Regenerative braking method for robot linear actuator

Abstract

The present invention relates to a regenerative braking method for a robot linear actuator. According to the present invention, the regenerative braking method for a robot linear actuator, performed by means of a control unit of the robot linear actuator, comprises the steps of: estimating, on the basis of a gait pattern of a robot, whether back electromotive force is generated and the generated amount thereof; detecting the phase position of a motor provided in the robot linear actuator and the generation of reverse torque through a signal of a sensor when a disturbance occurs; using a transistor to rectify, into direct current, the back electromotive force generated due to the generation of the reverse torque; charging a capacitor with the rectified back electromotive force; and charging a pre-provided battery with the back electromotive force charged in the capacitor.

Description

Regenerative braking method for linear actuators for robots

[0001] The present invention relates to a regenerative braking method for a linear actuator for a robot, and more specifically, to a regenerative braking method for a linear actuator for a robot that minimizes energy loss generated during the operation of the robot by performing regenerative braking using the back electromotive force generated during the operation of the robot.

[0002] Generally, legged robots have multiple leg sections and walk by swinging each leg section. Legged robots that walk on four legs like animals are called quadruped robots, and legged robots that walk while balancing on two legs like humans are called biped robots.

[0003] Each leg section is constructed by sequentially installing links corresponding to the thigh, calf, and sole sections from the robot's torso through the hip, knee, and ankle joints.

[0004] Each leg is configured to enable a total of 6 degrees of freedom of movement, including a femoral link connected to the upper body through a 3-degree-of-freedom femoral joint, a lower leg link connected to the femoral link through a 1-degree-of-freedom knee joint, and a foot connected to the lower leg link through a 2-degree-of-freedom ankle joint. As a result, not only walking movements such as running and walking but also various lower body movements are implemented.

[0005] Links corresponding to the thigh, calf, and sole are connected to each joint so as to be rotatable around a pitch axis that extends laterally of the leg-type robot. Each joint is equipped with a motor (actuator) that rotates the link.

[0006] By the motor outputting an appropriate driving force and controlling the rotation angle of the link, the leg-type robot can oscillate the leg portion back and forth relative to the torso portion.

[0007] When bipedal humanoid robots move agilely, their energy requirements skyrocket. Simply increasing the size of the battery to meet these energy demands resulted in a vicious cycle where the energy required for operation increased.

[0008] In addition, conventionally, when connecting a motor and a ball screw shaft, the motor and the ball screw shaft are connected through a reduction gear or a coupling to increase torque, so a separate sensor must be provided to detect disturbances acting on the ball screw shaft, which limits the miniaturization and weight reduction of the actuator.

[0009] In addition, one of the disadvantages of the motor was that it generated excessive heat during operation, which led to performance degradation during long-term use, and there was a problem with the rotor's low responsiveness, making it unable to perform rapid movement or change direction of motion.

[0010] Therefore, a means to minimize the loss of energy generated while the robot operates is required.

[0011] Currently, research on regenerative braking technology to minimize energy loss is actively underway; however, conventional regenerative braking methods rely on higher-level controllers or are implemented using simple control schemes, which limits their ability to achieve optimal energy efficiency and rigidity against disturbances in complex situations such as the walking of humanoid robots.

[0012] For prior art, refer to Korean Registration No. 10-2293693 (August 19, 2021).

[0013] The present invention aims to provide a regenerative braking method for a linear actuator for a robot that minimizes energy loss generated during operation by performing regenerative braking using the back electromotive force generated during operation of the robot.

[0014] The present invention relates to a regenerative braking method for a linear actuator for a robot, performed by a control unit of the linear actuator for a robot, comprising: a step of estimating whether and how much back EMF is generated based on the walking pattern of the robot; a step of detecting the upper position of a motor equipped in the linear actuator for the robot and the generation of reverse torque through a sensor signal when a disturbance occurs; a step of rectifying the back EMF generated due to the generation of reverse torque into direct current using a transistor; a step of charging the rectified back EMF into a capacitor; and a step of charging the back EMF charged in the capacitor into a battery already installed.

