Wearable walking assist robot and method for controlling the same

A wearable walking assist robot is provided that ensures high walking assistance performance without a complex calculation process by detecting a gait phase based on pressure distribution on feet and performing a corresponding control mode that is set in advance. The wearable walking assist robot includes a sensor unit that senses pressure on the soles of the feet of a wearer and a controller that determines gait phases of both a first leg to be operated and a second leg based on the sensed pressure. Additionally, the controller selects one of a plurality of control modes set in advance based on the determined gait phases and operates a joint-driving unit for the first leg to be operated.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2016-0061605, filed May 19, 2016, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND

Field of the Invention

The present invention relates to a wearable walking assist robot and a method for controlling the same and, more particularly, to a wearable walking assist robot that ensures high walking assistance performance without a complex calculation process by detecting a gait phase based on pressure distribution on feet and performing a corresponding control mode that is set in advance, and a method for controlling the wearable walking assist robot.

Description of the Related Art

In general, robots with legs for walking such as a walking assist robot have different dynamics when legs come in contact with the ground, which has been discussed in the name of hybrid dynamics. A technology of determining a gait phase is important for walking robots to process the dynamics of the legs which depends on the gait phases. However, the technologies that have been developed to determine gait phases in the related art divide gait phases into several steps for precise control and use complex algorithms as well to determine gait phases. A complex process of determining gait phases causes the control of robot legs to also be complex and thus, the complex algorithms for determining gait phases are merely theoretically explained and have not been verified in terms of effectiveness that they can be actually applied to robots and can control walking of the robots.

SUMMARY

Accordingly, the present invention provides a wearable walking assist robot that ensures high walking assistance performance without a complex calculation process by detecting a gait phase of legs through a simplified algorithm based on pressure distribution on feet and selectively controlling one of a plurality of simple control modes in accordance with the gait phase, and a method for controlling the wearable walking assist robot.

According to one aspect of the present invention, a wearable walking assist robot may include: a sensor unit configured to sense pressure on the soles of the feet of a user; and a controller configured to determine gait phases of both a leg to be operated and the other leg based on the pressure sensed by the pressure sensor unit, select one of a plurality of control modes set in advance based on the determined gait phases, and operate a joint-driving unit for the leg to be operated.

The pressure sensor unit may include a plurality of pressure sensors configured to detect pressure applied to the toes and the heels of the soles. The controller may be configured to determine that the toes and the heels are in contact with the ground when pressure applied to the toes and the heels is greater than a predetermined threshold, and determine that the toes and the heels are not in contact with the ground when the pressure is less than the threshold. The controller may further be configured to determine the gait phases by combining a ground-contact state and a non-ground-contact state of the toe and the heel of the leg to be operated with a ground-contact state and a non-ground-contact state of the toe and the heel of the other leg.

Additionally, the controller may be configured to determine as a gait phase that a corresponding leg is supported on the ground throughout the sole when the toe is in contact with the ground and the heel is in contact with the ground, determine as a gait phase that a corresponding leg is supported on the toe on the ground when the toe is in contact with the ground and the heel is not in contact with the ground, determine as a gait phase that a corresponding leg is supported on the heel on the ground when the toe is not in contact with the ground and the heel is in contact with the ground, and determine as a gait phase that a corresponding leg is in the air when both the toe and the heel are not in contact with the ground.

The controller may further be configured to determine one of a weight bearing mode, a compensation of mechanical impedance mode, a ground impact absorbing mode, a ground impact absorbing & extension of virtual leg mode, a pushing ground mode, and a ready for swing phase mode, as a control mode for the leg to be operated based on the gait phases of both the leg to be controlled and the other leg. The weight bearing mode may be a mode in which the controller may be configured to operate the joint-driving unit to push the wearer in a gravity direction with a predetermined force. The compensation of mechanical impedance mode may be a mode in which the controller may be configured to operate the joint-driving unit to compensate for friction at the joints and weight of the robot due to the gravity.

Further, the ground impact absorbing mode may be a mode in which the controller may be configured to generate a virtual spring-damper in a longitudinal direction of a line connecting hip joint and an end of the leg to each other of the walking assist robot and operate the joint-driving unit, using impedance control to make the leg of the robot absorb shock from the outside. The ground impact absorbing & extension of virtual leg mode may be a mode in which the controller may be configured to set a balance point in a impedance control direction for the virtual legs as 0 degree and operate the joint-driving unit to cause the virtual leg to be pulled to be vertically erected while generating a virtual spring-damper in a longitudinal direction of a line connecting a hip joint and the end of the leg to each other of the walking assist robot and operating the joint-driving unit, using impedance control to make the leg of the robot absorb shock from the outside.

