Electro-hydraulic actuator unit and pressurization and pressure maintaining method for lithium battery formation

Abstract

The application relates to the technical field of lithium battery manufacturing equipment, in particular to an electro-hydraulic actuator unit for lithium battery formation and a pressurizing and pressure maintaining method. The integrated electro-hydraulic actuator unit body comprises a servo motor, a bidirectional closed gear pump, a high-integration bidirectional hydraulic valve block, an electro-hydraulic actuator hydraulic oil cylinder and a sensor assembly, a closed volume speed regulation loop without external pipelines is formed through rigid flow channels in the valve block, the application adopts a hydraulic medium to realize high-rigidity and high-precision pressure-displacement compound control; in the long-period pressure maintaining stage, a hydraulic lock is used for self-locking energy storage, the servo motor is operated at low speed, mechanical wear and motor heating are avoided, and energy consumption is reduced; the application has the remarkable advantages of high precision, long service life, low energy consumption and high integration.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing equipment technology, and in particular to an electro-hydraulic actuator unit and a pressure-holding method for lithium battery formation. Background Technology

[0002] In the formation process of lithium batteries (especially pouch lithium batteries and square aluminum-cased lithium batteries), in order to ensure a smooth internal interface, reduce internal resistance, and promptly expel gases generated by the electrochemical reaction, it is usually necessary to apply a certain amount of mechanical pressure to the lithium battery core during charging and discharging. Currently, the mainstream pressurization methods in the industry are mainly divided into two forms: pneumatic cylinder pressurization and electric cylinder pressurization.

[0003] The cylinder pressurization system uses external compressed air as a power source. A proportional pressure reducing valve regulates the air pressure, driving the cylinder piston rod to press the pressure plate against the lithium battery pack. However, due to the high compressibility of gas, the system has extremely low mechanical rigidity. During the formation and charging / discharging process, the expansion of gas inside the lithium battery causes a reverse force, making it difficult to dynamically and adaptively adjust the air pressure within the cylinder at the microsecond level. This easily leads to large fluctuations in pressure and low pressure control accuracy. Furthermore, the cylinder system has high energy consumption, and the air source is prone to generating condensate and trace amounts of oil, posing a risk of contaminating the high-cleanliness formation workshop.

[0004] The electric cylinder pressurization system converts rotary motion into linear motion by driving a lead screw mechanism (ball screw or planetary roller screw) with a servo motor, and uses torque control or position control to pressurize and maintain the pressure of the lithium battery. However, the lithium battery formation process requires maintaining a constant pressure for a long time (several hours). During the constant pressure holding stage, the electric cylinder lead screw is almost stationary or in a state of slight movement. The balls or rollers of the lead screw bear huge static concentrated stress at the same position, which can easily lead to pitting, spalling, and fatigue of the lead screw track metal. After 2-3 years of operation, the accuracy of the equipment deteriorates significantly. In addition, the electric cylinder system must rely on the servo motor to continuously output stall torque to maintain mechanical thrust during pressure holding. The motor is in a high-current and heating state for a long time, which not only consumes a lot of energy, but also requires an additional cooling system. At the same time, the electric cylinder is a rigid and tightly driven transmission. When an abnormal and sudden expansion occurs inside the lithium battery, the impact force is directly and rigidly transmitted to the lead screw and reducer, which can easily cause mechanical jamming or gear breakage.

[0005] Therefore, there is a need to provide an electro-hydraulic actuator unit and a pressure-holding method for lithium battery formation. Summary of the Invention

[0006] This invention provides an electro-hydraulic actuator unit and a pressure-holding method for lithium battery formation to solve the aforementioned technical problems.

[0007] The present invention adopts the following technical solution: it includes a top crossbeam of a gantry frame and an integrated electro-hydraulic actuator unit body, wherein the integrated electro-hydraulic actuator unit body is vertically and rigidly suspended from the top crossbeam of the gantry frame.

[0008] The integrated electro-hydraulic actuator unit includes a servo motor, a bidirectional closed gear pump, a highly integrated bidirectional hydraulic valve block, an electro-hydraulic actuator hydraulic cylinder, a sensor assembly, and an electro-hydraulic actuator servo driver. The servo motor and the bidirectional closed gear pump are rigidly connected coaxially. The bidirectional closed gear pump and the electro-hydraulic actuator hydraulic cylinder are respectively sealed and connected to both ends of the highly integrated bidirectional hydraulic valve block. The oil ports of the bidirectional closed gear pump and the electro-hydraulic actuator hydraulic cylinder are connected through a rigid flow channel inside the valve block. The entire system has no external flexible hydraulic pipelines, forming a closed volumetric speed regulation circuit.

[0009] The highly integrated bidirectional hydraulic valve block includes a first hydraulically controlled check valve, a second hydraulically controlled check valve, a first safety relief valve, a second safety relief valve, a hydraulically controlled reversing unloading valve, a first replenishing check valve, and a second replenishing check valve.

