordinates of the maximum pressure value, reflecting the location of the main contact point.

[0094] Please see Figure 9 The control unit 401 uses an STM32G431CBT microcontroller, based on an ARM Cortex-M4 core, with an operating frequency of 160MHz, and runs the FreeRTOS real-time operating system. The control unit 401 manages the following tasks in parallel:

[0095] (1) Motor control task: According to the set cycle, send control frames to the servo motor 201 based on the target position command, and receive feedback data from the servo motor 201.

[0096] Specifically, CAN control frames are sent to the servo motor 201 via the CAN bus at a fixed period of 2ms, and feedback data from the motor 201 is received to achieve closed-loop control of finger position and torque. The motor operates in torque control mode at startup.

[0097] 1. Tactile perception task: Collect all 128 units of the four sensor arrays 403 via the SPI bus at fixed intervals, perform calibration, filtering and feature extraction, and determine the safety threshold.

[0098] (3) Torque detection task: Read the torque value, current value or equivalent output torque value fed back by the servo motor 201 at fixed intervals, estimate the external contact torque in combination with the position, speed and friction compensation parameters of the servo motor 201, and perform contact identification and clamping and holding control according to the contact judgment torque threshold and clamping and holding torque threshold.

[0099] Specifically, the control unit 401 performs multi-stage first-order low-pass filtering on the feedback torque of the servo motor 201 and records the zero-bias torque under no-load conditions. During the gripper closing process, the control unit 401 introduces a friction compensation term based on the movement direction and speed of the servo motor 201, and subtracts the zero-bias torque and friction torque from the filtered feedback torque of the servo motor 201 to obtain an estimated external contact torque. This estimated external contact torque is used to determine whether the finger module 300 is in contact with the gripped object 500, and is used to execute a clamping stop when the gripping holding threshold is reached.

[0100] When the estimated external contact torque exceeds the contact judgment threshold, the control unit 401 determines that the gripper has entered the contact state. When the estimated external contact torque reaches the clamping and holding threshold and is maintained for a preset control cycle, the control unit 401 records the current position of the servo motor 201 as the holding position, sets the target speed and feedforward torque to zero, and restricts the gripper from continuing to move in the closing direction, so that the finger module 300 maintains the current clamping posture. This torque detection mechanism, as an independent clamping and holding control method, does not use the total pressure, peak pressure, contact area, or maximum pressure position extracted by the tactile perception task as the judgment input.

[0101] More specifically, the tactile sensing task and the torque detection task are independent of each other. The tactile sensing task makes pressure safety judgments based solely on the sensing unit data within the coverage area of ​​the array tactile sensor 403. The torque detection task estimates external contact torque based solely on feedback data from the servo motor 201 and motion state data. The two tasks use different threshold parameters and output tactile safety latching state and torque clamping holding state, respectively.

[0102] (4) Communication bridging task: Receive Modbus RTU instruction frames from the host computer via RS485, parse the function codes (0x03 read register, 0x06 write single register, 0x10 write multiple registers), map them to internal registers for parameter reading and writing, and support remote control of the target position, speed, and torque of motor 201 as well as querying sensor 403 data and safety status.

[0103] (5) Rotary encoder reading task: According to the set cycle, read the absolute angle data output by the rotary encoder 402 through the SPI bus, calculate the difference between the real-time angle value and the pre-stored mechanical zero point, normalize it to the effective range, and calculate the opening and closing position of the gripper fingers. At the same time, use the absolute angle data as the position reference of the servo motor 201.

[0104] Specifically, using angle data from the absolute magnetic encoder 402 with a fixed period of 50ms, after each reading, the absolute angle of the current distal link 205 is subtracted from the mechanical zero point stored in Flash. After angle normalization, the opening and closing position of the finger is obtained. This absolute position also serves as the position reference for the coordinate system of the servo motor 201, used to calculate the offset mapping between the coordinates of the magnetic encoder 402 and the multi-turn coordinates of the motor 201. The magnetic encoder 402 has even parity and diagnostic functions. When reading data, it automatically checks the odd and even bits and detects error flags. If an anomaly is detected, the previous valid value is retained to ensure the continuity and reliability of the position data.

