A flexible clamping system and method based on a hardness parameter

Abstract

The application relates to the technical field of automation equipment, and discloses a flexible clamping system and method based on a hardness parameter. The system comprises a PLC controller, a mechanical arm, a clamping assembly and a detection assembly, a clamping jaw is composed of a fixed clamping part and a compensation feeding assembly, the compensation feeding assembly is provided with a cylinder and a movable clamping plate; the PLC controller is integrated with an input module and a storage unit, and the upper limit value of hardness, the proportional coefficient and the compensation coefficient of different hardness systems are prestored. The method adopts hierarchical feeding control, contact positioning is realized through first feeding, the hardness parameter is converted according to the hardness parameter, and the target displacement of second feeding and third feeding is calculated. The application can be adapted to multiple types of clamped articles, has strong universality, good flexible control effect, can effectively avoid workpiece damage and clamping slip, and improves the stability and reliability of automatic clamping operation.

Description

Technical Field

[0001] This invention relates to the field of automated equipment technology, specifically to a flexible clamping system and method based on hardness parameters. Background Technology

[0002] In the fields of automated logistics handling and multi-category material sorting, flexible clamping devices, as core actuators in automated production lines, need to adapt to the transfer requirements of workpieces of different materials and specifications. Currently, conventional clamping equipment mostly adopts a control method with preset fixed stroke or fixed load threshold, relying on displacement or pressure detection elements to realize the start and stop control of clamping action. Although some improved devices have added simple feedback adjustment links, the overall control logic is still relatively traditional.

[0003] In actual working conditions, such conventional clamping equipment lacks versatility. The operating parameters of the device lack a corresponding matching mechanism with the physical characteristics of the workpiece to be clamped. When switching between different types of workpieces, operators need to repeatedly debug the operating parameters on-site. The debugging process is cumbersome and inefficient, making it difficult to adapt to the application scenarios of continuous automated production of multiple types of workpieces.

[0004] In addition, existing equipment generally suffers from a lack of flexible control capabilities. Clamping impacts and imbalances in clamping force are prone to occur during the clamping process. During workpiece lifting and transfer, if the workpiece shifts relative to the grippers, the device cannot perform timely compensation adjustments, easily leading to loosening, slippage, or excessive compression causing workpiece damage. It is difficult to simultaneously ensure clamping stability and workpiece integrity, and the overall adjustment capability is limited. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, the present invention provides a flexible clamping system and method based on hardness parameters.

[0006] The technical solution adopted in this invention is: a flexible clamping system based on hardness parameters, including a PLC controller, a robotic arm, a clamping assembly, and a detection assembly. The PLC controller can control the movement of the robotic arm. The clamping assembly is installed at the front end of the robotic arm and includes two identical grippers driven by a drive device, which can move towards or away from each other. Each gripper includes a lower fixed clamping part and an upper compensation feed assembly. A first sensor and a second sensor are respectively embedded on the opposite end faces of the fixed clamping part. Each compensation feed assembly includes a cylinder and a movable clamping plate. The piston rod end of the cylinder is fixed to the opposite end face of the movable clamping plate. In the initial state, the opposite end faces of the movable clamping plate and the opposite end faces of the fixed clamping part are flush. The PLC controller integrates an input module, which communicates with the PLC controller to receive the user-inputted hardness parameter 'a' of the object to be clamped. The PLC controller also integrates a storage unit, which communicates with the PLC controller to pre-store the upper limit hardness value 'A', the proportional coefficient 'k', and the compensation coefficient 'λ' of the corresponding hardness system. The detection components include a current sensor, a pressure sensor, and two sets of displacement detection units. The current sensor is mounted on the drive unit to detect the load on the drive unit, and the pressure sensor is mounted on the cylinder to detect... The cylinder load is measured, and two sets of displacement detection units are respectively set for the drive device and the cylinder to collect the actual displacement of the gripper and the movable clamping plate. The current sensor, pressure sensor, and displacement detection units are all connected to the PLC controller. The PLC controller is configured to: control the gripper to complete the first feeding action based on the feedback signal of the first sensor until the gripper contacts the object to be clamped; according to the hardness parameter a, call the upper limit value A of the corresponding hardness system, the proportional coefficient k, and the compensation coefficient λ, first calculate the hardness parameter a′=Aa, then calculate the target displacement of the second feeding b=k×a′, and the target displacement of the third feeding. The quantity c = k × a′ × λ; based on the feedback signals from the current sensor and the corresponding displacement detection unit, the gripper is controlled to perform the second feed. When both conditions are met simultaneously—a sudden increase in the load on the drive device and the displacement increment approaching zero—the second feed action is terminated. Based on the feedback signal from the second sensor, it is determined whether the object to be gripped has undergone relative displacement. Based on the feedback signals from the pressure sensor and the corresponding displacement detection unit, the cylinder is controlled to drive the movable gripping plate to perform the third feed. When both conditions are met simultaneously—a sudden increase in the cylinder load and the displacement increment approaching zero—the third feed action is terminated. If the above termination conditions are not met, the third feed action is repeated.