[0010] Furthermore, the sensor assembly includes a magnetostrictive displacement sensor; the magnetostrictive displacement sensor is installed at the top of the hydraulic cylinder of the electro-hydraulic actuator, and its probe extends into a blind hole inside the piston rod of the cylinder for real-time acquisition of the axial displacement of the piston rod.

[0011] Furthermore, the sensor assembly also includes a first pressure sensor, a second pressure sensor, a replenishment chamber pressure sensor, and an independent temperature sensor; the first pressure sensor and the second pressure sensor are respectively installed in the rodless chamber and rod chamber pressure measurement interfaces of the valve block; the replenishment chamber pressure sensor and the independent temperature sensor are installed in the return oil flow channel.

[0012] Furthermore, it also includes an external tension / compression sensor, which is rigidly mounted on the connection end face between the piston rod of the electro-hydraulic actuator hydraulic cylinder and the upper pressure plate, and is used to directly measure the axial clamping force applied to the surface of the lithium battery.

[0013] Furthermore, as a low-cost implementation, it also includes an auxiliary atmospheric pressure oil tank, a water-cooled cooler, an integrated level and temperature sensor, an air filter, and a glass level gauge; the auxiliary atmospheric pressure oil tank is connected to the return oil channel, the water-cooled cooler is connected in series with the return oil pipeline, the integrated level and temperature sensor and the air filter are installed on the top of the auxiliary atmospheric pressure oil tank, and the glass level gauge is installed on the side wall of the auxiliary atmospheric pressure oil tank.

[0014] Furthermore, as an implementation method for fully airtight installation in any orientation, a high-pressure airtight accumulator is sealed at the end of the low-pressure common return oil circuit. The high-pressure airtight accumulator is pre-charged with inert gas. The accumulator's oil port is connected to the oil inlet of the first oil replenishment check valve and the second oil replenishment check valve. An accumulator locking base discharge port is provided at the bottom of the accumulator.

[0015] Furthermore, to adapt to the working conditions of ultra-large lithium batteries or multi-plate arrays, the integrated electro-hydraulic actuator unit body is a multi-point distributed micro electro-hydraulic actuator unit array, with multiple sets of micro electro-hydraulic actuator units suspended in parallel on the top beam of the gantry frame, and the piston rod of each set of micro electro-hydraulic actuator units connected to different geometric positions of the upper pressure plate.

[0016] Furthermore, to resolve the volume contradiction between rapid descent and micro-pressure holding, the power output end of the servo motor is coaxially connected to a large-displacement closed pump and a small-displacement closed pump. The highly integrated bidirectional hydraulic valve block is equipped with an electrically controlled selection channel to switch between single-pump oil supply mode and dual-pump combined oil supply mode.

[0017] The pressure application and holding method for electro-hydraulic actuators includes the following steps: Step 1: Initial rapid approach: After the lithium battery pack is in place and the charging and discharging circuit is connected, the main control unit issues a position control command, the servo motor drives the bidirectional closed gear pump to deliver oil, and drives the upper pressure plate to descend at a speed of 10~50mm / s. Step 2: Control mode switching: When the clamping force is detected to reach the contact threshold of 0.5~0.8MPa, the system seamlessly switches from position control mode to pressure-displacement composite control mode. The main control unit synchronously collects electrochemical parameters and mechanical pressure and displacement parameters at a period of ≤500μs. Step 3: Long-term constant pressure holding: The first and second hydraulic control check valves close and lock the oil circuit, relying on the energy storage of hydraulic oil to maintain the pressure, controlling the pressure within the range of 0.5MPa~25MPa, with a static pressure control accuracy of ±0.1MPa; the servo motor runs at a low speed of 1~50rpm or stops at zero speed to achieve pressure holding without stalling. Step 4: Dynamic compensation for gas expansion: When the lithium battery produces gas and expands, causing pressure and displacement fluctuations, the sensor collects data and uploads it to the main control unit. The main control unit controls the servo motor to rotate slightly in the opposite direction to dynamically relieve pressure and compensate for the pressure fluctuation error within ±2%. Step 5: Equipment Reset: After the formation process is completed, the servo motor rotates in the opposite direction, driving the upper pressure plate to retract to the initial position, completing one cycle.

[0018] Furthermore, in step 4, the main control unit performs two-dimensional coupling calculations on the mechanical stress parameters collected in real time and the lithium battery state of charge (SOC), voltage, and current parameters fed back by the lithium battery formation power module. Based on the gas generation characteristics of the lithium battery at a specific SOC stage, the reverse rotation angle and speed of the servo motor are dynamically determined to achieve coordinated control of electrochemical and mechanical stress.

