Movement assistance device, and synchrony based control method for movement assistance device

In a wearable motion assist device, a motion assist device for generating a motion pattern synchronized with a wearer while maintaining a certain phase difference between a motion of the wearer and a motion of the device, and a synchronization based control method for the device are provided. The motion assist device acquires a phase of torque generated by the wearer's motion, applies a value of the phase to a phase oscillator model as an input, performs arithmetic processing, and calculates target torque and a target angle of the device with the motion of the device synchronized with the wearer. It is possible to improve an assisting effect of the device by controlling the device based on the calculated values.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of PCT/JP2012/083326 filed on Dec. 21, 2012, which claims priority under 35 U.S.C. §119 of Japanese Application No. 2011-279362 filed on Dec. 21, 2011, the disclosures of which are incorporated by reference. The international application under PCT article 21(2) was not published in English.

TECHNICAL FIELD

The present invention relates to a wearable motion assist device and a synchronization based control method for the wearable motion assist device.

In recent years, a shortage of care workers who support elderly people has been a problem. Accordingly, research and development of welfare robots has been conducted briskly (Patent Document 1). It is expected that a wearable motion assist device, which is a kind of welfare robots, will be put to practical use as support for elderly people's daily life.

As one of control methods for such a wearable motion assist tool, a control method called synchronization based control for achieving a coordinated movement of a human and a device has been proposed (Non Patent Document 1). Synchronization based control makes it possible to adjust synchronism between a human and a device. By increasing synchronism, a device can be used for assistance to movement in which the device synchronizes its motion timing with that of a human. Conversely, it is expected that a device will be used as movement teaching rehabilitation in which the device hauls a human by reducing synchronism. A wearable movement support device for assisting a wearer to move more comfortably by this synchronization based control has been proposed until now (Patent Document 2).

PRIOR ART DOCUMENT

Patent Document

Non Patent Document

[Non Patent Document 1] Zhang Xia, “Synchronization Control for Motion Assist Using Neural Oscillators”, 2007, Master Thesis, Graduate School of Science and Technology, Shinshu University[Non Patent Document 2] Shin'ya Kotosaka, Strefan Schaal, “Parameter Learning of Neural Oscillators for Generating Blow Movement of a Robot”, Proceedings of the 17th Annual Conference of the Robotics Society of Japan, 1999, Vol. 3, p. 3541-3547[Non Patent Document 3] Gen Aoyama, Toshiyuki Kondo, Satoshi Murata, Koji Ito, “Walking Pattern Generation Based on the Interaction of Phase Oscillators and Dynamical Models”, The Institute of Electronics, Information and Communication Engineers, 2002, NC2001-155[Non Patent Document 4] Koji Ito, “Shintaichi Shisutemuron (Embodied Intelligence System Theory)”, Kyoritsu Shuppan Co., Ltd., 2005[Non Patent Document 5] Satoshi Ito, Hideo Yuasa, Zhi-wei Luo, Masami Ito, Dai Yanagihara, “A Model of Adaptation to Environmental Changes in Rhythmic Movements”, The Society of Instrument and Control Engineers collected papers, Vol. 34, No. 9, p. 1237-1245

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

A mutually inhibiting model of a neural oscillator is used for generating a movement pattern of synchronization based control in a wearable movement support device disclosed in Patent Document 1 (Non Patent Document 2). However, when an articulated object such as a human leg is actuated, a certain phase difference is generated between respective oscillators usually. Accordingly, there is a problem that, even if the pattern generated by the mutually inhibiting model can perform the synchronization, it is difficult to generate a phase difference. In addition, there is a problem that, when a motion pattern is generated using the mutually inhibiting model, it is necessary to set almost ten parameters to obtain an arbitrary output waveform for an oscillation input, and that adjustment thereof is difficult.

The present invention was made in view of solving the above described problems, and its object is to provide a motion assist device that allows motion with an arbitrary phase difference being generated in motions between a human and a motion assist device. In addition, another object of the present invention is to provide a control method for the motion assist device for controlling the motion assist device simply with a small number of parameters.

Means for Solving Problems

Namely, a motion assist device to solve the above described problems includes: a joint disposed corresponding to a wearer's bent movable region; a link connected to the joint, the link being installed in the wearer; an actuator configured to drive a motion of the joint; a phase acquisition unit configured to acquire a phase θ′hof a motion of the wearer's bent movable region; a target value calculation unit configured to calculate a target value of motion of the joint for synchronizing the motion of the wearer's bent movable region and the motion of the joint while maintaining a preset target phase difference based on a phase oscillator model whose the phase θ′hof the motion of the bent movable region acquired by the phase acquisition unit is an input oscillation; and a drive control unit configured to drive the actuator based on the target value of motion calculated by the target value calculation unit.