[0007] The upper part of the opposite end face of the two grippers is provided with through holes. The inner edge of the through holes extends outward to the gripper to form an installation channel. The cylinder is fixedly installed in the installation channel of the corresponding gripper. The cylinder piston rod is fixedly connected to the movable clamping plate of the gripper on the same side.

[0008] The driving device is a servo motor or a stepper motor. The displacement detection unit corresponding to the driving device adopts a rotary encoder, which is installed on the output shaft end of the driving device. The rotary encoder calculates the linear displacement of the gripper by detecting the rotation angle of the driving device. The displacement detection unit corresponding to the cylinder adopts a linear displacement sensor, which is installed along the movement direction of the movable clamping plate and directly collects the linear displacement of the movable clamping plate.

[0009] The proportional coefficient k and the compensation coefficient λ are preset calibration parameters.

[0010] The corresponding hardness systems include Mohs hardness, Shore hardness, Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, and other hardness systems commonly used in industry.

[0011] The reversible elastic deformation mentioned in the calibration experiment refers to the absence of visible damage and irreversible plastic deformation in the object to be clamped after clamping. Plastic deformation can be verified by precision measuring equipment.

[0012] The aforementioned flexible clamping method based on hardness parameters includes the following steps: Step 1: Input the hardness parameter 'a' of the object to be clamped through the input module to determine the corresponding hardness system. The PLC controller retrieves the upper limit value A of the hardness of the system, the proportional coefficient k, and the compensation coefficient λ pre-stored in the storage unit. Step 2: The PLC controller controls the two grippers to move towards each other. The first sensor detects the contact state between the grippers and the object to be clamped in real time. When contact is detected, the grippers are stopped, completing the first feed. Step 3: The PLC controller calculates the hardness parameter according to the formula a′=Aa, and then calculates the target displacement b=k×a′ for the second feed, controlling the grippers to continue feeding towards each other. During the feed process, the load and displacement signals of the drive device are collected in real time. Before the target displacement is reached, if a sudden increase in load and displacement are detected simultaneously, the system will stop the feed. If the load increases to near zero, the feed is terminated early. If the target displacement is reached and the termination conditions of a sudden increase in load and displacement increment approaching zero are not triggered, the feed stops normally, completing the second feed. Step 4: The PLC controller controls the robotic arm to lift the object to be clamped at a constant speed, and monitors in real time whether the object to be clamped is slipping relative to the gripper through the second sensor. Step 5: If slippage of the object to be clamped is detected, the PLC controller calculates the target displacement of the third feed c=k×a′×λ, and controls the cylinder to drive the movable clamping plate to perform the third feed. The cylinder pressure and displacement signals are collected in real time. If a sudden increase in load and displacement increment approaching zero are detected before the target displacement is reached, the third feed is terminated early. If the termination conditions are not met, the third feed is repeated until the termination conditions are met, and stable clamping is completed.

[0013] The criterion for determining that the displacement increment approaches zero is that the displacement value collected by the displacement detection unit per unit time is lower than the displacement increment threshold preset by the PLC controller.

[0014] During the second feeding process, the feed speed of the gripper is lower than that during the first feeding process, which reduces contact impact and avoids damage to the gripped item.

[0015] Each time the third feed action is repeated, the target displacement of the third feed is c=k×a′×λ, where a′=Aa, until the third feed termination condition is triggered.

[0016] The robotic arm lifts the object to be clamped at a constant speed to avoid relative displacement interference caused by reasons other than clamping failure, thus ensuring that the second sensor accurately detects the relative displacement of the object to be clamped.

[0017] The flexible clamping system and method provided by this invention, through optimization of structural design and control logic, effectively improves the limitations of existing clamping devices and has the following beneficial effects:

[0018] 1. This invention determines the matching coefficients through standardized calibration experiments and linear fitting, and stores these coefficients in the system. During operation, the corresponding feed displacement can be directly called and calculated based on the input workpiece-related parameters, realizing the quantitative matching of operating parameters and workpiece characteristics. This eliminates the need for repeated manual on-site debugging, significantly improving the device's adaptability to different types of workpieces, and making the system more versatile and practical in production scenarios with multiple workpiece switching.