The pushing ground mode may be a mode in which the controller may be configured to operate the joint-driving unit to push the end of the leg to be controlled in −x and −y directions in a rectangular coordinate system (e.g., a front direction of the robot is +x direction and a direction vertically going away from the ground is +y direction in the rectangular coordinate system). The ready for swing phase mode may be a mode in which the controller may be configured to operate the joint-driving unit to push the end of the leg to be controlled in +x and +y directions in a rectangular coordinate system for easier swing of the leg (e.g., a front direction of the robot is +x direction and a direction vertically going away from the ground is +y direction in the rectangular coordinate system). When the control mode changes, the controller may be configured to apply a transition parameter, which changes from 0 to 1 along a sinusoidal path for a predetermined time interval, to adjust torque applied to the joint-driving unit in a previous mode and to adjust torque to be applied to the joint-driving unit in a new changed control mode.

According to another aspect of the present invention, a method for controlling a wearable walking assist robot may include: sensing pressure on the soles of the feet of a wearer by a pressure sensor unit; and determining, by a controller, gait phases of both a leg to be operated and the other leg based on the pressure sensed by the pressure sensor unit; and selecting one of a plurality of control modes set in advance based on the determined gait phases, and operating a joint-driving unit of the leg to be. The operating of a joint-driving unit may include: determining whether the control mode changes; and when the control mode changes, applying a transition parameter, which changes from 0 to 1 along a sinusoidal path for a predetermined time interval, to adjust torque applied to the joint-driving units in a previous mode and to adjust torque to be applied to the joint-driving units in a new changed control mode.

As described above, according to the walking assist robot and the control method thereof of various exemplary embodiments of the present invention, it may be possible to more simply determine the gait phases of both a leg to be operated and the other leg in accordance with the load applied to the toe and the heel of the feet. Further, determined gait phases and predetermined walking modes may be matched and then legs may be operated and thus, it may be possible to ensure improved walking assistance performance without a complex calculation process. According to the walking assist robot and the control method thereof of various exemplary embodiments of the present invention, since it may be possible to determine walking assistant force through Jacobian transform regardless of the number of axes, the applicable range is wide.

DETAILED DESCRIPTION

Wearable walking assist robots and methods of controlling the wearable walking assist robot according to various exemplary embodiments of the present invention will be described hereafter with reference to the accompanying drawings.

FIG. 1is a block diagram illustrating a wearable walking assist robot according to an exemplary embodiment of the present invention. Referring toFIG. 1, a wearable walking assist robot according to an exemplary embodiment of the present invention may include a pressure sensor unit10configured to sense pressure on the soles of feet of a user (e.g., on an underside on a bottom of a shoe) and a controller20configured to determine gait phases of both a leg to be operated and the other leg (e.g., a first and second leg) based on the pressure sensed by the pressure sensor unit10, select one of a plurality of control modes set in advance based on the determined gait phases, and operate a joint-driving unit30for the leg to be operated.

FIGS. 2A and 2Bare views showing a pressure sensor unit for a wearable walking assist robot according to an exemplary embodiment of the present invention; As shown inFIGS. 2A and 2B, the pressure sensor unit10applied to the wearable walking assist robot according to an exemplary embodiment of the present invention may include a plurality pressure sensors11aand11bdisposed on the bottom of a shoe (e.g., on the sole of a shoe) to detect pressure applied to the sole. In an exemplary embodiment of the present invention, the pressure sensor unit10may include a first pressure sensor11apositioned proximate to the toe and a second pressure sensor11bpositioned proximate to the heel. The arrangement of the pressure sensor unit10may be applied to both feet of the robot wearer. The exemplary embodiment shown inFIGS. 2A and 2Bis an example illustrating two pressure sensors11aand11bare attached to a shoe of a robot wearer, but various modifications may be considered, for example, three or more pressure sensors may be applied or pressure sensors may be disposed on a sole support member of a robot instead of the shoe of a robot wearer.

Moreover, the controller20may be configured to receive signals from the pressure sensor unit10that senses pressure on both soles of a robot wearer, determine gait phases of both a first leg to be operated and a second leg based on the sensed pressure, select one of a plurality of control modes set in advance based on the determined gait phases, and operate the joint-driving unit of the leg to be operated. In particular, the controller20may be configured to receive signals from the pressure sensor unit10configured to sense the pressure on both soles and determine gait phases of the legs in accordance with to which one of the toe and the heel of the soles pressure is applied. For example, the portion to which pressure is applied may be the toe and/or the heel of a foot, and thus, the controller20may be configured to determine gait phases of both a leg in a total of four cases for one sole.

