Energy recovery and controllable damping system for lower limb exoskeletons

Abstract

This invention provides an energy recovery and controllable damping system for a lower limb exoskeleton, comprising: a rechargeable battery module, a motor, a motor drive board, a bidirectional DC-DC converter unit, a current detection unit, an overvoltage protection circuit, and a control unit. The control unit is configured to: identify the user's downward motion state based on motion sensor data; if a downward motion state is identified, determine a target charging current; and employ a closed-loop control strategy to adjust the bidirectional DC-DC converter unit so that the actual charging current approaches the target charging current, thereby recharging the battery with the electrical energy generated by the motor. This invention, by constructing a hardware system integrating energy recovery and controllable damping functions and implementing precise closed-loop control, achieves efficient energy recovery under all operating conditions and compliant damping matched to the motion state, while ensuring system reliability, significantly improving the battery life and user experience of the lower limb exoskeleton.

Description

Technical Field

[0001] This invention relates to the field of exoskeleton robot technology, specifically to an energy recovery and controllable damping system for a lower limb exoskeleton. Background Technology

[0002] Lower limb exoskeletons, as advanced wearable mechatronic devices, typically consist of core components such as rechargeable battery modules, main control boards, motor drive boards, and motors. Their primary design goal is to provide power assistance to users during activities such as walking on flat ground or climbing hills, thereby enhancing their athletic ability or reducing their physical burden.

[0003] However, existing technologies have significant limitations in scenarios where users wear lower limb exoskeletons for downward movements. A common approach is to allow the motors to rotate freely, but this provides no braking damping, increasing the burden on the user's muscle control and potentially leading to instability or even falls due to excessive speed. Some solutions employ mechanical brakes, but this significantly increases the overall weight and structural complexity of the system and fails to utilize the energy generated during the process. Other solutions use simple motor short-circuit braking, which produces some damping effect, but the damping force is uncontrollable and dissipates the user's gravitational potential energy entirely as heat, resulting in a significant waste of energy.

[0004] During descent, the user's body and the exoskeleton system continuously convert gravitational potential energy into kinetic energy. Current technology fails to effectively recover and utilize this energy, causing it to be wasted as heat, which directly shortens the endurance of the lower limb exoskeleton. Simultaneously, the user needs to rely on their own muscle strength to counteract gravity and control their descent speed, increasing muscle fatigue and joint impact.

[0005] Furthermore, during energy recovery, especially when the user is descending rapidly, the motor is driven in reverse at high speed, generating a high back electromotive force (EMF). Without an effective overvoltage protection mechanism, this back EMF can cause the bus voltage to rise sharply, exceeding the withstand voltage limits of critical electronic components such as power MOSFETs and bus capacitors on the motor drive board, leading to overvoltage breakdown and severely impacting system reliability and safety. Simultaneously, traditional energy recovery schemes typically only operate when the motor's generated voltage is higher than the battery voltage but less than or equal to the battery charging limit voltage. When the user slowly traverses a gentle slope, the motor's generated voltage is low, making energy recovery impossible and limiting the overall efficiency and applicable operating conditions of energy recovery. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide an energy recovery and controllable damping system for lower limb exoskeletons.

[0007] According to the present invention, an energy recovery and controllable damping system for a lower limb exoskeleton includes: a rechargeable battery module, a motor, a motor drive board, a bidirectional DC-DC converter unit, a damping strength control unit, and a control unit; The motor drive board is used to drive the motor; the bidirectional DC-DC converter unit is electrically connected between the rechargeable battery module and the motor drive board; The control unit includes a main control chip, a motion sensor, and a current detection unit; the main control chip is communicatively connected to the bidirectional DC-DC converter unit, the current detection unit, and the motion sensor. The damping strength control unit is integrated into the main control chip and can adjust the recovery current in real time through the bidirectional DC-DC converter unit based on the data collected by the motion sensor and the current detection unit, thereby controlling the damping strength.

[0008] This invention integrates a rechargeable battery module, a motor, a bidirectional DC-DC converter unit, and a control unit with a damping strength control unit to construct an integrated energy recovery and damping control hardware architecture. This architecture enables precise control of the lower limb exoskeleton's motion damping and autonomous recovery and storage of motion energy, simplifies the mechanical complexity of traditional damping structures, and effectively improves the exoskeleton device's battery life and motion adaptability.

[0009] Preferably, the control unit is configured to perform the following steps: Based on the motion data acquired from the motion sensor, it is determined whether the user's current motion state is a downlink motion state; If the downlink motion state is detected, a target charging current is determined based on at least one motion parameter characterizing the downlink motion state. A closed-loop control strategy is adopted. Based on the actual charging current feedback obtained from the current detection unit, the bidirectional DC-DC converter is adjusted by the damping strength control unit so that the actual charging current approaches and equals the target charging current, thereby recharging the electrical energy generated by the motor in the downward motion state back to the rechargeable battery module.

[0010] This invention identifies the user's descent motion state and matches the target charging current based on the descent motion parameters. Combined with current closed-loop feedback control, it achieves precise energy recovery and charging. It can specifically capture the redundant mechanical energy generated by the motor during the user's descent motion, achieving efficient energy recovery and utilization. At the same time, it ensures the stability of the damping output through precise current control, adapting to the assist damping requirements of descent motion.

[0011] Preferably, the motion sensor includes any one or more of the following sensors: hip joint angle sensor, joint angular velocity sensor, plantar pressure sensor, and inertial measurement unit (IMU); The motion data includes any one or more of the following: left and right hip joint angles, left and right hip joint angular velocities, left and right leg angle difference, gait cycle, range of motion (ROM) of joints in a single step or a whole step, peak joint angular acceleration, plantar pressure change, and trunk posture angle change. During data processing, the motion data is subjected to low-pass filtering and outlier removal. Zero-crossing detection is performed based on the difference in left and right hip joint angles to determine half-step events, and consecutive zero-crossing events in the same direction are paired into a complete gait cycle. For each complete gait cycle, feature values ​​within that cycle are extracted. These feature values ​​include average hip joint angle offset, peak hip joint angle offset, gait cycle duration, range of motion (ROM) within a single step or a whole step, mean angular velocity, peak angular acceleration, and left-right symmetry. When identifying the current movement state, the feature values ​​of the complete gait cycle are compared with a preset threshold or the user's historical baseline. When it is detected that the user's peak hip angle offset increases, the gait cycle and the range of motion (ROM) of the joint in a single step or a whole step show downward movement characteristics, the joint angular acceleration or impact peak is higher than the level of walking on flat ground, and multiple consecutive complete gait cycles meet the combination of these features, the current movement state is determined to be a downward movement state.

[0012] This invention integrates multi-dimensional gait motion data collected by multiple types of motion sensors, and extracts feature parameters through filtering, outlier removal, and gait cycle decomposition. Combined with multi-dimensional feature thresholds, it determines the downhill motion state, effectively avoiding detection errors from single sensor data, significantly improving the accuracy and stability of motion state recognition, providing reliable data support for subsequent damping control and energy recovery, and adapting to downhill motion scenarios for different users and on different road conditions.

[0013] Preferably, the bidirectional DC-DC converter unit is a four-switch buck-boost bidirectional DC-DC circuit; The four-switch buck-boost bidirectional DC-DC circuit includes: a first half-bridge, a second half-bridge, and a power inductor; The first half-bridge is connected to the rechargeable battery module, the second half-bridge is connected to the motor drive board, and the power inductor is connected between the first half-bridge and the second half-bridge; Both the first half-bridge and the second half-bridge are composed of power MOSFETs; The motion sensor is an inertial measurement unit; The system also includes an overvoltage protection circuit, which includes transient voltage suppression elements connected in parallel across the busbars of the motor drive board.

[0014] This invention employs a four-switch step-up bidirectional DC-DC circuit as the core of energy conversion, combined with an overvoltage protection circuit composed of transient voltage suppression components. This enables efficient bidirectional energy conversion between the battery and the motor, adapting to energy recovery requirements under different voltage conditions. Simultaneously, it effectively suppresses transient high voltage on the motor bus, protects the drive circuit and components, improves the safety and stability of the system, and extends the service life of the equipment.

