Linear actuator for robot

Abstract

The present invention provides a linear actuator for a robot, comprising: a motor unit in which a rotor rotates using magnetic force generated by magnetization of a stator, thereby generating rotational motion; a ball screw unit which is connected to the lower portion of the motor unit, and in which a nut coupled to a ball screw linearly moves in the longitudinal direction of the ball screw when the ball screw directly connected to the rotor of the motor unit rotates in conjunction with the rotation of the rotor; and a shaft which has one side connected to the nut of the ball screw unit and which linearly moves in conjunction with the linear motion of the nut, the linear actuator for a robot: having the motor unit provided as a DD motor type in which a ball screw shaft is directly connected to the rotor, so as to improve sensitivity to disturbance acting on the ball screw shaft such that a separate sensor for detecting disturbance is not required to be provided, thereby enabling back drivability, high speed, high responsiveness and reduced weight to be achieved; and having heat dissipation fins formed in a motor housing of the motor unit so as to dissipate, into the air, heat generated by the rotation of the rotor such that performance degradation caused by heating is prevented even if used for a long time, thereby being provided as a linear actuator for a humanoid robot.

Description

Linear actuator for robots

[0001] The present invention relates to a linear actuator for a robot, and more specifically, to a linear actuator for a robot that can be provided as a dedicated linear actuator for humanoids by achieving reverse driving capability, high speed and high responsiveness, and lightweighting as a ball screw shaft is directly connected to the rotor of a motor.

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

[0011] The present invention aims to provide a linear actuator for a robot that can be provided as a dedicated linear actuator for humanoids, by having a motor part in the form of a DD motor type in which a ball screw shaft is directly connected to a 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 forming heat dissipation fins 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 even after long-term use.

[0012] A linear actuator for a robot according to the present invention comprises: a motor part that generates rotational motion by rotating a rotor by means of a magnetic force generated by the magnetization of a stator; and a ball screw part that includes a ball screw shaft directly connected to the rotor of the motor part by a tapered pin and rotates in synchronization with the rotation of the rotor; wherein, when a disturbance acts on the ball screw shaft, the current applied to the motor part changes, and the external force is estimated based on the change in the current of the motor part.

[0013] At this time, the motor part according to the present invention comprises a motor housing, a stator that is magnetized by electromagnetic induction by a power source applied from the outside and has a coil wound in a slot formed along the inner circumference of a core, a rotor located in the center of the stator and rotating around the center as an axis due to the magnetization of the stator, and a plurality of heat dissipation fins that extend from the outer surface of the motor housing in an outer circumference direction and dissipate heat generated in the motor part to the outside.

[0014] The ball screw portion according to the present invention comprises: a screw housing having a length in the vertical direction and connected to the lower part of the motor housing; a ball screw shaft positioned at the center of the screw housing with one side inserted and coupled to the center of the rotor and rotating around the center as an axis in synchronization with the rotation of the rotor; a nut coupled by a ball to a groove formed spirally along the surface of the ball screw shaft and moving linearly along the length of the ball screw shaft in accordance with the rotation of the ball screw shaft; and a cam follower member connected to the nut inside the screw housing and guiding linear movement to the nut.

[0015] Here, the ball screw shaft according to the present invention has a portion coupled to the rotor that penetrates the rotor, and the tapered pin is arranged such that its longitudinal direction is perpendicular to the longitudinal direction of the ball screw shaft to couple the rotor and the ball screw shaft.

[0016] In addition, when the motor unit according to the present invention estimates a disturbance, the phase current of the motor applied to the motor unit ( , , ) and angle( Based on the motor state information including ), convert to the Cartesian coordinate system dq coordinate system , Step of generating a current value; generated , Among the current values Torque based on current value ( Step of estimating ); rotor speed( Change in momentum due to change ( Step of calculating ); estimated torque ( ) and change in momentum( It consists of a step of estimating the external force acting on the linear actuator by compensating for non-linear characteristics based on ).

