A full-automatic variable-distance flexible grabbing system and a control method thereof

Abstract

The application discloses a full-automatic variable-distance flexible grabbing system and a control method thereof, converts mechanical adjustment of X-axis, Z-axis and Y-axis into electrical parameter adjustment, and provides two control methods which are special for a clamping module of the full-automatic system and are used for servo drivers of the clamping module, namely, a software multi-circle backup is used to replace an internal battery of an encoder, and cross-rolling verification is combined, so that the servo driver of the clamping module can directly enter a clamping ready state without returning to an original point mechanically after being powered on; and a weak magnetic control algorithm is used to suppress reverse electromotive force from a source, replace passive protection devices on a sensor signal line, and guarantee that multi-sensor AND fusion determination logic is continuously reliable in a full-speed section. The application eliminates two delay sources of initialization waiting and sensor failure, and realizes a complete closed loop from structure to control, and releases a formula to zero-second transformation.

Description

Technical Field

[0001] This invention belongs to the field of intelligent manufacturing technology, specifically relating to a fully automatic variable-pitch flexible grasping system and its control method. Background Technology

[0002] Modern intelligent manufacturing is a new production method that deeply integrates next-generation information and communication technologies with advanced manufacturing technologies. Modern intelligent manufacturing (such as manufacturing energy storage battery pack lines) requires extremely high line changeover efficiency. During the line changeover process, gripping equipment plays a crucial role. However, existing gripping equipment is mostly a patchwork structure: pitch adjustment relies on manual hole positioning, downward pressure relies on cylinders and photoelectric switches, and clamping relies on pneumatic grippers. If a different product specification needs to be changed during processing, 2-3 workers are required to spend several hours on mechanical disassembly and sensor calibration, which severely restricts the OEE (Overall Equipment Effectiveness) of the production line.

[0003] To address this issue, the industry has proposed a fully electrically driven multi-axis linkage gripping system, converting all mechanical adjustments into electrical parameter adjustments. However, when these modules are cascaded to form a complete system, the gripping module at the very end, which directly contacts the product, reveals the following two hardware-dependent problems:

[0004] 1. The power-on initialization delay of the clamping module depends on the encoder battery.

[0005] The servo motor driving the synchronous belt opening and closing in the clamping module is equipped with a multi-turn absolute encoder. The encoder is used to record the cumulative number of rotations (i.e., multi-turn position) after the motor shaft exceeds the single-turn range. In the prior art, the multi-turn encoder relies on a built-in battery to maintain power supply to the multi-turn counting circuit during system power failure. Since the clamping module is located at the very end of the entire machine, it is subjected to frequent collisions, vibrations, and gravitational impacts during transportation; in the power failure state, the grippers are prone to passive displacement under transportation or external force. If the battery is removed to reduce costs, the multi-turn counter will not work when the shaft rotates after power failure, and the multi-turn position read after power is restored will deviate from the actual gripper opening. Therefore, a return-to-origin operation must be performed every time power is restored—the position must be re-established based on the mechanical limit origin, which takes several seconds to tens of seconds. In the three-axis linkage changeover process of the entire machine, the return-to-origin waiting of the clamping module becomes a significant bottleneck in one-click changeover.

[0006] 2. There is a risk of sensor burnout in the gripping module's grasping confirmation link.

[0007] The clamping module is the only module in the entire machine that directly determines whether material has been clamped. To achieve high reliability, the clamping module employs multi-sensor AND fusion logic, meaning that the clamping position signal and signals from multiple material detection sensors (such as diffuse reflection photoelectric sensors) must all simultaneously meet certain conditions before the system outputs a signal indicating reliable gripping. Because the servo motor of the clamping module exhibits a trapezoidal speed curve of "high-speed approach → rapid deceleration → clamping and holding" during clamping / release operations, high-acceleration start-stop cycles are extremely frequent. Therefore, the permanent magnet synchronous motor rotor generates a high back electromotive force during high-speed, high-acceleration rotation. Furthermore, due to the compact structure of the clamping module and the parallel routing of the motor power lines and sensor signal lines within a confined space, the back electromotive force can easily induce transient overvoltages exceeding the withstand voltage of the sensor's electronic components via parasitic coupling paths on the sensor signal lines, easily burning out the photoelectric components or signal conditioning circuits in the sensors. Once a sensor is damaged, the AND fusion judgment directly fails. Even if the grippers have physically clamped the workpiece, the system cannot confirm that the material is in place and can only stop the machine and issue an alarm. In the handling of high-value products such as lithium batteries, there is a risk of safety accidents caused by sensors being damaged and falling due to gaps. Existing technologies use TVS diodes or isolation circuits on the signal lines for passive protection, but these can only absorb transient overvoltages that have already occurred and cannot eliminate the back electromotive force at its source.

[0008] Both of the above problems stem from the fact that existing technologies rely on hardware components to perform critical reliability functions of the clamping module, while the hardware itself has lifespan limitations, maintenance burdens, and failure risks. At the system level, although the structure has achieved full electrification, the most critical end effector cannot achieve power-on and full-speed reliability due to hardware dependence. Therefore, the two hardware bottlenecks of the clamping module make it impossible to achieve a closed loop in the control chain for one-click changeover. Summary of the Invention

[0009] To address the aforementioned issues, this invention discloses a fully automatic variable-pitch flexible gripping system and its control method. It converts all mechanical adjustments of the X-axis (pitch), Z-axis (height), and Y-axis (opening) into electrical parameter adjustments. Furthermore, for the clamping module, which is responsible for the final gripping execution and confirmation in the overall system, two control methods specifically for the clamping module's servo driver are provided: First, software multi-turn backup replaces the encoder's built-in battery, combined with roll cross-checking, allowing the clamping module's servo driver to directly enter the gripping ready state without mechanical homing after power-on. Second, a weak-field control algorithm suppresses back electromotive force at its source, replacing passive protection devices on the sensor signal lines and ensuring continuous reliability of the multi-sensor AND fusion judgment logic across the entire speed range.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] A control method for a fully automatic variable-pitch flexible grasping system includes:

[0012] Step 1: The main control system sends instructions to the central control unit. The central control unit parses the instructions to obtain the pitch signal, pressing signal, and clamping signal. It then sends position pulses to the pitch motors in each automatic pitch module to automatically adjust the center distance between the two grippers to the product length. The system also sends the target torque / position to the linear drive component in the vertical pressing module to adapt to the product height. Finally, it sends the target opening instruction to the clamping drive motor in the large stroke clamping module.