[0019] The above-described at least one technical solution adopted in the embodiments of the present invention can achieve the following beneficial effects: Firstly, this invention employs an electro-hydraulic actuator closed-loop hydraulic system as the actuator, utilizing the incompressibility of the hydraulic oil medium to construct extremely high mechanical rigidity. Combined with the high-speed synchronous response (≤500μs) of the EtherCAT bus, it achieves high-dynamic composite closed-loop control with pressure control accuracy of ±0.1MPa and displacement resolution of 0.1~1.0μm. This can suppress and accurately compensate for the lattice and gas expansion of the lithium battery in the later stages of formation and charging / discharging, ensuring absolutely uniform stress on the lithium battery interface. This fundamentally avoids lithium battery deformation or internal lithium plating caused by uneven stress, significantly improving the density and uniformity of the SEI film in the finished lithium battery.

[0020] Secondly, during the constant pressure holding phase that lasts for several hours, this invention utilizes the closed oil circuit and the liquid energy storage of the hydraulic cylinder, as well as the self-locking characteristics of the valve block, to maintain the thrust. The mechanical stress is uniformly transmitted and borne by the hydraulic oil without wear, and the servo motor only needs to operate at extremely low speeds or even zero speeds. This completely avoids the pitting corrosion and metal fatigue spalling caused by the static concentrated stress on the lead screw of the traditional electric cylinder at the same position. Tests have shown that the mechanical fatigue life of the transmission mechanism of this invention is improved compared to the traditional electric cylinder system, significantly reducing the later maintenance costs.

[0021] Thirdly, this invention belongs to a volumetric speed regulation system without throttling losses. During the constant pressure holding stage, the servo motor automatically reduces to an extremely low speed (1~50rpm) or even a zero-speed stationary state, and the output current of the servo driver drops significantly. This completely avoids the serious heat generation and high energy consumption caused by the continuous output of stall torque in traditional electric cylinder systems. Compared with cylinder systems that require frequent exhaust and gas exchange and electric cylinder systems that require continuous high current stall, the overall operating energy consumption of the equipment in this invention is reduced, resulting in excellent energy-saving and emission-reduction benefits.

[0022] Fourth, this invention adopts a longitudinal, pipeline-free assembly structure with the cylinder, valve block, pump group, and motor arranged in a straight line, eliminating stress hysteresis caused by the expansion of high-pressure hoses and completely eliminating the hidden dangers of pipe bursts, oil leaks, and oil mist pollution in the production workshop. It perfectly adapts to the stringent environmental requirements of lithium battery manufacturing workshops for extreme dryness and high cleanliness. At the same time, by using the EtherCAT industrial bus to unify the electrochemical charge and discharge management system and the mechanical pressurization execution system under the same main control network, it realizes microsecond-level two-dimensional coupling calculation of the internal charge state and physical state of lithium batteries. This enables the system to automatically and intelligently adjust the pressurization output according to the intensity of the electrochemical reaction, significantly improving the process coordination efficiency of the fully automated production line.

[0023] Fifth, by replacing the atmospheric pressure oil tank with a high-pressure airtight accumulator, the entire system can be installed without atmospheric contact and in any orientation; by using a multi-point distributed micro electro-hydraulic actuator array, the local pressure of a large-area lithium battery can be finely adjusted; by using a dual-pump parallel switching configuration, the requirements for rapid descent and large displacement, as well as high-precision volume adjustment during micro-pressure holding, can be met. This invention has extremely strong process adaptability and scalability. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a three-dimensional solid isometric structural diagram of the integrated semi-closed electro-hydraulic actuator system provided in the first embodiment of the present invention; Figure 2 This is a three-dimensional solid isometric structural diagram of the integrated fully enclosed electro-hydraulic actuator system provided in the second embodiment of the present invention; Figure 3 A semi-closed hydraulic schematic diagram of the integrated electro-hydraulic actuator system provided in the first embodiment of the present invention; Figure 4 A fully enclosed hydraulic schematic diagram of the integrated electro-hydraulic actuator system provided in the second embodiment of the present invention; Figure 5 This is a cross-sectional view of the integrated electro-hydraulic actuator unit body in this invention; Figure 6 This is a schematic diagram of the integrated electro-hydraulic actuator unit body structure in this invention.

[0025] Reference numerals in the attached diagram: 1-Coaxial displacement sensor; 2-Electro-hydraulic actuator hydraulic cylinder; 3-First pressure sensor; 4-Second pressure sensor; 5-First hydraulic check valve; 6-Second hydraulic check valve; 7-First safety relief valve; 8-Second safety relief valve; 9-Hydraulic reversing unloading valve; 10-Bidirectional closed gear pump; 11-First replenishing check valve; 12-Second replenishing check valve; 13-Replenishing chamber pressure sensor; 14-Integrated level and temperature sensor; 15-Air filter; 16-Glass level gauge; 17-High-pressure airtight accumulator; 18-Independent temperature sensor; 19-Servo motor; 20-External tension / compression sensor; 21-Auxiliary atmospheric pressure oil tank; 22-Accumulator locking base discharge port. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] Reference Figures 1 to 6 The diagram shows an electro-hydraulic actuator unit for lithium battery formation and a pressure-holding method.

