Patent Description:
With the recent development of the robot technology, there emerges a need for an intelligent robot capable of performing various tasks in place of humans in addition to an industrial robot. Active research and development are carried out on the intelligent robot.

In order to develop the intelligent robot, advanced technologies, such as new materials, semiconductors, artificial robots and sensor software, in addition to the traditional technologies, such as machines and electronics, are necessary. Unlike the existing industrial robot, the intelligent robot may be said to be a robot having functions and performance required for the future market.

Furthermore, the intelligent robot can perform various tasks at places closer to humans. It is necessary to apply a series elastic actuator (SEA) technology to the robot so as to solve a problem that may occur in a cooperation process with humans.

The SEA is a technology for controlling a force and position using elasticity. The SEA controls not only a position like a robot joint, but both a position and force like the muscle of human, and thus enables a robot to operate in a rough place like an uneven ground or adaptively operate in response to external pressure.

The SEA has various types, but a bolt-driven SEA having a structure shown in <FIG> is commonly used.

Referring to <FIG>, a conventional bolt-driven SEA includes a bolt screw <NUM> rotatably coupled to a driving motor <NUM>, a nut part <NUM> performing a rectilinear motion left or right in the rotation direction of the bolt screw <NUM>, a rectilinear motion part <NUM> performing a rectilinear motion left or right through a spring <NUM> supporting the nut part <NUM>, and an arm <NUM> coupled to the rectilinear motion part <NUM>.

In the bolt-driven SEA, the bolt screw <NUM> is directly coupled to the driving motor <NUM> and rotated. The nut part <NUM> coupled to the bolt screw <NUM> performs a rectilinear motion left or right in the rotation direction of the bolt screw <NUM>.

When the bolt screw <NUM> performs a rectilinear motion, the rectilinear motion part <NUM> and the arm <NUM> perform a rectilinear motion in the same direction as the nut part <NUM> through the nut part <NUM> and the spring <NUM> supporting the nut part.

Such a conventional SEA has disadvantages in that the structure is complicated and the size is large because the entire rectilinear motion part including the spring must be designed to move.

Furthermore, it is difficult to apply an SEA having the above structure to a rotary motion. Accordingly, there is a need for a method of controlling an SEA, which is suitable for a rotary motion.

<CIT> discloses A force transducer, having first and second members which are coupled such as to be movable in one axis relative to one another; and a deformable elastic element which is disposed between the first and second members, such that a force as applied to one of the first and second members causes deformation of the elastic element and is transferred to the other of the first and second members, with the relative deflection of the first and second members corresponding to the applied force.

<CIT> discloses a robotic device and a shock absorber to buffer only an excessive torque while transmitting a proper torque.

<CIT> discloses an elastic actuator consisting of a motor and a motor drive transmission connected at an output of the motor. An elastic element is connected in series with the motor drive transmission, and this elastic element is positioned to alone support the full weight of any load connected at an output of the actuator. A single force transducer is positioned at a point between a mount for the motor and an output of the actuator. This force transducer generates a force signal, based on deflection of the elastic element, that indicates force applied by the elastic element to an output of the actuator. An active feedback force control loop is connected between the force transducer and the motor for controlling the motor. This motor control is based on the force signal to deflect the elastic element an amount that produces a desired actuator output force. The produced output force is substantially independent of load motion. The invention also provides a torsional spring consisting of a flexible structure having at least three flat sections each connected integrally with and extending radially from a central section. Each flat section extends axially along the central section from a distal end of the central section to a proximal end of the central section.

<CIT> discloses a robot apparatus having a multi-link structure including a plurality of links and joints serving as link movable sections, and in which at least some of the links are driven by combination of position control and force control is disclosed. The apparatus includes: position control means for performing the position control on the links, which are driven by position control and force control; position control means with force constraint for placing the force control before the position control so as not to cause the magnitude of an external force to exceed a set value; force control means for performing the force control on the links; and integrated force/position control means for controlling driving of the joints by switching the position control means, the position control means with force constraint, and the force control means, and unifies the position control and the force control.