[0013] Step 2: During normal operation of the clamping module, the controller writes the software multi-turn backup data to the non-volatile storage unit in each control cycle; the software multi-turn backup data includes: the current encoder single-turn reading, multi-turn overflow count value, calculated motion direction and absolute position value;

[0014] Step 3: When the clamping module loses power and the system is powered on, the controller reads the hardware multi-turn count value from the encoder and reads the software multi-turn backup data saved before the last power failure from the non-volatile storage unit.

[0015] Step 4: Calculate the compensated multi-turn overflow count value using the following formula:

[0016] ,

[0017] C(d,Δθ) = d·Δθ,

[0018] Δθ = θ_cur - θ_mem

[0019] Where W′ is the compensated multi-turn overflow count value, W is the current multi-turn overflow count value, d is the direction of motion, θ_mem is the position saved in the last control cycle before power failure, and θ_cur is the current encoder single-turn reading. For indicator functions;

[0020] Step 5: The controller uses W′+ θ_cur as the absolute multi-turn position after power-on and directly enters the motion control ready state without performing mechanical return to the origin.

[0021] Furthermore, it also includes the following steps:

[0022] After receiving the motion command, the servo controller of the clamping module parses the target acceleration parameter a_target in the motion command and compares it with the preset acceleration threshold a_th:

[0023] When a_target≤a_th, the direct-axis current i_d = 0 is maintained, the motor operates at the maximum torque-current ratio, and the VM bus voltage is within the safe range;

[0024] When a_target > a_th, the controller injects a negative d-axis current into the vector control loop before starting the clamping motion to perform field weakening control, and the VM bus voltage is suppressed within the sensor power supply tolerance range.

[0025] Furthermore, the negative d-axis current i_d has a value of -0.2.

[0026] Furthermore, before step 4 is executed, a verification step is also included: if the hardware multi-turn value is consistent with or the deviation is within the allowable range of the multi-turn overflow count value in the software backup, the verification is passed; if the verification is passed, step 3 is executed.

[0027] Furthermore, in step 4, the compensated multi-turn overflow count value includes the following three cases:

[0028] When d = -1, Δθ > 0, W′ = W - 1;

[0029] When d = 1, Δθ < 0, W′ = W + 1;

[0030] When d · Δθ ≥ 0 and d ≠ 0, W′ = W.

[0031] Furthermore, in step 4, if d ≠ 0 and Δθ is not within the legal range, the encoder data is determined to be unreliable, and the controller immediately outputs an alarm signal and stops the motion.

[0032] This invention also provides a fully automatic variable-pitch flexible gripping system for implementing a control method for the fully automatic variable-pitch flexible gripping system, comprising: an overall support frame, and a large-stroke clamping module, an automatic variable-pitch module, and a vertical pressing module installed on and electrically interconnected on the overall support frame; the large-stroke clamping module is located within the overall support frame, there are two automatic variable-pitch modules, each mounted on one of the two sets of clamping movable components of the large-stroke clamping module, each automatic variable-pitch module comprising two variable-pitch movable components capable of changing the distance between them, and four vertical pressing modules, each installed at the bottom of each variable-pitch movable component, each vertical pressing module comprising a pressing component and a bottom gripper.

[0033] Furthermore, the large-stroke clamping module includes a clamping base, a clamping drive motor and guide rails fixed on the clamping base; the clamping drive motor drives the closed-loop synchronous belt to rotate; there are two guide rails, which are arranged in parallel on the clamping base, and each guide rail is provided with a left clamping slider and a right clamping slider. The left clamping slider is connected to a first adapter plate, and the right clamping slider is connected to a second adapter plate. The first adapter plate and the second adapter plate are fixedly connected to the upper transmission section and the lower transmission section of the closed-loop synchronous belt, respectively.

[0034] Furthermore, the two automatic pitch-changing modules are fixedly connected to the first adapter plate and the second adapter plate, respectively. Each automatic pitch-changing module includes: a guide rail, a pitch-changing drive motor, and a transmission shaft arranged parallel to the shaft of the pitch-changing drive motor. The pitch-changing drive motor drives the transmission shaft to rotate through a synchronous pulley and a synchronous belt. The transmission shaft is fitted with two nut seats, which are connected to two nut adapter seats by pins. The two nut adapter seats are fixedly connected to two sliding seats, which are fitted on the guide rail. The guide rail is parallel to the transmission shaft.

[0035] Furthermore, the four vertical pressing modules are respectively fixed on the sliding seats of the automatic pitch-changing module. The vertical pressing module includes a linear drive assembly, an elastic buffer assembly, a pressing plate and a bottom gripper. The pressing plate is connected to the driving end of the linear drive assembly through the elastic buffer assembly. The bottom gripper is fixedly connected to the main body of the linear drive assembly. The pressing plate is located above the bottom gripper.

[0036] The beneficial effects of this invention are as follows:

[0037] 1. The system structure of this invention realizes fully electrified control of the X / Y / Z axes. The dedicated control method of the clamping module eliminates two sources of delay: initialization waiting and sensor failure. From structure to control, a complete closed loop is realized from formula issuance to zero-second changeover.

[0038] 2. This invention uses software multi-turn backup of ferroelectric FRAM to replace the encoder's built-in battery. The software multi-turn backup includes at least the current encoder single-turn reading, multi-turn overflow count value, direction of motion, and absolute position value. Upon power-up, a comparison and verification are performed during recovery from the FRAM to prevent data errors. This invention downgrades homing from a routine, essential operation to a recovery method after a collision or verification anomaly.