[0015] In addition, after the step of charging the rectified back EMF into the capacitor, if the use of the back EMF through battery charging is impossible and power supply to the motor is required, the method may further include a step of directly using the back EMF to drive the motor.

[0016] In addition, after the step of charging the rectified back EMF into the capacitor, if the use of the back EMF through battery charging is impossible and the use of the back EMF through power supply to the motor is also impossible, the method may further include a step of dissipating the back EMF as heat using a resistor.

[0017] According to the present invention, by performing regenerative braking using the back electromotive force generated during the operation of the humanoid robot, the loss of energy generated while the humanoid robot is operating is minimized, thereby improving the energy efficiency of the humanoid robot.

[0018] In addition, the energy recovery rate can be maximized by generating an optimized regenerative braking profile through a higher-level controller and employing a Look-Up Table (LUT)-based regenerative braking controller, and the system's disturbance robustness can be secured by appropriately responding to disturbances input to the system through prediction via Model Predictive Control (MPC) and supplementary control based on LUTs.

[0019] In addition, MPC and regenerative braking profile-based regenerative braking control can be easily extended to various walking motion scenarios and easily applied to new types of robots.

[0020] FIG. 1 is a schematic diagram showing the configuration of a linear actuator for a robot according to one embodiment of the present invention.

[0021] FIG. 2 is a diagram illustrating the flow of a regenerative braking method for a linear actuator for a robot according to one embodiment of the present invention.

[0022] FIG. 3 is a perspective view showing a linear actuator for a robot according to an embodiment of the present invention.

[0023] FIG. 4 is a cross-sectional view showing a cross-section of a linear actuator for a robot according to an embodiment of the present invention.

[0024] FIG. 5 is an exemplary diagram showing a state in which a cam follower member is provided in a nut according to an embodiment of the present invention.

[0025] FIG. 6 is an exemplary diagram showing a cam follower member and a corresponding guide member according to an embodiment of the present invention.

[0026] FIG. 7 is an illustrative diagram showing an example of use of a linear actuator for a robot according to an embodiment of the present invention.

[0027] FIGS. 8 and 9 are block diagrams showing a disturbance estimation algorithm and a control algorithm for a linear actuator for a robot according to an embodiment of the present invention.

[0028] Then, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0029] Throughout the specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "electrically connected" with other components interposed between them. Furthermore, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0030] FIG. 1 is a schematic diagram showing the configuration of a linear actuator for a robot according to one embodiment of the present invention.

[0031] As illustrated in FIG. 1, a linear actuator (10) for a robot according to one embodiment of the present invention includes a motor part (100), a ball screw part (200), and a control part (400).

[0032] The motor unit (100) can generate rotational motion by rotating the rotor due to the magnetic force generated by the magnetization of the stator.

[0033] The ball screw section (200) is directly connected to the rotor of the motor section (100) by a tapered pin and generates linear motion through the rotational motion generated by the motor section (100).

[0034] The control unit (400) can estimate an external force based on the change in current when a disturbance occurs in the ball screw unit (200) and a change in the current applied to the motor unit (100) is detected.

[0035] At this time, the control unit (400) is configured to include an upper controller and a lower controller.

[0036] In addition, the control unit (400) can perform regenerative braking of the robot using the back electromotive force generated during the robot's walking.

[0037] The present invention below proposes a regenerative braking method for a linear actuator (10) for a robot.

[0038] A regenerative braking method for a linear actuator (10) for a robot according to one embodiment of the present invention can be performed by a control unit (400) within the linear actuator.

[0039] FIG. 2 is a diagram illustrating the flow of a regenerative braking method for a linear actuator for a robot according to one embodiment of the present invention.

[0040] As illustrated in FIG. 2, first, the control unit (400) estimates whether back electromotive force is generated and the amount generated based on the robot's walking pattern (S210).

[0041] At this time, the walking pattern may include at least one of walking speed, walking angle, decrease and acceleration during walking, and jump.