Further, the controller20may be configured to operate the joint-driving units of the robot (e.g., one unit for each leg) based on the gait phases determined for the legs. Accordingly, the controller20may be configured to maintain controls modes for the gait phases of both the first leg to be operated and the second leg, and select control modes for the gait phases of both the first leg to be operate and the second leg and operate the joint-driving unit of the first leg to be operate, thereby providing force for assisting walking. The control technique of the controller20may be more clearly understood from the following description about the method for controlling a wearable walking assist robot according to various exemplary embodiments of the present invention.

FIG. 3is a flowchart illustrating a method for controlling a wearable walking assist robot according to an exemplary embodiment of the present invention. Referring toFIG. 3, a method for controlling a wearable walking assist robot according to an exemplary embodiment of the present invention may include: sensing, by a pressure sensor unit10, pressure applied to the soles of a user (S11); determining, by a controller20, gait phases of legs based on the sensed pressure (S12); selecting, by the controller20, one of a plurality of control modes set in advance based on the determined gait phases (S13); and operating, by the controller20, the joint-driving unit of the leg to be operated (S14). In other words, one leg is to be operated and the controller may be configured to determine the gait phase of each leg and then the joint-driving unit of the leg that is to be operated may be operated.

First, the sensing of pressure on feet (S11) may include detecting pressure at the toe and the heel of each sole of a user using the pressure sensor unit10, as described with reference toFIGS. 2A and 2B. For example, a total of four sensing signals may be provided to the controller20by two first pressure sensors11aconfigured to sense the pressure at the toe of each sole and two second pressure sensors11bconfigured to sense the pressure at the heel of each sole.

In the determining of gait phases (S12), the controller20may be configured to determine gait phases that correspond to the soles based on the four sensing signals. The following table 1 shows an example that the controller20determines gait phases based on the results of sensing pressure on a sole.

As shown in the table, the controller20may be configured to determine the gait phases for each leg as an air state, a heel-strike state, a support state, and a toe-off state. Determination of the gait phases may depend on the intensity of the sensing signals from the first pressure sensor11aand the second pressure sensor11band this determination technique is described below with reference toFIG. 4.FIG. 4is a view showing an example of sensing signals from a sensor unit of a wearable walking assist robot according to an exemplary embodiment of the present invention.

As shown inFIG. 4, the first pressure sensor11aand second pressure sensor11bon the left sole and the first pressure sensor11aand the second pressure sensor11bon the right sole may be configured to output voltages that correspond to the intensity of sensed pressure as sensing signals. The controller20may be configured to compare the intensity of the sensing signals from the pressure sensors with a threshold Th set in advance, determine that the portions corresponding to corresponding sensors are in contact with the ground when the sensing signals are greater than the threshold Th, and determine that the portions (the toe and the heel) corresponding to corresponding pressure sensors are not in contact with the ground when the sensing signals are less than the threshold Th.

Accordingly, the controller20may be configured to determine the gait phases of the legs of the soles, as in the table, in accordance with whether the toes and the heels of the feet are in contact with the ground sensed by the first pressure sensors11aand the second pressure sensors11b.When the gait phases of the legs are determined, the controller20may be configured to determine the control modes for the legs (S13). The controller20may then be configured to operate a leg by determining one of a plurality of control modes set in advance, based on the gait phases of both a first leg to be operated and a second leg.

FIG. 5is a view showing an example of determining control modes based on gait phases of legs in a wearable walking assist robot according to an exemplary embodiment of the present invention. Referring toFIG. 5, the controller20may be configured to select one of a total of six control modes in accordance with the gait phases of both the leg to be operated and the other leg. The six control modes may be determined in advance.

In an exemplary embodiment of the present invention, the six control modes may include a weight bearing mode M1, a compensation of mechanical impedance mode M2, a ground impact absorbing mode M3, a ground impact absorbing & extension of virtual leg mode M4, a pushing ground mode M5, and a ready for swing phase mode M6. For example, when the left leg is in the heel-strike state and the right leg is the support state, the controller20may be configured to operate the left leg in the ground impact absorbing & extension of virtual leg mode M4and the right leg in the weight bearing mode M1.