[0019] 2. This invention employs a graded execution process of first feed, second feed, and third feed, combined with dual judgment conditions of sudden load increase and displacement increment approaching zero, to achieve gradual clamping control, effectively reducing the impact risk caused by a single feed. During the material transfer process, dynamic compensation can be performed on the workpiece displacement, balancing clamping reliability and workpiece protection requirements, significantly improving the flexibility of the device's control level, reducing workpiece extrusion deformation and slippage problems, and improving the overall stability and safety of the operation.

[0020] 3. The system is equipped with a dedicated detection unit to achieve real-time acquisition of contact status, load, and displacement information. Combined with a split gripper and independent compensation execution structure, the detection feedback and control execution response are direct, resulting in higher operational accuracy. System control parameters are pre-calibrated and stored through a standardized process, eliminating the need for frequent on-site calibration. This ensures strong overall consistency and facilitates integration into automated production lines, effectively improving continuous operation efficiency. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the system logic of the present invention;

[0022] Figure 2 This is a flowchart of the method of the present invention;

[0023] Figure 3 This is a schematic diagram of the connection structure between the robotic arm and the gripping assembly of the present invention;

[0024] Figure 4 This is a three-dimensional structural diagram of the clamping component of the present invention;

[0025] Figure 5 This is a schematic diagram showing the movement changes of the gripper during operation of the clamping assembly of the present invention;

[0026] The markings in the diagram are: 1. Robotic arm; 2. Gripping assembly; 3. Gripper; 31. Compensating feed assembly; 311. Cylinder; 312. Movable gripping plate; 32. Fixed gripping part; 33. First sensor; 34. Second sensor; 35. Mounting channel. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] like Figure 1-5As shown, a flexible clamping system and method based on hardness parameters are disclosed. The flexible clamping system includes a PLC controller, a robotic arm 1, a clamping assembly 2, and a detection assembly. The PLC controller controls the movement of the robotic arm 1. The clamping assembly 2 is mounted on the front end of the robotic arm 1 and includes two identical grippers 3 driven by a drive device, capable of moving towards or away from each other. Each gripper 3 includes a lower fixed clamping part 32 and an upper compensation feed assembly 31. A first sensor 33 and a second sensor 34 are respectively embedded on the opposite end faces of the fixed clamping part 32. Each compensation feed assembly 31 includes a cylinder 311 and a movable clamping plate 312. The cylinder 311... The piston rod ends are fixedly connected to the opposite end faces of the movable clamping plate 312. In the initial state, the opposite end faces of the movable clamping plate 312 are flush with the opposite end faces of the fixed clamping part 32. The PLC controller integrates an input module, which is communicatively connected to the PLC controller to receive the user-inputted hardness parameter 'a' of the object to be clamped. The PLC controller also integrates a storage unit, which is communicatively connected to the PLC controller to pre-store the upper limit value of hardness A, the proportional coefficient k, and the compensation coefficient λ of the corresponding hardness system. The detection components include a current sensor, a pressure sensor, and two sets of displacement detection units. The current sensor is mounted on the drive device to detect the load on the drive device, and the pressure sensor is mounted on... Placed on cylinder 311, it is used to detect the load of cylinder 311. Two sets of displacement detection units are respectively set for the drive device and cylinder 311, and are used to collect the actual displacement of gripper 3 and movable clamping plate 312 respectively. The current sensor, pressure sensor and displacement detection unit are all connected to the PLC controller. The PLC controller is configured to: control gripper 3 to complete the first feeding action according to the feedback signal of the first sensor 33, until gripper 3 contacts the object to be clamped; according to the hardness parameter a, call the upper limit value A of the corresponding hardness system, proportional coefficient k and compensation coefficient λ, first calculate the hardness parameter a′=Aa, then calculate the second feeding target displacement b=k×a′, and the third The target displacement for the second feed is c = k × a′ × λ. Based on the feedback signals from the current sensor and the corresponding displacement detection unit, the gripper 3 is controlled to perform the second feed. When both conditions are met simultaneously—a sudden increase in the load on the drive device and the displacement increment approaching zero—the second feed action is terminated. Based on the feedback signal from the second sensor 34, it is determined whether the object to be gripped has undergone relative displacement. Based on the feedback signals from the pressure sensor and the corresponding displacement detection unit, the cylinder 311 is controlled to drive the movable clamping plate 312 to perform the third feed. When both conditions are met simultaneously—a sudden increase in the load on the cylinder 311 and the displacement increment approaching zero—the third feed action is terminated. If the above termination conditions are not met, the third feed is repeated.