[0042] At this time, the control unit (400) calculates the optimal regenerative braking timing and amount using walking patterns and Model Predictive Control (MPC) from the upper controller, and is designed to execute the optimal regenerative braking profile using data calculated from the lower controller, and performs optimal regenerative braking in real time without a command from the upper controller by applying Look-Up Table (LUT)-based control.

[0043] More specifically, first, the upper controller collects the robot's walking pattern in real time.

[0044] At this time, the walking state vector x(t) can be calculated using the collected walking pattern as shown in Equation 1 below.

[0045]

[0046] At this time, is the speed of walking, and is the walking angle, and is walking acceleration.

[0047] Next, the higher-level controller can predict the robot's future state using the walking state vector and the humanoid robot model.

[0048] Next, the upper controller [determines] the strength of regenerative braking as shown in Equation 2 below. and point in time (start point and termination point Determine ) to optimize regenerative braking and generate a regenerative braking profile accordingly.

[0049]

[0050] At this time, E regen (t) is the amount of energy recovered by regenerative braking, and C(t) is the energy loss due to regenerative braking.

[0051] When the lower controller receives a regenerative braking profile from the upper controller, it determines the intensity and timing of the regenerative braking to be applied according to the received profile.

[0052] On the other hand, if the lower controller does not receive the regenerative braking profile from the upper controller, it searches for an optimal profile by comparing the walking pattern with the LUT as shown in Equation 3 below.

[0053]

[0054] At this time, the LUT includes a regenerative braking profile stored according to the walking pattern as shown in Table 1 below.

[0055] Table 1 is an example of a LUT that stores a regenerative braking profile according to walking motion.

[0056]

[0057] Next, the sub-controller determines the strength and timing of the regenerative braking to be applied according to the profile found, as shown in Equation 4 below.

[0058]

[0059] Next, the control unit (400) detects the upper position and reverse torque of the motor equipped in the linear actuator for the robot through the signal of the sensor already mounted in the motor unit (100) when a disturbance occurs (S220).

[0060] At this time, the sensor may include at least one of a Hall sensor, a current sensor, and a phase voltage sensor.

[0061] In addition, the control unit (400) can calculate the magnitude of the reverse torque generated using the previously estimated external force and the sensor signal.

[0062] Next, the control unit (400) rectifies the back electromotive force generated by the generation of reverse torque into direct current using a transistor (S230).

[0063] Next, the control unit (400) charges the rectified back electromotive force into the capacitor (S240).

[0064] At this time, the rectified back EMF can be converted into voltage through a DC / DC converter.

[0065] Next, when the control unit (400) is in a state where the back EMF can be used through battery charging, it charges the back EMF charged in the capacitor to the installed battery (S250).

[0066] At this time, the control unit (400) can charge the back electromotive force to the installed battery through the BMS (Battery Management System).

[0067] Additionally, the control unit (400) can measure the energy state of the back EMF through the BMS and adjust or optimize the operation.

[0068] At this time, the control unit (400) is in a state where it is impossible to use back EMF through battery charging, and if power supply to the motor is required, the back EMF can be used directly to drive the motor (S260).

[0069] On the other hand, when the control unit (400) is in a state where it is impossible to use back EMF through battery charging and it is also impossible to use back EMF through power supply to the motor, it can dissipate the back EMF as heat using a resistor (S270).

[0070] According to one embodiment of the present invention, by performing regenerative braking using the back electromotive force generated during the operation of the humanoid robot, the loss of energy generated while the humanoid robot is operating can be minimized, thereby improving the energy efficiency of the humanoid robot.

[0071] In addition, the energy recovery rate can be maximized by generating an optimized regenerative braking profile through a higher-level controller and employing a LUT-based regenerative braking controller, and the system's disturbance robustness can be secured by appropriately responding to disturbances input to the system through prediction via MPC and supplementary control based on LUTs.

[0072] In addition, MPC and regenerative braking profile-based regenerative braking control can be easily extended to various walking motion scenarios and easily applied to new types of robots.

[0073] Hereinafter, the configuration of the linear actuator for a robot of FIG. 1 to which the regenerative braking method according to an embodiment of the present invention is applied will be explained in more detail based on FIGs. 3 to 9.