[0105] The control system implements rich parameter configuration and status query functions through Modbus RTU register mapping. The register address space includes:

[0106] - Device information area (0x0000~0x0001): Device ID signature and firmware version;

[0107] - Control configuration area (0x0010~0x0016): Motor CANID, control mode, enable status, fault clearing, unit configuration, zero position storage;

[0108] -Persistent status area (0x0018~0x001F): Flash persistent status and bias information of zero-position calibration data;

[0109] - Target command area (0x0020~0x0027): velocity target, position target, PID parameters and feedforward torque;

[0110] - Feedback data area (0x0100~0x0109): Motor position feedback, error status, temperature information, tactile safety signs, and statistical data;

[0111] - Safety parameter area (0x0030~0x0034): Total pressure threshold, maximum pressure threshold and unlock command.

[0112] Please see Figure 9 The security latching protection mechanism of this invention is based on real-time data from the array-type tactile sensor 403, and achieves active security protection against grasping force. Its working process is as follows:

[0113] S1: Threshold setting: Set two threshold parameters for safety protection through the ModbusRTU communication interface: total pressure threshold and unit maximum pressure threshold. The threshold can be remotely adjusted by the host computer according to the actual grasping requirements.

[0114] S2: Real-time monitoring: In each tactile perception task cycle, the sum of pressures (sum) obtained from feature extraction is compared with the sum of pressures threshold, and the maximum pressure value (max) is compared with the maximum pressure threshold.

[0115] S3: Latch Trigger: Compare the various feature values ​​extracted from the tactile perception task with the preset safety threshold. When the total pressure or peak pressure exceeds the corresponding safety threshold, the safety latch flag is triggered.

[0116] Specifically, if the total pressure exceeds the total pressure threshold, or the maximum pressure value exceeds the maximum pressure threshold, the safety latch flag is set, the trigger type (total exceeding limit or maximum value exceeding limit) is recorded, and feedback is provided to the outside world through the safety flag register.

[0117] S4: Motor Lock-up: After the safety latch flag is set, the motor control task detects the latched state in the next control cycle and immediately stops sending drive commands to the servo motor 201, causing the motor 201 to stop rotating. Because the transmission mechanism formed by the lead screw 202 and the nut slider 203 has a self-locking characteristic, the finger will maintain its current position and no longer apply force. Simultaneously, the finger module 300 maintains its posture when in contact with the object 500, stably gripping the object 500.

[0118] S5: Safety latch release: The host computer sends an unlock command to the control unit 401 via the Modbus RTU communication interface. After receiving the unlock command, the control unit 401 enters the pressure relief waiting state. In this state, only the servo motor 201 is allowed to perform the release action, and the running speed is not greater than the preset safety speed threshold. At the same time, the servo motor 201 is prohibited from performing the clamping action to release the residual contact pressure of the gripper. When the total pressure and peak pressure are detected to drop below their respective preset release thresholds, and this state is maintained for a preset number of sampling frames, the safety latch flag is cleared, and the full stroke motion control authority of the servo motor 201 is restored.

[0119] Specifically, the host computer writes a specific unlock code (e.g., 0xA55A) to the control system. Upon receiving the unlock command, the control system clears the latch flag and enters a pressure relief waiting state. In this waiting state, to ensure safety, the motor control task executes motion-restricted logic: only the servo motor 201 is allowed to move in the release direction, and the movement speed is limited to a preset safe speed threshold (in this embodiment, the safe speed threshold is 30° / s); simultaneously, the system forcibly prevents the servo motor 201 from moving in the clamping direction or applying any active feedforward torque, thereby controlling the release of residual contact pressure between the finger module 300 and the clamped object 500. During the pressure relief process, the control system continuously monitors the data fed back by the array-type tactile sensor 403 through a high-frequency task of the real-time operating system (RTOS). In this embodiment, the set safety release condition is:

[0120] 1. The total pressure detected in real time drops to below one-quarter (25%) of the safety protection threshold;

[0121] 2. And the maximum single-point pressure value simultaneously drops to below one-quarter (25%) of the safety protection threshold;

[0122] 3. The above conditions must be maintained for more than 5 consecutive frames within the sampling period of the control algorithm.