<CIT> discloses that a force and moment which a manipulator receives from an external environment is detected, and this detected value is multiplied by a gain inversely proportional to a virtual spring constant set by a tool coordinate system, and the product is further converted to a value in each joint coordinate system of the manipulator so as to determine a detection torque. A command value of force and moment is converted to a value in each joint coordinate value of the manipulator in the same way as described above, so as to determine a command torque. A difference between a position command value and a position detection value is multiplied by a virtual spring constant in each joint coordinate system of the manipulator obtained by converting the virtual spring constant, and a differential torque is obtained by converting the aforementioned difference to a force and moment corresponding to the difference. A targeted torque is determined by adding the command torque and the differential torque, and feedback control is affected such that the detected torque of each joint of the manipulator coincides with the targeted torque.

<CIT> discloses that a robot controller is provided which can smoothly switch the mode between a position control in a free space and a position or force control to a contact surface.

The present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an SEA having a structure capable of an efficient operation.

Furthermore, an object of the present invention is to provide a method of controlling an SEA having a structure suitable for a rotary motion and an SEA system using the same.

A series elastic actuator according to claim <NUM> is provided. An embodiment of the present invention include a motor-side rotation unit coupled to a driving motor and rotated by rotatory power of the driving motor, a load-side rotation unit coupled to the motor-side rotation unit to transfer the rotatory power of the driving motor to a load, and at least one pair of elastic members provided in spaces between the motor-side rotation unit and the load-side rotation unit, wherein a frame having accommodation spaces to which the pair of elastic members is fixed is formed in any one of the motor-side rotation unit and the load-side rotation unit.

A series elastic actuator according to embodiment of the present invention includes a motor-side rotation unit coupled to a driving motor and rotated by rotatory power of the driving motor, a load-side rotation unit coupled to the motor-side rotation unit to transfer the rotatory power of the driving motor to a load, and at least one pair of elastic members fixed to spaces between the motor-side rotation unit and the load-side rotation unit. A first frame for supporting the pair of elastic members therein is formed in the motor-side rotation unit, and a second frame for supporting the pair of elastic members on the outside is formed in the load-side rotation unit.

A method of controlling a series elastic actuator according to claim <NUM> is provided. Further embodiment is described in the dependent claim <NUM>. An embodiment of the present invention includes controlling a series elastic actuator (SEA) including a motor-side rotation unit and load-side rotation unit coupled to transfer rotatory power of a driving motor to a load and elastic members. The method includes measuring relative displacement between the motor-side rotation unit and the load-side rotation unit, calculating external torque by an external force applied to the load side based on the measured displacement and hardness (K) of the elastic member, comparing the calculated external torque with a critical torque, and switching a control mode of the SEA to any one of torque control and position control based on a result of the comparison. When the external torque increases to a value greater than the critical torque, the control mode switches from the position control to the torque control. When the external torque decreases to a value obtained by subtracting given torque from the critical torque or less, the control mode switches from the torque control to the position control.

At least one pair of the elastic members are provided in spaces between the motor-side rotation unit and the load-side rotation unit, and any one of the pair of elastic members are compressed toward a rotation direction of the motor-side rotation unit.

The steps of the control method may be configured in a computer program form so that they are executed in an SEA system according to an embodiment of the present invention. The corresponding computer program may be stored in a computer-readable medium.

A series elastic actuator system according to an embodiment of the present invention includes a motor-side rotation unit coupled to a driving motor and rotated by rotatory power of the driving motor, a load-side rotation unit coupled to the motor-side rotation unit to transfer the rotatory power of the driving motor to a load, and at least one pair of elastic members provided in spaces between the motor-side rotation unit and the load-side rotation unit, a sensor part configured to measure relative displacement between the motor-side rotation unit and the load-side rotation unit, and a controller configured to calculate external torque by an external force applied to the load side using the measured displacement and switch a control mode to any one of torque control and position control based on a result of a comparison between the calculated external torque and a critical torque.

