Patent Publication Number: US-2021162263-A1

Title: Method and device for providing resistance to user of wearable device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0158819 filed on Dec. 3, 2019, and Korean Patent Application No. 10-2020-0136562 filed on Oct. 21, 2020, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Field 
     At least one example embodiment relates to a method and/or device for providing resistance to a user of a wearable device. For example, at least one example embodiment relates to a method and/or device for providing resistance to a user of a wearable device without providing energy to a motor of the wearable device. 
     2. Description of the Related Art 
     A change into aging societies has contributed to a growing number of people who experience inconvenience and pain from reduced muscular strength or joint problems due to aging. Thus, there is a growing interest in walking assist devices that enable elderly users or patients with reduced muscular strength or joint problems to walk with less effort. 
     SUMMARY 
     Some example embodiments relate to a method of operating a wearable device to provide a resistance force to a user. 
     In some example embodiments, the method includes measuring, via a sensor, a first angle of a first joint of the user, determining a resistance level to apply to the first joint based on the first angle, determining a connection ratio between a connected time for which a motor driver circuit electrically connected to a motor of the wearable device is controlled to be a closed loop and a disconnected time for which the motor driver circuit is controlled to be an open loop, based on the resistance level, and controlling the motor through the motor driver circuit based on the connection ratio. 
     In some example embodiments, the motor driver circuit may include at least one switch configured to be controlled based on the connection ratio. 
     In some example embodiments, the connection ratio may be represented by a pulse width modulation (PWM). 
     In some example embodiments, the resistance level to be provided to the user may be adjusted based on the connection ratio such that as the connected time for which the motor driver circuit is controlled to be the closed loop increases, the resistance force may increase. 
     In some example embodiments, when the motor driver circuit is controlled to be the closed loop, the motor may operate as a generator with respect to an external force by the user. 
     In some example embodiments, when the motor operates as the generator, the method may further include charging a battery of the wearable device based on energy generated by the generator. 
     In some example embodiments, the method may further include receiving, from the user, an instruction to set an operation mode of the wearable device to an exercise mode. 
     In some example embodiments, when the exercise mode is set, the motor may not be provided with energy from the battery of the wearable device. 
     In some example embodiments, the method may further include receiving, from the user, an instruction to set an operation mode of the wearable device to an assistance mode, calculating an assistance torque value to apply to the first joint based on the first angle in response to the assistance mode being received, and providing an assistance force to the user by controlling the motor based on the assistance torque value. 
     Some example embodiments relate to a wearable device configured to provide a resistance force to a user. 
     In some example embodiments, the wearable device includes a memory configured to store a program that includes instructions to provide the resistance force to the user, a sensor configured to measure a first angle of a first joint of the user, a motor driver circuit, a motor electrically connected to the motor driver circuit, and a processor configured to execute the program to measure, via the sensor, the first angle of the first joint of the user, determine a resistance level to apply to the first joint based on the first angle, determine a connection ratio between a connected time for which the motor driver circuit is controlled to be a closed loop and a disconnected time for which the motor driver circuit is controlled to be an open loop based on the resistance level, and control the motor through the motor driver circuit based on the connection ratio. 
     In some example embodiments, the motor driver circuit may include at least one switch configured to be controlled based on the connection ratio. 
     In some example embodiments, the connection ratio may be represented by a PWM, and the resistance force to be provided to the user may be adjusted based on the connection ratio such that, as the connected time for which the motor driver circuit is controlled to be the closed loop increases, the resistance force may increase. 
     In some example embodiments, when the motor driver circuit is controlled to be the closed loop, the motor may operate as a generator with respect to an external force by the user. 
     In some example embodiments, when the motor operates as the generator, the processor is further configured to charge a battery of the wearable device based on energy generated by the generator. 
     In some example embodiments, the processor is further configured to receive, from the user, an instruction to set an operation mode of the wearable device to an exercise mode, and determine the resistance level to apply to the first joint based on the exercise mode and the first angle. 
     In some example embodiments, when the exercise mode is set, the motor may not be provided with energy from the battery by the wearable device. 