In the motion assist device, the phase acquisition unit includes an interaction force detection sensor configured to detect interaction force of the motion of the wearer's bent movable region and the motion of the joint; a joint angle sensor configured to detect a joint angle of the joint; and a phase estimation unit configured to estimate the phase θ′hof the motion of the wearer's bent movable region based on the interaction force detected by the interaction force detection sensor and the joint angle detected by the joint angle sensor.

In the motion assist device, the phase estimation Unit estimates torque τ′hof the wearers bent movable region by the following Equation (1) from interaction force λ detected by the interaction force detection sensor and the joint angle q detected by the joint angle sensor;
τ′h=Mh{umlaut over (q)}+Ghq+λ(1)
(in Equation (1), Mhand Ghdenote a human inertia term and a gravity Lenin, respectively)

estimates maximum torque τ′h_maxand minimum torque τ′h_minof a human in motion by further using the Equation (I), substitutes τ′h_maxand τ′h_mininto the following Equation (2), and calculates amplitude A′hof the estimated torque τ′h;

calculates a y-coordinate of a phase angle on polar coordinates by the following Equation (3) from the torque τ′hand the amplitude A′h;

calculates an x-coordinate by the following Equation (4) from the Pythagorean theorem;
•{dot over (y)}≧0 •{dot over (y)}<0
x=√{square root over (1−y2)}x=√{square root over (1−y2)}  (4)

performs polar coordinate transformation by the following Equation (5); and
θ′h=α tan 2(y,x)(−π≦θ′h≦π)  (5)

estimates the phase θ′hof the motion of the wearer's bent movable region.

In the motion assist device, the target value calculation unit calculates driving torque of the joint by Output of Equation (7) as the target value of motion based on a mathematical model composed of a phase oscillator that has relationships of the following Equation (6) and Equation (7)
{dot over (θ)}a=ωα+Ksin(θ′h−θα+θα)  (6)
Output=Aαsin θα−Aαsin θαθ(7)
(in Equation (6), ωα, θα, and K denote a natural frequency, phase angle, and synchronization gain of the joint, respectively, and θddenotes the target phase difference, and in Equation (7), Aaand θaθdenote amplitude of an Output waveform and an initial phase of an oscillator, respectively, and a second term of a right side in Equation (7) is a term for setting an initial value of the Output waveform at 0).

In the motion assist device, the drive control unit performs feedback control of the actuator based on the target value of motion calculated by the target value calculation unit.

A synchronization based control method for a motion assist device includes a joint disposed corresponding to a wearer' s bent movable region, a link connected to the joint, the link being installed in the wearer, an actuator configured to drive a motion of the joint, and assisting a motion of the wearer, the control method comprising: a phase acquisition step of acquiring a phase θ′hof a motion of the wearer's bent movable region; a target value calculation step of calculating a target value of motion of the joint for synchronizing the motion of the wearer's bent movable region and the motion of the joint while maintaining a preset target phase difference based on a phase oscillator model with the phase θ′hof the motion of the bent movable region acquired in the phase acquisition step being an input oscillation; and a drive control step of driving the actuator based on the target value of motion calculated in the target value calculation step.

In the synchronization based control method for the motion assist device, the phase acquisition step includes an interaction force detection step of detecting interaction force of the motion of the wearer's bent movable region and the motion of the joint; a joint angle detection step of detecting a joint angle of the joint; and a phase estimation step of estimating the phase θ′hof the motion of the wearer's bent movable region based on the interaction force detected in the interaction force detection step and the joint angle detected in the joint angle detection step.

In the synchronization based control method for the motion assist device, the phase estimation step includes: a torque estimation step of estimating torque τ′hof the wearer's bent movable region by Equation (1) from interaction force λ detected in the interaction force detection step and the joint angle q detected in the joint angle detection step; a torque amplitude calculation step of estimating maximum torque τ′h_maxand minimum torque τ′h_minof a human in motion by further using above Equation (1); substituting τ′h_maxand τ′h_mininto Equation and calculating amplitude A′hof the estimated torque τ′h; a y-coordinate calculation step of calculating a y-coordinate of a phase angle on polar coordinates by Equation (3) from the torque T′hand the amplitude A′h; an x-coordinate calculation step of calculating an x-coordinate by Equation (4) from the Pythagorean theorem; and a phase transformation step of performing polar coordinate transformation by Equation (5), and calculating a phase θ′h of the motion of the wearer's bent movable region.