In an exemplary embodiment of the present invention, when the leg to be operated is in the air state and the support state, the compensation of mechanical impedance mode M2and the weight bearing mode M1are determined regardless of the gait phase of the other leg, and in other cases, the control mode may be determined in accordance with the state of the other leg (e.g., the second leg). The weight bearing mode M1of the six control modes is a mode for adjusting torque of the joint-driving unit (e.g., an actuator) disposed at a joint to push the wearer in the gravity direction (e.g., perpendicularly to the ground) with a desired force set in advance.

For example, a body, thighs, and calves are sequentially connected through joints in common walking assist robots. The body and the thighs are connected through a hip joint-driving unit and the thighs and the calves are connected through a knee-driving unit. An inertia sensor may be disposed on the body, and thus, the pitch angle of the body may be sensed, and an encoder31may be disposed at each of the joint-driving units30, and thus, the rotational angles of the joints may be sensed. The controller20may thus be configured to estimate the direction of gravity from the sensing information. The controller20may further be configured to create a Jacobian composed of an inertia sensor, a hip joint rotation angle, and a knee joint rotation angle and operate the driving units of the joints to push the ground with a predetermined force in the gravity direction.

Further, the compensation of mechanical impedance mode M2is provided to compensate for mechanical friction or weight of the walking assist robot. For example, the compensation of mechanical impedance mode M2is a mode in which the controller20may be configured to operate the joint-driving units to compensate for friction at the joints and the weight of links for the body, thighs, and calves. The compensation of mechanical impedance mode M2is a mode that enables a wearer to more easily move legs without feeling the weight of the legs or friction of the walking assist robot.

The ground impact absorbing mode M3is a mode for making the legs of the walking assist robot absorb shock from the outside, in which the controller20may be configured to generate virtual spring-dampers in the longitudinal directions of virtual legs (e.g., lines from the hip joints to the ends of the robot legs) and operate the driving units for the joints, using impedance control. The virtual legs may be lines from the hip joints to the ends of the legs of the walking assist robot and the controller20, in the ground impact absorbing mode M3, may be configured to generate virtual spring-dampers in the lines corresponding to the virtual legs, thereby absorbing shock from the outside.

The ground impact absorbing & extension of virtual leg mode M4is a mode in which the controller20may be configured to set a balance point in the impedance control direction for the virtual legs as 0 degree and additionally pull the virtual legs to vertically erect the legs while performing the mode M3. Additionally, the pushing ground mode M5is a mode performed when the legs are in a delayed stance phase, in which the controller20may be configured to push the upper body by operating the driving units for the joints to push the ends of the legs in −x and −y directions (e.g., horizontal directions). Finally, the ready for swing phase mode M6is a mode in which the controller20may be configured to operate the driving units for the joints to push the ends of the legs in +x and +y directions to allow the user to more easily swing the legs.

A technique of actually applying the control modes M1to M6to the robot is described in more detail hereafter.FIG. 6is a view simply showing the wearable walking assist robot according to an exemplary embodiment of the present invention, in which the robot may include a body B, a link T for a thigh, a link for a calf, a hip joint41connecting the body B and the thigh link T, and a knee joint42connecting the thigh link T and the calf link S. The body B may be equipped with an inertial measurement unit (IMU) to sense pitch angles of the body B, while the hip joint41and the knee joint42may be equipped with a joint-driving unit (for example, an actuator) operated by the controller20and an encoder31configured to sense the rotational angles of the joints. A pitch angle of the body sensed by the inertial measurement unit and a rotational angle of a joint sensed by the encoder31may be provided to the controller20.

Referring toFIG. 6, the end of a leg may be located with respect to the position of the hip joint in a rectangular coordinate system, as in the following Equation 1.

wherein L1 is the length of the thigh link T, L2 is the length of the calf link S, θpis the pitch angle of the body B, θhis the rotational angle of the hip joint, and θkis the rotational angle of the knee joint Further, the subscript i indicates the right leg.

Further, the end43of a leg may be located in a polar coordinate system as in the following Equation 2, using Equation 1.

A Cartesian Jacobian and a polar Jacobian based on the hip joint may be obtained from Equations 1 and 2, as in the following Equations 3 and 4.

whereinqis the rotational angles of the joints sensed by the encoder31, which can be expressed asqi=[θh,iθk,i]T.

Accordingly, the speed at the end43of the leg may be calculated in a rectangular coordinate system and a polar coordinate system, using the Jacobians, as in the following Equations 4 and 5.

The control modes M1to M6may be induced as follows, using the Jacobians induced as described above. The weight bearing mode M1, the pushing ground mode M5, and the ready for swing phase mode M6may be performed by feedfoward control for directly providing force in the x-axial and/or y-axial direction, so the following Equation 7 may be obtained.