[0015] Preferably, the closed-loop control strategy is proportional-integral-derivative PID control.

[0016] Preferably, at least one motion parameter characterizing the downward motion state includes the user's motion slope or joint angular velocity.

[0017] Preferably, the control unit is further configured to control the bidirectional DC-DC converter unit to operate in direct mode when the generator voltage of the motor is close to the charging limit voltage VCHG of the rechargeable battery module.

[0018] Preferably, after determining the target charging current, the control unit is further configured to perform a ramp-type soft-start process on the target charging current.

[0019] This invention employs a ramp-type soft-start process for the target charging current, which avoids the damping impact caused by the sudden change in current at the moment of energy recovery initiation, eliminates the jerky feeling of exoskeleton movement, and improves the stability of wearable movement.

[0020] Preferably, the control unit is further configured to limit the actual charging current to no more than a maximum charging current threshold.

[0021] Preferably, the bidirectional DC-DC converter unit includes: a first field-effect transistor, a second field-effect transistor, a third field-effect transistor, a fourth field-effect transistor, a power inductor, a bus capacitor, a first resistor, a second resistor, a third resistor, a fourth resistor, and an operational amplifier; The overvoltage protection circuit includes a transient voltage suppression diode; the current detection unit includes a current sampling resistor; The positive terminal of the rechargeable battery module is connected to the drain of the first field-effect transistor and one end of the first resistor, respectively, and the negative terminal of the rechargeable battery module is connected to one end of the current sampling resistor and the inverting input terminal of the operational amplifier, respectively. The other end of the current sampling resistor is connected to the non-inverting input terminal of the operational amplifier, one end of the second resistor, the source of the second field-effect transistor, the source of the fourth field-effect transistor, one end of the fourth resistor, one end of the bus capacitor, one end of the transient voltage suppression diode, and the negative terminal of the motor drive board. The output terminal of the operational amplifier is connected to the first connection terminal of the main control chip of the control unit. The other end of the first resistor is connected to the second connection terminal of the main control chip and the other end of the second resistor, respectively; The gate of the first field-effect transistor is connected to the third connection terminal of the main control chip, and the source of the first field-effect transistor is connected to one end of the power inductor and the drain of the second field-effect transistor, respectively. The gate of the second field-effect transistor is connected to the fourth connection terminal of the main control chip; The other end of the power inductor is connected to the drain of the fourth field-effect transistor and the source of the third field-effect transistor, respectively. The gate of the fourth field-effect transistor is connected to the fifth connection terminal of the main control chip; the gate of the third field-effect transistor is connected to the sixth connection terminal of the main control chip. The drain of the third field-effect transistor is connected to one end of the third resistor, the other end of the bus capacitor, the other end of the transient voltage suppression diode, and the positive terminal of the motor drive board, respectively. The other end of the third resistor is connected to the seventh connection terminal of the main control chip and the other end of the fourth resistor, respectively.

[0022] Preferably, when the generator voltage VBUS of the motor is greater than the charging limit voltage VCHG of the rechargeable battery module, a buck mode is triggered, the first field-effect transistor is normally on, the second field-effect transistor is normally off, and the third and fourth field-effect transistors operate in a complementary PWM mode; the generator voltage VBUS of the motor and the charging limit voltage VCHG of the rechargeable battery module satisfy the following relationship: VCHG=D×VBUS, where D is the PWM duty cycle; When the generator voltage VBUS of the motor is less than the charging limit voltage VCHG of the rechargeable battery module, the boost mode is triggered. The third field-effect transistor is normally on, the fourth field-effect transistor is normally off, and the first and second field-effect transistors operate in a complementary PWM mode. The generator voltage VBUS of the motor and the charging limit voltage VCHG of the rechargeable battery module satisfy the following relationship: VBUS = (1-D) × VCHG, where D is the PWM duty cycle. When the generator voltage VBUS of the motor is equal to the charging limit voltage VCHG of the rechargeable battery module, the shoot-through mode is triggered, the first field-effect transistor and the fourth field-effect transistor are turned on, and the second field-effect transistor and the third field-effect transistor are turned off.

[0023] Based on the relationship between the generator voltage of the motor and the charging limit voltage of the battery, this invention adaptively switches between three working modes: buck, boost, and direct. It can comprehensively cover the energy recovery needs under different generator voltage conditions, achieve efficient energy conversion over a wide voltage range, and adapt to the generator characteristics of the motor under different downward movement speeds and loads.

[0024] Preferably, the control unit is configured to perform the following steps: The motion sensor collects acceleration, angular velocity, and slope data of the hip joint. The acceleration and angular velocity data are processed by the attitude calculation algorithm to determine whether the current motion state is downstairs or downhill. If so, the damping mode and energy recovery function are activated. If not, the energy recovery circuit is turned off, and the lower limb exoskeleton system enters normal assist mode. In the enabled damping mode, the target damping force is calculated based on the descent gradient, descent speed, and joint angular velocity. The calculation formula is as follows:

[0025] in, Let α be the target damping force and α be the descent slope angle. For the user's speed in the downward direction, For hip joint angular velocity, This is the slope damping coefficient. The velocity damping coefficient, This is the joint angular velocity damping coefficient. Basic damping force; The calculated target damping force is converted into a target charging current using the following formula:

[0026] in, For the target charging current, Let Kt be the target damping force, Kt be the torque constant of the motor, η be the efficiency of the lower limb exoskeleton system, and GR be the reduction ratio of the planetary reducer. The current charging current is sampled in real time by the current detection unit. Calculate the current error Based on the current error, the PID controller outputs the PWM duty cycle adjustment amount and controls the bidirectional DC-DC converter unit. According to the current working mode, the PWM signal output by the PID controller is applied to the corresponding field-effect transistor in the bidirectional DC-DC converter unit to control the charging current, thereby controlling the damping strength.

[0027] This invention accurately identifies the downhill motion scenario through attitude calculation, calculates the target damping force based on multi-dimensional parameters such as slope, speed, and joint angular velocity, and converts it into the target charging current. This achieves precise matching between motion conditions and damping output and energy recovery power, which not only meets the buffering and damping requirements of downhill motion, but also maximizes the recovery of redundant motion energy.

[0028] Preferably, the target charging current is calculated based on the descent slope, descent speed, hip joint angular velocity, and impact intensity, using the following formula:

[0029] in, To reduce the slope angle, This is the mapping coefficient from slope to charging current; For the user's speed in the downward direction, This is the mapping coefficient from speed to charging current; For hip joint angular velocity, This is the mapping coefficient from angular velocity to target current; For impact eigenvalues, This is the mapping coefficient from impact strength to charging current; The current charging current is sampled in real time by the current detection unit. Calculate the current error Based on the current error, the PID controller outputs the PWM duty cycle adjustment amount and controls the bidirectional DC-DC converter unit. According to the current working mode, the PWM signal output by the PID controller is applied to the corresponding field-effect transistor in the bidirectional DC-DC converter unit to control the charging current, thereby controlling the damping strength.

[0030] This invention uses impact characteristic values ​​as charging current calculation parameters and integrates multi-dimensional motion parameters to construct a current mapping model. It can accurately adapt to the impact load conditions during the downward motion process, dynamically adjust the energy recovery power and damping strength, effectively buffer the motion impact, improve wearability comfort, and optimize energy recovery efficiency.

[0031] Preferably, the control unit detects the bus voltage of the bidirectional DC-DC converter unit and the charging limit voltage VCHG of the rechargeable battery module. By comparing the bus voltage and the charging limit voltage VCHG, the bidirectional DC-DC converter unit enters the corresponding mode: when the bus voltage is greater than the charging limit voltage VCHG, a buck mode is triggered; when the bus voltage is less than the charging limit voltage VCHG, a boost mode is triggered; and when the bus voltage is equal to the charging limit voltage VCHG, a pass-through mode is triggered. After determining the operating mode of the bidirectional DC-DC converter unit, PID control is then executed, specifically as follows: In damped regenerative braking mode, the control unit periodically samples the actual charging current and calculates the current error compared to the target charging current. The calculation formula is as follows:

[0032] in, For the first Current error per control cycle For the first The target charging current for each control cycle For the first The actual charging current obtained by sampling in each control cycle; Based on the current error, the PWM duty cycle adjustment is calculated using a PID controller. The calculation formula is as follows:

[0033] in, This is the PWM duty cycle adjustment amount. This is the proportionality coefficient. The integral coefficient is... These are the differential coefficients. To control the cycle, For the first - Current error over 1 control cycle Let be the current error in the i-th control cycle; Update the PWM duty cycle based on the PWM duty cycle adjustment:

[0034] in, For the first PWM duty cycle per control cycle For the first -1 control cycle of PWM duty cycle; Based on the comparison result between the bus voltage and the charging limit voltage VCHG, the control unit selects the corresponding switching transistor for PWM control.