[0029] This invention aims to improve the versatility and flexible control capabilities of clamping devices by establishing a quantitative matching relationship between hardness parameters and feed displacement to achieve flexible clamping. The hardness parameter 'a' of the item to be clamped is obtained by sampling and measuring the batch of items using existing hardness testing equipment and conventional testing methods. The specific testing methods are existing technology and will not be elaborated here. For items of different batches and materials, the corresponding clamping strategy can be quickly switched and matched by re-testing and recording the corresponding hardness parameters, thereby achieving dedicated flexible clamping for each batch of items. The upper limit of hardness A is the known standard upper limit of each hardness system, directly selected according to the general specifications of the corresponding testing system. The hardness parameter a' is calculated according to the formula a'=Aa, which is used to characterize the relative softness and hardness of the item to be clamped. The larger the difference between the item's hardness and the upper limit value, the softer the texture, and vice versa. Based on a', the target feed displacement b=k×a' is calculated by combining the proportional coefficient k, so that the feed stroke is adjusted according to the hardness of the item, fundamentally balancing the clamping force and the item protection requirements. The compensation coefficient λ is a dimensionless constant less than 1. The target displacement c of the third feed is calculated using the formula c=k×a′×λ, which is essentially a proportional conversion of the compensation displacement to the reference displacement of the second feed. Therefore, the compensation displacement is always less than the reference displacement of the second feed. The design intent of this setting is that the third feed is only used to eliminate the minor slippage and fit clearance generated during the workpiece lifting and transfer process. It is a correction compensation and does not require repeating the second feed stroke. The above-mentioned quantitative control logic and graded feed method can ensure that the compensation amount matches the workpiece's hardness and strictly control the compensation amplitude, avoiding excessive compensation stroke that could cause secondary extrusion, plastic deformation, or clamping overload of the workpiece. This achieves precise and gentle flexible compensation control, effectively solving the technical problems of poor versatility, insufficient flexibility, and easy damage to workpieces in traditional clamping equipment.

[0030] In this invention, the upper limit value A of the corresponding hardness system is the upper limit of the known standard range of each hardness system, which is common knowledge in the field and can be directly selected according to industry-standard norms. The proportional coefficient k and the compensation coefficient λ are calibration parameters adapted to the control logic of this system, obtained through preset calibration experiments: samples with various known standard hardness are selected for clamping tests, with stable workpiece clamping and only reversible elastic deformation as the standard, and the proportional coefficient k is calculated through test data; the compensation coefficient λ is determined through multiple sets of comparative tests with the ability to eliminate clamping slippage and not cause irreversible plastic deformation of the workpiece as the judgment standard, and finally the above parameters are pre-stored in the storage unit.

[0031] In this invention, a sudden increase in the load of the drive device is detected by real-time acquisition of the drive device's operating current using a current sensor. A preset load threshold is established within the PLC controller. When the real-time current significantly increases relative to the no-load reference current and exceeds the threshold, a sudden load increase is identified, indicating that the gripper 3 has formed effective contact and force with the object to be clamped. Displacement increments approaching zero are detected by a displacement detection unit acquiring displacement data at fixed intervals. The PLC controller calculates the displacement change per unit time. When the displacement increment is lower than a preset small displacement threshold, it is determined that the displacement increment is approaching zero, indicating that the gripper 3's feed is obstructed and a tight clamping has been achieved. This system sets the above two conditions as a combined logical AND judgment rule, terminating the feed only when both conditions are simultaneously met. This avoids the susceptibility to false triggering due to interference from a single load condition and prevents the inability to effectively determine clamping position due to a single displacement condition, improving the accuracy and reliability of clamping control while balancing clamping stability and object protection.

[0032] In this invention, both the first sensor 33 and the second sensor 34 are contact proximity sensors or photoelectric displacement sensors. The first sensor 33 is embedded in the opposite end face of the fixed clamping part 32 and is used to detect the initial contact state between the gripper 3 and the item to be clamped. When the detection end face contacts the surface of the item, it immediately feeds back a level change signal to the PLC controller as the basis for stopping the first feed. The second sensor 34 is also embedded in the opposite end face of the fixed clamping part 32. Its detection accuracy is higher than that of the first sensor 33. It is used to detect in real time whether there is relative slippage and displacement gap between the item to be clamped and the gripper 3 during the lifting and transfer process. If a change in gap or contact state is detected, it is determined that the item has slipped relatively, and a trigger signal is fed back to the PLC controller to start the third feed compensation action.