[0123] Only after all the above numerical conditions are met does the system officially release the pressure relief waiting state and restore the omnidirectional control capability of the servo motor 201. This progressive, phased unlocking strategy, by limiting the physical direction of movement and specific pressure ratio values, effectively avoids the safety risk of the object 500 popping out or the mechanism rebounding violently due to mis-locking while the finger is still in a high-pressure contact state.

[0124] This invention discloses an adaptive underactuated robot gripper with integrated tactile sensing as follows:

[0125] Please see Figure 10 When performing parallel gripping on a small object 500 or a larger object 500 with opposing surfaces, in the initial state, the front torsion spring 2071 and rear torsion spring 2072 between the distal finger link 205 and the proximal finger link 206 do not deflect at any angle and remain collinear. At this time, the second finger link 302 will move according to the parallelogram linkage system. The servo motor 201 rotates, driving the slider 203 to move linearly, and the driving link 204 pulls the distal finger link 205 to rotate around its rotating boss 2054. The rotating distal finger link 205 pushes... The proximal finger link 206 moves inward and upward, and the thrust is transmitted to the second finger link 302 through the proximal finger link 206. At the same time, the first finger link 301, as the main skeleton, leads the entire finger to rotate inward around the fourth connecting shaft 3015. The second finger link 302 is constrained by the preload of the front torsion spring 2071 and the rear torsion spring 2072 to maintain its initial posture. It moves parallel to the parallelogram link system, gradually reducing the distance between the second finger links 302 of the two finger modules 300, until the second finger link 302 touches the clamping object 500 and can no longer move, thus completing the grasping operation.

[0126] Please see Figure 11When the geometry of the object 500 being gripped does not meet the parallel gripping conditions, this embodiment can perform an envelope gripping. The servo motor 201 rotates forward, and the two finger modules 300 first move in a parallel gripping manner. At this time, the front torsion spring 2071 and the rear torsion spring 2072 between the distal finger link 205 and the proximal finger link 206 do not deflect at an angle and remain collinear. The second finger 302 moves according to the parallelogram link system that plays a dominant role until the first finger 301 contacts the object 500 and is blocked from moving. Subsequently, the drive module 200 continues to drive, the lead screw 202 continues to move downwards and exert force, the drive link 204 continues to pull the distal link 205 to rotate, and the thrust transmitted from the distal link 205 to the second link 302 through the proximal link 206 increases sharply. Since the first link 301 is blocked by the clamped object 500, the thrust finally overcomes the preload torque of the front torsion spring 2071 and the rear torsion spring 2072 in the distal link 205 system, causing the rotating pair between the distal link 205 and the proximal link 206 to rotate relative to each other. The two no longer remain collinear, thus breaking the original parallelogram geometric relationship. The four-bar system changes from a parallelogram link system to a general four-bar system, pushing the second link 302 to continue to rotate inward around the third connecting axis 3014 until the second link 302 contacts the clamped object 500, completing the adaptive envelope gripping of the object 500.

[0127] After the grasping is completed, the servo motor 201 stops rotating, and the finger module 300 can still maintain the posture when in contact with the clamped object 500, stably grasping the clamped object 500. When releasing the object 500, the servo motor 201 in the drive module 200 reverses, and the subsequent process is exactly the reverse of the above-described grasping process of the object 500, which will not be described again.

[0128] The technical solution of the present invention has been described in detail above with reference to specific embodiments. The specific embodiments described are used to help understand the concept of the present invention. Derivations and modifications made by those skilled in the art based on the specific embodiments of the present invention also fall within the scope of protection of the present invention.