As regards synchronization based control method for the motion assist device, in the target value calculation step, driving torque of the joint is calculated by Output of Equation (7) as the target value of motion based on a mathematical model composed of a phase oscillator that has relationships of Equation (6) and Equation (7).

As regards synchronization based control method for the motion assist device, in the drive control step, feedback control of the actuator is performed based on the target value of motion calculated by the target value calculation unit.

Effects of the Invention

The motion assist device and the synchronization based control method therefor according to the present invention employ a phase oscillator model as an oscillator model used at a time of generating a movement pattern that determines an output of the motion assist device, make the wearer's motion an input oscillation of the phase oscillator, and make it possible to generate a pattern with an arbitrary phase difference generated with respect to a motion of a human. This makes it possible to perform synchronization based control so that the motion assist device moves in synchronization while maintaining the arbitrary phase difference from the wearer's motion.

The wearable motion assist device and the synchronization based control method therefor according to the present invention make it possible to perform motion pattern generation for the motion assist device efficiently by simple parameter setting.

MODE FOR CARRYING OUT THE INVENTION

The following describes a wearable motion assist device and an embodiment for performing a synchronization based control method therefor according to the present invention.

First, a phase oscillator model will be described. The phase oscillator model is a pattern generation model used between oscillators that perform simple harmonic oscillation. The phase oscillator model, which allows synchronization with another oscillator and preparation of a phase difference, is used for movement pattern generation or the like for each joint of an articulated robot (Patent Document 3, Non Patent Documents 3 to 5). In these pieces of existing research, pattern generation according to the phase oscillator model is performed in order to control a motion of each joint of the articulated robot and a motion of right and left legs of a bipedal walking robot. On the other hand, the present invention is a control method for performing motion pattern generation according to the phase oscillator model by using a wearer's motion as an input oscillation in a motion of the motion assist device that is installed in a human body, and is novel in that processing is not performed in an identical robot. In addition, the present invention is novel in that, on an assumption that part of the wearer's body is also one oscillator, a motion between the human body and the device is controlled based on synchronization while maintaining an arbitrary phase difference.

FIG. 1illustrates a model illustrating connection of a plurality of phase oscillators, and the following Equation (8) expresses a model equation of the phase oscillators.

In Equation (8), θ denotes a phase angle of each of the oscillators, ω denotes a natural angular frequency, n denotes a number of adjacent oscillators, and Kijdenotes strength of an interaction that takes place between oscillators i-j. A second term of a right side is an interaction term between the oscillators, which causes entrainment and synchronization among the plurality of oscillators. Equation (8) is an equation representing that an oscillator i interacts with n oscillators. j (=1 to n) represents a surrounding oscillator.

<Overview of Synchronization Based Control>

FIG. 2illustrates an example of an overview of synchronization based control according to the present invention. First, a wearer's torque (Expected Human's Torque) is estimated from interaction force (Interaction Torque) which arises from an interaction of a motion of a joint (Each joint of Motion Assist) of a device and a motion of the wearer's (Human) bent movable region, and from a joint angle of the device. Next, a phase θ′hof the torque is estimated as a phase θ′hof the wearer's motion from the wearer's estimated torque (EOM (Estimation Of Motion) of Human Model). Next, the phase θ′hof the wearer's motion is substituted into the model equation of a phase oscillator as an input oscillation of the phase oscillator, and arithmetic is performed. Target values (Output) of motion, such as target torque and a target angle, are calculated by the model equation of the phase oscillator as an output that synchronizes with the wearer's motion. At this time, in the model equation for performing arithmetic processing, it is possible to generate an arbitrary phase difference for an input. Then, next motion of the device is generated according to the target value of motion. By repeating such a series of motions, a motion of the device is synchronized with the wearer's motion.

<Example of a Model of the Wearer's Bent Movable Region>

FIG. 3illustrates a human body100that serves as a wearer. Herein, as an example, an example in which the wearer's bent movable region (joint) is a knee joint is illustrated. The human body100has a thigh region101, a knee joint102, and a leg region103as a leg (Human Leg).FIG. 4illustrates a single-degree-of-freedom knee joint model (Human Leg) that models the leg of the human body illustrated inFIG. 3.FIG. 4illustrates a movable mechanism2of the motion assist device1in a state of installation in the single-degree-of-freedom knee joint model. The motion assist device estimates a phase of a torque waveform of the knee joint102(an example of the bent movable region) as a phase of the motion of the bent movable region based on an estimated value of the wearer's torque in the present model.