     In some example embodiments, the processor is further configured to, receive, from the user, an instruction to set an operation mode of the wearable device to an assistance mode, calculate an assistance torque value to apply to the first joint based on the first angle in response to the assistance mode being received, and provide an assistance force to the user by controlling the motor based on the assistance torque value. 
     Additional aspects of example embodiments will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the accompanying drawings of which: 
         FIGS. 1A through 1D  are diagrams illustrating an example of a wearable device according to at least one example embodiment; 
         FIG. 2  is a diagram illustrating an example of a wearable device communicating with an electronic device according to at least one example embodiment; 
         FIG. 3  is a diagram illustrating an example of a gait state according to at least one example embodiment; 
         FIG. 4  is a diagram illustrating an example of a transition in gait state according to at least one example embodiment; 
         FIG. 5  is a diagram illustrating an example of a trajectory of an ankle joint angle with respect to a gait cycle according to at least one example embodiment; 
         FIG. 6  is a diagram illustrating an example of a trajectory of an ankle torque with respect to a gait cycle according to at least one example embodiment; 
         FIGS. 7 through 10  are diagrams illustrating an example of a motor driver circuit of a wearable device according to at least one example embodiment; 
         FIG. 11  is a flowchart illustrating an example of a method of providing a resistance force according to at least one example embodiment; 
         FIG. 12  is a diagram illustrating an example of a resistance force profile output from a user terminal according to at least one example embodiment; 
         FIG. 13  is a flowchart illustrating another example of a method of providing a resistance force according to at least one example embodiment; 
         FIG. 14  is a diagram illustrating an example of a motor driver circuit of an open loop according to at least one example embodiment; 
         FIGS. 15 and 16  are diagrams illustrating examples of a motor driver circuit of a closed loop according to at least one example embodiment; 
         FIG. 17  is a diagram illustrating an example of a motor driver circuit of a closed loop according to at least one example embodiment; 
         FIG. 18  is a diagram illustrating an example of a motor driver circuit of a closed loop including a braking resistor according to at least one example embodiment; 
         FIG. 19  is a diagram illustrating an example of a motor driver circuit of a closed loop including a resistor according to at least one example embodiment; 
         FIG. 20  is a diagram illustrating an example of a motor driver circuit of a closed loop including a brushless direct current (BLDC) motor according to at least one example embodiment; 
         FIG. 21  is a diagram illustrating an example of a driver of a wearable device according to at least one example embodiment; and 
         FIGS. 22 through 24  are diagrams illustrating an example of a whole body-type wearable device according to at least one example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, some example embodiments will be described in detail with reference to the accompanying drawings. Regarding the reference numerals assigned to the elements in the drawings, it should be noted that the same elements will be designated by the same reference numerals, wherever possible, even though they are shown in different drawings. Also, in the description of embodiments, detailed description of well-known related structures or functions will be omitted when it is deemed that such description will cause ambiguous interpretation of the present disclosure. 
     It should be understood, however, that there is no intent to limit this disclosure to the particular example embodiments disclosed. On the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the example embodiments. Like numbers refer to like elements throughout the description of the figures. 
     In addition, terms such as first, second, A, B, (a), (b), and the like may be used herein to describe components. Each of these terminologies is not used to define an essence, order or sequence of a corresponding component but used merely to distinguish the corresponding component from other component(s). It should be noted that if it is described in the specification that one component is “connected,” “coupled,” or “joined” to another component, a third component may be “connected,” “coupled,” and “joined” between the first and second components, although the first component may be directly connected, coupled or joined to the second component. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure of this application pertains. Terms, such as those defined in commonly used dictionaries, are to be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art, and are not to be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Also, in the description of example embodiments, detailed description of structures or functions that are thereby known after an understanding of the disclosure of the present application will be omitted when it is deemed that such description will cause ambiguous interpretation of the example embodiments. 
     Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are shown. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. 
     Hereinafter, examples will be described in detail with reference to the accompanying drawings, and like reference numerals in the drawings refer to like elements throughout. 