[0035] This invention first determines the circuit operating mode by voltage comparison, and then iteratively updates the PWM duty cycle in real time based on the PID algorithm, realizing adaptive switching of operating conditions and high-precision closed-loop control of current, which greatly reduces current control error, ensures the real-time, accuracy and stability of damping intensity adjustment, and improves the dynamic response performance of the system.

[0036] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention enables energy recovery under all operating conditions with high efficiency. By employing a four-switch boost-buck bidirectional DC-DC circuit and automatically switching between boost and buck modes based on the real-time relationship between the motor's generator voltage and the battery's charging limit voltage, this invention overcomes the limitation of traditional solutions that can only recover energy when the generator voltage is higher than the battery voltage but less than or equal to the battery's charging limit voltage. Regardless of whether the user is descending a steep slope quickly or a gentle slope slowly, the system can efficiently convert the mechanical energy generated during braking into electrical energy to recharge the battery, significantly improving energy recovery efficiency and equipment runtime.

[0037] 2. The present invention provides adjustable and smooth damping force. The present invention monitors the motion posture in real time through the main control board and calculates the target damping force based on information such as descent slope and speed. Then, it uses PID closed-loop control to precisely adjust the charging current to achieve dynamic adjustment of the damping force. Combined with the damping force soft-start strategy, the damping force provided by the system is not only controllable in magnitude, but also smooth and impact-free. It can provide users with smooth braking assistance that is adapted to the scene, effectively protect the lower limb joints, and greatly improve the safety and comfort of use.

[0038] 3. This invention features high reliability and high integration. By adding a transient voltage suppression diode at the motor bus end, this invention constructs a hardware-level fast overvoltage protection mechanism, effectively preventing damage to the drive circuit caused by the high back electromotive force generated by the high-speed reverse drag of the motor, and significantly improving the operational reliability of the system. At the same time, braking damping is achieved through motor power generation, eliminating the need for additional mechanical braking devices, making the system structure more compact and lighter, improving integration, and making it more suitable for wearable exoskeleton devices with strict requirements on size and weight. Attached Figure Description

[0039] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a block diagram of the overall structure of an energy recovery and controllable damping system for a lower limb exoskeleton. Figure 2 This is a schematic diagram of a four-switch step-up / step-down circuit and an overvoltage protection circuit. Figure 3 This is a schematic diagram of the control flow of the control unit; Figure 4 This is a schematic diagram of the overall structure of the lower limb exoskeleton. Detailed Implementation

[0040] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0041] First, let's explain some key terms used in this instruction manual. A lower limb exoskeleton system refers to a wearable mechatronic device for the lower limbs, providing assistance, support, or other functions. A bidirectional DC-DC converter unit is a circuit unit capable of bidirectional energy flow between two DC ports at different voltage levels; in this invention, it's used for energy conversion between the motor's generator and the battery. Downward motion refers to the user's movement state when wearing the exoskeleton, such as going downhill or down stairs, where the body's center of gravity potential energy decreases. Target charging current refers to the preset current value expected to recharge the rechargeable battery module to achieve a specific damping effect. Overvoltage protection circuit refers to a circuit that clamps the voltage within a safe range through a rapid response when the circuit bus voltage abnormally rises, protecting subsequent circuit components. Bus terminal refers to the DC power input terminal of the motor drive board, i.e., the power bus shared by its internal power devices.

[0042] Example 1 This embodiment provides an energy recovery and controllable damping system for a lower limb exoskeleton. From a system-level perspective, the system includes the core hardware components required for energy recovery and controllable damping: a rechargeable battery module, serving as the system's energy source and a storage unit for recovered energy; a motor, acting as an actuator, outputting torque in assist mode and functioning as a generator in recovery mode; a motor drive board for driving the motor; a bidirectional DC-DC converter unit, electrically connected between the battery and the motor drive board, crucial for achieving bidirectional energy flow; a current detection unit for feedback of the actual charging current; an overvoltage protection circuit, located at the bus terminal of the motor drive board, to prevent damage from overvoltage; and a control unit, including a processor and motion sensors, acting as the system's "brain" to coordinate the operation of each component. These hardware components together constitute the basic platform for realizing energy recovery and controllable damping.

[0043] Furthermore, this embodiment defines the core control logic executed by the control unit, which includes the following steps: First, the control unit identifies whether the user's current motion state is downward based on motion data acquired from motion sensors. For example, by analyzing IMU data through attitude calculation algorithms (such as Kalman filtering), it determines the tilt angle and angular velocity of the body or limbs, thereby identifying the intention to go downstairs or downhill.

[0044] The motion sensor may include one or more of the following: hip joint angle sensor, joint angular velocity sensor, plantar pressure sensor, and inertial measurement unit (IMU). The motion data acquired by the system includes at least: left and right hip joint angles, left and right hip joint angular velocities, left and right leg angle difference, gait cycle, range of motion (ROM) of joints in a single step or a full step, peak joint angular acceleration, and optional plantar pressure changes and trunk posture angle changes.

[0045] During data processing, the system first performs low-pass filtering and outlier removal on the raw angle and angular velocity data to reduce the impact of sensor noise. Then, it performs zero-crossing detection based on the difference in left and right hip joint angles to determine half-step events, and pairs consecutive zero-crossing events in the same direction into a complete gait cycle. For each complete gait cycle, the system extracts feature values ​​within that cycle, including average hip joint angle offset, peak hip joint angle offset, gait cycle duration, range of motion (ROM) within a single step or a whole step, mean angular velocity, peak angular acceleration, and left-right symmetry.

[0046] When identifying the current movement state, the system compares the aforementioned full-step features with preset thresholds or the user's historical baseline. If the system detects an increase in the user's peak hip angle offset, downward movement characteristics in the gait cycle and the range of motion (ROM) within a single step or full step, or a joint angular acceleration or impact peak higher than the level for walking on flat ground, and this combination of features is met for multiple consecutive gait cycles, the current movement state is determined to be a downward movement state. To avoid false positives, the system can employ a continuous multi-step confirmation mechanism, switching to a downward movement state only when two or more consecutive complete gait cycles are identified as exhibiting downward characteristics.

[0047] Therefore, the solution in this embodiment does not make a judgment based on a single instantaneous sensor value, but rather performs filtering, gait segmentation, whole-step feature extraction, and multi-step stability confirmation on the continuous motion data collected by the motion sensor to comprehensively identify whether the user is in a downward motion state.

[0048] Secondly, if a downward motion state is detected, the control unit determines a target charging current based on the motion parameters characterizing this state (such as downward slope, joint angular velocity, etc.). The magnitude of this target charging current is positively correlated with the desired damping force, reflecting the controllability of the damping.

[0049] Finally, the control unit employs a closed-loop control strategy, using the target charging current as the setpoint and the actual charging current measured by the current detection unit as the feedback value. By comparing the difference between the two, a control signal is generated to dynamically adjust the operating state of the bidirectional DC-DC converter unit (such as the PWM duty cycle) so that the actual charging current quickly and stably approaches the target charging current. Through this closed-loop control, the electrical energy generated by the motor is precisely fed back to the battery, while simultaneously generating braking damping at the motor shaft end corresponding to the target current.