<Example of a Configuration of the Motion Assist Device>

The movable mechanism2of the motion assist device1illustrated inFIG. 4includes a joint11, a link12, a link13, an actuator21, an interaction force detection sensor22, a joint angle sensor23, an installation tool15, and an installation tool16. A resistor and a piston pump illustrated inFIG. 4equivalently represent that the device1gives load and driving force to the human leg, and do not constitute the device1.

The joint11is disposed corresponding to the knee joint102that is the wearer's bent movable region. In this example, the joint11for rotating with single degree of freedom (one axis) is used corresponding to a degree of freedom of the knee joint102. Herein, when a motion assist device is installed in a bent movable region that moves with multiple degrees of freedom such as a wrist, it is preferable to use a joint that has multiple degrees of freedom.

The joint11connects the link12and the link13. This makes the link12and the link13rotatable around the joint11as a pivot. The link12is formed to have a length installable along the thigh region101, and has the installation tool15for fixing the link12to the thigh region101. The installation tool15is, for example, a belt for fastening and fixing the link12and the thigh region101together. The link13is formed to have a length installable along the leg region103, and has the installation tool16for fixing the link13to the leg region103. The installation tool16is, for example, a belt for fastening and fixing the link13and the leg region103together. Herein, for example, as in a case of installation of the motion assist device1in a wearer in a state of sitting on a chair, even if the installation tool15is not provided, when it is possible to fix a position of the link12relative to the wearer, the link12may not have the installation tool15. That is, only a link that moves together with a motion of the wearer's bent movable region needs to have the installation tool.

The actuator21drives a motion of the joint11. The actuator21is, for example, an electric-powered motor. Hereinafter, the actuator21is also referred to as a motor21. A motion of the actuator21, such as a rotational speed, rotational angle, and rest position, is controlled by a drive control unit34to be described later. Driven by the actuator21, the joint11moves, and the link12and the link13move relatively. A speed reducer with an appropriate reduction ratio may be attached to the motor21.

The interaction force detection sensor22detects interaction force generated by a motion of the wearer's knee joint102and a motion of the joint11, and is provided in the joint11. As the interaction force detection sensor22, a torque sensor is used in this example. Hereinafter, the interaction force detection sensor22is also referred to as a torque sensor22. As the interaction force detection sensor22, a force sensor or a wrist force sensor that detects force may be used to calculate torque.

The joint angle sensor23detects a joint angle of the joint11. Since the joint angle can be determined from the rotational angle of the motor21, the joint angle sensor23may detect the rotational angle of the motor21. In the present embodiment, an encoder that detects the rotational angle of the motor21is used as the joint angle sensor23. Hereinafter, the joint angle sensor23is also referred to as an encoder23.

FIG. 5illustrates a block diagram of an electric system of the motion assist device1.

The motion assist device1includes a movable mechanism2, a computer (PC)3, and an interface circuit4. As described above, the movable mechanism2includes the motor21, the torque sensor22, and the encoder23. The computer3is intended to control a motion of the movable mechanism2. The computer3operates in accordance with a program stored in a built-in memory. As the computer3, a general-purpose computer including a body and a display as illustrated inFIG. 5may be used, or the computer3may be downsized using a substrate, a module, and the like on which a central processing unit (CPU), a memory for storing the program, and the like are mounted.

The interface circuit4is a circuit for connecting the movable mechanism2and the computer3. The interface circuit4includes, for example, an amplifier (Amp) for amplifying a detection value of the torque sensor22to an appropriate level, an analog-to-digital converter (A/D) for converting an output of the amplifier from an analog signal into a digital signal, a motor driver, a digital-to-analog converter (D/A) for converting a digital signal for driving the motor21outputted from the computer3into an analog signal, and a counter for inputting an output of the encoder23into the computer3. Herein, a general-purpose inter face board installed in an expansion card slot of the computer3is used, the inter face board including A/D, D/A, and the counter.

The computer3and the interface circuit4may be downsized and integrated with the movable mechanism2. In this case, preferably the device1has a built-in battery and operates on the battery.