[0029] This invention provides an electro-hydraulic actuator unit for lithium battery formation and a pressure holding method, including an integrated electro-hydraulic actuator unit body, which is vertically and rigidly suspended from the top beam 23 of the gantry frame; The integrated electro-hydraulic actuator unit mainly consists of a servo motor 19, a bidirectional closed gear pump 10, a highly integrated bidirectional hydraulic valve block, an electro-hydraulic actuator hydraulic cylinder 2, a sensor assembly, and an electro-hydraulic actuator servo driver. The servo motor 19 is fixedly assembled with the transmission flange. Its power output shaft and the input shaft of the bidirectional closed gear pump 10 are connected in a coaxial rigid manner to ensure that the power transmission is gapless and low-loss. The bidirectional closed gear pump 10 and the electro-hydraulic actuator hydraulic cylinder 2 are respectively sealed and connected to the upper and lower ends of the highly integrated bidirectional hydraulic valve block through thread sealing or flange clamping.

[0030] The two sets of inlet and outlet ports of the bidirectional closed gear pump 10, and the rodless chamber port and rod chamber port of the electro-hydraulic actuator hydraulic cylinder 2 are all interconnected by a closed rigid flow channel machined inside the valve block. The entire hydraulic system abandons traditional external flexible pipelines such as high-pressure rubber hoses and metal hoses, forming a compact, closed volumetric speed regulation circuit with zero risk of external leakage.

[0031] The highly integrated bidirectional hydraulic valve block serves as the core integrated carrier, with multiple sets of hydraulic control components embedded inside: the first hydraulically controlled check valve 5 and the second hydraulically controlled check valve 6 cooperate to form a bidirectional hydraulic lock for self-locking of the oil circuit during the pressure holding stage; the first safety relief valve 7 and the second safety relief valve 8 correspond to the rodless chamber and rod chamber of the cylinder, respectively, and play a role in overpressure unloading and overload protection; the hydraulically controlled reversing unloading valve 9 is used for emergency pressure relief and oil circuit pressure balance regulation; the first replenishing oil check valve 11 and the second replenishing oil check valve 12 are arranged in the low-pressure replenishing oil circuit to realize automatic oil replenishment during the reciprocating motion of the cylinder. The valve block is longitudinally clamped between the bidirectional closed gear pump 10 and the electro-hydraulic actuator hydraulic cylinder 2. With the central axis of the valve block as the reference, the first hydraulic control check valve 5 and the second hydraulic control check valve 6 are arranged symmetrically inside the valve block. They are connected in parallel to the main working oil circuit, and their oil outlets correspond one-to-one with the rodless chamber oil port and the rod chamber oil port of the electro-hydraulic actuator hydraulic cylinder 2, respectively.

[0032] Each sensor component performs its specific function to complete comprehensive monitoring of operating conditions: Coaxial displacement sensor 1 is preferably a magnetostrictive displacement sensor, whose base is firmly installed on the top of the hydraulic cylinder 2 of the electro-hydraulic actuator. The detection probe extends coaxially into the blind hole in the center of the piston rod of the cylinder to collect the absolute linear displacement of the piston rod in real time, accurately feeding back the thickness change during the lithium battery formation process; First pressure sensor 3 and second pressure sensor 4 are respectively sealed and installed on the pressure measuring interfaces of the rodless chamber and rod chamber of the corresponding cylinder of the valve block to detect the oil pressure inside the two chambers in real time; Oil replenishment chamber pressure sensor 13 and independent temperature sensor are arranged in series in the system return oil channel to continuously monitor the low-pressure circuit reference pressure and hydraulic oil working temperature; An external tension and compression sensor 20 is rigidly installed between the end face of the piston rod of the cylinder and the upper pressure plate to directly and without distortion detect the actual axial clamping force applied to the surface of the lithium battery, providing a high-precision feedback signal for pressure closed-loop control.

[0033] This embodiment is equipped with an auxiliary oil supply and heat dissipation component: the auxiliary atmospheric pressure oil tank 21 is connected to the system return oil channel, and a water-cooled cooler is connected in series in the return oil pipeline to force heat dissipation of the circulating hydraulic oil. The integrated level and temperature sensor 14 and the air filter 15 are installed on the top of the auxiliary atmospheric pressure oil tank 21 to monitor the oil level and oil temperature in the tank, maintain the air pressure balance inside and outside the tank, and filter external impurities. The glass level gauge 16 is embedded in the side wall of the oil tank, which makes it easy for maintenance personnel to visually observe the oil level.