[0074] The linear actuator for a robot according to an embodiment of the present invention is provided with a motor part in which the electric oil pump is a DD motor type in which a ball screw shaft is directly connected to the rotor, thereby improving sensitivity to disturbances acting on the ball screw shaft and eliminating the need for a separate sensor to detect disturbances, thus enabling reverse driving performance, high speed and high responsiveness, and lightweighting. Additionally, heat dissipation fins are formed on the motor housing of the motor part so that heat generated by the rotation of the rotor is dissipated into the air, thereby preventing performance degradation due to heat generation even after long-term use, and thus can be provided as a linear actuator for a robot dedicated to humanoids. The following is a description with reference to the drawings.

[0075] A linear actuator (10) for a robot according to an embodiment of the present invention with reference to FIGS. 3 to 9 includes a motor part (100), a ball screw part (200), and a shaft (300). First, the motor part (100) generates rotational motion based on a signal applied from the outside and is configured to form a Direct Drive Servo Motor (DD motor) that drives by directly connecting the load and the motor.

[0076] At this time, the motor unit (100) includes a stator (110) and a rotor (120) as in a conventional electric motor, and the stator (110) is equipped with a coil wound in a slot formed in a tubular core with a hollow center, and is magnetized by electromagnetic induction by power applied from the outside to rotate the rotor (120) located at the center.

[0077] And one side of the ball screw shaft (210) is connected to the center of the rotor (120).

[0078] Here, the rotor (120) and the ball screw shaft (210) are joined by a tapered pin (221) so as to be linked as one unit, and the tapered pin (221) penetrates the ball screw shaft (210) such that its length is perpendicular to the length of the ball screw shaft (210), which is horizontal to the length of the rotor (120).

[0079] Therefore, there is no need to machine keyways on the ball screw shaft (210) and rotor (120), thereby improving productivity.

[0080] And on the outer surface of the stator (110), a motor housing (130) is provided for insulation of the stator (110), and on one side and the other side of the motor housing (130), bearings (not shown) are provided to support a ball screw shaft (210) that is coupled through the rotor (120).

[0081] Accordingly, the motor unit (100) is in the form of a Direct Drive Servo Motor (DD motor) in which a ball screw shaft (210), which is a load, is directly connected to the rotor (120) to drive it.

[0082] Here, a heat dissipation fin (131) is formed extending outwardly in the motor housing (130), so that heat generated by the operation of the motor unit (100) is dissipated to the outside, thereby cooling the motor unit (100).

[0083] In addition, a motor cap (140) that finishes the upper part of the motor housing (130) is attached, and a connecting member (141) that is rotatably connected to a robot leg link member is provided on the upper side of the motor cap (140).

[0084] And the ball screw unit (200) is connected to the motor unit (100) and generates linear motion through rotational motion generated by the motor unit (100). When the ball screw shaft (210) connected to the rotor (120) of the motor unit (100) rotates due to the rotation of the rotor (120), the nut (220) provided on the ball screw shaft (210) moves linearly along the longitudinal direction of the ball screw shaft (210).

[0085] At this time, the ball screw shaft (210) has a groove formed in a spiral shape along the surface of the ball screw shaft (210) like a conventional screw, and a nut (220) is coupled to the groove by a plurality of balls.

[0086] In addition, the portion of the ball screw shaft (210) facing the motor part (100) that does not have a groove penetrates the hollow formed in the center of the rotor (120), and a through hole (211) is formed in a direction perpendicular to the length in one of the portions penetrating the rotor (120), so that the tapered pin (221) is coupled through the through hole (211), thereby allowing the ball screw shaft (210) and the rotor (120) to be interconnected as a single unit.

[0087] Therefore, it is preferable that the length of the tapered pin (221) is greater than the thickness of the ball screw shaft (210).

[0088] The ball screw shaft (210) and nut (220) are housed inside a screw housing (230), which forms a space with a horizontal cross-section that is cylindrical or polygonal, and the ball screw shaft (210) and nut (220) are positioned at the center of the space.