By operating in accordance with the program, the computer3functions as a phase estimation unit32, a target value calculation unit33, and a drive control unit34, as illustrated inFIG. 6. As illustrated inFIG. 6, a phase acquisition unit31includes the torque sensor (interaction force detection sensor)22, the encoder (joint angle sensor)23, and the phase estimation unit32. The phase acquisition unit31acquires a phase θ′hof a motion of the wearer's bent movable region. The phase estimation unit32estimates the phase θ′hof the motion of the wearer's bent movable region based on the interaction force (torque) detected by the torque sensor22and the joint angle detected by the encoder23. The target value calculation unit33calculates a target value of motion of the joint11for synchronizing a motion of the wearer's bent movable region (knee joint102) and a motion of the joint11based on a phase oscillator model with the phase θ′hof the motion of the bent movable region being an input oscillation while maintaining a preset target phase difference. The target value of motion is, for example, target torque and target joint angle of the joint11. The drive control unit34drives the motor21based on the target value of motion calculated by the target value calculation unit33.

<Application of the Phase Oscillator Model to the Synchronization Based Control>

The model equation of a phase oscillator is a pattern generation model used among the oscillators that perform a simple harmonic oscillation. In order to achieve synchronization of motions between the phase oscillator that generates a motion of the motion assist device1and the wearer, it is assumed that the wearer also moves in accordance with an oscillator similar to the oscillator of the device, and a phase of the motion of the wearer's bent movable region is estimated. The following describes details.

FIG. 7is a flow chart illustrating a synchronization based control method for the motion assist device1.

In an interaction force detection step S1, the computer3(seeFIG. 5) detects interaction force of the motion of the wearer's bent movable region and the motion of the joint11from the torque sensor22. Then, in a joint angle detection step S2, the computer3detects the joint angle of the joint11from the encoder23. Although either step S1or step S2may be performed first, step S1and step S2are performed almost simultaneously.

Subsequently, in a torque estimation step S3, the computer3estimates τ′htorque of a motion of the wearer's bent movable region (knee joint102). The torque τ′his calculated by an estimation equation expressed by the following Equation (1).
τ′h=Mh{umlaut over (q)}+Ghq+λ(1)

In Equation (1), Mh, Gh, and λ denote a human inertia term, a gravity term, and interaction force, respectively. The interaction force is a detection value of the torque sensor22. The human inertia term and the gravity term may be determined from an existing known database, or measured values may be used. Examples of known databases include a document “Michiyoshi Ae, Tang Hai-peng, Takashi Yokoi, “Estimation of Inertia Properties of the Body Segments in Japanese Athletes”, the Biomechanism 11, (1992), pp. 23-33”. On an assumption that a joint angle q of the bent movable region (knee joint) when the device is installed and a joint angle of the joint11are equivalent, a joint angle determined from a detection value of the encoder23is defined as q.

Furthermore, in a torque amplitude calculation step S4, the computer3determines maximum torque τ′h_maxand minimum torque τ′h_minof the human in motion by using Equation (1). Amplitude A′hof the estimated torque is determined by substituting maximum torque τ′h_maxand minimum torque τ′h_mininto the following Equation (2).

In Equation (2), as the maximum torque τ′h_maxand minimum torque τ′h_min, values of a motion one period before the time of arithmetic are used. An initial value is set at an arbitrary value.

Subsequently, in a y-coordinate calculation step S5, the computer3calculates a y-coordinate of the phase angle on polar coordinates by the following Equation (3) from τ′hdetermined by Equation (1) and A′hdetermined by Equation (2).

Next, in an x-coordinate calculation step S6, the computer3calculates an x-coordinate by the following Equation (4) from the Pythagorean theorem.
{dot over (y)}≧0{dot over (y)}<0
x=√{square root over (1−y2)}x=−√{square root over (1−y2)}  (4)

Next, in a phase transformation step S7, the computer3performs, by the following Equation (5), polar coordinate transformation of the y-coordinate and x-coordinate calculated by Equation (3) and Equation (4), respectively, to determine the phase (phase angle) θ′hof the motion (torque) of the wearer's bent movable region.
θ′h=α tan 2(y,x)(−π≦θ′h≦π)  (5)

Thus, it is possible to estimate (acquire) the phase θ′hof the motion of the wearer's bent movable region.

Next, in a target value calculation step S8, the computer3calculates a target value of motion of the joint11for synchronizing the motion of the wearer's bent movable region and the motion of the joint11while maintaining the preset target phase difference based on the phase oscillator model with the phase θ′hof the motion of the bent movable region acquired in the phase estimation step (steps S1to S7) being an input oscillation.

The target value of motion is calculated based on a mathematical model composed of a phase oscillator having relationships of Equation (6) and Equation (7) described below.