Claims

1. An adaptive underactuated robot gripper with integrated tactile sensing, characterized in that, include: The gripper housing (100) has a mounting cavity inside, and the mounting cavity has assembly openings on both sides at the upper end; The drive module (200) includes a servo motor (201), a slider (203), and a linkage group. The servo motor (201) is fixedly installed in the lower part of the mounting cavity. The slider (203) is slidably disposed at the output end of the servo motor (201). The linkage group consists of two groups, symmetrically arranged on opposite sides of the slider (203). Each linkage group includes a proximal link (206), a distal link (205), and a distal link (206). The distal link (205) passes through the assembly opening and is rotatably connected to the gripper housing (100). The two ends of the distal link (205) are respectively hinged to the lower end of the proximal link (206) and the upper end of the drive link (204). The lower end of the drive link (204) is hinged to the side wall of the slider (203). An elastic damping element is provided at the hinge of the proximal link (206) and the distal link (205). The finger module (300) consists of two sets, each corresponding to a link group. Each finger module (300) includes a first finger rod (301) and a second finger rod (302). The lower end of the second finger rod (302) is hinged to the upper end of the proximal finger link (206). The upper claw surface of the second finger rod (302) is provided with an elastic sleeve (303). One end of the first finger rod (301) is rotatably mounted in the top of the mounting cavity. The other end of the first finger rod (301) is hinged to the lower end of the second finger rod (302). The first finger rod (301), the second finger rod (302), and the proximal finger link (206) are arranged radially with the lower end of the first finger rod (301) as the center. The system includes a control unit (401), a rotary encoder (402), and an array of tactile sensors (403). The array of tactile sensors (403) is fixed to the gripping surface at the upper end of the second finger rod (302) and covered by an elastic sleeve (303). The rotary encoder (402) is sleeved at the connection between the distal finger link (205) and the gripper housing (100) and rotates synchronously with the distal finger link (205). The rotary encoder (402) and the array of tactile sensors (403) are both electrically connected to the control unit (401).

2. The adaptive underactuated robot gripper with integrated tactile sensing according to claim 1, characterized in that: The distal link (205) includes a front link (2051), a rear link (2052), and a link spacing support (2053). The front link (2051) and the rear link (2052) are both arc-shaped structures and are arranged in parallel opposite directions. The link spacing support (2053) is fixedly located between the middle sections of the front link (2051) and the rear link (2052). One end of the front link (2051) and the rear link (2052) is hinged to the lower end of the proximal link (206) through a first connecting shaft (2055). The other end of the front link (2051) and the rear link (2052) is hinged to the upper end of the drive link (204) through a second connecting shaft (2056).

3. The adaptive underactuated robot gripper with integrated tactile sensing according to claim 2, characterized in that: The front connecting plate (2051) and the rear connecting plate (2052) are coaxially fixed with rotating bosses (2054) located between the upper ends of the connecting rod spacing support (2053) and the drive connecting rod (204). The two rotating bosses (2054) can rotatably pass through the front and rear side walls of the gripper housing (100). The rotary encoder (402) is an absolute magnetic encoder. The rotary encoder (402) is located on the outside of the gripper housing (100) and is fixedly connected to the outer end of any rotating boss (2054). The rotary encoder (402) is connected to the control unit (401) through the SPI bus interface and is used to measure the absolute rotation angle of the distal connecting rod (205).

4. The adaptive underactuated robot gripper with integrated tactile sensing according to claim 3, characterized in that: The elastic damping element includes a pair of front torsion springs (2071) and rear torsion springs (2072). The front connecting plate (2051) and the rear connecting plate (2052) each have a first groove (2057) on their opposite sidewalls. The proximal connecting rod (206) has second grooves (2061) on its opposite sidewalls. The front torsion spring (2071) and the rear torsion spring (2072) are both sleeved on the outer periphery of the first connecting shaft (2055). The front torsion spring (2071)... The first groove (2057) of the front connecting plate (2051) and the second groove (2061) on one side of the finger link (206) are accommodated. The rear torsion spring (2072) is accommodated in the first groove (2057) of the rear connecting plate (2052) and the second groove (2061) on the other side of the finger link (206). The legs of the front torsion spring (2071) and the rear torsion spring (2072) respectively abut against the inner sidewalls of the corresponding first groove (2057) and second groove (2061).

5. The adaptive underactuated robot gripper with integrated tactile sensing according to claim 2, characterized in that: The first finger (301) includes a first front finger (3011), a first rear finger (3012), and a finger spacing support (3013). The finger spacing support (3013) is fixedly disposed between the middle sections of the first front finger (3011) and the first rear finger (3012). One end of the first front finger (3011) and the first rear finger (3012) is hinged to the lower end of the second finger (302) through a third connecting shaft (3014). The other end of the first front finger (3011) and the first rear finger (3012) is hinged to the opposite side wall of the gripper housing (100) through a fourth connecting shaft (3015).