[0089] Accordingly, the ball screw shaft (210) and the nut (220) are protected by the screw housing (230), allowing the nut (220) to move smoothly in a straight line along the length of the ball screw shaft (210) without any obstruction.

[0090] And the nut (220) is provided with a cam follower member (240) so that the nut (220) can move along the length of the ball screw shaft (210) without rotating in sync with the rotation of the ball screw shaft (210).

[0091] The cam follower member (240) includes a bracket (241) provided on the nut (220) and a cam follower roller (242) provided on one side of the bracket (241).

[0092] The above cam follower roller (242) minimizes friction and improves precision.

[0093] Additionally, a guide member (250) for guiding the cam follower roller (242) is coupled to the screw housing (230), and a straight rail (251) is formed along the longitudinal direction on the surface of the guide member (250) facing the cam follower roller (242).

[0094] The cam follower roller (242) is housed inside the rail (251), and when the nut (220) moves linearly along the length of the ball screw shaft (210), the cam follower roller (242) controls the rotation of the nut (220) so that it does not synchronize with the rotation of the ball screw shaft (210), and slides along the rail (251) to guide the linear movement of the nut (220).

[0095] And the upper side of the shaft (300) is connected to the lower side of the ball screw shaft (210). At this time, the shaft (300) is a hollow tubular body, the lower side of the ball screw shaft (210) is inserted into the upper hollow side of the shaft (300), and the upper side of the shaft (300) is connected to a bracket (241) connected to the nut (220).

[0096] Accordingly, when the nut (220) moves linearly along the length of the ball screw shaft (210), the shaft (300) moves linearly along the length of the ball screw shaft (210) in conjunction with the linear movement of the nut (220).

[0097] In addition, the lower side of the shaft (300) is exposed to the outside from the lower side of the screw housing (230), and is supported by a support bushing (310) provided on the lower side of the screw housing (230), so that when the shaft (300) moves in a straight line, foreign matter is prevented from entering through the gap between the shaft (300) and the screw housing (230), shaking is prevented, and lubrication is provided.

[0098] And at the bottom of the shaft (300), a joint member (320) is provided that is rotatably connected to a robot leg link member.

[0099] Accordingly, the linear actuator for a robot according to an embodiment of the present invention forms a DD motor type by directly connecting the rotor of the motor part to the ball screw shaft, and as the nut moves linearly along the length of the ball screw shaft in response to the rotation of the ball screw shaft, the length of the shaft connected to the nut moves linearly with respect to the screw housing, thereby enabling the linear actuator to perform its function.

[0100] In addition, since the above motor unit is controlled based on current, high speed and reverse driving capability can be secured.

[0101] The linear actuator for a robot according to the embodiment of the present invention can achieve reverse driving capability, high speed and high responsiveness, and lightweighting. Additionally, since the gear ratio is 1, the external force applied to the linear actuator rotates the rotor of the motor part without significant loss, thereby allowing the external force to be sensitively recognized through changes in current.

[0102] The external force estimation of a linear actuator for a robot according to an embodiment of the present invention with reference to FIG. 8 is performed by the following process.

[0103] The phase current (i) of the motor applied to the above motor unit a , i b , i cWhen motor state information including ) and angle (θ) is input to the field-oriented control (FOC) controller, the field-oriented control controller converts the three-phase current into the orthogonal coordinate system dq and i d , i q Generates a current value.

[0104] At this time, the three-phase current (i a , i b , i c When converting the angle θ of the motor and the dq coordinate system, the Clarke Transform and the Park Transform are performed sequentially.

[0105] Here, the Clark transform uses the following mathematical formulas 5 and 6.

[0106]

[0107]

[0108] Here, i α , i β is the current value in the α-β coordinate system, which is a non-rotating coordinate system.

[0109] And the Park transform is i obtained in the above α-β coordinate system α , i β Converts to a dp coordinate system rotating with respect to the motor angle θ.

[0110] At this time, using the following mathematical formula 7, the three-phase current (i a , i b , i c ) to i d , i q Convert to.