First, a phase angle of the joint11is calculated by the following Equation (6) that is based on the phase oscillator model of Equation (8). The phase θ′his inputted into the following Equation (6).
{dot over (θ)}a=ωa+Ksin(θ′h−θa+θd)  (6)

In Equation (6), ωa, θa, and K are a natural frequency, phase angle, and synchronization gain of the device1, respectively, and θddenotes a target phase difference between the motion of the wearer's bent movable region and the motion of the joint11of the device1.

The computer3makes Output determined by the following Equation (7) from the phase angle of the joint11of the device1determined by Equation (6) as a target value of motion. In this example, an output waveform of Output is defined as driving torque to be generated by the joint11.
Output=Aasin θa−Aasin θa0(7)
In Equation (7), Aaand θa0denote amplitude of the output waveform and an initial phase of the oscillator, respectively. In addition, a second term in a right side in Equation (7) is a term for setting an initial value of the output at 0.

Next, in a drive control step S9, the computer3performs drive control of the actuator21based on the target value of motion. Specifically, the computer3generates a motion pattern for the motor21and drives the motor21so that the joint11generates the driving torque with the waveform of Output that is the target value of motion.

In the drive control step S9, the motor21is preferably feedback-controlled based on the target value of motion.

The computer3repeats a series of motions of steps S1to S9.

Herein, the computer3(seeFIG. 5) operates as the phase estimation unit32(seeFIG. 6) in the interaction force detection step S1, the joint angle detection step S2, the torque estimation step S3, the torque amplitude calculation step S4, the y-coordinate calculation step S5, the x-coordinate calculation step S6, and the phase transformation step S7. The computer3operates as the target value calculation unit33(seeFIG. 6) in the target value calculation step S8, and operates as the drive control unit34in the drive control step S9. In addition, the interaction force detection step S1to the phase transformation step S7correspond to a phase acquisition step of acquiring the phase θ′hof the motion of the wearer's bent movable region in the present invention. In addition, the torque estimation step S3to the phase transformation step S7correspond to a phase estimation step of estimating the phase θ′hof the motion of the wearer's bent movable region based on the interaction force detected in the interaction force detection step S1and the joint angle detected in the joint angle detection step S2in the present invention.

Herein, an example has been described in the target value calculation step S8in which the waveform of the driving torque of the joint11is calculated as a target value of motion. However, the joint angle (target angle) of the joint11or the rotational speed of the joint11may be calculated as the target value of motion, Since the driving torque, joint angle, and rotational speed of the joint11are mutually transformable, a parameter suitable for control may be calculated.

In the present embodiment, the wearer's torque and the phase of the torque are estimated by arithmetic from the interaction force between the wearer and the device, and the joint angle. However, in order to carry out the present invention, an acquisition method of torque and phase is not restricted, but can be suitably changed to another method. For example, the wearer's accurate torque and phase may be acquired by attaching a sensor directly to the wearer. In this case, it means that the sensor attached to a measurer is connected to the device. When the sensor is attached directly to the wearer to acquire the wearer's torque, steps S1to S4of the flow chart inFIG. 7can be omitted. When the sensor is attached directly to the measurer to acquire the wearer's phase, steps S1to S7can be omitted.

An example has been described in which a motion pattern for the device is generated based on a mathematical model of the phase oscillator expressed by Equation (6) and Equation (7). However, a model based on another mathematical model may be used for the mathematical model of the phase oscillator.

An example has been described in which the motion assist device1includes the single-degree-of-freedom joint11. However, the present invention is applicable to a motion assist device that includes a plurality of joints with each of the joints connected by a link. When the plurality of joints are connected by the link, on an assumption that a plurality of phase oscillators correspond to the number of connections of the joints, an influence of each phase oscillator may be added to calculate a phase of motion of the wearer's joint based on Equation (8). For a multi-degree-of-freedom joint, addition and calculation may be performed similarly.

<Synchronization Based Control Experiment by Simulation>

In order to evaluate an effect of the present invention, a verification experiment was conducted by simulation. In the simulation, an interaction between the motion assist device to be controlled based on synchronization and the wearer was simulated on an assumption that the wearer of the device always maintains his or her own motion. In the synchronization based control experiment by the simulation and a real device to be described later, data on a Japanese young man described in the above-described known document “Estimation of Inertia Properties of the Body Segments in Japanese Athletes” was used as an inertia term and a gravity term. Each numerical value used in the simulation was set at each coefficient of Mh=1.5×10−1kg·m2, Ma=4.1×10−2kg·m2, Ch=0.1 m2/s, Ca=0.1 m2/s, Gh=5.7 N·m, Ga=1.7 N·m, k1=263.6 N/rad, and k2=26.4 N/rad2, where mass of a human leg mh=3.0 kg, length lh=3.9×10−1m, mass of a device ma=1.0 kg, and length la=3.5×10−1m.