The following contents illustrate only the principle of the present invention. Although various devices have not been clearly described or illustrated in this specification, those skilled in the art may implement the devices that implement the principle of the present invention and are included in the concept and scope of the present invention as defined by the appended claims.

Furthermore, it should be understood that all the detailed descriptions that list given embodiments in addition to the principle, aspects, and embodiments of the present invention are intended to include the structural and functional equivalents of such matters. Furthermore, it should be understood that the equivalents include equivalents to be developed in the future, that is, all devices invented to perform the same function by substituting some elements, in addition to known equivalents.

Accordingly, it should be understood that a block diagram of this specification, for example, is indicative of a conceptual viewpoint of an exemplary circuit that materializes the principle of the present disclosure. Likewise, it should be understood that all flowcharts, state change diagrams, and pseudo code may be substantially represented in computer-readable media and are indicative of various processes that are executed by computers or processors regardless of whether the computers or processors are evidently illustrated.

The functions of processors or the functions of various devices illustrated in the drawings that include function blocks illustrated as a similar concept may be provided by the use of hardware capable of executing software in relation to proper software, in addition to dedicated hardware. When being provided by a processor, the function may be provided by a single dedicated processor, a single sharing processor, or a plurality of separated processors, and some of them may be shared.

The above objects, characteristics, and merits will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

Hereinafter, embodiments of the present invention are described in detail with reference to the accompanying drawings.

<FIG> and <FIG> are exploded perspective views for illustrating the configuration of an SEA according to an embodiment of the present invention. The SEA includes a motor-side rotation unit <NUM>, a load-side rotation unit <NUM> and elastic members <NUM> and <NUM>.

Referring to <FIG> and <FIG>, the motor-side rotation unit <NUM> is coupled to a driving motor (not shown) and rotated by rotatory power of the driving motor. The load-side rotation unit <NUM> functions to transfer the rotatory power of the driving motor to a load.

To this end, the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> are coupled. The load-side rotation unit <NUM> may be configured to rotate in response to the rotation of the motor-side rotation unit <NUM>.

At least one pair of elastic members <NUM> is provided in the spaces between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>.

According to an embodiment of the present invention, a frame having accommodation spaces to which the at least one pair of elastic members <NUM> is fixed is formed in one of the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> together rotated by the rotatory power of the driving motor.

Furthermore, a frame for supporting the pair of elastic members therein is formed in the other of the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>.

In this case, any one of the elastic members may be compressed in the relative rotation direction of the motor-side rotation unit <NUM> on the basis of the load-side rotation unit <NUM>, thereby being capable of implementing an SEA capable of force or torque control in a rotary motion.

The SEA according to an embodiment of the present invention is suitable for a rotary motion and has a simple structure, and thus has an advantage in that it can be implemented in a small size.

The elastic members <NUM> and <NUM> may be made of an elastic material, such as silicon or urethane, but the present invention is not limited thereto. The elastic members may be made of various elastic substances or a mixture of two or more elastic substances in addition to silicon and urethane.

The elastic member <NUM>, <NUM> may have a cylindrical shape as shown in <FIG>, but is not limited thereto. The elastic member may have various shapes in addition to the cylindrical shape.

The material, shape or size of the elastic members <NUM> and <NUM> may be changed, and thus hardness K of the elastic member may vary.

Referring back to <FIG> and <FIG>, an inner frame <NUM> for supporting the pair of elastic members <NUM> therein is formed in the motor-side rotation unit <NUM>. An outer frame <NUM> for supporting the pair of elastic members <NUM> on the outside may be formed in the load-side rotation unit <NUM>.

As shown in <FIG>, accommodation spaces S in which the pair of elastic members <NUM> can be received and fixed by the outer frame <NUM> formed in the load-side rotation unit <NUM> may be provided in the load-side rotation unit <NUM>.