6. The adaptive underactuated robot gripper with integrated tactile sensing according to claim 1, characterized in that: The servo motor (201) is a direct-drive servo motor. The servo motor (201) communicates with the control unit (401) through an industrial bus and supports torque control mode, position control mode, speed control mode and force-position hybrid control mode.

7. The adaptive underactuated robot gripper with integrated tactile sensing according to claim 1, characterized in that: The control system also includes a communication interface, which includes a Modbus RTU serial communication interface and a CAN bus interface. The Modbus RTU serial communication interface is used to communicate with a host computer or an external controller, and the CAN bus interface is used to communicate with the servo motor (201).

8. The adaptive underactuated robot gripper with integrated tactile sensing according to claim 1, characterized in that: The second finger sticks (302) in the two sets of finger modules (300) have different widths. The gripping surface of the wider second finger stick (302) is attached with three sets of arrayed tactile sensors (403), and the gripping surface of the narrower second finger stick (302) is attached with one set of arrayed tactile sensors (403). Each set of arrayed tactile sensors (403) includes 32 pressure-sensitive sensing units. The arrayed tactile sensors (403) of the wider second finger stick (302) and the arrayed tactile sensors (403) of the narrower second finger stick (302) are connected to the control unit (401) through independent SPI bus interfaces.

9. A control method for an adaptive underactuated robot gripper with integrated tactile perception based on any one of claims 1 to 8, characterized in that: The control unit (401) is equipped with and runs a real-time operating system, and performs five control tasks in parallel: Motor control task: According to the set cycle, send control frames to the servo motor (201) via CAN bus based on the target position command, and receive feedback data from the servo motor (201); Rotary encoder reading task: According to the set cycle, read the absolute angle data output by the rotary encoder (402) through the SPI bus, calculate the difference between the real-time angle value and the pre-stored mechanical zero point, normalize it to the effective range, and calculate the opening and closing position of the finger. At the same time, use the absolute angle data as the position reference of the servo motor (201). Tactile sensing task: According to a set period, the sampling data of all sensing units of the array-type tactile sensor (403) is collected through the SPI bus, and the following signal processing steps are executed in sequence: S1: Calibration phase: During the initial power-on phase, multiple frames of data are collected and averaged to serve as the baseline value for each sensing unit; S2: Difference Calculation: Calculate the difference between the real-time acquired raw value and the baseline value, and clamp negative values ​​to zero; S3: Digital Filtering: Perform a first-order IIR low-pass filter on the difference obtained from the calculation to filter out high-frequency interference noise in the signal; S4: Feature extraction: Calculate the total pressure of all sensing units, the maximum pressure value, the contact area, and the location of the maximum pressure; Torque detection task: Read the torque value fed back by the servo motor according to the set cycle, and execute the feedback acquisition, filtering and zero bias compensation, friction compensation, threshold judgment and clamping and holding steps in sequence; when the estimated value of external contact torque reaches the clamping and holding threshold and continues for the preset control cycle, record the current motor position as the holding position, set the target speed and feedforward torque to zero, so that the gripper stops closing and maintains the current clamping state; The safety protection task compares the feature values ​​extracted from the tactile perception task with the preset safety threshold. When the total pressure or peak pressure exceeds the corresponding safety threshold, the safety latch flag is triggered, and the servo motor (201) is immediately controlled to stop outputting drive torque, limiting the gripper from continuing to perform clamping action.

10. The control method according to claim 9, characterized in that, The process of releasing the safety latch is as follows: the host computer sends an unlocking command to the control unit (401). After receiving the unlocking command, the control unit (401) enters the pressure relief waiting state. In this state, only the servo motor (201) is allowed to perform the release action, and the running speed is not greater than the preset safety speed threshold. At the same time, the servo motor (201) is prohibited from performing the clamping action to release the residual contact pressure of the gripper. When the total pressure and peak pressure are both detected to drop below their respective preset release thresholds, and this state is maintained for a preset number of sampling frames, the safety latch flag is cleared and the full-stroke motion control authority of the servo motor (201) is restored.

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