The simulation was performed with a model ofFIG. 4. In addition, the following Equation (9) represents an equation of motion in the present model. In Equation (9), a first term to fourth term of a right side represent an inertia term, a viscous term, a gravity term, and an interaction force term, respectively. Herein, among these terms, the interaction force term was derived using the following Equation (10). (Both coefficients of viscosity Chand Cawere 0.1 as described above.)

In the present simulation, the wearer was assumed to maintain a preset torque waveform and to perform a periodic movement. In the present simulation, a frequency of the torque waveform was set at 0.80 Hz, and amplitude was set at 0.80 Nm. The wearer was assumed to determine torque by proportional-derivative (PD) control from a target orbit and a current angle, and to perform movement. Moreover, in the simulation, on an assumption that the device could estimate the wearer's torque accurately, the wearer's torque value was used as it is for an estimated value. A natural angular frequency ωaof the oscillator of the device was set at 5.7 rad/s (frequency of 0.90 Hz). An initial phase θa0was set at 1.5π rad. Amplitude Aaof the torque waveform to output was set at 1.0 Nm. According to a flow of the synchronization based control described above, the device was assumed to obtain an output of the phase oscillator based on the estimated value of the wearer's torque. In the present experiment, the simulation was performed of the interaction for each of cases where a target phase difference θdof the device was set at 0 rad and synchronization gains were set at 0.1, 1.0, and 5.0.

FIG. 8illustrates a graph of the torque waveforms resulting from the simulation. Among the waveforms illustrated inFIG. 8, a waveform expressed by a solid line represents a sinusoidal waveform of the wearer's (knee joint102) phase θ′h. Waveforms expressed by dashed lines represent sinusoidal waveforms of the phase θaof the device (joint11) for each of the synchronization gains. It is observed fromFIG. 8that a frequency of the device approaches a natural frequency as the synchronization gain decreases. Conversely, it is observed that the frequency of the device approaches the wearer's frequency as the synchronization gain increases.

FIG. 9illustrates a graph of a joint angle of the wearer (knee joint102) resulting from the simulation. Among waveforms illustrated inFIG. 9, a waveform expressed by a solid line represents a joint angle of the wearer in a case of performing movement without an interaction with the device. Waveforms expressed by dashed lines represent a joint angle of the wearer in a case of interacting with the device controlled with each of the synchronization gains. It is observed fromFIG. 9that the device moves in accordance with the wearer's rhythm, which amplifies amplitude of movement of the knee joint in a case of installing a device with the synchronization gain being set greatly as compared with a case of performing movement without installing the device. This shows that a high assisting effect on the wearer's movement is obtained by controlling the wearable motion assist device1by synchronization based control according to the present embodiment.

(Phase Difference Adjustment Experiment by Simulation)

In order to confirm that an output waveform of the motion assist device that moves by the synchronization based control method according to the present invention synchronizes with the wearer's motion while maintaining an arbitrary phase difference, a phase difference adjustment experiment was conducted by simulation. In simulation, the synchronization gain K was set at 5.0. The interaction was simulated for each of cases where target phase differences θdwere rad, 0.33π rad, and 0.67π rad. Other conditions were similar to conditions of the above-described simulation experiment.

FIG. 10illustrates a graph of torque waveforms resulting from the simulation. It is observed fromFIG. 10that it is possible to adjust a phase difference of the device from a phase of the wearer's motion by setting a target phase difference.

<Synchronization Based Control Experiment with a Real Device>

As illustrated inFIG. 4, an experiment with a real device was conducted by installing the movable mechanism2of the device1in a human leg. A product of Harmonic Drive Systems Inc. with a reduction ratio of 50 was used as a motor. A rated torque of the motor was 5.4 Nm and a maximum torque was 24 Nm. In addition, a torque sensor was built in the speed reducer, which detects interaction force generated between the wearer and the device.

Motion of the device1, which has already been described, will be summarized with reference toFIG. 5. The computer3determines a command voltage from torque calculated by the phase oscillator, gives the voltage from D/A converter via the driver to the motor21, and drives an arm (corresponding to the link13ofFIG. 4). Then, a joint angle of the arm after being driven is measured with the encoder23, and the interaction force is measured with the torque sensor22. The joint angle and the interaction force are incorporated into the computer3via the amplifier and the driver from A/D converter and the counter, respectively. Based on these pieces of information, torque of the following device is calculated by the phase oscillator.