As described above, since the pair of elastic members <NUM> is supported on the inside and outside by the inner frame <NUM> of the motor-side rotation unit <NUM> and the outer frame <NUM> of the load-side rotation unit <NUM>, the elastic members <NUM> and <NUM> can be fixed to the spaces between the coupled motor-side rotation unit <NUM> and load-side rotation unit <NUM>.

For example, as shown in <FIG>, when the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> are coupled in the state in which the elastic members <NUM> and <NUM> have been mounted on the inner frame <NUM> of the motor-side rotation unit <NUM>, the elastic members <NUM> and <NUM> may be compressed and fixed to the accommodation spaces S formed by the outer frame <NUM> of the load-side rotation unit <NUM>.

As described above, the elastic members <NUM> and <NUM> are supported by the inner frame <NUM> of the motor-side rotation unit <NUM> and the outer frame <NUM> of the load-side rotation unit <NUM> and compressed and fixed to the accommodation spaces S. Accordingly, the elastic members <NUM> and <NUM> may not need to be fixed to the motor-side rotation unit <NUM> or the load-side rotation unit <NUM> using a separate fixing member.

Accordingly, if the coupling of the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> is to be released, the elastic members <NUM> and <NUM> are automatically separated, thereby being capable of facilitating the replacement of the elastic members <NUM> and <NUM>.

The SEA according to an embodiment of the present invention further includes a sensor part for measuring relative displacement between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>.

The sensor part is configured to include a magnetic body <NUM> and a hall sensor <NUM> respectively formed at the corresponding positions of the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>.

<FIG> is a diagram for illustrating an embodiment of the structure in which the elastic members <NUM> and <NUM> are fixed to the spaces between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>. A description of an element that belongs to the illustrated elements and that is the same as that described with reference to <FIG> and <FIG> is omitted hereunder.

Referring to <FIG>, the pair of elastic members <NUM> may be fixed to the spaces between the inner frame <NUM> of the motor-side rotation unit <NUM> and the outer frame <NUM> of the load-side rotation unit <NUM> in the compressed state.

Separated spaces D are present in the outside region of the SEA between the inner frame <NUM> of the motor-side rotation unit <NUM> and the outer frame <NUM> of the load-side rotation unit <NUM>. A portion of the elastic members <NUM> and <NUM> may be exposed to the outside through the separated spaces.

When the elastic members <NUM> and <NUM> are compressed, they may expand in the direction perpendicular to the compression direction. The separated spaces D may be used as reserved spaces for the perpendicular expansion of the elastic members <NUM> and <NUM>.

Furthermore, in <FIG>, four pairs of the elastic members (total of <NUM>) have been illustrated as being formed in the SEA, but the present invention is not limited thereto. Three pairs or five pairs or more of the elastic members may be formed in the SEA, if necessary.

When an external force is applied to the SEA having the above construction, the elastic members are compressed, so relative displacement between occurs between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>.

The external force applied to the SEA may mean torque generated by rotatory power of the driving motor, torque generated by a force applied to the load side, or torque according to a reduction or addition between the torques.

More specifically, any one of the pair of elastic members <NUM> is compressed in the relative rotation direction of the motor-side rotation unit <NUM> with respect to the load-side rotation unit <NUM> (or the relative rotation direction of the load-side rotation unit <NUM> with respect to the motor-side rotation unit <NUM>). Relative displacement corresponding to the compressed elastic members may occur.

Hereinafter, embodiments of the operation of the SEA according to an embodiment of the present invention are described more specifically with reference to <FIG>. The frames formed in the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> are rotated, but have been illustrated as having displacement similar to a straight line in <FIG>, for convenience sake.

In the state in which torque has not been applied to the SEA, as shown in <FIG>, the elastic members <NUM> and <NUM> may have been fixed to the spaces between the inner frame <NUM> and the outer frame <NUM> on the basis of a reference position R.