       FIGS. 1A through 1D  are diagrams illustrating an example of a wearable device according to at least one example embodiment. 
     Referring to  FIGS. 1A through 1C , a wearable device  100  may be worn on a user and configured to assist the user in walking more readily. For example, the wearable device  100  may be a device that assists the user in walking. The wearable device  100  may also be an exercise device that provides an exercise function by providing the user with a resistance force to assist the user in doing an exercise. The resistance force to be provided to the user may not be a force that is actively applied to the user, for example, a force output by a device such as a motor, but a force that hinders a movement of the user, for example, a force acting in a direction opposite to a direction in which the user moves. That is, the resistance force may also be referred to as an exercise load. 
     Although  FIGS. 1A and 1B  illustrate an example of a hip-type wearable device, a type of a wearable device is not limited to the illustrated hip type, and the wearable device may be provided in a type that supports a whole lower body, supports a portion of the lower body, for example, a portion of the lower body up to a knee and a portion of the lower body up to an ankle, or supports a whole body. 
     Although example embodiments to be described hereinafter with reference to  FIGS. 1A and 1B  are applicable to a hip-type wearable device, for example, the wearable device  100 , the example embodiments are not limited to the hip-type wearable device, but applicable to all types of wearable devices. 
     Referring to  FIGS. 1A through 1D , the wearable device  100  includes a driver  110 , a sensor  120 , an inertial measurement unit (IMU)  130 , a controller  140 , and a battery  150 . 
     The driver  110  includes a motor  114  and a motor driver circuit  112  configured to drive the motor  114 . The sensor  120  includes at least one sensor  121 . The controller  140  includes a processor  142 , a memory  144 , and an input interface  146 . Although a single sensor  121 , a single motor driver circuit  112 , and a single motor  114  are illustrated in  FIG. 1C , examples are not limited thereto. For another example, a wearable device  100 - 1  may include a plurality of sensors  121  and  121 - 1 , a plurality of motor driver circuits  112  and  112 - 1 , and a plurality of motors  114  and  114 - 1 , as illustrated in  FIG. 1D . In addition, according to implementation, the wearable device  100  may include a plurality of processors. The number of motor driver circuits, the number of motors, or the number of processors may vary according to a body part on which the wearable device  100  is to be worn. 
     The following descriptions of the sensor  121 , the motor driver circuit  112 , and the motor  114  are also applicable to the sensor  121 - 1 , the motor driver circuit  112 - 1 , and the motor  114 - 1  illustrated in  FIG. 1D . 
     The driver  110  may drive hip joints of the user wearing the wearable device  100 . For example, the driver  110  may be disposed in a portion of a right hip of the user and/or a portion of a left hip of the user. The driver  110  may be additionally disposed in a portion of knees of the user and a portion of ankles of the user. The driver  110  includes the motor  114  configured to generate a rotational torque and the motor driver circuit  112  configured to drive the motor  114 . 
     The sensor  120  may measure a hip joint angle of the user when the user walks. Here, information associated with the hip joint angle sensed by the sensor  120  may include an angle of a right hip joint, an angle of a left hip joint, a difference between the angle of the right hip joint and the angle of the left hip joint, and/or a hip joint movement direction. For example, the sensor  121  may be disposed in the driver  110 . Based on a position of the sensor  121 , the sensor  120  may additionally measure a knee angle of the user and an ankle angle of the user. 
     For example, the sensor  120  may include a potentiometer. The potentiometer may sense an R-axis joint angle and an L-axis joint angle, and an R-axis joint angular velocity and an L-axis joint angular velocity, based on a walking motion of the user. 
     The IMU  130  may measure acceleration information and pose information when the user walks. For example, the IMU  130  may sense an X-axis acceleration, a Y-axis acceleration, and a Z-axis acceleration, and an X-axis angular velocity, a Y-axis angular velocity, and a Z-axis angular velocity, based on a walking motion of the user. 
     The wearable device  100  may detect a point at which a foot of the user lands based on the acceleration information measured by the IMU  130 . 