[0039] 3. This invention uses weak magnetic control to reduce the reverse electromotive force from the physical source and simultaneously suppress the overvoltage of the VM bus, ensuring that the sensor hardware survives → the signal is available → the AND fusion judgment process is executed normally, eliminating the risk of production line shutdown and clamping failure due to sensor burnout causing clamping failure to be confirmed.

[0040] 4. In this invention, the position link (three-phase consistency arbitration → ferroelectric data integrity → power-on recovery without initialization) and the grasp confirmation link (weak magnetic source suppression → DC-DC power supply integrity → multi-sensor AND fusion) are independent and redundant within the clamping module; the STO hardware security layer is independent of all software arbitration paths, ensuring that the clamping torque is unconditionally cut off in extreme scenarios. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the overall structure of the fully automatic variable-distance flexible grasping system provided by the present invention.

[0042] Figure 2 This is a schematic diagram of the large-stroke clamping module structure.

[0043] Figure 3 This is a detailed schematic diagram of the long-stroke clamping module.

[0044] Figure 4 This is a schematic diagram of the longitudinal section of a fully automated variable-pitch flexible gripping system.

[0045] Figure 5 This is a schematic diagram of an automatic pitch control module, in which the housing of the pitch control drive motor has been removed, and the signal lines are not shown.

[0046] Figure 6 for Figure 5 Partial cross-section diagram.

[0047] Figure 7 This is a cross-sectional schematic diagram of the automatic pitch control module at an elevation angle.

[0048] Figure 8 This is a schematic diagram of the vertical downward pressing module structure.

[0049] Figure 9 This is a schematic diagram of the vertically downward pressing module from another perspective.

[0050] Figure 10 This is a schematic diagram of the fixed support structure.

[0051] Figure 11 This is a schematic diagram of the vertical downward pressing module structure, in which the fixing bracket has been removed.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1-Bearing frame, 2-Large stroke clamping module, 201-Clamping base, 202-Linear guide rail, 203-Left clamping slider, 204-Right clamping slider, 205-First adapter plate, 206-Second adapter plate, 207-Clamping drive motor, 208-Driving synchronous pulley, 209-Driven synchronous pulley, 210-Precision reducer, 211-Closed-loop synchronous belt, 212-Upper transmission section, 213-Lower transmission section, 214 Toothed pressure plate, 215-Tensioning base, 216-Tension adjusting screw, 217-Main controller, 3-Automatic pitch changing module, 301-Crossbeam, 302-Pitch changing drive motor, 303-Drive shaft, 304-Nut seat, 305-Linear guide rail, 306-Drive nut, 307-Pin 308-Drag chain, 309-Drip-proof isolation groove, 310-Variable pitch synchronous pulley, 311-Nut adapter seat, 312-Sliding seat, 313-Main harness junction box, 314-Signal line, 315-Storage slot, 316-U-shaped synchronous belt, 317-Drag chain seat, 318-Power supply and communication line, 4-Vertical pressing module, 401-Linear drive assembly, 402-First elastic buffer assembly, 403-Pressing plate, 404-Bottom gripper, 405-Fixed bracket, 406-Diffuse reflection photoelectric sensor, 407-Sliding bracket, 408-Photoelectric switch, 409-Sensing plate, 410-Second elastic buffer assembly, 411-Slide rail, 412-Pressing slider, 413-SR connector, 5-Extension bracket. Detailed Implementation

[0054] The technical solutions provided by the present invention will be described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0055] This invention provides a fully automatic variable-pitch flexible gripping system, comprising an integral support frame 1, and a large-stroke clamping module 2, an automatic variable-pitch module 3, and a vertical pressing module 4, all mounted on and electrically interconnected with the integral support frame 1. Figure 1 As shown, the long-stroke clamping module 2 is located within the overall support frame, the automatic pitch-changing module 3 is mounted on the clamping movable component of the long-stroke clamping module 2, and the vertical pressing module 4 is located at the bottom of the automatic pitch-changing module 3. The servo / stepper motor / cylinder / push rod and other drive components of the three modules are all connected to a central control unit (PLC or industrial computer) via a bus (such as EtherCAT). The central control unit receives new product specification formula instructions from the production line main control system and synchronously sends corresponding position / torque / opening instructions to the pitch-changing motor, linear drive assembly, and clamping drive motor. The support frame 1 is also connected to an extension bracket 5. The main wiring harness connected to the main controller inside the long-stroke clamping module 2 passes through the side of the support frame and the extension bracket before entering the main wiring harness junction box 313 of the automatic pitch-changing module.

[0056] like Figure 2 As shown, the long-stroke clamping module 2 includes a clamping base 201 and two parallel linear guide rails 202 fixed on the clamping base 201. Each guide rail has a left clamping slider 203 and a right clamping slider 204. The left clamping sliders 203 on both guide rails are in the same position and are connected to a first adapter plate 205. The right clamping sliders 204 on both guide rails are in the same position and are connected to a second adapter plate 206. A main controller 217 is fixed on the clamping base 201, and a clamping drive motor 207 is also mounted on the clamping base 201. The main controller 217 controls the operation of the clamping drive motor 207. One end of the clamping base 201 has a driving synchronous pulley 208, and the other end has a driven synchronous pulley 209. The clamping drive motor 207 is connected to the driving synchronous pulley 208 through a precision reducer 210. The driving and driven synchronous pulleys are linked by a closed-loop synchronous belt 211 fitted between them. The closed-loop synchronous belt 211 is naturally tensioned between the two wheels, forming a parallel upper transmission section 212 and a lower transmission section 213. The upper transmission section 212 refers to the section of the closed-loop synchronous belt 211 that is relatively far away from the clamping base 201, and the lower transmission section 213 refers to the section of the closed-loop synchronous belt 211 that is relatively close to the clamping base 201. The first adapter plate 205 is fixedly locked to the upper transmission section 212, and the second adapter plate 206 is fixedly locked to the lower transmission section 213. The closed-loop synchronous belt is driven to rotate by the forward and reverse rotation of the motor. The upper and lower transmission sections always move in opposite directions, so as to accurately convert the rotation of the motor into a perfectly synchronized, equidistant linear motion of the two sliders in opposite directions (clamping) or back-to-back (opening), achieving perfect mechanical center alignment. At least one of the left and right clamping sliders is equipped with a material detection sensor (such as a diffuse reflection photoelectric sensor). The material detection sensor emits and receives signals downwards to detect whether there is material between the jaws after the clamping action is completed. It is usually suitable for detecting larger volume materials. Its signal and the clamping position signal of the clamping drive motor are jointly connected to the AND fusion judgment logic - the system outputs "reliable gripping" confirmation only when all signals are satisfied at the same time.