In the state in which the load-side rotation unit <NUM> has been fixed to the load side so that it does not rotate, when counterclockwise torque is applied to the SEA by rotatory power of the driving motor, as shown in <FIG>, the left elastic member <NUM> of the pair of elastic members <NUM> and <NUM> is compressed, so relative displacement (Δθ) toward the left direction (i.e., counterclockwise) of the reference position R occurs in the motor-side rotation unit <NUM>.

In this case, the torque by the rotatory power of the driving motor may be calculated using Equation <NUM> below.

In Equation <NUM>, τ is torque by the rotatory power of the driving motor, K is the hardness of the elastic member, and Δθ is relative displacement for the reference position R.

When the relative displacement (Δθ) is detected using the sensor part (the magnetic body <NUM> and the hall sensor <NUM>) provided in the SEA, the torque (τ) by the rotatory power of the driving motor may be calculated according to Equation <NUM>.

In the state in which the load side has been fixed, when clockwise torque is applied to the SEA by rotatory power of the driving motor, as shown in <FIG>, the right elastic member <NUM> of the pair of elastic members <NUM> and <NUM> is compressed, so relative displacement (Δθ) toward the right direction (i.e., clockwise) of the reference position R occurs in the motor-side rotation unit <NUM>.

Even in this case, the torque by the rotatory power of the driving motor may be calculated based on the relative displacement (Δθ) detected by the sensor part according to Equation <NUM>.

In <FIG>, the torque (τ) calculated using Equation <NUM> may indicate torque transferred to the load by the rotatory power of the driving motor.

The operation of the SEA according to an embodiment of the present invention has been described above with reference to <FIG> by taking a case where torque is applied by the rotatory power of the driving motor in the state in which the load side has been fixed as an example, but the present invention is not limited thereto. Although torque is applied to the SEA by a force applied to the load side, the SEA according to an embodiment of the present invention may operate as described above with reference to <FIG>.

For example, when clockwise torque is applied to the SEA on the load side, as shown in <FIG>, the left elastic member <NUM> of the pair of elastic members <NUM> and <NUM> is compressed, so relative displacement (Δθ) toward the right direction (i.e., clockwise) of the reference position R occurs in the load-side rotation unit <NUM>.

In contrast, when counterclockwise torque is applied to the SEA on the load side, as shown in <FIG>, the right elastic member <NUM> of the pair of elastic members <NUM> and <NUM> is compressed, so relative displacement (Δθ) toward the left direction (i.e., counterclockwise) of the reference position R occurs in the load-side rotation unit <NUM>.

In this case, the torque (τ) applied to the load side may be calculated based on the relative displacement (Δθ) detected by the sensor part using Equation <NUM>.

If torque applied to the load side and torque by rotatory power of the driving motor have opposite directions, the torque (τ) calculated using Equation <NUM> may indicate a value, that is, the sum of a torque value applied to the load side and a torque value according to rotatory power of the driving motor.

Referring to <FIG>, in order to measure relative displacement (Δθ) between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>, such as that described above, the magnetic body <NUM> for generating a magnetic field may be positioned in the motor-side rotation unit <NUM> and the hall sensor <NUM> may be positioned at a location of the load-side rotation unit <NUM> that faces the magnetic body <NUM>.

The hall sensor <NUM> may detect the direction and size of a magnetic field using a hall effect in which a voltage occurs in the direction perpendicular to current and the magnetic field when the magnetic field is applied to a conductor through which current flows.

Accordingly, the direction and size of a magnetic field generated from the magnetic body <NUM> are measured using the output signal of the hall sensor <NUM>. The relative rotation direction and displacement of the motor-side rotation unit <NUM> (or relative rotation direction and displacement of the load-side rotation unit <NUM>) may be detected based on a result of the detection.

<FIG> and <FIG> are perspective views showing the configuration of an SEA according to another embodiment of the present invention. A description of an element and operation that belong to the illustrated elements and operation of the SEA and that are the same as those described with reference to <FIG> is omitted hereunder.