[0050] Furthermore, the bidirectional DC-DC converter unit is specifically a four-switch buck-boost bidirectional DC-DC circuit. This topology enables bidirectional energy flow and combines boost and buck functions. This solves the technical challenge of effectively recovering energy under different operating conditions (e.g., the motor's generator voltage is higher than the battery voltage when descending a steep slope quickly, or the motor's generator voltage is lower than the battery voltage when descending a gentle slope slowly).

[0051] Furthermore, such as Figure 2 As shown, the four-switch buck-boost bidirectional DC-DC circuit includes a first half-bridge (e.g., composed of a first field-effect transistor Q1 and a second field-effect transistor Q2) connected to the rechargeable battery module, a second half-bridge (e.g., composed of a third field-effect transistor Q3 and a fourth field-effect transistor Q4) connected to the motor drive board, and a power inductor L1 connected between the midpoints of the two half-bridges. This structure clearly illustrates the specific implementation details of the circuit. The first field-effect transistor Q1, the second field-effect transistor Q2, the third field-effect transistor Q3, and the fourth field-effect transistor Q4 are all power field-effect transistors.

[0052] Furthermore, both the first and second half-bridges are composed of power MOSFETs. The advantages of using power MOSFETs as switching elements are their fast switching speed, low drive power, and low on-resistance, which effectively reduce switching and conduction losses, thereby improving the efficiency of the entire energy conversion system.

[0053] Furthermore, the motion sensor is an inertial measurement unit (IMU). An IMU typically integrates a three-axis accelerometer and a three-axis gyroscope, which can provide rich attitude and motion information, making it easy to accurately identify the user's motion intentions and states (such as going downhill or down stairs) through algorithms, and providing reliable data input for subsequent damping control.

[0054] Furthermore, to enhance system reliability, the overvoltage protection circuit includes a transient voltage suppression element, such as a transient voltage suppression diode (TVS1), connected in parallel across the busbar of the motor drive board. Its working principle is as follows: under normal voltage, this element is in a high-resistance state and has no effect on the circuit; when a transient overvoltage occurs on the busbar due to reasons such as high-speed reverse drag of the motor, this element will rapidly conduct at a sub-nanosecond speed, discharging the surge current to ground, thereby clamping the busbar voltage to a safe level and effectively protecting key components such as power MOSFETs on the motor drive board.

[0055] Furthermore, the closed-loop control strategy can specifically be a proportional-integral-derivative (PID) control. The PID controller controls the current error (e=I) based on the current error. target -I actual The adjustment amount of the PWM duty cycle of the bidirectional DC-DC converter unit is calculated through the operation of three stages: proportional (P), integral (I), and derivative (D), thereby realizing accurate, fast, and stable tracking of the charging current and ensuring the smoothness of the damping force and the timeliness of the response.

[0056] Furthermore, to achieve adaptive damping, the motion parameters characterizing the downward motion state may include the user's motion gradient or joint angular velocity. For example, a positive correlation can be established between the target charging current and these parameters, i.e., the greater the gradient or the faster the speed, the greater the required damping and the larger the set target current, thereby achieving adaptive damping control that matches the user's intention and the external environment.

[0057] In damping mode, the target damping force is calculated based on the descent gradient and descent speed. This target damping force is not a fixed value but is calculated in real-time based on the user's descent motion intensity. The control unit can calculate the user's desired damping force during descent based on motion parameters such as descent gradient, descent speed, and joint angular velocity. One possible calculation method is as follows:

[0058] in, Let α be the target damping force and α be the descent slope angle. For the user's speed in the downward direction, For hip joint angular velocity, This is the slope damping coefficient. The velocity damping coefficient, This is the joint angular velocity damping coefficient. It is the basic damping force.

[0059] The target damping force can then be converted into a target charging current, using the following conversion formula:

[0060] in, For the target charging current, Let Kt be the target damping force, Kt be the torque constant of the motor, η be the efficiency of the lower limb exoskeleton system, and GR be the reduction ratio of the planetary reducer. Besides calculating the target charging current from the target damping force, the target charging current can also be determined directly based on motion parameters such as descent slope, descent speed, hip joint angular velocity, and impact intensity. The target current can be determined using one or more parameters. Multi-parameter fusion avoids misjudgments caused by relying on a single sensor, resulting in a smoother target charging current that better reflects the user's actual descent conditions. The conversion formula is as follows:

[0061] in, To reduce the slope angle, This is the mapping coefficient from slope to charging current. For the downward velocity, This is the mapping coefficient from speed to charging current. For hip joint angular velocity, This is the mapping coefficient from angular velocity to target current. For impact eigenvalues, This is the mapping coefficient from impact strength to charging current.

[0062] The current charging current is sampled in real time by the current detection unit. Calculate the current error Based on the current error, the PID controller outputs the PWM duty cycle adjustment amount and controls the bidirectional DC-DC converter unit. According to the current working mode, the PWM signal output by the PID controller is applied to the corresponding field-effect transistor in the bidirectional DC-DC converter unit to control the charging current, thereby controlling the damping strength.

[0063] Furthermore, to further optimize system efficiency, the control unit can also be configured to operate the bidirectional DC-DC converter in shoot-through mode when the motor's generator voltage VBUS is close to the battery's charging limit voltage VCHG. In this mode, the current bypasses the high-frequency switching circuit and flows directly between the battery and the motor drive, which can significantly reduce switching losses and improve the overall system efficiency under this specific operating condition.

[0064] Furthermore, to enhance the user experience, the control unit can perform a ramp-type soft-start process after determining the target charging current. This avoids sudden changes in damping force caused by a step change in the target current, ensuring a smooth transition in the application and change of damping force, thus improving the smoothness and comfort of the user experience.

[0065] The control unit detects the bus voltage of the bidirectional DC-DC converter (equal to the generator voltage VBUS of the motor) and the charging limit voltage VCHG of the battery module. By comparing the bus voltage and the charging limit voltage VCHG of the battery module, it determines whether the converter enters the corresponding mode. When the bus voltage is greater than the charging limit voltage VCHG of the rechargeable battery module, a buck mode is triggered. When the bus voltage is less than the charging limit voltage VCHG of the rechargeable battery module, a boost mode is triggered. When the bus voltage is equal to the charging limit voltage VCHG of the rechargeable battery module, a pass-through mode is triggered.

[0066] After determining the operating mode of the bidirectional DC-DC converter unit, PID control is then executed, specifically as follows: In damped regenerative braking mode, the control unit periodically samples the actual charging current. The current error is obtained by comparing it with the target charging current.

[0067] in, For the first Current error per control cycle For the first The target charging current for each control cycle For the first The actual charging current is obtained by sampling during each control cycle.

[0068] The PID controller calculates the PWM duty cycle adjustment based on the error:

[0069] in, This is the PWM duty cycle adjustment amount. This is the proportionality coefficient. The integral coefficient is... These are the differential coefficients. To control the cycle, This represents the current error from the previous control cycle.

[0070] Update the PWM duty cycle based on this adjustment:

[0071] in, This represents the current PWM duty cycle. This represents the PWM duty cycle of the previous cycle.

[0072] Subsequently, the control unit selects the corresponding switching transistor for PWM control based on the aforementioned voltage comparison results.

[0073] Within each control cycle, the system repeats the following process: sampling → Calculate e(k) → Calculate ΔD(k) using PID control → Update D(k) → Drive the DC-DC switch → Resample .

[0074] Through the above closed-loop process, the actual charging current gradually approaches the target charging current, thereby achieving stable control of the energy recovery current and further realizing controllable adjustment of the damping strength.

[0075] To ensure safety, the control unit is also configured to limit the actual charging current to no more than a maximum charging current threshold. This serves a dual purpose: first, to protect the battery from overcurrent charging, preventing overheating or reduced battery life; and second, to prevent excessive damping force from causing motor seizure or user instability, thus providing a safety barrier for the user.

[0076] like Figure 2 As shown, this embodiment provides a specific circuit structure. The bidirectional DC-DC conversion unit includes: a first field-effect transistor Q1, a second field-effect transistor Q2, a third field-effect transistor Q3, a fourth field-effect transistor Q4, a power inductor L1, a bus capacitor C1, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and an operational amplifier; the overvoltage protection circuit includes a transient voltage suppression diode TVS1; and the current detection unit includes a current sampling resistor R_sense.