[0057] like Figure 3 As shown, a toothed pressure plate 214 is provided at the connection points of the first adapter plate 205, the second adapter plate 206, and the closed-loop synchronous belt 211. The closed-loop synchronous belt 211 has serrations, and the toothed pressure plate has meshing tooth surfaces that match the tooth profile of the closed-loop synchronous belt 211. Specifically, the first adapter plate 205 rigidly clamps and fixes the toothed pressure plate, the closed-loop synchronous belt, and the adapter plate together with bolts, forming a mechanical hard interference that can absolutely prevent relative slippage and tooth skipping of the belt body during large-stroke heavy-load start-stop.

[0058] As an improvement, the driven synchronous pulley 209 is rotatably mounted on a sliding tension base 215. The tension base 215 is bolted to the sides in a groove, and a tension adjusting screw 216 is threaded through the end of the tension base 215. When the bolts in the groove are loosened, rotating the tension adjusting screw drives the tension base to make a slight displacement along the belt conveying direction. This compensates for the plastic tensile fatigue generated by the large-stroke synchronous belt after long-term high-frequency operation, ensuring the transmission rigidity and alignment accuracy of the clamping mechanism throughout its entire lifespan. After adjusting the tension base to the appropriate position, the bolts in the groove are tightened.

[0059] There are two automatic pitch control modules 3, which are respectively fixed on the first adapter plate 205 and the second adapter plate 206, and move with the two adapter plates. Specifically, the automatic pitch control module 3 is fixedly connected to the adapter plates through a triangular adapter. Figure 4 , Figure 5 , Figure 6 , Figure 7 As shown, the automatic pitch-changing module 3 includes a horizontally arranged crossbeam 301, a pitch-changing drive motor 302, and a drive shaft 303. The pitch-changing drive motor 302 is offsetly mounted on the side or above the crossbeam 301, and its motor shaft is parallel to the drive shaft 303. It is driven by the controller of the automatic pitch-changing module 3, and the motor shaft transmits power to the pitch-changing synchronous pulley 310 through a U-shaped synchronous belt 316, significantly shortening the overall axial length of the module. The pitch-changing synchronous pulley 310 drives the drive shaft 303 to rotate. The drive shaft 303 preferably uses a double-acting lead screw or two independent lead screws. At least two nut seats 304 are fitted on the drive shaft. Specifically, two transmission nuts 306 are sleeved on the drive shaft 303, and nut seats 304 are fixed to the outside of the nuts. Nut adapter seats 311 are fixed on the nut seats 304, and the two are connected by a transmission pin 307. The pin provides rigid push-pull in the drive shaft direction but allows for freedom of movement in the radial direction, thereby releasing the radial force on the drive shaft and transferring all the cantilever bending moment generated by the nut seat 304 to the double guide rails, protecting the drive shaft from breakage or deformation. A sliding seat 312 is provided below each of the two nut adapter seats 311. At least two parallel linear guide rails 305 are provided on the side or bottom of the crossbeam 301. The sliding seat 312 can slide on the linear guide rails, and the wide-spaced double guide rails resist the overturning torque generated by the heavy-duty gripper suspension below.

[0060] Furthermore, the automatic pitch-changing module 3 also includes a flexible cable chain 308, which is located outside the automatic pitch-changing module. One end of the flexible cable chain is fixed to the sliding seat 312, and the other end is connected to the cable chain seat 317. The cable chain seat 317 is fixed to the crossbeam 301. Storage slots 315 are provided on the facing side walls of the two movable bases. A controller is installed inside the main wiring harness junction box 313. The main cable branches off within the main wiring harness junction box 313 as the power supply and communication line 318 for the linear drive assembly, and the signal lines 314 for the photoelectric switch and diffuse reflection sensor. The photoelectric switch and diffuse reflection sensor signal lines 314 are inserted into the cable chain and move with it. The power supply and communication line 318 for the linear drive assembly is located within the storage slot 315, effectively preventing interference, compression, or even cutting of the air pipe or high-voltage wires when the pitch-changing module closes close. As an improvement, a U-shaped or L-shaped anti-drip isolation groove 309 is horizontally fixed at the bottom of the crossbeam 301. The anti-drip isolation groove is the same length as the crossbeam 301, and its projected area completely covers the drive shaft and guide rail track above. All the grease dripping from the friction of the transmission components will fall into the anti-drip isolation groove.