Referring to <FIG>, a driving motor <NUM> is coupled to the motor-side rotation unit <NUM> of the SEA, and a decelerator <NUM> and a decelerator fixing stage <NUM> may be additionally coupled to the motor-side rotation unit <NUM>.

Furthermore, although not shown in <FIG>, a belt (or chain) and pulley for transferring rotatory power of the driving motor <NUM> to the motor-side rotation unit <NUM> may be provided in the SEA.

Furthermore, a bearing <NUM> may be coupled to the load-side rotation unit <NUM> of the SEA.

Referring to <FIG>, a bearing fixing stage <NUM> and a bearing cover <NUM> may be coupled the SEA coupled as shown in <FIG>.

<FIG> and <FIG> illustrate an embodiment of the configuration of the SEA coupled to the driving motor. An SEA according to an embodiment of the present invention is not limited to the SEA of <FIG> and <FIG>. Some of the illustrated elements may be omitted or an additional element may be added, if necessary.

According to another embodiment of the present invention, a force (or torque) and position in the joint of a robot or other industrial machines may be together controlled using an SEA having a configuration, such as that described with reference to <FIG>.

For example, a motion of a robot joint may be controlled using torque (τ) calculated based on relative displacement (Δθ) between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>.

More specifically, an external force applied to the load side depending on relative displacement between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> may be detected. The control mode of the SEA may switch to torque control or position control based on a result of a comparison between the external force and a reference value.

An SEA system according to an embodiment of the present invention may be configured to include an SEA having a configuration, such as that described with reference to <FIG>, and a controller for controlling the SEA.

Hereinafter, embodiments of a method of controlling the SEA are described more specifically with reference to <FIG>.

<FIG> is a flowchart illustrating a method of controlling the SEA according to various aspects, and shows a method for the controller of the SEA system to control the operation of the SEA according to an embodiment of the present invention.

Referring to <FIG>, the controller measures relative displacement between the motor-side rotation unit <NUM> and load-side rotation unit <NUM> of the SEA (step S900).

At step S900, as described above, relative displacement between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> is measured using the magnetic body <NUM> and the hall sensor <NUM> respectively positioned at the corresponding positions of the motor-side rotation unit <NUM> and the load-side rotation unit <NUM>.

The controller calculates external torque by an external force applied to the load side based on the displacement measured at step S900 and hardness K of the elastic members provided in the SEA (step S910).

Referring to <FIG>, when an external force (Fl) is applied to a load <NUM> coupled to the load-side rotation unit <NUM>, torque (τl) that rotates the load <NUM> by the external force (Fl) occurs.

For example, torque (τl) may occur when external force (Fl) is applied to the load <NUM> that does not rotate and maintains a current position, or torque (τl) may occur when external force (Fl) having a direction opposite the rotation direction of the load <NUM> that rotates until it reaches a specific position is applied to the load <NUM>.

Alternatively, torque (τl) may occur when external force (Fl) having the same direction as the rotation direction of the load <NUM> is applied to the load <NUM> that rotates.

As described above, the external torque (τl) by the external force (Fl) applied to the load <NUM> compresses any one of the pair of elastic members <NUM> and <NUM>, so relative displacement between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> may occur.

Accordingly, the external torque (τl) occurring due to the external force (Fl) may be calculated based on the relative displacement (Δθ) between the motor-side rotation unit <NUM> and the load-side rotation unit <NUM> and the hardness K of the elastic members using Equation <NUM>.

Thereafter, the controller compares the external torque calculated at step S910 with preset critical torque (step S920), and switches the control mode of the SEA to torque control or position control based on a result of the comparison (step S930).

In this case, in the torque control, the driving motor is controlled so that the load <NUM> connected to the load-side rotation unit <NUM> of the SEA generates a given torque (or force). As shown in <FIG>, the controller may receive feedback for torque (τe) transferred to the load side, may compare the torque (τe) with reference torque (τr), and may control the driving motor.