[0111]

[0112] For example, i a is 5A, i b is -2.5A, i c ne -(i a - i b), that is, when -2.5A and θ=30°, if this is substituted into the mathematical formulas for the Clark transform and the Park transform, respectively, according to the mathematical formula for the Clark transform,

[0113]

[0114]

[0115] It can be calculated as,

[0116] By the mathematical formula of the above Park transformation,

[0117]

[0118]

[0119] It can be calculated as.

[0120] Therefore, the transformed dq coordinate system current value is i d =4.33 A, i q =-2.5A.

[0121] i generated by the above electric field directional control controller d , i q The current value is applied to the External Torque Estimator, and in the said External Torque Estimator, i q Torque applied to the motor based on the current value ( Estimate ) and output it as a Nonlinear Compensation Unit.

[0122] At this time, the torque applied to the motor ( ) is i q It is in a directly proportional relationship with the current value and can be expressed by the following mathematical formula 8, which is the torque estimation formula.

[0123]

[0124] Here k t ε is a torque constant determined by the characteristics of the motor (generally indicated in the datasheet of a BLDC motor) and represents the ratio of torque to current.

[0125] For example, the motor torque constant k t is 0.1 N / m, and i q When it is 3A,

[0126]

[0127] Therefore, the estimated torque value is 0.3 N / m.

[0128] And the Speed ​​to Momentum Analyzer analyzes the change in motor speed (ω) to calculate the change in momentum (Δp) and applies it to the nonlinear compensation unit.

[0129] At this time, the change in momentum (Δp) in rotational motion is calculated through the change in velocity (Δω), and momentum P is the product of the moment of inertia J and the angular velocity ω, and by differentiating this with respect to time, the change in momentum and the change in velocity can be calculated using the following mathematical equation 9.

[0130]

[0131] The above nonlinear compensation unit compensates for nonlinear characteristics based on the estimated torque and changes in momentum, thereby estimating the external force acting on the linear actuator and estimating the disturbance using the estimated external force.

[0132] Here, examining the process of deriving the disturbance (force) acting on the linear actuator using the estimated torque and the change in momentum, the motor torque is converted into an external force for the linear actuator, the change in momentum is reflected, and the final disturbance is estimated.

[0133] At this time, the force applied to the linear actuator can be calculated using the motor torque and the lead of the ball screw, as shown in Equation 10 below, to convert the motor torque into an external force of the linear actuator.

[0134]

[0135] Here, l is the lead of the ball screw, which is the distance the nut moves when the ball screw completes one rotation, and η is the efficiency of the ball screw mechanism, where a good back drive means that the efficiency is high and has a value of 0.8 to 0.9.

[0136] And, as shown in Equation 11 below, if the change in momentum is reflected in the estimated external force, it can indicate how much the linear actuator must resist the disturbance.

[0137]

[0138] Here, F disturbance is the additional force (N) that must be resisted, Δp = change in momentum (kg*m / s), and Δt = time interval (s) during which the change in momentum occurred.

[0139] Therefore, the disturbance acting on the linear actuator can be derived from the estimated torque and momentum changes using the following mathematical equation 12.

[0140]

[0141] Therefore, the above disturbance causes the motor to rotate through the ball screw, and the motor acts as a generator, so the current generated in that situation can be measured through the current sensor of the motor driver, and the disturbance can be estimated using the above mathematical formula 12.

[0142] FIG. 9 is an algorithm showing the control of the motor part of a linear actuator for a robot according to an embodiment of the present invention. Looking at the process, the target position / velocity, torque / force, current position / velocity, and torque / force are input from their respective compensation units, errors caused by disturbances are compensated, and the input is applied to the motion update unit. The motion update unit then controls the adjusted motion based on the target position / velocity, torque / force, current position / velocity, and torque / force. adjust Prints ).

[0143] Here, the error compensation process caused by disturbances is performed by correcting the error using the difference between the target and current values ​​in the position / velocity compensation unit and the force / torque compensation unit, respectively.

[0144] At this time, the position / velocity compensation unit calculates the error through the following mathematical formula 13.