[0061] like Figure 8 , Figure 9 As shown, the vertical pressing module 4 is fixed below the sliding seat 312 and includes a linear drive assembly 401, a first elastic buffer assembly 402, a pressing plate 403, a bottom gripper 404, a fixed bracket 405, and a sliding bracket 407. The top of the fixed bracket 405 is connected to the automatic pitch control module 3, as shown. Figure 10 , Figure 11 As shown, a slide rail 411 is provided on its side, and a downward sliding block 412 is provided on the sliding bracket 407. This sliding block can slide back and forth on the slide rail of the fixed bracket 405. The linear drive assembly 401 is fixedly connected to the side of the sliding bracket 407. The bottom gripper 404 is fixedly connected to the bottom of the sliding bracket 407. Power supply and communication line 318 ( Figure 8(Power and communication lines not shown) are connected to the linear drive assembly 401 via SR connector 413 and control the operation of the linear drive assembly 401. The output terminal of the linear drive assembly 401 is connected to the lower pressure plate 403 via the first elastic buffer assembly 402. The bottom gripper 404 is fixedly connected to the main body of the linear drive assembly 401. The lower pressure plate 403 is located above the bottom gripper 404. The elastic buffer assembly 402 can be a helical spring sleeved on the guide post or a polyurethane flexible buffer pad. When the lower pressure plate contacts the product, the elastic buffer assembly allows it to have a small absorption stroke that recoils upward along the Z-axis. A buffer component can also be provided on the side of the lower pressure plate facing the bottom gripper 404. The buffer component can be made of a material such as rubber that can deform under external force and play a buffering role. The linear drive assembly 401 can be an electric push rod with a built-in absolute encoder or a pneumatic actuator cylinder. When the linear drive assembly 401 extends downward and contacts the lower pressure plate, the elastic buffer assembly can absorb excess kinetic energy to prevent crushing. A second elastic buffer assembly 410 (shown as a spring, but can be replaced with other components capable of buffering) is also provided between the fixed bracket 405 and the sliding bracket 407. A photoelectric switch 408 is mounted on the fixed bracket 405, and a sensing element 409 is mounted on the sliding bracket 407. The photoelectric switch 408 is connected to the main controller via a signal line 314 (not shown in the figure). Under normal conditions, the sensing element is in contact with the photoelectric switch. When the bottom of the hook is accidentally struck, or the lower block accidentally presses against the battery, the sliding bracket 407 and its mounted linear drive assembly 401 will slide upwards, the second elastic buffer assembly 410 will contract, the sensing element will disengage from the photoelectric switch, an alarm will sound, and all equipment will stop operating to prevent accidental production incidents.

[0062] The fully automatic variable-pitch flexible gripping system has a total of four vertical pressing modules 4. Two automatic variable-pitch modules 3 are synchronously controlled to align the positions of the two opposing vertical pressing modules 4. Diffuse reflection photoelectric sensors 406, connected to the main controller, are installed on the bottom grippers 404 below the two opposing (vertically or obliquely) vertical pressing modules 4 to detect the presence of material between the grippers. The diffuse reflection photoelectric sensors 406 are connected to the main controller via signal lines 314. In operation, the main controller of the fully automatic variable-pitch flexible gripping system drives the left and right gripping sliders 203 and 204 to slide, thereby moving the first adapter plate 205, the second adapter plate 206, and their connected automatic variable-pitch modules 3 to a suitable position, maintaining an appropriate distance between the two automatic variable-pitch modules 3. The variable-pitch drive motor 303 in the automatic variable-pitch module 3 is controlled by a controller located in the main wiring harness junction box 313, driving the transmission shaft 303 to rotate, causing the nut seat and sliding seat to move to a suitable position, and the bottom gripper 404 to move under the material. The controller in the automatic variable-pitch module 3 also controls the linear drive component 401 in the vertical pressing module 4 to drive the lower pressure plate to press down and clamp the material. After the material is moved to the target position, the linear drive component 401 in the vertical pressing module 4 drives the lower pressure plate to move up a certain distance, and by controlling the actions of the large-stroke gripping module and the automatic variable-pitch module, the bottom gripper leaves the material area. As an improvement, when the linear drive assembly uses an electric push rod, when the electric push rod moves downward and the pressure plate contacts the product surface, due to the presence of the first elastic buffer component, the push rod will not stall instantly, but will continue to compress the first elastic buffer component downward. At this time, the motor output torque (or current value) begins to rise smoothly. The controller samples the motor torque in real time at high frequency. When the torque reaches the preset contact torque threshold, it is determined that the optimal clamping force has been reached. The controller immediately outputs a stop signal, and the push rod stops. The current encoder position data can then be used as the thickness reference for this batch of products.

[0063] To address the issue of the clamping module requiring a return to the origin upon power-up due to encoder battery dependence, this invention proposes a dedicated control method for the clamping module, enabling software-based multi-turn position compensation without initialization. The method includes the following steps:

[0064] (1) During normal operation of the clamping module, its servo controller atomically writes the current encoder single-turn reading, multi-turn overflow count value, calculated motion direction and absolute position value into the non-volatile memory unit in each control cycle as software multi-turn backup data. The non-volatile memory unit can still retain data after the system is powered off. The non-volatile memory unit adopts ferroelectric memory (FRAM) and communicates with the servo controller through the SPI interface. The reason for choosing FRAM instead of EEPROM or Flash is: (1) FRAM has extremely high erase and write endurance - ferroelectric supports 10 14It can withstand ultra-high frequency cycles of writing once per control cycle (e.g., 125 μs), while conventional EEPROMs can only withstand about 10 write / read cycles. 6 Next, Flash approximately 10 5 (1) The write operation may fail within a few months under this high-frequency writing scenario; (2) The writing of FRAM does not require waiting for the erase cycle and can complete the non-volatile data within one SPI clock cycle, satisfying the atomic writing timing constraints within the control cycle; (3) Ferroelectric data retention time exceeds 10 years after power failure, and it can work reliably in the entire temperature range (-40°C to +85°C), adapting to the industrial vibration and high and low temperature environment of the clamping module.

[0065] Because the clamping module's motor movement repeatedly oscillates between the clamping and opening limits, multiple-turn overflow events occur frequently (the number of motor rotations far exceeds the single-turn range). Timely backup for each control cycle is crucial to ensuring accuracy recovery after a power outage. The controller writes the absolute position value into the backup, allowing it to be directly retrieved upon power-on recovery without secondary calculation.