For example, the controller may perform the torque control to control the driving motor so that the reference torque (τr) continues to be transferred to the load <NUM> by performing pulse width modulation (PWM) control using Equation <NUM>.

In Equation <NUM>, F(s) indicates the torque control function of a PID controller, and KP, KD and KF indicate parameters for PID control.

A method for the controller to perform the torque control has been described above with reference to <FIG> and Equation <NUM>, but the present invention is not limited thereto. The controller may control driving motor using various known torque control methods.

In the position control, the driving motor is controlled so that the load <NUM> coupled to the load-side rotation unit <NUM> of the SEA is moved as much as a given rotation angle (or position). As shown in <FIG>, the controller may receive the rotation angle (θm) of the motor-side output stage as feedback, may compare the received rotation angle (θm) with a reference angle (θr), and may control the driving motor.

For example, the controller may perform the position control to control the driving motor so that the load <NUM> is rotated as much as the reference angle (θr) by performing PWM control using Equation <NUM> below.

In Equation <NUM>, P(s) indicates the position control function of the PID controller, and KP and KD indicate parameters for PID control.

A method for the controller to perform the position control with reference to <FIG> and Equation <NUM> has been described above, but the present invention is not limited thereto. The controller may control the driving motor using various known position control methods.

Equation <NUM> below shows an embodiment of a method for the controller to change the control mode of the SEA between the torque control and the position control based on a result of the comparison between the external torque (τl) and the critical torque (τth) at step S930.

Referring to Equation <NUM>, when external torque (τl) is a critical torque (τth) or less, the controller may switch the control mode of the SEA to the position control.

When the external torque (τl) is greater than the critical torque (τth), the controller may switch the control mode of the SEA to the torque control.

For example, when torque (τl) attributable to an external force (Fl) occurs during the position control in which the load <NUM> does not rotate, the driving motor may generate torque having an opposite direction until the external torque (τl) reaches a critical torque (τth), so the position control is maintained. When the external torque (τl) exceeds the critical torque (τth), the position control may switch to the torque control.

Thereafter, if the external force (Fl) is removed and the external torque (τl) drops to the critical torque (τth) or less, the torque control may switch to the position control, so the load <NUM> returns to the original position by the rotation of the driving motor.

During the position control in which the load <NUM> rotates at a given angle, when torque (τl) having an opposite direction occurs due to an external force (Fl), the driving motor may continue to rotate the load <NUM> until the external torque (τl) reaches the critical torque (τth), so the position control is maintained. When the external torque (τl) exceeds the critical torque (τth), the position control may switch to the torque control.

Thereafter, if the external force (Fl) is removed and the external torque (τl) drops to the critical torque (τth) or less, the torque control switches to the position control again, so the load <NUM> is rotated at a given angle by the driving motor.

Furthermore, during the position control in which the load <NUM> is rotated at the given angle, when torque (τl) having the same direction occurs due to an external force (Fl), the driving motor continues to rotate the load <NUM> until the external torque (τl) reaches the critical torque (τth), so the position control is maintained. When the external torque (τl) exceeds the critical torque (τth), the position control may switch to the torque control.

As described above, if the control mode switches between the position control and the torque control based on the critical torque (τth), oscillation may occur in a transition region near the critical torque (τth).

Referring to <FIG>, the position control switches to the torque control at a point of time (t1) at which the external torque (τl) increases and exceeds the critical torque (τth). After the control mode switches to the torque control, torque (τl) may be reduced.

The torque control switches to the position control again at a point of time (t2) at which the torque (τl) decreases and reaches the critical torque (τth). After the control mode switches to the position control, torque (τl) may increase.

As described above, the control mode repeatedly switches between the position control and the torque control in the transition region near the critical torque (τth), so oscillation may occur on the load side.