[0033] The upper part of the opposite end face of the two grippers 3 is provided with through holes. The inner edge of the through holes extends outward to form an installation channel 35. The cylinder 311 is fixedly installed in the installation channel 35 of the corresponding gripper 3. The piston rod of the cylinder 311 is fixedly connected to the movable clamping plate 312 of the gripper 3 on the same side.

[0034] The driving device is a servo motor or a stepper motor. The displacement detection unit corresponding to the driving device adopts a rotary encoder. The rotary encoder is installed at the output shaft end of the driving device and calculates the linear displacement of the gripper 3 by detecting the rotation angle of the driving device. The displacement detection unit corresponding to the cylinder 311 adopts a linear displacement sensor. The linear displacement sensor is installed along the movement direction of the movable clamping plate 312 and directly collects the linear displacement of the movable clamping plate 312.

[0035] The proportional coefficient k and compensation coefficient λ are preset calibration parameters, obtained through preset calibration experiments: Select samples with various known standard hardnesses and perform clamping tests under standard system conditions, setting the corresponding upper limit value A for the corresponding hardness system; obtain the feed displacement when different samples are stably clamped and only reversible elastic deformation occurs through testing, and calculate the proportional coefficient k according to the formulas a′=Aa and k=b / a′; the compensation coefficient λ is a fixed value less than 1, selected through calibration experiments to effectively eliminate clamping slippage and prevent excessive compression of the object to be clamped, and the above parameters are pre-stored in the storage unit of the PLC controller.

[0036] The corresponding hardness system described in this invention includes Mohs hardness, Shore hardness, Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, and other hardness systems commonly used in industry. The specific hardness system used depends on the actual batch of items to be clamped.

[0037] The specific calibration process for the proportionality coefficient k is as follows:

[0038] Multiple sets of samples with known standard hardness values ​​from the same hardness system are selected. The hardness values ​​of the samples are uniformly distributed within the commonly used testing range of this system to ensure accurate calibration data. The system is set to a standard no-load condition, with the drive device and detection components in their initial states. The no-load current of the drive device and the initial readings of the displacement detection unit are recorded to determine the system's reference parameters. For a known hardness of a... i The standard sample is input into the input module to record its hardness value. The system then calls the upper limit value A of the corresponding hardness system according to known standards, and calculates the hardness according to the formula a′. i =Aa i The hardness parameters of the sample were calculated; the system was started to execute the clamping process. After the first feed contact positioning was completed, the second feed was executed step by step. The endpoint was determined when the sample was stably clamped and only reversible elastic deformation occurred, without irreversible plastic deformation and without external damage. The actual feed displacement b corresponding to this point was recorded. i According to the formula k=b i / a′ i Substitute the hardness parameter a′ of the sample into the input. i Compared with the measured effective feed displacement b i The calibration ratio coefficient is calculated. The above steps are repeated with samples of different standard hardness to obtain multiple sets of valid data and calculate multiple sets of k values. The average value of each set of data is taken as the final calibration ratio coefficient and stored in the storage unit of the PLC controller for subsequent clamping calculations of actual workpieces.

[0039] The compensation coefficient λ is a dimensionless correction coefficient with a value less than 1, determined through a simple verification calibration experiment. The experiment was conducted based on the principle that after the system completes the compensation action, it can effectively eliminate relative slippage of the object to be clamped without causing irreversible plastic deformation. During the experiment, several commonly used preset values ​​less than 1 were first selected for group testing. The clamping compensation effects of each group were gradually fine-tuned and compared. Finally, the value with the best overall performance, which best balances slippage compensation and object protection requirements, was selected as the compensation coefficient λ under this hardness system and pre-stored in the PLC controller's storage unit.

[0040] The reversible elastic deformation mentioned in the calibration experiment refers to the absence of visible damage and irreversible plastic deformation in the object to be clamped after clamping. Plastic deformation can be verified by precision measuring equipment.