[0017] The effects produced by the linear actuator for a robot according to the present invention are as follows.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] FIG. 1 is a perspective view showing a linear actuator for a robot according to an embodiment of the present invention.

[0023] FIG. 2 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. 3 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. 4 is an exemplary diagram showing a cam follower member and a corresponding guide member according to an embodiment of the present invention.

[0026] FIG. 5 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. 6 and 7 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] The present invention provides a linear actuator for a robot comprising a motor unit that generates rotational motion by rotating a rotor by means of a magnetic force generated by the magnetization of a stator, and a ball screw unit that includes a ball screw shaft directly connected to the rotor of the motor unit by a tapered pin and rotates in synchronization with the rotation of the rotor, wherein when a disturbance acts on the ball screw shaft, the current applied to the motor unit changes, and the external force is estimated based on the change in the current of the motor unit.

[0029] Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, and based on the principle that the inventor can appropriately define the concepts of the terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0030] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that there may be equivalent variations that can replace them at the time of filing this application.

[0031] The present invention relates to a linear actuator for a robot that can be provided as a dedicated linear actuator for humanoids, wherein the motor part is formed as a DD motor type in which the rotor is directly connected to a ball screw shaft, and 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 achieving reverse driving performance, high speed and high responsiveness, and preventing performance degradation due to heat generation even after long-term use. Referring to the drawings, the invention is as follows.

[0032] A linear actuator (10) for a robot according to an embodiment of the present invention with reference to FIGS. 1 to 5 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.

[0033] 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.

[0034] And one side of the ball screw shaft (210) is connected to the center of the rotor (120).

[0035] 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).

[0036] Therefore, there is no need to machine keyways on the ball screw shaft (210) and rotor (120), thereby improving productivity.

[0037] 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).

[0038] 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.

[0039] 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).

[0040] 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).

[0041] 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).

[0042] 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.

[0043] 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.

[0044] Therefore, it is preferable that the length of the tapered pin (221) is greater than the thickness of the ball screw shaft (210).

[0045] 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.

[0046] 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.

[0047] 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).

[0048] 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).

[0049] The above cam follower roller (242) minimizes friction and improves precision.

[0050] 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).

[0051] 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).

[0052] 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).

[0053] 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).

[0054] 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.

[0055] And at the bottom of the shaft (300), a joint member (320) is provided that is rotatably connected to a robot leg link member.

[0056] 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.

[0057] In addition, since the above motor unit is controlled based on current, high speed and reverse driving capability can be secured.

[0058] 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.

[0059] The external force estimation of a linear actuator for a robot according to an embodiment of the present invention with reference to FIG. 6 is performed by the following process.

[0060] The phase current of the motor applied to the above motor unit ( , , ) and angle( When motor status information including ) is input to the field-oriented control (FOC) controller, the field-oriented control controller converts the three-phase current into the dq coordinate system, which is an orthogonal coordinate system, and , Generates a current value.

[0061] At this time, the three-phase current ( , , When converting the angle θ of the motor and the ) to the dq coordinate system, the Clarke Transform and Park Transform are performed sequentially.

[0062] Here, the Clarke Transform uses the following [Equation 1] and [Equation 2].

[0063] [Mathematical Formula 1]

[0064]

[0065] [Mathematical Formula 2]

[0066]

[0067] Here, , is the current value in the α-β coordinate system, which is a non-rotating coordinate system.

[0068] And the Park Transform is obtained in the above α-β coordinate system , Converts to a dq coordinate system rotating with respect to the motor angle θ.

[0069] At this time, using [Mathematical Equation 3] below, the three-phase current ( , , )cast , Convert to.

[0070] [Mathematical Formula 3]

[0071] ,

[0072] For example is 5A, is -2.5A, Is -( + Since ), when -2.5A and θ=30°, if these are substituted into the mathematical formulas of the Clarke Transform and the Park Transform, respectively, according to the mathematical formula of the Clarke Transform above,

[0073] ,

[0074] It can be calculated as,

[0075] According to the mathematical formula of the above Park Transform,

[0076] ,

[0077] It can be calculated as.