[0066] After a power outage, the gripper may experience passive displacement ranging from hundreds of micrometers to several millimeters due to gravity or external forces (within the resolution range of a single-turn encoder, this does not cause a change in the multi-turn count). Upon power-up, the gripper's servo controller reads the hardware multi-turn count from the encoder and simultaneously retrieves the software multi-turn backup data saved before the last power outage from the non-volatile memory unit. The controller compares and verifies the hardware multi-turn value with the software backup value. If the verification passes, the absolute multi-turn position recovered after power-off multi-turn compensation is directly used as the current gripper opening position, and the servo enters motion control ready state without needing to perform mechanical homing initialization. At this point, the gripper can receive changeover commands and move directly to the target opening. Upon power-up recovery, the software backup provides the correct overflow circle value before the power outage, and the hardware single-turn reading reflects the actual shaft position after the power outage—the combination of these two uniquely determines the absolute position. Specifically, the verification passes when the hardware multi-turn value matches the overflow circle value in the software backup (or the deviation is within the allowable range), indicating that no large rotation exceeding the single-turn range occurred during the power outage. The power outage multi-turn compensation specifically includes the following steps:

[0067] After the servo controller is powered on, it reads the position θ_mem and the direction of motion d (d ∈ {-1, 0, 1}, -1 = reverse / open, 1 = forward / close, 0 = stationary) saved in the last control cycle before the power failure from the ferroelectric data source, and at the same time reads the current hardware position θ_cur from the encoder.

[0068] The positional difference is defined as follows:

[0069] Δθ = θ_cur - θ_mem

[0070] Define the consistency discriminant function for direction-difference:

[0071] C(d,Δθ) = d·Δθ

[0072] In the above formula, the physical meaning of the symbols is as follows: C < 0 indicates that the direction of motion is opposite to the direction of position change - that is, the encoder crossed the single-turn count boundary during the power-off period (multi-turn overflow occurred); C ≥ 0 and d ≠ 0 indicates that the direction is consistent with the position change and no overflow occurred; d = 0 indicates that the motor was stationary before the power-off, the position change was caused by external force, and it does not involve multi-turn overflow, and θ_cur is the single-turn value obtained from the encoder when the power is on.

[0073] Let the current multi-lap overflow count be W, and the compensated multi-lap overflow count be W′. The compensation rule is as follows:

[0074]

[0075] in This is an indicator function that takes the value 1 if the condition is true, and 0 otherwise.

[0076] Expanded into the three operating conditions shown in Table 1:

[0077] Table 1

[0078]

[0079] After compensation, the controller uses W′ + θ_cur as the absolute multi-turn position after power-on and directly enters the motion control ready state without performing mechanical homing. The direction d is packaged and written to the ferroelectric backup frame along with the position θ_mem in each control cycle. The d retrieved from the ferroelectric frame at power-on is the motion direction last successfully written by the controller just moments before power-off—this ensures strict alignment of the direction and position information on the time axis, avoiding time deviations such as "direction is 2 ms before power-off, position is 0 ms before power-off" leading to inaccurate Δθ calculations. The reciprocating clamping / opening motion of the clamping module consists of "high-speed closing → deceleration approach → clamping and holding pressure → high-speed opening → deceleration limit" within each working cycle, with the motion direction remaining constant within each segment. After storing the direction d in the ferroelectric backup frame, the motion direction of the gripper just moments before power-off can be accurately restored upon power-on. Even if the power outage happens to occur near the direction switching point (when d approaches 0), the algorithm does not modify W when d = 0. Instead, it restores the position by combining the passive displacement of the external force and the single-turn reading of the encoder, thus avoiding overflow direction misjudgment near the switching point.

[0080] If d ≠ 0 and Δθ does not meet the legal value range of any of the above three working conditions (i.e., the encoder position data shows an inexplicable jump), then the encoder data is determined to be unreliable, the controller immediately outputs an alarm signal and stops the movement.

[0081] STO (Safe Torque Off) Hardware Safety Layer Settings: When the STO (Safe Torque Off) hardware signal is lost, the servo controller of the clamping module immediately and unconditionally stops torque output and enters a safe stop state. Since the clamping module is in direct contact with the product, the STO safety layer ensures that even in extreme scenarios such as communication interruption or controller software crash, the clamping force can be unconditionally cut off, preventing the grippers from continuously applying pressure and damaging the product. After power is restored, the power-on recovery and verification process is executed—if the verification passes, it directly enters the ready state. Only when the power-on comparison verification fails or the direction comparison triggers an alarm, the servo controller of the clamping module performs a controlled mechanical return-to-origin operation once, reconstructing the correct multi-turn position data with the mechanical limit origin of the clamping module as the absolute reference; after reconstruction, the data is written to the non-volatile storage unit, and then it returns to the motion control ready state.

[0082] To address the issue of material detection sensor burnout caused by high-acceleration back electromotive force coupling in the clamping module, this invention provides a dedicated control method for the clamping module, achieving active protection of the material detection sensor based on weak magnetic field control. When a permanent magnet synchronous motor rotates at high speed and high acceleration, the amplitude of the back electromotive force induced in the stator windings by the rotor permanent magnets is proportional to the product of the rotational speed and the rotor flux linkage. In the clamping module, the power supply and signal lines of the clamping drive motor and the material detection sensor are arranged in parallel within a compact clamp housing. The back electromotive force is fed back to the DC bus (i.e., the VM voltage rail) via the motor power lines, generating transient overvoltage spikes on the bus. These spikes threaten the sensor through the following paths:

[0083] Conductive coupling: The VM voltage spike is conducted through the board-level DC-DC converter to the low-voltage power supply rail of the sensor, causing the sensor power supply terminal to be subjected to overvoltage pulses that exceed the design tolerance range.

[0084] Electromagnetic coupling: High-frequency pulse current in the power line induces differential / common-mode transient voltages on the signal lines of nearby sensors through the spatial electromagnetic field.

[0085] This invention conducted actual measurements of the VM bus voltage of the clamping module under different acceleration conditions in a dual-grip working state, and recorded the maximum VM voltage at each acceleration level. The results are shown in Table 2 below:

[0086] Table 2

[0087] 8,000 24.4 15,000 34.0 20,000 59.6

[0088] Actual measurement data shows that when the acceleration increases from 8,000 mm / s² to 20,000 mm / s², the maximum voltage of the VM bus surges from 24.4 V to 59.6 V, an increase of 144%. Conventional material detection sensors (such as diffuse reflection photoelectric sensors) typically have a rated power supply withstand voltage of 30 V—at an acceleration of 15,000 mm / s², VM reaches 34.0 V, exceeding the sensor's power supply withstand threshold; at 20,000 mm / s², VM reaches a staggering 59.6 V, far exceeding the sensor's limit, sufficient to cause permanent sensor burnout within several high-acceleration clamping cycles.