[0041] The aforementioned flexible clamping method based on hardness parameters includes the following steps: Step 1: Input the hardness parameter 'a' of the object to be clamped through the input module to determine the corresponding hardness system. The PLC controller retrieves the upper limit value A of the hardness of the system, the proportional coefficient k, and the compensation coefficient λ pre-stored in the storage unit. Step 2: The PLC controller controls the two grippers 3 to move towards each other. The first sensor 33 detects the contact state between the grippers 3 and the object to be clamped in real time. When contact is detected, the grippers 3 are stopped, completing the first feed. Step 3: The PLC controller calculates the hardness parameter according to the formula a′=Aa, and then calculates the target displacement b=k×a′ for the second feed, controlling the grippers 3 to continue feeding towards each other. During the feed process, the load and displacement signals of the drive device are collected in real time. Before the target displacement is reached, if a sudden increase in load and the displacement increment approaching the target displacement are detected simultaneously... If the load increases to zero, the feed is terminated early. If the target displacement is reached and the termination conditions of load surge and displacement increment approaching zero are not triggered, the feed stops normally and the second feed is completed. Step 4: The PLC controller controls the robotic arm 1 to lift the object to be clamped at a constant speed. The second sensor 34 monitors in real time whether the object to be clamped has relatively slipped within the gripper 3. Step 5: If slippage of the object to be clamped is detected, the PLC controller calculates the target displacement of the third feed c=k×a′×λ and controls the cylinder 311 to drive the movable clamping plate 312 to perform the third feed. The pressure and displacement signals of the cylinder 311 are collected in real time. If a load surge and displacement increment approaching zero are detected before the target displacement is reached, the third feed is terminated early. If the termination conditions are not met, the third feed is repeated until the termination conditions are met and stable clamping is completed.

[0042] The criterion for determining that the displacement increment approaches zero is that the displacement value collected by the displacement detection unit per unit time is lower than the displacement increment threshold preset by the PLC controller.

[0043] During the second feeding process, the feeding speed of the gripper 3 is lower than that during the first feeding process, which reduces contact impact and avoids damage to the object to be gripped.

[0044] Each time the third feed action is repeated, the target displacement of the third feed is c=k×a′×λ, where a′=Aa, until the third feed termination condition is triggered.

[0045] The robotic arm 1 lifts the object to be clamped at a constant speed to avoid relative displacement interference caused by reasons other than clamping failure, and to ensure that the detection results of the relative displacement of the object to be clamped by the second sensor 34 are accurate.

[0046] This system uses a PLC controller as the core control unit. The robotic arm 1, gripping assembly 2, detection assembly, input module, and storage unit work together to form a complete flexible gripping closed-loop system. The input module is used to input the hardness parameter 'a' of the item to be gripped and determine the corresponding hardness system. The storage unit pre-stores the upper limit value A, proportional coefficient k, and compensation coefficient λ corresponding to each hardness system. All of these parameters are obtained through preset calibration experiments.

[0047] The detection assembly includes a current sensor, a pressure sensor, and two sets of displacement detection units. The current sensor is located on the drive device and is used to collect the load signal of the drive device. The pressure sensor is located on the cylinder 311 and is used to collect the load signal of the cylinder 311. The two sets of displacement detection units are arranged corresponding to the drive device and the cylinder 311, respectively, and collect the actual displacement of the gripper 3 and the movable clamping plate 312. All detection signals are uploaded to the PLC controller in real time.

[0048] The system employs a graded feed control logic, executing the first, second, and third feeds sequentially. The first feed is executed by the PLC controller based on the feedback signal from the first sensor 33, controlling the grippers 3 to move towards each other until they contact the object to be gripped, thus completing contact positioning. Subsequently, the PLC controller, based on the hardness parameter 'a', calls the parameters of the corresponding hardness system, first calculating the hardness parameter a′=Aa, and then calculating the target displacement b=k×a′ for the second feed and the target displacement c=k×a′×λ for the third feed.

[0049] During the second feed, the PLC controller, based on feedback signals from the current sensor and the corresponding displacement detection unit, controls the gripper 3 to continue feeding. When both conditions are met simultaneously—a sudden increase in the load on the drive device and the displacement increment approaching zero—the second feed is immediately terminated, achieving initial stable clamping. Afterward, the PLC controller controls the robotic arm 1 to lift the object to be clamped at a constant speed, monitoring for relative displacement of the object via the second sensor 34. If relative slippage is detected, the PLC controller initiates the third feed, controlling the cylinder 311 to drive the movable clamping plate 312 to perform a compensation action. Based on feedback signals from the pressure sensor and the corresponding displacement detection unit, the termination condition is again a sudden increase in load and the displacement increment approaching zero. If the condition is not met, the third feed is repeated until the termination condition is met, completing the final stable clamping.