[0034] The electrical control terminal of the entire equipment is equipped with a main control unit, which can be an industrial PLC or an industrial IPC. The main control unit establishes communication connections with the electro-hydraulic actuator servo driver and the lithium battery formation power module through the EtherCAT high-speed industrial bus, so as to realize the synchronous acquisition and linkage control of mechanical pressurization parameters and electrochemical charging and discharging parameters.

[0035] 2. Workflow and Pressure Holding Control Method Step 1: Initial rapid approach phase (position control mode) The lithium battery pack to be processed is transported to the designated station of the lower pressure plate by the automated logistics equipment. After the charging and discharging lines are connected, the main control unit sends a position control command to the electro-hydraulic actuator servo driver through the EtherCAT bus. The servo driver drives the servo motor 19 to run in the forward direction at high speed, which drives the bidirectional closed gear pump 10 to output hydraulic oil at full capacity. The high-pressure oil flows into the rodless chamber of the electro-hydraulic actuator hydraulic cylinder 2 through the forward flow channel inside the valve block. The oil inside the rod chamber of the cylinder is drawn back by the pump body, which pushes the piston rod to drive the upper pressure plate to descend smoothly at a set speed of 10~50mm / s until the bottom surface of the upper pressure plate contacts the upper surface of the lithium battery pack.

[0036] Step 2: Seamless switching of control modes and initialization of composite control When the upper pressure plate contacts the lithium battery, the external tension and pressure sensor 20 collects the axial clamping force in real time. When the pressure value reaches the preset contact light load threshold of 0.5~0.8MPa, and the typical value in this embodiment is 0.5MPa, the main control unit triggers a logic switch, seamlessly switching the system from a simple position control mode to a pressure-displacement composite control mode. After the switch is completed, the main control unit reads the electrochemical parameters such as lithium battery SOC, working voltage, and working current fed back by the formation power module with a microsecond-level synchronization cycle of ≤500μs. On the other hand, it simultaneously collects the mechanical parameters such as the output pressure of the electro-hydraulic actuator unit and the piston rod displacement, and establishes linkage control logic based on the lithium battery formation process curve.

[0037] Step 3: Long-cycle constant-voltage formation and low-energy-consumption pressure holding stage The lithium battery charging and discharging formation process lasts for several hours. During this stage, the main control unit stably controls the surface clamping force of the lithium battery within the process range of 0.5MPa to 25MPa. After entering the constant pressure holding condition, the first hydraulic control check valve 5 and the second hydraulic control check valve 6 inside the valve block automatically close, and the bidirectional hydraulic lock locks the oil circuit of the rodless chamber of the cylinder; utilizing the near-incompressible physical properties of hydraulic oil, the clamping thrust of the upper pressure plate is maintained by relying on the energy storage of the oil.

[0038] At the same time, the electro-hydraulic actuator servo driver actively regulates the servo motor 19, reducing its speed to an extremely low range of 1~50 rpm, or directly controlling the motor to enter a zero-speed stationary state. At this time, the motor output current drops to an extremely low level, completely abandoning the working method of the traditional electric cylinder that relies on the motor to continuously output stall torque to maintain pressure. This fundamentally solves the problems of motor heat generation and high energy consumption. In this stage, the static pressure control accuracy of the system can reach ±0.1MPa. The magnetostrictive displacement sensor continuously monitors the thickness change of the lithium battery, with a displacement detection resolution of 0.1~1μm, accurately capturing the lattice growth and slight expansion deformation of the lithium battery.

[0039] Step 4: Dynamic Compensation Stage for Gas Production Expansion in the Mid-to-Late Stages of Formation As the formation process enters the middle and late stages, the electrochemical reaction inside the lithium battery intensifies, a large amount of SEI film is generated and accompanied by gas production, and the lithium battery body exhibits significant volume expansion, which creates an instantaneous reverse mechanical impact on the upper pressure plate. The coaxial displacement sensor 1 collects the micron-level thickness change Δd of the lithium battery in real time, and the external tensile and compressive pressure sensor 20 simultaneously captures the instantaneous pressure fluctuation ΔP. The two sets of data are transmitted back to the main control unit in real time via the EtherCAT bus.

[0040] The main control unit, combining the current voltage, current, and SOC of the lithium battery with an electrochemical parameter, accurately calculates the volume overflow of the hydraulic circuit caused by the expansion of the lithium battery using a two-dimensional electrochemical-mechanical stress coupling algorithm. It then sends a micro-adjustment command to the electro-hydraulic actuator servo drive. Upon receiving the command, the servo motor 19 performs a micro-amplitude, high-dynamic reverse rotation, driving the bidirectional closed gear pump 10 to pump oil in the reverse direction. The overloaded hydraulic oil in the rodless chamber of the cylinder dynamically depressurizes and flows back through a pre-set overflow reset channel inside the valve block, quickly offsetting the reverse stress caused by the lithium battery expansion. This dynamic compensation mechanism can stably control the dynamic pressure fluctuation error throughout the entire cycle within ±2% of the process setting value, effectively avoiding problems such as uneven stress, deformation, and lithium plating in the lithium battery.