[0077] The first field-effect transistor Q1, the second field-effect transistor Q2, the third field-effect transistor Q3, and the fourth field-effect transistor Q4 are all power field-effect transistors.

[0078] The positive terminal of the rechargeable battery module is connected to the drain of the first field-effect transistor Q1 and one end of the first resistor R1, respectively. The negative terminal of the rechargeable battery module is connected to one end of the current sampling resistor R_sense and the inverting input terminal of the operational amplifier, respectively. The other end of the current sampling resistor R_sense is connected to the non-inverting input terminal of the operational amplifier, one end of the second resistor R2, the source of the second field-effect transistor Q2, the source of the fourth field-effect transistor Q4, one end of the fourth resistor R4, one end of the bus capacitor C1, one end of the transient voltage suppression diode TVS1, and the negative terminal of the motor drive board, respectively. The output terminal of the operational amplifier is connected to the first connection terminal of the main control chip of the control unit.

[0079] The other end of the first resistor R1 is connected to the second connection terminal of the main control chip and the other end of the second resistor R2, respectively; the gate of the first field-effect transistor Q1 is connected to the third connection terminal of the main control chip, and the source of the first field-effect transistor Q1 is connected to one end of the power inductor L1 and the drain of the second field-effect transistor Q2, respectively; the gate of the second field-effect transistor Q2 is connected to the fourth connection terminal of the main control chip; the other end of the power inductor L1 is connected to the drain of the fourth field-effect transistor Q4 and the source of the third field-effect transistor Q3, respectively; the gate of the fourth field-effect transistor Q4 is connected to the fifth connection terminal of the main control chip; the gate of the third field-effect transistor Q3 is connected to the sixth connection terminal of the main control chip; the drain of the third field-effect transistor Q3 is connected to one end of the third resistor R3, the other end of the bus capacitor C1, the other end of the transient voltage suppression diode TVS1, and the positive terminal of the motor drive board, respectively; the other end of the third resistor R3 is connected to the seventh connection terminal of the main control chip and the other end of the fourth resistor R4, respectively.

[0080] The first resistor R1 and the second resistor R2 are used to acquire the battery voltage VBAT, which is used to monitor the battery voltage. The third resistor R3 and the fourth resistor R4 are used to acquire the generator voltage VBUS of the motor.

[0081] When the generator voltage VBUS of the motor is greater than the charging limit voltage VCHG of the rechargeable battery module, the buck mode is triggered. The first field-effect transistor Q1 is normally on, the second field-effect transistor Q2 is normally off, and the third field-effect transistor Q3 and the fourth field-effect transistor Q4 operate in complementary PWM mode. The generator voltage VBUS of the motor and the charging limit voltage VCHG of the rechargeable battery module satisfy the following relationship: VCHG=D×VBUS, where D is the PWM duty cycle.

[0082] When the generator voltage VBUS of the motor is less than the charging limit voltage VCHG of the rechargeable battery module, the boost mode is triggered. The third field-effect transistor Q3 is normally on, the fourth field-effect transistor Q4 is normally off, and the first field-effect transistor Q1 and the second field-effect transistor Q2 operate in complementary PWM mode. The generator voltage VBUS of the motor and the charging limit voltage VCHG of the rechargeable battery module satisfy the following relationship: VBUS=(1-D)×VCHG, where D is the PWM duty cycle.

[0083] When the generator voltage VBUS of the motor is equal to the charging limit voltage VCHG of the rechargeable battery module, the shoot-through mode is triggered, the first field-effect transistor Q1 and the fourth field-effect transistor Q4 are turned on, and the second field-effect transistor Q2 and the third field-effect transistor Q3 are turned off.

[0084] Example 2 Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1.

[0085] like Figures 1 to 4 As shown, in one application scenario, the user wears this lower limb exoskeleton system (such as...). Figure 4 (As shown) Downhill slope. The overall functional block diagram of the system is as follows. Figure 1 As shown, the motion sensor within the control unit of the system detects the downhill condition. The processor within the control unit then calculates a target charging current value. Simultaneously, a general-purpose closed-loop controller (implemented in software within the processor) continuously adjusts the operating state of a general-purpose bidirectional DC-DC converter unit based on the actual charging current fed back by the current detection unit. This allows the electrical energy generated by the passive rotation of the motor during downhill driving to be recharged back to the rechargeable battery module at a current close to the target value, thereby generating braking damping at the motor shaft end and assisting the user in stabilizing the descent. This basic embodiment demonstrates the core idea of ​​this invention: achieving energy recovery and controllable damping through closed-loop control of the bidirectional DC-DC converter unit.

[0086] Furthermore, this embodiment defines the specific structure of the bidirectional DC-DC conversion unit. For example... Figure 2 As shown, this unit is specifically a four-switch buck-boost bidirectional DC-DC circuit. The circuit consists of a first half-bridge connected to the battery (composed of a first field-effect transistor Q1 and a second field-effect transistor Q2), a second half-bridge connected to the bus of the motor drive board (composed of a third field-effect transistor Q3 and a fourth field-effect transistor Q4), and a power inductor L1. By applying different PWM controls to these four field-effect transistors, the circuit can flexibly operate in boost, buck, and pass-through modes. For example, when the user is slowly descending a gentle slope and the motor's generating voltage VBUS is lower than the battery's charging limit voltage VCHG, the circuit operates in boost mode; when the user is rapidly descending a steep slope and the motor's generating voltage VBUS is higher than the charging limit voltage VCHG, the circuit operates in buck mode. This ensures effective energy recovery under all downhill operating conditions.

[0087] Furthermore, this embodiment provides a detailed description of the overvoltage protection circuit. For example... Figure 2 As shown, the overvoltage protection circuit is specifically a transient voltage suppression element, which is connected in parallel across the busbar of the motor drive board (i.e., across the busbar capacitor C1). Specifically, a transient voltage suppression diode (TVS1) can be used, with its anode connected to the busbar and its cathode connected to the positive terminal of the busbar. When the busbar voltage momentarily exceeds the breakdown voltage of the transient voltage suppression diode TVS1 due to an emergency (such as emergency braking), the transient voltage suppression diode TVS1 will quickly conduct, absorbing the surge current and clamping the voltage within the safe operating area of ​​components such as the third field-effect transistor Q3 and the fourth field-effect transistor Q4, thereby effectively protecting the hardware.

[0088] Furthermore, this embodiment optimizes the control strategy. After recognizing the downlink state, the processor within the control unit will determine the motion slope and joint angular velocity calculated by the IMU. velocity This allows for dynamic calculation of the target charging current. For example, the greater the slope or the faster the speed, the greater the damping provided, achieving adaptive control. Furthermore, when the target current I... target When a step change occurs (such as starting from 0), the control unit does not immediately use that value as the setpoint for the PID controller. Instead, it linearly increases the value from the current value to the new target value within 100ms. This ramp-type soft-start process avoids abrupt changes in damping force, providing users with a smoother and more comfortable experience.

[0089] Furthermore, combined Figure 1 , Figure 2 , Figure 3 Describe the complete workflow.

[0090] The hardware configuration of the lower limb exoskeleton system is as follows: Figure 1 and Figure 2 As shown, its control flow is as follows Figure 3 As shown.

[0091] In the motion state recognition step, the IMU in the control unit continuously collects motion data, and the processor analyzes the data through attitude calculation algorithms to identify the user's motion state in real time (such as walking on flat ground, going uphill, going downhill, etc.).

[0092] The downlink status determination step involves the processor determining whether the current state is downlink motion. If not, it may enter boost mode or direct-through mode, in which case the bidirectional DC-DC converter unit may be configured to power the motor from the battery or to perform direct-through with minimal loss.

[0093] The target current calculation and processing steps involve activating energy recovery and damping control modes in a downhill state. The processor calculates the target charging current I based on parameters such as motion gradient and joint angular velocity. target Subsequently, a ramp-type soft-start process is applied to the target value, followed by a limiting process to ensure that it does not exceed the preset maximum charging current threshold.