In Equation 7, τh,Iand τk,iare torque at the joint-driving units of the hip joint and the knee joint, respectively, Fxare Fyare force set in advance to be applied to the ends of the legs in the weight bearing mode M1, the pushing ground mode M5, and the ready for swing phase mode M6.

For example, force may be applied only in the −y-axial direction in the weight bearing mode M1, so Fxmay be 0 and Fymay have a predetermined negative value. Further, force may be applied in the −x and −y directions in the pushing ground mode M5in the pushing ground mode M5, so Fxand Fyboth may have predetermined negative values, while force may be applied in +x and +y directions in the ready for swing phase mode M6, so Fxand Fyboth may have predetermined positive values.

Furthermore, the compensation of mechanical impedance mode M2is a mode in which the controller20may be configured to operate the joint-driving units to compensate for friction at the joints or weight due to the gravity and negative feedback may be applied in a rectangular coordinate system. The joints may be operated, as in the following Equation 8, in the ground impact absorbing mode” M3.

[τh,iτk,i]=-Jc,iT⁡[000Kd,y]⁢E.c,iEquation⁢⁢8
wherein Kd,yis a virtual constant that is experimentally determined and the unit may be Nsec/deg.

The ground impact absorbing mode M3is a mode for operating the driving units of the joints under the assumption that there is a virtual spring-damper in the longitudinal direction of each of the lines from the hip joints and the ends of the legs

Additionally, the ground impact absorbing & extension of virtual leg mode M4is a mode in which the controller M3may be configured to set a balance point in the impedance control for the virtual legs as 0 degree (θp,i=0 inFIG. 6) and additionally vertically pull the virtual legs, and the torque at the joint-driving units may be adjusted as in the following Equation 10.

[τh,iτk,i]=Jp,iT⁡([Kp,r000]⁢Δ⁢⁢Ep,i+[Kd,r00Kp,θ]⁢Δ⁢⁢E.p,i)Equation⁢⁢10
When Kp,θis 0 in Equation 10, it becomes Equation 9. In Equation 10, Kp,θis a value that is not 0 and the unit is N/deg.

FIG. 7is a view showing a control technique that is applied to a wearable walking assist robot and a method for controlling the wearable walking assist robot according to an exemplary embodiment of the present invention, in which the impedance control in a rectangular coordinate system indicated by ‘71’ may be applied in the compensation of mechanical impedance mode M2, the direct feedforward control indicated by ‘72’ may be applied in the weight bearing mode M1, the pushing ground mode M5, and the ready for swing phase mode M6, and the impedance control in a polar coordinate system indicated by ‘73’ may be applied in the ground impact absorbing mode M3and the ground impact absorbing & extension of virtual leg mode M4.

Moreover, an exemplary embodiment of the present invention may determine whether a control mode changes (S15) to prevent a discontinuous section due to a sudden change of torque at the points where control modes change, and when it is determined that a control mode has changed, it may be possible to perform control for interpolating the discontinuous torque of the joints (S16). For the control for interpolating the discontinuous torque that is performed in the step S16, a technique in which a controller20applies a transition parameter, which changes from 0 to 1 along a sinusoidal path for a predetermined time interval, to previous control torque and new control torque may be used.

The transition parameter ‘p’ is expressed as in the following Equation11and control torque applied to a transition period using the transition parameter may be expressed as in the Equation 12.

In Equations 11 and 12, tpis a predetermined time interval and SAT is a saturation function, in which SAT (x, a, b) has the value x for a<x<b, the value a for a <x, and the value b for x<b. Further, τh,posteriorand τk,posteriorare control torque at the joint-driving units in the changed control mode and τt,priorand τk,priorare control toque of the joint-driving units in the previous control mode before changed.

As described above, according to a walking assist robot and a control method thereof of various exemplary embodiments of the present invention, it may be possible to more simply determine the gait phases of both a leg to be operated and the other leg based on load applied to the toe and the heel of the feet. Further, determined gait phases and predetermined walking modes may be matched and then legs may be operated, and thus, it may be possible to ensure improved walking assistance performance without a complex calculation process. According to a walking assist robot and a control method thereof of various exemplary embodiments of the present invention, since it may be possible to determine waling assistant force through simple Jacobian transform regardless of the number of axes, the applicable range is wide.

Although the present invention was described with reference to specific exemplary embodiments shown in the drawings, it is apparent to those skilled in the art that the present invention may be changed and modified in various ways without departing from the scope of the present invention, which is described in the following claims.