[0041] Step 5: Process Completion and Equipment Reset Stage After the lithium battery completes all charging, discharging, and gas emission processes, the main control unit issues a system reset command. The electro-hydraulic actuator servo driver drives the servo motor 19 to rotate in reverse at high speed. The bidirectional closed gear pump 10 switches the oil flow direction, and high-pressure oil enters the rod chamber of the electro-hydraulic actuator hydraulic cylinder 2, pushing the piston rod to retract rapidly and lifting the upper pressure plate to the initial zero position. The equipment completes a single pressurization and pressure holding cycle, awaiting the next batch of lithium batteries to be fed.

[0042] II. Example 2: Fully enclosed high-voltage accumulator type, fully airtight, arbitrary orientation installation configuration Based on the structure and control logic of the basic embodiment, this embodiment optimizes and modifies the low-pressure oil replenishment circuit, making it suitable for lithium battery formation production lines with high cleanliness requirements and limited equipment installation space.

[0043] 1. Explanation of structural differences This embodiment completely eliminates the external atmospheric pressure oil tank components in the basic scheme, such as the auxiliary atmospheric pressure oil tank 21, the integrated level and temperature sensor 14, the air filter 15, and the glass level gauge 16. At the end of the system's low-pressure common return oil circuit, a high-pressure airtight accumulator 17 is installed using a sealed connection. The high-pressure airtight accumulator 17 is pre-filled with high-purity nitrogen gas, with a standard pre-fill pressure of 1 Bar. The oil port of the accumulator is connected to the oil inlet of the first replenishing oil check valve 11 and the second replenishing oil check valve 12. The bottom end is provided with an accumulator locking base discharge port 22 for easy equipment maintenance and oil discharge.

[0044] 2. Working principle The hydraulic cylinder 2 of the electro-hydraulic actuator has a single-rod asymmetric structure. When the piston reciprocates linearly, there is a fixed volume difference between the oil volume entering and exiting the rodless chamber and the rod chamber. When the servo motor 19 drives the bidirectional closed gear pump 10 to rotate in the opposite direction and the cylinder 2 performs a retraction action, the volume of oil discharged from the rodless chamber of the cylinder is greater than the volume of oil sucked into the rod chamber. The excess volume difference oil is pressed into the hydraulic chamber of the high-pressure airtight accumulator 17 through the low-pressure flow channel inside the valve block, and compresses the internal nitrogen to complete the energy storage. When the servo motor 19 rotates in the forward direction and the cylinder 2 extends downward to apply pressure, the oil intake required by the rodless chamber of the cylinder is greater than the oil discharge of the rod chamber. At this time, the high-pressure nitrogen inside the accumulator 17 expands and actively replenishes the stored hydraulic oil into the main hydraulic circuit through the first replenishment check valve 11 or the second replenishment check valve 12, dynamically balancing the volume difference of the cylinder.

[0045] This configuration achieves a fully enclosed hydraulic circuit with zero atmospheric contact, completely isolating the hydraulic oil from workshop dust and moisture, eliminating problems such as oil deterioration and circuit contamination. Simultaneously, it overcomes the limitations of traditional gravity-based oil tank levels, allowing the entire electro-hydraulic actuator unit to be arranged in any orientation, including horizontal, inverted, or tilted installations, adapting to high-density, modular automated production lines. Except for the low-pressure replenishment circuit, the remaining mechanical structure, sensor placement, electrical connections, and the entire pressurization and pressure-holding control process are consistent with the basic embodiment.

[0046] III. Example 3: Multi-point distributed micro electro-hydraulic actuator array configuration, dedicated to large-size, multi-plate lithium batteries This embodiment is designed for application scenarios such as ultra-large square lithium batteries and multi-cavity formation fixtures, and improves the uniformity of force on large-area lithium batteries through array layout.

[0047] 1. Structural Modification Plan The single high-output integrated electro-hydraulic actuator unit in the basic embodiment is replaced with a multi-point distributed micro electro-hydraulic actuator unit array. Multiple sets of micro electro-hydraulic actuator units of uniform specifications are arranged in parallel and symmetrically suspended on the top beam of the gantry frame top beam 23. Each set of micro electro-hydraulic actuator units is independently equipped with a servo motor, a two-way closed gear pump, an integrated hydraulic valve block and a micro hydraulic cylinder, and is an independent power execution unit. The piston rods of all micro cylinders are respectively connected to different geometric points on the upper pressure plate.