[0094] The DC-DC operating mode determination step involves the processor comparing the motor bus voltage (equal to the motor's generating voltage VBUS) with the battery's charging limit voltage VCHG to determine whether the bidirectional DC-DC converter unit should operate in boost mode (motor generating voltage VBUS < battery charging limit voltage VCHG) or buck mode (motor generating voltage VBUS > battery charging limit voltage VCHG).

[0095] The PID closed-loop control execution steps involve the PID controller starting up. It uses the processed target charging current as the setpoint and the actual charging current measured by the current detection unit as the feedback value.

[0096] In the PWM signal generation and driving steps, the PID controller calculates the PWM duty cycle adjustment based on the current error and generates the corresponding PWM control signal according to the determined working mode. This signal drives the first field-effect transistor Q1, the second field-effect transistor Q2, the third field-effect transistor Q3, and the fourth field-effect transistor Q4 in the four-switch circuit, thereby accurately controlling the actual charging current to track the target value and achieving energy recovery and controllable damping.

[0097] Throughout the process, the overvoltage protection circuit (transient voltage suppression diode TVS1) remains in standby mode, immediately activating to protect the system should an overvoltage occur. This process repeats continuously, achieving efficient, safe, comfortable, and intelligent energy recovery and damping control for the lower limb exoskeleton.

[0098] Example 3 Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1 and Embodiment 2.

[0099] This embodiment provides an energy recovery and controllable damping system for a lower limb exoskeleton, comprising: a rechargeable battery module, a main control board, two motor drive boards, two BLDC motors, a four-switch buck-boost bidirectional DC-DC circuit, a damping strength control unit, and an overvoltage protection circuit.

[0100] The rechargeable battery module is used to power the various components of the system and store the recovered electrical energy.

[0101] The main control board integrates an MCU main control chip, an IMU inertial measurement unit, and a voltage / current sampling circuit, which is responsible for motion state recognition, damping control, and circuit coordination.

[0102] Two motor drive boards drive the BLDC motors on the left and right sides respectively, realizing the forward and reverse rotation of the motors and power generation control.

[0103] Two BLDC motors serve as actuators for lower limb assistance. They integrate planetary reducers and can output torque in drive mode to provide assistance to the human lower limbs. In regeneration mode, they are dragged backward by the human body to generate back electromotive force and generate electricity.

[0104] The four-switch buck-boost bidirectional DC-DC circuit is connected in series between the battery and the motor drive board. It is used to convert the back electromotive force of the motor into a voltage suitable for battery charging, realizing the switching between boost, buck and direct-through modes. This circuit is connected in series between the battery and the bus capacitor of the motor drive board and is the core component for realizing energy recovery and voltage adaptation.

[0105] The four-switch buck-boost bidirectional DC-DC circuit specifically includes: a first field-effect transistor Q1, a second field-effect transistor Q2, a third field-effect transistor Q3, a fourth field-effect transistor Q4, a power inductor L1, a bus capacitor C1, and a current sampling resistor R_sense.

[0106] The first field-effect transistor Q1 and the second field-effect transistor Q2 form a battery-side half-bridge, constituting a battery-side switching network. The first field-effect transistor Q1 is the high-side switch, and the second field-effect transistor Q2 is the low-side switch.

[0107] The third field-effect transistor Q3 and the fourth field-effect transistor Q4 form a motor-side half-bridge, constituting a motor-side switching network. The third field-effect transistor Q3 is the high-side switch, and the fourth field-effect transistor Q4 is the low-side switch.

[0108] The power inductor L1 serves as an energy storage element for energy conversion during the step-up and step-down process.

[0109] The bus capacitor C1 is used to stabilize the bus voltage on the motor side, absorb high-frequency ripple in the circuit, and ensure stable circuit operation.

[0110] The current sampling resistor R_sense is connected in series in the negative terminal circuit of the battery to detect the charging / discharging current of the system in real time and provide feedback for the current closed-loop control.

[0111] The positive terminal of the battery is connected to the drain of the first field-effect transistor Q1; the source of the first field-effect transistor Q1 is split into two paths: one path is connected to the drain of the second field-effect transistor Q2, and the other path is connected to one end of the power inductor L1; the source of the second field-effect transistor Q2 is grounded (system ground); the other end of the power inductor L1 is split into two paths: one path is connected to the drain of the fourth field-effect transistor Q4, and the other path is connected to the source of the third field-effect transistor Q3; the source of the fourth field-effect transistor Q4 is grounded (system ground); the drain of the third field-effect transistor Q3 is connected to the positive terminal of the motor drive board bus capacitor (i.e., the positive terminal of the motor drive board power supply); the ground of the motor drive board is grounded (system ground); the current sampling resistor R_sense is connected in series between the negative terminal of the battery and the system ground, and the negative terminal of the battery is connected to the system ground through the current sampling resistor R_sense; the leads at both ends of the current sampling resistor R_sense are connected to the ADC pin of the current detection chip or MCU to detect bidirectional current (charging / discharging current).

[0112] The four-switch buck-boost bidirectional DC-DC circuit can achieve three operating modes to adapt to different working conditions: a. Buck Mode: Triggering condition: Motor's generating voltage (VBUS) > battery charging limit voltage (VCHG) (e.g., rapid descent down a steep slope). Switching states: The first field-effect transistor Q1 is normally on, the second field-effect transistor Q2 is normally off, and the third field-effect transistor Q3 and the fourth field-effect transistor Q4 operate in complementary PWM (pulse width modulation) mode; Voltage relationship: VCHG = D × VBUS (where D is the PWM duty cycle).

[0113] b. Boost Mode: Triggering condition: Motor's generating voltage (VBUS) < battery charging limit voltage (VCHG) (e.g., slow downhill slope scenario); Switching states: The third field-effect transistor Q3 is normally on, the fourth field-effect transistor Q4 is normally off, and the first field-effect transistor Q1 and the second field-effect transistor Q2 operate in complementary PWM mode. Voltage relationship: VBUS=(1-D)×VCHG (where D is the PWM duty cycle).

[0114] c. Pass-Through Mode: Triggering conditions: When walking on flat ground, going uphill, or when the generator voltage is close to the battery's charging limit voltage VCHG; Switching state: First field-effect transistor Q1 and fourth field-effect transistor Q4 are turned on, and second field-effect transistor Q2 and third field-effect transistor Q3 are turned off; Function: The battery directly powers the motor drive board, eliminating switching losses and improving system efficiency.

[0115] The damping strength control unit is integrated into the main control chip and is used to adjust the recovery current in real time based on the data collected by the IMU, thereby controlling the damping strength.

[0116] Overvoltage protection circuits are used to prevent damage to circuit components when the back electromotive force of the motor is too high, thus ensuring system safety.

[0117] To prevent damage to the motor drive board and the four-switch step-up / step-down circuit when the back EMF of the motor is too high, an overvoltage protection circuit is specially set up at the system bus end (both ends of the motor drive board bus), and a hardware overvoltage clamping scheme is used to achieve transient protection.

[0118] Overvoltage protection specific solution: a. Protection component: Transient voltage suppression diode TVS1, connected in parallel across the two ends of the motor drive board busbar; b. Selection of transient voltage suppressor diode TVS1: SMBJ30A (30V unidirectional transient voltage suppressor diode); c. Reverse cutoff voltage (VRWM): 30V — Ensures that the transient voltage suppression diode TVS1 does not conduct during normal operation, and the leakage current is extremely small; d. Breakdown voltage (VBR): 33.3V ~ 36.8V — When the voltage exceeds this range, the transient voltage suppressor diode TVS1 begins to enter the breakdown region, and the impedance decreases rapidly; e. Clamping voltage (VC): Typical value 48.4V (@ Ipp=12.4A) - only reached under extreme transient peak current, the bus voltage is limited to 36~38V in actual overvoltage scenarios; f. Peak pulse power: 600W, meeting the requirements for transient overvoltage energy absorption; g. Response time: Sub-nanosecond level (<1ns), fast response.