[0145]

[0146] Here, e x is the position error, and x target is the target position, and x current is the current location, and e v is the speed error, and v target is the target speed, and v current is the current speed.

[0147] First, the error is calculated by comparing the position and velocity of the current situation and the target situation, and based on that error, the qp solver calculates the optimal compensation value and transmits it to the compensation unit.

[0148] This value is adjusted via gain, and the position / velocity compensation value u pos / vel It is expressed as shown in mathematical formula 14 below.

[0149]

[0150] Here k x wa k v is a compensation gain for position and velocity errors. This value compensates for errors caused by disturbances in position and velocity.

[0151] And the force / torque compensation unit calculates the error through the following mathematical formula 15.

[0152]

[0153] Here, e F is the force error, and F target is the target force, and F current It is the current power.

[0154] Regarding force errors, the compensation unit calculates an optimal compensation value to respond to changes in force and torque caused by disturbances, and the compensation value u F It can be expressed by the following mathematical formula 16.

[0155]

[0156] The final output motion of the motion updater unit can be defined as follows.

[0157]

[0158] Here, Motion ref is a reference value for target position / velocity and target force, and u pos / vel is the disturbance compensation value for position / velocity, and u F is the disturbance compensation value for force / torque.

[0159] At this time, it is desirable that the target position / velocity be applied to the position / velocity compensation unit by deriving an appropriate controller gain value through the qp solver.

[0160] Here, the controller gain is expressed as a mathematical optimization problem regarding the control objective (error minimization), and an appropriate gain value is found by solving it with a qp solver. The qp solver is a method primarily used in robot control to efficiently achieve a given goal.

[0161] The process of deriving the controller gain value is carried out as follows.

[0162] First, the control error function is defined. The control error function is an objective function that minimizes the error between the target position and velocity and the current position and velocity, and can be expressed as shown in Equation 17 below.

[0163]

[0164] And the controller gain value is set as a variable, which can be expressed by the following mathematical equation 18.

[0165]

[0166] Here, k x is the gain value for position, and k v is the gain value for speed.

[0167] To include the gain value of the controller in the objective function, the optimization problem is transformed into a form of minimizing squared error, and the new objective function including the compensation item with the applied gain value can be expressed as Equation 19 as follows.

[0168]

[0169] Optimization problems are solved using a qp solver, which minimizes the given objective function J and satisfies the constraints k x wa k v Derive the optimal value of the gain value.

[0170] Therefore, it receives target position / velocity and torque / force as input and performs feedback control based on the actuator's current state (position / velocity, torque / force).

[0171] And the reference motion generated by the WBC (Whole Body Controller) (Motion ref Optimize and update ).

[0172] In this context, Whole Body Control (WBC) comprehensively controls all of the robot's joints and sensors to enable the robot to perform target movements. This WBC allows the robot to perform various tasks simultaneously and maintains balance by distributing appropriate force to each joint. Consequently, it enables the robot to maintain a specific position or posture while simultaneously performing diverse tasks such as picking up external objects or reacting to changes in the environment.

[0173] In other words, to implement WBC, it must be possible to receive feedback on external forces for all actuators, and it must perform operations after synthesizing this data and making a judgment.

[0174] And reference motion (Motion ref Optimization of ) is the targeted reference motion (Motionref ) and actual motion (Motion adjust It involves minimizing the error between ), and while it is often difficult to accurately perform the target motion in robot systems due to disturbances or load changes, the optimization process involves the reference motion (Motion) including the target position, velocity, and force ref Adjust ) to enable the robot to actually achieve motion.

[0175] The effects produced by the linear actuator for a robot according to the present invention are as follows.

[0176] By providing a motor section in the form of a DD motor type in which the ball screw shaft is directly connected to the rotor, sensitivity to disturbances acting on the ball screw shaft is improved, and since there is no need to provide a separate sensor to detect disturbances, reverse driving capability, high speed and high responsiveness, and lightweighting can be achieved, so it can be provided as a linear actuator dedicated to humanoids.