[0048] 2. Working characteristics and application advantages The main control unit relies on the EtherCAT bus to independently and collaboratively control each micro electro-hydraulic actuator unit in the array. It can adjust the output pressure and stroke of each micro cylinder individually according to the force state of different areas of the upper pressure plate. For ultra-large plate lithium batteries and multi-plate lithium batteries, it can achieve local pressure fine adjustment and plate tilt compensation, completely solving the problem of uneven force on the edge and center of large workpieces, further improving the uniformity of pressurization throughout the entire area, and ensuring consistent formation quality of the entire batch of lithium batteries. The hydraulic principle, single-unit control logic and process steps of this embodiment all follow the basic embodiment scheme.

[0049] IV. Example 4: Single motor dual pump parallel switching configuration, adaptable to high and low flow conditions This embodiment optimizes the conflicting operating conditions between the equipment's high-flow-rate downlink demand and the demand for pressure holding, micro-compensation, low-flow-rate, and high-precision operation, while taking into account operational efficiency, control accuracy, and energy-saving effects.

[0050] 1. Structural Modification Plan Upgrades were made to the power components: the power output shaft of the same servo motor 19 was coaxially connected in series with a large-displacement closed pump and a small-displacement closed pump to form a dual-pump parallel combination structure. At the same time, an electrically controlled flow channel was added inside the highly integrated bidirectional hydraulic valve block to switch the oil supply path of different pumps through electromagnetic logic.

[0051] 2. Operating Condition Switching and Working Principle Initial rapid approach phase: The electronic control selects the flow channel to open, and the large-displacement closed pump and the small-displacement closed pump simultaneously supply oil to the rodless chamber of the hydraulic cylinder 2 of the electro-hydraulic actuator. The large flow output is achieved by relying on the confluence of the two pumps, which ensures that the upper pressure plate descends rapidly and improves the overall operating rhythm of the equipment. Pressure-displacement composite control, constant pressure holding, and dynamic compensation stage: The electronic control selects the flow channel to cut off the oil supply path of the large displacement closed pump, so that the large displacement pump is unloaded and runs under no-load, and only the small displacement closed pump participates in the work. Relying on the fine volume adjustment capability of the small displacement pump, micron-level stroke and pressure fine adjustment are completed.

[0052] This structure can meet the requirements of both high-speed operation and high-precision micro-motion without increasing the rated power of the servo motor. It effectively reduces the reactive power loss and basic heat generation of the servo motor during the pressure holding and compensation stages. It is suitable for high-end lithium battery formation production lines with stringent requirements for energy consumption, pressure control accuracy and production efficiency. The oil circuit structure, sensor configuration, electrical communication architecture and the entire pressure holding process of this embodiment are consistent with the basic embodiment.

[0053] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. An electro-hydraulic actuator unit for lithium battery formation, comprising a top crossbeam (23) of a gantry frame, characterized in that: Also includes: An integrated electro-hydraulic actuator unit body, which is rigidly suspended from the top crossbeam (23) of the gantry frame. The integrated electro-hydraulic actuator unit includes a servo motor (19), a bidirectional closed gear pump (10), a highly integrated bidirectional hydraulic valve block, an electro-hydraulic actuator hydraulic cylinder (2), a sensor assembly, and an electro-hydraulic actuator servo driver. The servo motor (19) is rigidly connected to the bidirectional closed gear pump (10) on the same axis. The bidirectional closed gear pump (10) and the electro-hydraulic actuator hydraulic cylinder (2) are respectively sealed and connected to both ends of the high-integration bidirectional hydraulic valve block. The high-integration bidirectional hydraulic valve block is provided with a rigid flow channel inside. The oil ports of the bidirectional closed gear pump (10) and the electro-hydraulic actuator hydraulic cylinder (2) are connected through the rigid flow channel inside the high-integration bidirectional hydraulic valve block to form a closed volumetric speed regulation circuit. The highly integrated bidirectional hydraulic valve block is embedded with a first hydraulic control check valve (5), a second hydraulic control check valve (6), a first safety relief valve (7), a second safety relief valve (8), a hydraulic control reversing unloading valve (9), a first replenishing oil check valve (11), and a second replenishing oil check valve (12).

2. The electro-hydraulic actuator unit for lithium battery formation according to claim 1, characterized in that, The sensor assembly includes a magnetostrictive displacement sensor. The electro-hydraulic actuator hydraulic cylinder (2) is provided with a piston rod. The magnetostrictive displacement sensor is installed on the electro-hydraulic actuator hydraulic cylinder (2) to collect the axial displacement of the piston rod in real time.

3. The electro-hydraulic actuator unit for lithium battery formation according to claim 2, characterized in that, The sensor assembly also includes a first pressure sensor (3), a second pressure sensor (4), a replenishing chamber pressure sensor (13), and an independent temperature sensor (18). The first pressure sensor (3) and the second pressure sensor (4) are respectively provided with rod chamber pressure measuring interfaces. The integrated bidirectional hydraulic valve block is provided with a return oil flow channel. The replenishing chamber pressure sensor (13) and the independent temperature sensor (18) are installed in the return oil flow channel.