[0078] Therefore, the transformed dq coordinate system current value is =4.33 A, =-2.5A.

[0079] generated by the above electric field directional control controller , The current value is applied to an external torque estimator, and in the said external torque estimator Torque applied to the motor based on the current value ( Estimate ) and output it as a Nonlinear Compensation Unit.

[0080] At this time, the torque applied to the motor ( )Is It is in a directly proportional relationship with the current value and can be expressed by the torque estimation formula [Equation 4] below.

[0081] [Mathematical Formula 4]

[0082]

[0083] Here ε is a torque constant determined by the characteristics of the motor (generally indicated in the BLDC motor datasheet) and represents the ratio of torque to current.

[0084] For example, motor torque constant is 0.1 N / m and, When it is 3A,

[0085]

[0086] Therefore, the estimated torque value is 0.3 N / m.

[0087] And the Speed ​​to Momentum Analyzer is the motor speed ( By analyzing the change, the amount of change in momentum ( Calculate ) and apply it to the nonlinear compensation unit.

[0088] At this time, the change in momentum in rotational motion ( ) is the amount of change in velocity( It is calculated through ), and momentum P is the product of moment of inertia J and angular velocity ω, and by differentiating it with respect to time, the change in momentum and the change in velocity can be calculated using [Equation 5] below.

[0089] [Mathematical Formula 5]

[0090]

[0091] In the above nonlinear compensation unit, the estimated torque ( ) and change in momentum( By compensating for nonlinear characteristics based on ), the external force acting on the linear actuator can be estimated, and the disturbance can be estimated using the estimated external force.

[0092] Here, estimated torque ( ) and change in momentum( If we look at the process of deriving the disturbance (force) acting on a linear actuator using ), the motor torque is converted into an external force of the linear actuator, the change in momentum is reflected, and the final disturbance is estimated.

[0093] In this case, converting the motor torque into an external force for the linear actuator allows the force applied to the linear actuator to be calculated using the motor torque and the ball screw lead.

[0094] [Mathematical Formula 6]

[0095]

[0096] 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.

[0097] Furthermore, reflecting the change in momentum—by incorporating the change in momentum (Δp) into the estimated external force—can indicate how much the linear actuator must resist the disturbance.

[0098] [Mathematical Formula 7]

[0099]

[0100] Here, = additional force to be resisted (N), Δp = change in momentum (kg*m / s), and Δt = time interval (s) during which the change in momentum occurred.

[0101] Therefore, the disturbance acting on the linear actuator can be derived from the estimated torque and momentum changes using [Equation 8] below.

[0102] [Mathematical Formula 8]

[0103]

[0104] Therefore, the above disturbance causes the motor to rotate through the ball screw, and at this time, 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 [Equation 8].

[0105] FIG. 7 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 ( Prints ).

[0106] 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.

[0107] At this time, the position / velocity compensation unit calculates the error through the following [Equation 9].

[0108] [Mathematical Formula 9]

[0109] ,

[0110] Here, is the position error, and is the target location, and is the current location, and is the speed error, is the target speed, and is the current speed.

[0111] 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.

[0112] This value is adjusted via gain and is a position / velocity compensation value It is expressed as [Mathematical Formula 10] below.

[0113] [Mathematical Formula 10]

[0114]

[0115] Here and is a compensation gain for position and velocity errors. This value compensates for errors caused by disturbances in position and velocity.

[0116] And the force / torque compensation unit calculates the error through the following [Equation 11].

[0117] [Mathematical Formula 11]

[0118]

[0119] Here, is the force error, and It is the goal power, and It is the current power.

[0120] 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 It can be expressed by the following [Equation 12].