[0050] This embodiment uses the Shore D hardness system to clamp plastic workpieces on an automated production line. The system's pre-stored calibration parameters are as follows: upper limit of hardness A=90, proportional coefficient k=0.02mm / hardness unit, compensation coefficient λ=0.3, and displacement increment threshold set to 0.001mm / s. A servo motor is used as the drive device, with a rotary encoder as the corresponding displacement detection unit; the cylinder 311 uses a linear displacement sensor as its corresponding displacement detection unit. The first feed speed is set to 50mm / s, and the second feed speed is set to 10mm / s. The second feed speed is significantly lower than the first, and the feed speed is reduced as the workpiece approaches to minimize the risk of impact and compression.

[0051] The operator inputs the hardness parameter a=60 (Shore D) of the workpiece to be clamped through the input module. After the PLC controller recognizes the hardness system, it retrieves the corresponding pre-stored parameter in the storage unit. The PLC controller controls the servo motor to drive the two sets of grippers 3 to move towards each other at a speed of 50mm / s. The first sensor 33 detects the contact state in real time. When it detects that the gripper 3 has just made contact with the workpiece surface, it controls the gripper 3 to stop, completing the first feed.

[0052] The PLC controller then calculates the hardness parameter according to the formula a′=Aa, obtaining a′=30, and calculates the second feed target displacement b=0.6mm and the third feed target displacement c=0.18mm.

[0053] The PLC controller controls gripper 3 to continue the second feed at a speed of 10 mm / s. The current sensor and rotary encoder upload load and displacement signals in real time. When the feed displacement reaches 0.55 mm, the PLC controller detects a sudden increase in the servo motor load and the displacement increment is less than 0.001 mm / s, which meets the double termination condition. The PLC controller then terminates the second feed prematurely, completing the initial clamping.

[0054] The PLC controller then controls the robotic arm 1 to lift the workpiece at a constant speed. The second sensor 34 detects a slight relative slippage in the workpiece, triggering the third feed process. The PLC controller controls the cylinder 311 to drive the movable clamping plate 312 to perform the third feed, with the pressure sensor and linear displacement sensor providing real-time feedback signals. When the feed displacement reaches 0.16mm, the load on the cylinder 311 suddenly increases and the displacement increment is below the threshold, meeting the termination condition. The system terminates the third feed, with no visible damage or irreversible plastic deformation to the workpiece, no further slippage during the transfer process, and stable and reliable clamping.

[0055] If the workpiece is replaced with one of different hardness within the same system, the corresponding hardness parameters only need to be re-entered, and the system can automatically complete the parameter call and displacement calculation without the need for on-site manual adjustment, thus possessing good versatility and flexible clamping effect.

Claims

1. A flexible clamping system based on hardness parameters, comprising a PLC controller, a robotic arm, a clamping assembly, and a detection assembly; the PLC controller controls the movement of the robotic arm; the clamping assembly is mounted on the front end of the robotic arm; the clamping assembly includes two identical grippers driven by a driving device and capable of moving towards or away from each other; characterized in that... Each gripper includes a lower fixed gripping part and an upper compensating feed assembly; The opposite end faces of the fixed clamping part are respectively fitted with a first sensor and a second sensor; Each compensation feed assembly includes a cylinder and a movable clamping plate. The piston rod end of the cylinder is fixedly connected to the opposite end face of the movable clamping plate. In the initial state, the opposite end face of the movable clamping plate is flush with the opposite end face of the fixed clamping part. The PLC controller integrates an input module, which is connected to the PLC controller to receive the user-inputted hardness parameter 'a' of the object to be clamped. The PLC controller integrates a storage unit, which is connected to the PLC controller to pre-store the upper limit value of hardness A, the proportional coefficient k, and the compensation coefficient λ of the corresponding hardness system. The detection component includes a current sensor, a pressure sensor, and two sets of displacement detection units. The current sensor is set on the drive device to detect the load of the drive device, and the pressure sensor is set on the cylinder to detect the load of the cylinder. The two sets of displacement detection units are set for the drive device and the cylinder respectively, and are used to collect the actual displacement of the gripper and the movable clamping plate respectively. The current sensor, pressure sensor, and displacement detection unit are all connected to the PLC controller. The PLC controller is configured to: control the gripper to complete the first feeding action based on the feedback signal from the first sensor until the gripper contacts the object to be gripped; based on the hardness parameter a, call the upper limit value A of the corresponding hardness system, the proportional coefficient k, and the compensation coefficient λ, first calculate the hardness parameter a′=Aa, then calculate the target displacement of the second feeding b=k×a′, and the target displacement of the third feeding c=k×a′×λ; based on the feedback signals from the current sensor and the corresponding displacement detection unit, control the gripper to perform the second feeding, and terminate the second feeding action when both the load on the drive device suddenly increases and the displacement increment approaches zero are met simultaneously; based on the feedback signal from the second sensor, determine whether the object to be gripped has undergone relative displacement; based on the feedback signals from the pressure sensor and the corresponding displacement detection unit, control the cylinder to drive the movable gripping plate to perform the third feeding, and terminate the third feeding action when both the load on the cylinder suddenly increases and the displacement increment approaches zero are met simultaneously; if the above termination conditions are not met, repeat the third feeding.