[0177] By forming heat dissipation fins on the motor housing of the motor unit, heat generated by the rotation of the rotor is dissipated into the air, so that performance degradation due to heat does not occur even during prolonged use.

[0178] As a tapered pin is inserted to directly connect the ball screw and the rotor, there is no need to machine keyways on the ball screw and the rotor, thereby improving productivity.

[0179] Friction is minimized and the precision of the linear motion is improved by a cam follower (roller) that guides the linear motion of the nut while controlling the rotation of the nut.

[0180] The present invention has been described with reference to embodiments illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. A regenerative braking method for a linear actuator for a robot, performed by a control unit of the linear actuator for a robot, A step of estimating whether back EMF is generated and the amount generated based on the robot's walking pattern; A step of detecting the upper position and reverse torque of the motor equipped in the linear actuator for the robot through the sensor signal when a disturbance occurs; A step of rectifying the back electromotive force generated by the generation of the above reverse torque into direct current using a transistor; A step of charging the above rectified back EMF into a capacitor; and A regenerative braking method for a linear actuator for a robot, comprising the step of charging the back electromotive force charged in the above capacitor to a pre-installed battery.

2. In Paragraph 1, After the step of charging the capacitor with the above-mentioned rectified back EMF, A regenerative braking method for a linear actuator for a robot, which further includes the step of using the back EMF directly to drive the motor when the use of the back EMF through the above-mentioned battery charging is impossible and power supply to the motor is required.

3. In Paragraph 1, After the step of charging the capacitor with the above-mentioned rectified back EMF, A regenerative braking method for a linear actuator for a robot, comprising an additional step of dissipating the back EMF as heat using a resistor in a state where the use of the back EMF through the battery charging is impossible and the use of the back EMF through power supply to the motor is also impossible.

4. In Paragraph 1, The step of estimating whether the above-mentioned back EMF is generated and the amount generated is, A regenerative braking method for a linear actuator for a robot, wherein the upper controller of the control unit calculates the optimal timing and amount of regenerative braking using a walking pattern and Model Predictive Control (MPC), and the lower controller of the control unit utilizes the calculated data to execute the optimal regenerative braking profile.

5. In Paragraph 4, The above-mentioned upper controller is, Collect the walking pattern of the above robot in real time, and Calculate a walking state vector using the above walking pattern, and A regenerative braking method for a linear actuator for a robot, which predicts the future state of the robot using the above walking state vector and robot model, determines the strength and timing of regenerative braking to optimize regenerative braking, and generates a regenerative braking profile accordingly.

6. In Paragraph 5, The above-mentioned upper controller is, The following mathematical formula Calculate the walking state vector x(t) through, and is the speed of walking, and is the walking angle, and Regenerative braking method for a linear actuator for a robot, which is walking acceleration.

7. In Paragraph 5, The above-mentioned upper controller is, The following mathematical formula The intensity of regenerative braking through and start time and termination point Determines to optimize regenerative braking, generates a regenerative braking profile accordingly, and E regen (t) is the amount of energy recovered by regenerative braking, and C(t) is the energy loss due to regenerative braking. A regenerative braking method for a linear actuator for a robot.

8. In Paragraph 5, The above sub-controller is, A regenerative braking method for a linear actuator for a robot, which determines the strength and timing of regenerative braking to be applied according to the received profile when a regenerative braking profile is received from the above-mentioned upper controller.

9. In Paragraph 5, The above sub-controller is, If the regenerative braking profile is not received from the above-mentioned upper controller, the following mathematical formula As shown above, optimal regenerative braking is performed in real time without commands from a higher-level controller by searching for an optimal profile by comparing the walking pattern with a Look-Up Table (LUT), and is the speed of walking, and is the walking angle, and is a regenerative braking method for a linear actuator for a walking acceleration robot.

10. In Paragraph 9, The above sub-controller is, The following mathematical formula As such, the intensity and timing of regenerative braking to be applied are determined according to the profile found above, and is the strength of regenerative braking, and is the starting point and is a regenerative braking method for a linear actuator for a robot at the termination point.

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