[0121] [Mathematical Formula 12]

[0122]

[0123] The final output motion of the motion updater unit can be defined as follows.

[0124]

[0125] Here, is a reference value for target position / velocity and target force, and is a disturbance compensation value for position / velocity, and is the disturbance compensation value for force / torque.

[0126] 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.

[0127] 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.

[0128] The process of deriving controller gain values ​​is as follows: first, the control error function is defined, and as an objective function that minimizes the error between the target position and velocity and the current position and velocity, it can be expressed as [Equation 13] below.

[0129] [Mathematical Formula 13]

[0130]

[0131] And the controller gain value is set as a variable, which can be expressed by [Equation 14] below.

[0132] [Mathematical Formula 14]

[0133] ,

[0134] Here, is the gain value for the position, and is the gain value for speed.

[0135] 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 15] as follows.

[0136] [Mathematical Formula 15]

[0137]

[0138] Optimization problems are solved using a qp solver, which minimizes a given objective function J and satisfies constraints and Derive the optimal value of the gain value.

[0139] 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).

[0140] And the reference motion generated by the WBC (Whole Body Controller) Optimize and update ).

[0141] 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.

[0142] 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.

[0143] And reference motion ( Optimization of ) is the targeted reference motion ( ) and actual motion( 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 a reference motion including target position, velocity, and force ( Adjust ) to enable the robot to actually achieve motion.

[0144] 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 motor unit that generates rotational motion by rotating a rotor due to a magnetic force generated by the magnetization of a stator; and A ball screw section including a ball screw shaft that is directly connected to the rotor of the motor section via a tapered pin and rotates in synchronization with the rotation of the rotor; wherein A linear actuator for a robot characterized by estimating an external force based on the change in current of the motor part when a disturbance acts on the ball screw shaft.

2. In Claim 1. The above motor unit is, Motor housing and, A stator is provided with a coil wound in a slot formed along the inner surface of a core and is magnetized by electromagnetic induction by an externally applied power source, and A rotor located at the center of the stator and rotating around the center axis due to the magnetization of the stator, and A linear actuator for a robot comprising a plurality of heat dissipation fins extending outward from the outer surface of the motor housing to dissipate heat generated in the motor part to the outside.

3. In Claim 2, The above ball screw part is, A screw housing connected to the lower part of the motor housing and having a length in the vertical direction, and A ball screw shaft that is positioned at the center of the screw housing with one side inserted and coupled to the center of the rotor and rotates around the center as an axis in synchronization with the rotation of the rotor, and A nut coupled by a ball to a groove formed spirally along the surface of the ball screw shaft, and which moves linearly along the length of the ball screw shaft in rotation of the ball screw shaft, and A linear actuator for a robot comprising a cam follower member connected to the nut inside the screw housing and guiding linear motion to the nut.

4. In Claim 3, The above ball screw shaft is, A linear actuator for a robot in which a part coupled to the rotor penetrates the rotor.

5. In Claim 4, The above-mentioned tapered pin is, A linear actuator for a robot that combines the rotor and the ball screw shaft, with its longitudinal direction arranged perpendicular to the longitudinal direction of the ball screw shaft.

6. In Claim 3, The above cam follower member is, A bracket provided on the above nut, and A cam follower roller provided on one side of the above bracket, and A linear actuator for a robot comprising a guide member coupled to the screw housing and forming a rail on which the cam follower roller is accommodated and slides on a surface facing the ball screw shaft.

7. In Claim 1, In the motor unit estimating disturbances, The phase current of the motor applied to the above motor unit ( , , ) and angle( Based on the motor state information including ), convert to the Cartesian coordinate system dq coordinate system , Step of generating a current value; generated , Among the current values Torque based on current value ( Step of estimating ); Rotor speed ( Change in momentum due to change ( Step of producing ); Estimated torque ( ) and change in momentum( A linear actuator for a robot comprising the step of estimating an external force acting on a linear actuator by compensating for nonlinear characteristics based on ).

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