[0089] The stator voltage equation of the permanent magnet synchronous motor in the rotor synchronous rotating coordinate system (dq axis) is as follows:

[0090] d-axis voltage: u_d = R_s · i_d + L_d · di_d / dt - ω_e · L_q · i_q

[0091] Q-axis voltage: u_q = R_s · i_q + L_q · di_q / dt + ω_e · (L_d · i_d + ψ_f)

[0092] Where i_d is the direct-axis current, i_q is the quadrature-axis current, ψ_f is the flux linkage of the rotor permanent magnet, and ω_e is the electric angular velocity. The magnitude of the back electromotive force is mainly contributed by the term ω_e · ψ_f.

[0093] When a negative current (i_d < 0) is injected into the d-axis, the resulting electromagnetic field is opposite in direction to the permanent magnet's magnetic field, effectively reducing the effective flux linkage from ψ_f to (ψ_f + L_d · i_d). At the same electric angular velocity ω_e, the magnitude of the back electromotive force decreases accordingly, and the VM bus voltage is suppressed at its source. This is field weakening control—reducing the back electromotive force at a physical level at the cost of sacrificing some torque output.

[0094] This invention employs a weak magnetic field control entry strategy:

[0095] After receiving motion commands, the servo controller of the clamping module parses the target acceleration parameter a_target and compares it with the preset acceleration threshold a_th:

[0096] When a_target≤a_th, the direct-axis current i_d = 0 is maintained, the motor operates at the maximum torque-current ratio, and the VM bus voltage is within the safe range;

[0097] When a_target > a_th, the controller injects i_d = -0.2 (negative d-axis current) into the vector control loop before starting the clamping motion to perform field weakening control, and the VM bus voltage is suppressed within the sensor power supply tolerance range.

[0098] In a preferred embodiment of the invention, a_th = 5,000 mm / s². This threshold is calibrated based on a comparison between the measured VM voltage and the sensor's withstand voltage—5,000 mm / s² is within the safe range of VM (in the experiment, VM was 24.4 V at 8,000 mm / s², which still has a margin from the sensor's 30 V withstand threshold), ensuring that magnetic weakening is not triggered under low acceleration conditions (preserving full torque output capability), and that there is a protective lead time only under high acceleration conditions.

[0099] When a_target ≤ a_th (such as when the clamping motion enters the deceleration stage or the clamping and holding stage), the controller exits the field weakening control, i_d returns to 0, and the motor resumes full torque output to ensure sufficient clamping force margin during the clamping and holding stage.

[0100] The entry and exit of field weakening control are both completed before the motion command is executed—i_d is stably injected before the acceleration segment of the speed curve begins and exited before the deceleration segment begins. During motion, i_d remains constant and does not participate in the real-time adjustment of the position and speed closed loops, avoiding the impact of dynamic changes in the field weakening current on the torque control loop.

[0101] Since the motion trajectory of the clamping module is pre-planned—the target position, velocity, and acceleration are determined when the motion command is issued—whether a_target exceeds the threshold can be predicted during the command parsing stage. Field weakening control can be initiated and stabilized before the motor starts running, ensuring that the protection action takes effect before dangerous conditions and without disturbing the accuracy of the clamping motion trajectory. Field weakening only changes the d-axis flux linkage, not the q-axis torque current—after exiting the field weakening phase in the clamping and holding pressure section, the motor immediately restores its full torque capacity, and the clamping force remains unaffected.

[0102] Weak magnetic field control ensures the hardware survival of the material detection sensor under high-acceleration conditions (the power supply end is not attacked by electrical stress, and the signal end is not burned out by transient overvoltage), making the sensor signal continuously available across the entire speed range. The sensor signal and the clamping position signal are jointly input into the AND fusion judgment logic—when all signals are satisfied simultaneously, the controller outputs a "reliable gripping" signal to the central control unit, allowing subsequent handling operations. If any sensor signal is lost (e.g., the sensor is still burned out due to abnormality), the AND judgment fails, the system immediately alarms and stops the handling.

[0103] This invention provides a control method for a fully automatic variable-pitch flexible grasping system, comprising the following steps:

[0104] Step 1: The production line main control system sends a single formula instruction containing the new product specifications (length, width, height) to the central control unit. The central control unit simultaneously parses the instruction, obtaining the pitch (X-axis) signal, pressing (Z-axis) signal, and clamping (Y-axis) signal. It then sends position pulses to the pitch motor to automatically adjust the center distance between the two grippers to the product length; sends the target torque / position to the linear drive assembly to adapt to the product height; and sends the target opening instruction to the clamping drive motor.

[0105] Step 2: During normal operation of the clamping module, the servo controller atomically writes the current encoder single-turn reading, multi-turn overflow count, calculated motion direction, and absolute position value into the non-volatile memory unit in each control cycle as software multi-turn backup data. When the system recovers from a power outage, the servo controller reads the hardware multi-turn count value from the encoder and simultaneously reads the software multi-turn backup data saved before the last power outage from the non-volatile memory unit for comparison and verification. If the verification passes, the recovered absolute multi-turn position is directly used as the current gripper opening position of the clamping module, and the servo enters the motion control ready state without performing mechanical homing initialization. The recovered absolute multi-turn position is compensated using the aforementioned power-off multi-turn compensation method to obtain the compensated absolute multi-turn position. Since the clamping module is controlled without initialization, when receiving a changeover command, the clamping module is already in a ready state after power-on and can directly respond to opening changes without waiting for homing.

[0106] Step 3: During the acceleration phase as the clamping module approaches the target opening at high speed, a weak magnetic field control entry strategy is employed. The target acceleration parameter is compared with a preset acceleration threshold. When the target acceleration parameter is not greater than the preset threshold, the motor operates at its maximum torque-to-current ratio. When the target acceleration parameter is greater than the preset threshold, i_d = 0 is maintained, and the motor operates at its maximum torque-to-current ratio. Under this strategy, the material detection sensor is actively protected and will not be burned out due to back electromotive force.