4. The electro-hydraulic actuator unit for lithium battery formation according to claim 3, characterized in that, It also includes an external tension and compression sensor (20), and a lithium battery is installed inside the top crossbeam (23) of the gantry. The external tension and compression sensor (20) is rigidly mounted on the piston rod of the hydraulic cylinder (2) of the electro-hydraulic actuator to directly measure the axial clamping force applied to the surface of the lithium battery.

5. An electro-hydraulic actuator unit for lithium battery formation according to claim 4, characterized in that, It also includes an auxiliary atmospheric pressure oil tank (21), a water-cooled cooler, an integrated level and temperature sensor (14), an air filter (15), and a glass level gauge (16). The highly integrated bidirectional hydraulic valve block has an internal return oil channel. The auxiliary atmospheric pressure oil tank (21) is connected to the return oil channel. The water-cooled cooler is connected in series with the return oil channel. The integrated level and temperature sensor (14) and the air filter (15) are installed on the top of the auxiliary atmospheric pressure oil tank (21). The glass level gauge (16) is installed on the side wall of the auxiliary atmospheric pressure oil tank (21).

6. An electro-hydraulic actuator unit for lithium battery formation according to claim 3, characterized in that, The end of the return oil channel is sealed with a high-pressure airtight accumulator (17). The high-pressure airtight accumulator (17) is pre-filled with inert gas. An accumulator oil port is provided on the body of the high-pressure airtight accumulator (17). The accumulator oil port is connected to the oil inlet of the first oil replenishment check valve (11) and the second oil replenishment check valve (12). An accumulator locking base discharge port (22) is provided at the bottom of the high-pressure airtight accumulator (17).

7. An electro-hydraulic actuator unit for lithium battery formation according to claim 6, characterized in that, The integrated electro-hydraulic actuator unit body is a multi-point distributed micro electro-hydraulic actuator unit array. Multiple sets of micro electro-hydraulic actuator units are suspended in parallel on the top beam (23) of the gantry frame. It also includes an upper pressure plate. The geometric center of the upper pressure plate is coaxially aligned with the axis of the piston rod of the hydraulic cylinder (2) of the electro-hydraulic actuator. The piston rod of each set of micro electro-hydraulic actuator units is connected to different geometric positions of the upper pressure plate.

8. An electro-hydraulic actuator unit for lithium battery formation according to claim 7, characterized in that, The power output end of the servo motor (19) is coaxially connected to a large-displacement closed pump and a small-displacement closed pump. The highly integrated bidirectional hydraulic valve block is equipped with an electrically controlled selection channel for switching between single-pump oil supply mode and dual-pump combined oil supply mode.

9. A pressure-pressurizing and pressure-holding method for an electro-hydraulic actuator unit for lithium battery formation based on any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Initial rapid approach: After the lithium battery pack is in place and the charging and discharging circuit is connected, the main control unit issues a position control command, and the servo motor (19) drives the bidirectional closed gear pump (10) to deliver oil, driving the upper pressure plate to descend at a speed of 10~50mm / s; Step 2: Control mode switching: When the clamping force is detected to reach the contact threshold of 0.5~0.8MPa, the system seamlessly switches from position control mode to pressure-displacement composite control mode. The main control unit synchronously collects electrochemical parameters and mechanical pressure and displacement parameters at a period of ≤500μs. Step 3: Long-term constant pressure holding: The first hydraulic control check valve (5) and the second hydraulic control check valve (6) close and lock the oil circuit, relying on the hydraulic oil energy storage to maintain the pressure, and control the pressure within the range of 0.5MPa~25MPa, with a static pressure control accuracy of ±0.1MPa; the servo motor (19) runs at a low speed of 1~50rpm or stops at zero speed to achieve pressure holding without stalling. Step 4: Dynamic compensation for gas expansion: When the lithium battery generates gas expansion and produces pressure and displacement fluctuations, the sensor collects data and uploads it to the main control unit. The main control unit controls the servo motor (19) to rotate slightly in the opposite direction to dynamically relieve pressure and compensate for the pressure fluctuation error within ±2%. Step 5: Equipment reset: After the formation process is completed, the servo motor (19) rotates in the opposite direction, driving the upper pressure plate to retract to the initial position, completing a single cycle.

10. A pressure-pressurizing and pressure-holding method for an electro-hydraulic actuator unit for lithium battery formation according to claim 9, characterized in that: In step 4, the main control unit performs two-dimensional coupling calculations on the mechanical stress parameters collected in real time and the lithium battery charge state, voltage and current parameters fed back by the lithium battery formation power module. Based on the gas generation characteristics of the lithium battery at a specific SOC stage, the reverse rotation angle and speed of the servo motor (19) are dynamically determined to achieve coordinated control of electrochemical mechanical stress.

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