[0119] Operating Principle: When the motor's bus voltage (equal to the motor's generating voltage VBUS) is within the normal operating range (≤30V), the transient voltage suppressor diode TVS1 is in the off state, with minimal leakage current, and does not affect the circuit. When the bus voltage abnormally rises above the breakdown voltage (approximately 33.3V), the transient voltage suppressor diode TVS1 enters the breakdown region, its impedance rapidly decreases, and it begins to conduct and discharge current. In typical back EMF overvoltage scenarios, the transient voltage suppressor diode TVS1 limits the bus voltage to 36~38V, effectively protecting downstream circuits. Even under extreme transient high current surges, the clamping voltage (48.4V) of the transient voltage suppressor diode TVS1 lasts for an extremely short time (microseconds), which is sufficient for the avalanche withstand capability of the field-effect transistor, ensuring system safety and reliability.

[0120] Damping strength control strategy: The main control chip uses an IMU to detect hip joint angle, angular velocity, and slope information in real time. Combined with PID closed-loop control, it achieves precise and smooth adjustment of damping strength. The specific control process is as follows: (1) Motion state recognition.

[0121] The IMU collects triaxial acceleration and angular velocity data in real time, processes the data through attitude calculation algorithms (such as Kalman filtering algorithm), and accurately determines the current motion state (going upstairs, going downstairs, going uphill, going downhill, walking on flat ground).

[0122] (2) Damping mode enable judgment.

[0123] When the system detects a downhill or downhill situation, it automatically enables the damping mode and starts the energy recovery function; otherwise, it shuts off the energy recovery circuit and the system enters the normal assist mode (providing assistance on flat ground and uphill).

[0124] (3) Determination of damping strength.

[0125] The target damping force is calculated based on the descent trend (slope angle, descent speed), and then converted into the target charging current using the following formula:

[0126] Wherein, is the target charging current, is the target damping force, Kt is the motor torque constant, η is the system efficiency, and GR is the reduction ratio of the planetary gear reducer.

[0127] (4) PID closed-loop control.

[0128] The current sampling resistor R_sense is used to sample the current charging current in real time , calculate the current error . The PID controller outputs the PWM duty cycle adjustment amount according to the error to control the four-switch buck-boost circuit. According to the current working mode (buck / boost), the PWM signal is applied to the corresponding switching transistor (the first field-effect transistor Q1 and the third field-effect transistor Q3 are controlled in the buck mode, and the second field-effect transistor Q2 and the fourth field-effect transistor Q4 are controlled in the boost mode), so as to achieve precise and stable control of the charging current, and then control the damping intensity.

[0129] (5) Damping compliance processing.

[0130] a. Soft start: The target current gradually increases in the form of a ramp function to avoid sudden changes in the damping force and prevent the user from feeling jerks; b. Current limit: Set the maximum charging current threshold to prevent the motor from being locked or the battery from being overcharged, and ensure user safety and battery life; c. Data filtering: Perform low-pass filtering on the data collected by the IMU to eliminate damping fluctuations caused by body shaking and external interference, and improve damping compliance.

[0131] The system working process is as follows: start → the IMU collects motion data → attitude calculation to identify the motion state → judge whether it is going downstairs / downhill → if not, enter the direct-through mode and the system normally provides assistance → if so, enable the damping mode → calculate the target damping force and convert it into the target charging current → sample the bus voltage (equal to the generated voltage VBUS of the motor) and the charging limit voltage (VCHG) of the battery, and judge the working mode (if VBUS > VCHG, it is the buck mode, if VBUS < VCHG, it is the boost mode, otherwise it is the direct-through mode) → the PID adjusts the PWM duty cycle to control the charging current to stabilize at the target value → the electrical energy converted by the motor back electromotive force is used to recharge the battery → return to the loop and continuously monitor the motion state.

[0132] The system of this embodiment can provide adjustable and compliant damping during downhill or down stair processes, protect the user's lower limb joints, and enhance the user's sense of security.

[0133] This embodiment converts the kinetic energy during downhill / down stair into electrical energy and recharges the battery, extending the device's battery life.

[0134] The system in this embodiment can still recover energy when the generator voltage is lower than the battery voltage (gentle slope, slow speed scenario), covering all downhill conditions.

[0135] This embodiment can prevent the drive board circuit from burning out when the back electromotive force of the motor is too high, thus improving the reliability of system operation.

[0136] The system in this embodiment can achieve energy recovery under all operating conditions. Regardless of the downhill speed (high or low motor voltage), the system can stably charge the battery by switching between boost and buck modes through the four-switch boost-buck bidirectional DC-DC circuit, which significantly improves energy recovery efficiency and avoids kinetic energy waste.

[0137] The system in this embodiment can achieve adjustable and smooth damping. It can dynamically adjust the damping strength according to the slope angle and descent speed, so that users can obtain a suitable smooth damping force, protect the lower limb joints, avoid the feeling of jerking, and greatly improve the safety and comfort of use.

[0138] The system in this embodiment can extend the device's battery life, recover energy during descent / downhill movement to recharge the battery, reduce battery charging frequency, and increase the exoskeleton's continuous working time.

[0139] The system in this embodiment does not require additional mechanical brakes. It achieves damping braking by generating electricity from a motor, eliminating the need for additional braking devices, reducing system weight, and improving system integration. The system in this embodiment has a compact structure, with a four-switch buck-boost circuit integrated with the main control board. It is small in size and light in weight, making it suitable for the miniaturization requirements of wearable exoskeletons.

[0140] The system in this embodiment can achieve reliable overvoltage protection, transient voltage suppression diode transient clamping design, and rapid response to scenarios where the motor back EMF is too high, ensuring the safe operation of core components such as the motor drive board and four-switch circuit, and improving system reliability.

[0141] This invention achieves efficient energy recovery under all operating conditions and compliant damping that matches the motion state by constructing a hardware system that integrates energy recovery and controllable damping functions and implementing precise closed-loop control. At the same time, it ensures system reliability and can significantly improve the battery life and user experience of lower limb exoskeletons.

[0142] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. An energy recovery and controllable damping system for a lower limb exoskeleton, characterized in that, include: Rechargeable battery module, motor, motor drive board, bidirectional DC-DC converter unit, damping strength control unit, and control unit; The motor drive board is used to drive the motor; The bidirectional DC-DC converter unit is electrically connected between the rechargeable battery module and the motor drive board; The control unit includes a main control chip, a motion sensor, and a current detection unit; the main control chip is communicatively connected to the bidirectional DC-DC converter unit, the current detection unit, and the motion sensor. The damping strength control unit is integrated into the main control chip and can adjust the recovery current in real time through the bidirectional DC-DC converter unit based on the data collected by the motion sensor and the current detection unit, thereby controlling the damping strength.

2. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 1, characterized in that, The control unit is configured to perform the following steps: Based on the motion data acquired from the motion sensor, it is determined whether the user's current motion state is a downlink motion state; If the downlink motion state is detected, a target charging current is determined based on at least one motion parameter characterizing the downlink motion state. A closed-loop control strategy is adopted. Based on the actual charging current feedback obtained from the current detection unit, the bidirectional DC-DC converter is adjusted by the damping strength control unit so that the actual charging current approaches and equals the target charging current, thereby recharging the electrical energy generated by the motor in the downward motion state back to the rechargeable battery module.

3. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 2, characterized in that, The motion sensor includes any one or more of the following sensors: hip joint angle sensor, joint angular velocity sensor, plantar pressure sensor, and inertial measurement unit (IMU); The motion data includes any one or more of the following: left and right hip joint angles, left and right hip joint angular velocities, left and right leg angle difference, gait cycle, range of motion (ROM) of joints in a single step or a whole step, peak joint angular acceleration, plantar pressure change, and trunk posture angle change. During data processing, the motion data is subjected to low-pass filtering and outlier removal. Zero-crossing detection is performed based on the difference in left and right hip joint angles to determine half-step events, and consecutive zero-crossing events in the same direction are paired into a complete gait cycle. For each complete gait cycle, feature values ​​within the cycle are extracted. These feature values ​​include average hip joint angle offset, peak hip joint angle offset, gait cycle duration, range of motion (ROM) within a single step or a whole step, mean angular velocity, peak angular acceleration, and left-right symmetry. When identifying the current movement state, the feature values ​​of the complete gait cycle are compared with a preset threshold or the user's historical baseline. When it is detected that the user's peak hip angle offset increases, the gait cycle and the range of motion (ROM) of the joint in a single step or a whole step show downward movement characteristics, the joint angular acceleration or impact peak is higher than the level of walking on flat ground, and multiple consecutive complete gait cycles meet the feature combination, the current movement state is determined to be a downward movement state.

4. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 1, characterized in that, The bidirectional DC-DC converter unit is a four-switch buck-boost bidirectional DC-DC circuit; The four-switch buck-boost bidirectional DC-DC circuit includes: a first half-bridge, a second half-bridge, and a power inductor; The first half-bridge is connected to the rechargeable battery module, the second half-bridge is connected to the motor drive board, and the power inductor is connected between the first half-bridge and the second half-bridge; Both the first half-bridge and the second half-bridge are composed of power MOSFETs; The motion sensor is an inertial measurement unit; The system also includes an overvoltage protection circuit, which includes transient voltage suppression elements connected in parallel across the busbars of the motor drive board.

5. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 2, characterized in that, The closed-loop control strategy is proportional-integral-derivative PID control. And / or, after determining the target charging current, the control unit is also configured to perform a ramp-type soft-start process on the target charging current.

6. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 4, characterized in that, The bidirectional DC-DC converter unit includes: a first field-effect transistor, a second field-effect transistor, a third field-effect transistor, a fourth field-effect transistor, a power inductor, a bus capacitor, a first resistor, a second resistor, a third resistor, a fourth resistor, and an operational amplifier; The overvoltage protection circuit includes a transient voltage suppression diode; the current detection unit includes a current sampling resistor; The positive terminal of the rechargeable battery module is connected to the drain of the first field-effect transistor and one end of the first resistor, respectively, and the negative terminal of the rechargeable battery module is connected to one end of the current sampling resistor and the inverting input terminal of the operational amplifier, respectively. The other end of the current sampling resistor is connected to the non-inverting input terminal of the operational amplifier, one end of the second resistor, the source of the second field-effect transistor, the source of the fourth field-effect transistor, one end of the fourth resistor, one end of the bus capacitor, one end of the transient voltage suppression diode, and the negative terminal of the motor drive board. The output terminal of the operational amplifier is connected to the first connection terminal of the main control chip of the control unit. The other end of the first resistor is connected to the second connection terminal of the main control chip and the other end of the second resistor, respectively; The gate of the first field-effect transistor is connected to the third connection terminal of the main control chip, and the source of the first field-effect transistor is connected to one end of the power inductor and the drain of the second field-effect transistor, respectively. The gate of the second field-effect transistor is connected to the fourth connection terminal of the main control chip; The other end of the power inductor is connected to the drain of the fourth field-effect transistor and the source of the third field-effect transistor, respectively. The gate of the fourth field-effect transistor is connected to the fifth connection terminal of the main control chip; the gate of the third field-effect transistor is connected to the sixth connection terminal of the main control chip. The drain of the third field-effect transistor is connected to one end of the third resistor, the other end of the bus capacitor, the other end of the transient voltage suppression diode, and the positive terminal of the motor drive board, respectively. The other end of the third resistor is connected to the seventh connection terminal of the main control chip and the other end of the fourth resistor, respectively.

7. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 6, characterized in that, When the generator voltage VBUS of the motor is greater than the charging limit voltage VCHG of the rechargeable battery module, a buck mode is triggered. The first field-effect transistor is normally on, the second field-effect transistor is normally off, and the third and fourth field-effect transistors operate in a complementary PWM mode. The generator voltage VBUS of the motor and the charging limit voltage VCHG of the rechargeable battery module satisfy the following relationship: VCHG = D × VBUS, where D is the PWM duty cycle. When the generator voltage VBUS of the motor is less than the charging limit voltage VCHG of the rechargeable battery module, the boost mode is triggered. The third field-effect transistor is normally on, the fourth field-effect transistor is normally off, and the first and second field-effect transistors operate in a complementary PWM mode. The generator voltage VBUS of the motor and the charging limit voltage VCHG of the rechargeable battery module satisfy the following relationship: VBUS = (1-D) × VCHG, where D is the PWM duty cycle. When the generator voltage VBUS of the motor is equal to the charging limit voltage VCHG of the rechargeable battery module, the shoot-through mode is triggered, the first field-effect transistor and the fourth field-effect transistor are turned on, and the second field-effect transistor and the third field-effect transistor are turned off.

8. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 2, characterized in that, The control unit is configured to perform the following steps: The motion sensor collects acceleration, angular velocity, and slope data of the hip joint. The acceleration and angular velocity data are processed by the attitude calculation algorithm to determine whether the current motion state is downstairs or downhill. If so, the damping mode and energy recovery function are activated. If not, the energy recovery circuit is turned off, and the lower limb exoskeleton system enters normal assist mode. In the enabled damping mode, the target damping force is calculated based on the descent gradient, descent speed, and joint angular velocity. The calculation formula is as follows: in, Let α be the target damping force and α be the descent slope angle. For the user's speed in the downward direction, For hip joint angular velocity, This is the slope damping coefficient. The velocity damping coefficient, This is the joint angular velocity damping coefficient. Basic damping force; The calculated target damping force is converted into a target charging current using the following formula: in, For the target charging current, Let Kt be the target damping force, Kt be the torque constant of the motor, η be the efficiency of the lower limb exoskeleton system, and GR be the reduction ratio of the planetary reducer. The current charging current is sampled in real time by the current detection unit. Calculate the current error Based on the current error, the PID controller outputs the PWM duty cycle adjustment amount and controls the bidirectional DC-DC converter unit. According to the current working mode, the PWM signal output by the PID controller is applied to the corresponding field-effect transistor in the bidirectional DC-DC converter unit to control the charging current, thereby controlling the damping strength.

9. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 2, characterized in that, The target charging current is calculated based on the descent slope, descent speed, hip joint angular velocity, and impact intensity. The calculation formula is as follows: in, To reduce the slope angle, This is the mapping coefficient from slope to charging current; For the user's speed in the downward direction, This is the mapping coefficient from speed to charging current; For hip joint angular velocity, This is the mapping coefficient from angular velocity to target current; For impact eigenvalues, This is the mapping coefficient from impact strength to charging current; The current charging current is sampled in real time by the current detection unit. Calculate the current error Based on the current error, the PID controller outputs the PWM duty cycle adjustment amount and controls the bidirectional DC-DC converter unit. According to the current working mode, the PWM signal output by the PID controller is applied to the corresponding field-effect transistor in the bidirectional DC-DC converter unit to control the charging current, thereby controlling the damping strength.

10. The energy recovery and controllable damping system for a lower limb exoskeleton according to claim 8 or 9, characterized in that, The control unit detects the bus voltage of the bidirectional DC-DC converter and the charging limit voltage VCHG of the rechargeable battery module. By comparing the bus voltage and the charging limit voltage VCHG, the bidirectional DC-DC converter enters the corresponding mode: when the bus voltage is greater than the charging limit voltage VCHG, a buck mode is triggered; when the bus voltage is less than the charging limit voltage VCHG, a boost mode is triggered; when the bus voltage is equal to the charging limit voltage VCHG, a pass-through mode is triggered. After determining the operating mode of the bidirectional DC-DC converter unit, PID control is then executed, specifically as follows: In damped regenerative braking mode, the control unit periodically samples the actual charging current and calculates the current error compared to the target charging current. The calculation formula is as follows: in, For the first Current error per control cycle For the first The target charging current for each control cycle For the first The actual charging current obtained by sampling in each control cycle; Based on the current error, the PWM duty cycle adjustment is calculated using a PID controller. The calculation formula is as follows: in, This is the PWM duty cycle adjustment amount. This is the proportionality coefficient. The integral coefficient is... The differential coefficients are... To control the cycle, For the first - Current error over 1 control cycle Let be the current error in the i-th control cycle; Update the PWM duty cycle based on the PWM duty cycle adjustment: in, For the first PWM duty cycle per control cycle For the first -1 control cycle of PWM duty cycle; Based on the comparison result between the bus voltage and the charging limit voltage VCHG, the control unit selects the corresponding switching transistor for PWM control.

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