[0107] The entire process takes only a few seconds and requires no human intervention. Once the changeover is complete, the clamping module can perform its first gripping action—from the weak magnetic protection during the clamping acceleration phase to the AND fusion determination after clamping, reliability is guaranteed across the entire speed range.

[0108] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A control method for a fully automatic variable-pitch flexible grasping system, characterized in that, include: Step 1: The main control system sends instructions to the central control unit. The central control unit parses the instructions to obtain the pitch signal, pressing signal, and clamping signal. It then sends position pulses to the pitch motors in each automatic pitch module to automatically adjust the center distance between the two grippers to the product length. The system also sends the target torque / position to the linear drive component in the vertical pressing module to adapt to the product height. Finally, it sends the target opening instruction to the clamping drive motor in the large stroke clamping module. Step 2: During normal operation of the clamping module, the controller writes the software multi-cycle backup data to the non-volatile storage unit in each control cycle. The software multi-turn backup data includes: the current encoder single-turn reading, multi-turn overflow count value, calculated motion direction and absolute position value; Step 3: When the clamping module loses power and the system is powered on, the controller reads the hardware multi-turn count value from the encoder and reads the software multi-turn backup data saved before the last power failure from the non-volatile storage unit. Step 4: Calculate the compensated multi-turn overflow count value using the following formula: ， C(d,Δθ) = d·Δθ, Δθ = θ_cur - θ_mem Where W′ is the compensated multi-turn overflow count value, W is the current multi-turn overflow count value, d is the direction of motion, θ_mem is the position saved in the last control cycle before power failure, and θ_cur is the current encoder single-turn reading. For indicator functions; Step 5: The controller uses W′+ θ_cur as the absolute multi-turn position after power-on and directly enters the motion control ready state without performing mechanical return to the origin.

2. The control method for the fully automatic variable-pitch flexible grasping system according to claim 1, characterized in that, It also includes the following steps: After receiving the motion command, the servo controller of the clamping module parses the target acceleration parameter a_target in the motion command and compares it with the preset acceleration threshold a_th: When a_target≤a_th, the direct axis current i_d = 0 is maintained, the motor operates at the maximum torque-current ratio, and the VM bus voltage is within the safe range; When a_target > a_th, the controller injects a negative d-axis current into the vector control loop before starting the clamping motion to perform field weakening control, and the VM bus voltage is suppressed within the sensor power supply tolerance range.

3. The control method for the fully automatic variable-pitch flexible grasping system according to claim 2, characterized in that, The negative d-axis current i_d has a value of -0.

2.

4. The control method for the fully automatic variable-pitch flexible grasping system according to claim 1, characterized in that, Before step 4 is executed, a verification step is also included: when the hardware multi-turn value is consistent with the multi-turn overflow count value in the software backup or the deviation is within the allowable range, the verification is passed; If the verification passes, proceed to step 3.

5. The control method for the fully automatic variable-pitch flexible grasping system according to claim 1, characterized in that, In step 4, the compensated multi-turn overflow count value includes the following three cases: When d = -1, Δθ > 0, W′ = W - 1; When d = 1, Δθ < 0, W′ = W + 1; When d · Δθ ≥ 0 and d ≠ 0, W′ = W.

6. The control method for the fully automatic variable-pitch flexible gripping system according to claim 1, characterized in that, In step 4, if d ≠ 0 and Δθ is not within the legal range, the encoder data is determined to be unreliable, and the controller immediately outputs an alarm signal and stops the motion.

7. A fully automatic variable-distance flexible gripping system, characterized in that, A control method for implementing the fully automatic variable-pitch flexible gripping system according to any one of claims 1-6 includes: an overall support frame, and a large-stroke clamping module, an automatic variable-pitch module, and a vertical pressing module installed on and electrically interconnected on the overall support frame; the large-stroke clamping module is located within the overall support frame; there are two automatic variable-pitch modules, each mounted on one of the two sets of clamping movable components of the large-stroke clamping module; each automatic variable-pitch module includes two variable-pitch movable parts capable of changing the distance between them; there are four vertical pressing modules, each installed at the bottom of each variable-pitch movable part; each vertical pressing module includes a pressing component and a bottom gripper.

8. The fully automatic variable-distance flexible gripping system according to claim 7, characterized in that, The long-stroke clamping module includes a clamping base, a clamping drive motor and guide rails fixed on the clamping base; the clamping drive motor drives the closed-loop synchronous belt to rotate; there are two guide rails, which are arranged in parallel on the clamping base, and each guide rail is provided with a left clamping slider and a right clamping slider. The left clamping slider is connected to a first adapter plate, and the right clamping slider is connected to a second adapter plate. The first adapter plate and the second adapter plate are fixedly connected to the upper transmission section and the lower transmission section of the closed-loop synchronous belt, respectively.

9. The fully automatic variable-distance flexible gripping system according to claim 8, characterized in that, Two automatic pitch-changing modules are fixedly connected to the first adapter plate and the second adapter plate, respectively. Each automatic pitch-changing module includes: a guide rail, a pitch-changing drive motor, and a transmission shaft arranged parallel to the shaft of the pitch-changing drive motor. The pitch-changing drive motor drives the transmission shaft to rotate through a synchronous pulley and a synchronous belt. The transmission shaft is fitted with two nut seats, which are connected to two nut adapter seats by pins. The two nut adapter seats are fixedly connected to two sliding seats, which are fitted on the guide rail. The guide rail is parallel to the transmission shaft.

10. The fully automatic variable-pitch flexible gripping system according to claim 7, characterized in that, Four vertical pressing modules are fixed on the sliding seats of the automatic pitch-changing module. Each vertical pressing module includes a linear drive assembly, an elastic buffer assembly, a pressing plate, and a bottom gripper. The pressing plate is connected to the drive end of the linear drive assembly through the elastic buffer assembly. The bottom gripper is fixedly connected to the main body of the linear drive assembly. The pressing plate is located above the bottom gripper.

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