According to an embodiment of the present invention, in order to reduce such oscillation in the transition region, if external torque (τl) is decreased to a value or less obtained by subtracting given torque (τhys) from the critical torque (τth), the controller may operate so that the control mode of the SEA switches from the torque control to the position control.

Referring to Equation <NUM>, when the external torque (τl) reaches the critical torque (τth), the control mode switches from the position control to the torque control. If the external torque (τl) decreases up to a value (τth-τhys) obtained by subtracting given torque from the critical torque, the control mode may switch to from the torque control to the position control.

Referring to <FIG>, the position control switches to the torque control at a point of time (T1) at which the external torque (τl) increases and exceeds the critical torque (τth). After the control mode switches to the torque control, the torque (τl) may be decreased.

At a point of time at which the torque (τl) decreases and reaches the critical torque (τth), the control mode does not switch and maintains the torque control. Accordingly, the torque (τl) transferred to the load <NUM> may maintain a desired reference torque value.

Thereafter, at a point of time (T2) at which the external force (Fl) is removed and the external torque (τl) reaches a value (τth-τhys) obtained by subtracting given torque from the critical torque, the torque control may switch to the position control.

In accordance with an embodiment of the present invention, the frame having the accommodation spaces to which the pair of elastic members is fixed is formed in any one of the motor-side rotation unit and the load-side rotation unit rotated along with rotatory power of the driving motor. Accordingly, the SEA suitable for a rotary motion and having a simple structure can be provided because any one of the elastic members is compressed in the relative rotation direction of the motor-side rotation unit. Accordingly, a small-sized SEA can be implemented.

In accordance with another embodiment of the present invention, an external force applied to the load side is detected based on relative displacement between the motor-side rotation unit and the load-side rotation unit. The control mode of the SEA switches to any one of the torque control and the position control based on a result of a comparison between an external force and a reference value. Accordingly, the SEA can stably control a force and position according to circumstances.

The aforementioned methods according to the embodiments of the present invention may be produced in the form of a program to be executed by a computer. The program may be stored in a computer-readable recording medium. The computer-readable recording medium may include ROM, RAM, CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device, for example. Furthermore, the computer-readable recording medium includes media implemented in the form of carrier waves (e.g., transmission through the Internet).

The computer-readable recording medium may be distributed to computer systems connected over a network, and computer-readable code may be stored and executed in a distributed manner. Furthermore, a functional program, code and code segments for implementing the method may be easily reasoned by programmers those skilled in the art to which the present invention pertains.

Claim 1:
A method of controlling a series elastic actuator (SEA) comprising a motor-side rotation unit (<NUM>) and load-side rotation unit (<NUM>) coupled to transfer rotatory power of a driving motor to a load and elastic members (<NUM>) and a sensor part comprising a magnetic body (<NUM>) and a hall sensor (<NUM>), the method comprising:
measuring relative displacement between the motor-side rotation unit and the load-side rotation unit;
calculating external torque by an external force applied to the load side based on the measured displacement and hardness (K) of the elastic member;
comparing the calculated external torque with a critical torque (τth); and
switching a control mode of the SEA to any one of torque control and position control based on a result of the comparison,
when the external torque increases to a value greater than the critical torque (τth), the control mode switches from the position control to the torque control, and
when the external torque decreases to a value (τth-τhys) obtained by subtracting given torque (τhys) from the critical torque (τth) or less, the control mode switches from the torque control to the position control,
wherein an outer frame having accommodation spaces to which the pair of elastic members is fixed is formed in any one of the motor-side rotation unit and the load-side rotation unit,
wherein an inner frame for supporting the pair of elastic members therein is formed in another of the motor-side rotation unit and the load-side rotation unit,
wherein the displacement is measured using the magnetic body and the hall sensor respectively positioned at corresponding positions of the motor-side rotation unit and the load-side rotation unit, and
wherein the magnetic body is positioned between the two inner frames adjacent to each other, and the hall sensor is positioned on the outer frame.