A test subject performs movement in a state of sitting on a stand with a level at which a leg does not touch a ground. The test subject fixes a cervix of a right leg to the link13of the device with a band for fixing (installation tool16), and causes movements of the device and the test subject to interact. The link12was fixed so as not to move with respect to the sitting stand (seeFIG. 4). Since the test subject was in the state of sitting on a chair and neither the thigh region101nor the link12moves with respect to the sitting stand, installation of the installation tool15illustrated inFIG. 4was omitted. In addition, in order to evaluate the movement of the test subject at a time of the experiment, surface muscle action potential is measured. Measuring points are five points of a rectus femoris muscle, vastus medialis muscle, and vastus lateralis muscle which are used at a time of knee joint extension, and a biceps femoris muscle and semitendinous muscle which are used for bending the leg.

In the present experiment, the wearer performs movement at 0.80 Hz, and the interaction with the device was verified. A natural angular frequency ωaof the oscillator of the device was set at 5.7 rad/s (frequency of 0.90 Hz), an initial phase θa0was set at 0.10π rad, and amplitude Aaof a torque waveform to output was set at 6.0 Nm. First,FIG. 11,FIG. 12, andFIG. 13illustrate sinusoidal waveforms of a phase of each oscillator and an estimated phase of the wearer when a synchronization gain K was adjusted at 0.1, 1.0, and 5.0, respectively. It is observed from each Fig. that a frequency of the device approaches a natural frequency of the device as the synchronization gain decreases, and that the frequency of the device approaches the wearer's natural frequency conversely as the synchronization gain increases. In addition, the estimated phase of the wearer is easily distorted when K is 0.1 and 1.0. This is considered because a case where the device becomes assistance to the wearer's motion and a case where the device conversely inhibits the wearer's motion are intermingled due to a difference in the frequency of motion between the device and the wearer, and accordingly an estimated value of the wearer's torque easily varies, and an estimated value of the wearer's phase that is determined based on the estimated value of the wearer's torque also varies.

In order to verify an assisting effect of the device with the synchronization gain set at K=5.0 on the movement of the wearer, maximum voluntary contraction strength (% MVC) was derived using a root mean square (RMS) of the measured muscle action potential. For verification, as illustrated inFIG. 4, a muscle action potential sensor201for measuring muscle action potential was attached to the wearer. A muscle action potential measuring instrument was connected to a tip of wiring of the muscle action potential sensor201, although not illustrated. The maximum voluntary contraction strength was calculated by dividing an average of the RMS value during 10 seconds by RMS at a time of maximum voluntary contraction. Table 1 illustrates the maximum voluntary contraction strength of five muscles measured in a case of performing movement only by the wearer and in a case where an interaction is performed with the device.

It is observed from Table 1 that the maximum voluntary contraction strength in a case of performing an interaction with the device has a tendency to decrease compared with a case of movement only by the wearer. Particularly, decrease of about 10% is observed in the maximum voluntary contraction strength of the rectus femoris muscle, vastus medialis muscle, and vastus lateralis muscle used for extension. This shows that the device that undergoes synchronization based control in accordance with the present embodiment assists the wearer's motion effectively. In contrast, regarding the semitendinous muscle, it is observed that the maximum voluntary contraction strength rises when the interaction is performed with the device. This is considered because force that pulls the wearer's leg in a pivot direction of the joint on a motor side is applied by a fixing band for fixing at a time of extension of the knee joint.

INDUSTRIAL APPLICABILITY

The motion assist device and the synchronization based control method for the motion assist device according to the present invention can generate the motion pattern for the motion assist device with the arbitrary phase difference generated with respect to the wearer's motion, thereby allowing appropriate assistance to the wearer's motion even when assisting a motion of an articulated object such as a leg. The present device and the synchronization based control method therefor can adjust synchronism of the device with respect to a human by appropriately setting the phase difference and the synchronization gain. Therefore, the present device and the synchronization based control method therefor can be used for assistance to a movement in which the device synchronizes its motion timing with that of a human by increasing synchronism. Moreover, the present device and the synchronization based control method therefor can be used for movement teaching rehabilitation in which the device hauls a human by decreasing synchronism.

EXPLANATIONS OF LETTERS OR NUMERALS