2. The flexible clamping system based on hardness parameters according to claim 1, characterized in that, Two grippers have through holes on their upper parts at opposite ends. The inner edge of the through holes extends outward from the grippers to form an installation channel. A cylinder is fixedly installed in the installation channel of the corresponding gripper. The cylinder piston rod is fixedly connected to the movable clamping plate of the gripper on the same side.

3. The flexible clamping system based on hardness parameters according to claim 1, characterized in that, The drive unit is a servo motor or a stepper motor. The displacement detection unit corresponding to the drive unit adopts a rotary encoder, which is installed on the output shaft end of the drive unit. The rotary encoder calculates the linear displacement of the gripper by detecting the rotation angle of the drive unit. The displacement detection unit corresponding to the cylinder adopts a linear displacement sensor, which is installed along the movement direction of the movable clamping plate and directly collects the linear displacement of the movable clamping plate.

4. The flexible clamping system based on hardness parameters according to claim 1, characterized in that, The proportional coefficient k and the compensation coefficient λ are preset calibration parameters.

5. The flexible clamping system based on hardness parameters according to claim 4, characterized in that, The reversible elastic deformation mentioned in the calibration experiment refers to the absence of visible damage and irreversible plastic deformation in the object to be clamped after clamping. Plastic deformation can be verified by precision measuring equipment.

6. A flexible clamping method based on a hardness parameter, characterized in that, The flexible clamping system described in any one of claims 1 to 5 includes the following steps: Step 1: Input the hardness parameter 'a' of the object to be clamped through the input module to determine the corresponding hardness system. The PLC controller retrieves the upper limit value A of the hardness of the system, the proportional coefficient k, and the compensation coefficient λ pre-stored in the storage unit. Step 2: The PLC controller controls the two grippers to move towards each other. The first sensor detects the contact state between the grippers and the object to be clamped in real time. When contact is detected, the grippers are controlled to stop, completing the first feed. Step 3: The PLC controller calculates the hardness parameter according to the formula a′=Aa, and then calculates the target displacement b=k×a′ for the second feed, controlling the grippers to continue feeding towards each other. During the feed process, the load and displacement signals of the drive device are collected in real time. Before the target displacement is reached, if a sudden increase in load and displacement are detected simultaneously, the system will stop feeding. If the displacement increment approaches zero, the feed is terminated early. If the target displacement is reached and the termination conditions of load surge and displacement increment approaching zero are not triggered, the feed stops normally, and the second feed is completed. Step 4: The PLC controller controls the robotic arm to lift the object to be clamped at a constant speed, and the second sensor monitors in real time whether the object to be clamped is relatively slipping in the gripper. Step 5: If slippage of the object to be clamped is detected, the PLC controller calculates the target displacement of the third feed c=k×a′×λ, and controls the cylinder to drive the movable clamping plate to perform the third feed. The cylinder pressure and displacement signals are collected in real time. If a load surge and displacement increment approaching zero are detected before the target displacement is reached, the third feed is terminated early. If the termination conditions are not met, the third feed is repeated until the termination conditions are met, and stable clamping is completed.

7. The flexible clamping method based on hardness parameters according to claim 6, characterized in that, The criterion for determining that the displacement increment approaches zero is that the displacement value collected by the displacement detection unit per unit time is lower than the displacement increment threshold preset by the PLC controller.

8. The flexible clamping method based on hardness parameters according to claim 6, characterized in that, During the second feed, the feed speed of the gripper is lower than the movement speed of the gripper during the first feed.

9. The flexible clamping method based on hardness parameters according to claim 6, characterized in that, Each time the third feed action is repeated, the target displacement for the third feed is c=k×a′×λ, where a′=Aa, until the termination condition for the third feed is triggered.

10. The flexible clamping method based on hardness parameters according to claim 6, characterized in that, The robotic arm lifts the object to be gripped at a constant speed.

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