     In addition, a pressure sensor (not shown) may be disposed on a sole of a foot of the user and detect a point in time at which the foot of the user lands. 
     In addition to the sensor  120  and the IMU  130 , the wearable device  100  may include other sensors configured to sense a change in a quantity of motion of the user or a change in biosignal based on a walking motion of the user. The sensors may include an electromyogram (EMG) sensor, for example. 
     According an example embodiment, the processor  142  of the controller  140  may control the driver  110  to provide a resistance force to the user. The driver  110  may provide the resistance force to the user through back-drivability of the motor  114  without outputting a torque to the user. Here, back-drivability of the motor  114  may indicate reactivity of a rotation axis of the motor  114  in response to an external force. For example, high back-drivability of the motor  114  may indicate readily responding to an external force applied to the rotation axis of the motor  114 , that is, the rotation axis of the motor  114  rotates readily. For example, even though the same external force is applied to the rotation axis of the motor  114 , a degree of a rotation of the rotation axis of the motor  114  may directly vary depending on a level of back-drivability. 
     A method of providing a resistance force to a user will be described in detail hereinafter with reference to  FIGS. 7 through 21 . 
     According another example embodiment, the processor  142  of the controller  140  may control the driver  110  to output a torque, for example, an assistance torque, to assist the user in walking. For example, the driver  110  may be provided as two drivers for the right hip and the left hip, respectively, in the wearable device  100  of the hip type, and the controller  140  may output a control signal for controlling the driver  110  such that the torque is generated. 
     The driver  110  may generate the torque based on the control signal output by the controller  140 . Here, a torque value used to generate the torque may be set externally or set by the controller  140 . For example, to indicate a magnitude of the torque value, the controller  140  may use a magnitude of a current with respect to a signal transmitted to the driver  110 . That is, as the magnitude of the current received by the driver  110  increases, the torque value may increase. 
     The battery  150  may provide power to components of the wearable device  100 . For example, there may be a circuit, for example, a power management integrated circuit (PMIC) that is configured to convert power of the battery  150  to an operating voltage of each of the components of the wearable device  100  and then provide the power to the components. In addition, the battery  150  may provide or not provide power to the motor  114  based on an operation mode of the wearable device  100 . That is, the battery  150  may provide power to the motor  114  in an assistance mode, and not provide power to the motor  114  in an exercise mode. Thus, less power may be consumed in the battery  150  in the exercise mode, and thus an available time for using the wearable device  100  may increase. 
       FIG. 2  is a diagram illustrating an example of a wearable device communicating with an electronic device according to at least one example embodiment. 
     Referring to  FIG. 2 , the wearable device  100  may communicate with an electronic device  200 . The electronic device  200  may include, for example, a smartphone, a tablet personal computer (PC), a smart watch, eyeglasses, and the like, but examples are not limited thereto. For example, the electronic device  200  may be an electronic device associated with a user of the wearable device  100 . For another example, the user may do exercise together with a trainer with the wearable device  100  on. In such a case, the electronic device  200  may be an electronic device associated with the trainer. 
     According to implementation, the wearable device  100  and the electronic device  200  may communicate with each other via a server (not shown) using a short-range wireless communication method or a cellular mobile communication method. 
     The electronic device  200  may display, on a display  200 - 1 , a user interface (UI) for controlling an operation of the wearable device  100 . For example, the UI may include at least one softkey that enables the user to control the wearable device  100 . 
     The user or the trainer may input a control instruction for controlling an operation of the wearable device  100  through the UI on the display  200 - 1  of the electronic device  200 . The electronic device  200  may transmit the control instruction to the wearable device  100 . The wearable device  100  may operate according to the received control instruction, and transmit a control result to the electronic device  200 . The electronic device  200  may display a message indicating control completion on the display  200 - 1  of the electronic device  200 . 
       FIG. 3  is a diagram illustrating an example of a gait state according to at least one example embodiment. 
     Referring to  FIG. 3 , a gait state or a gait phase of one of legs of a user of a wearable device may be defined (or, alternatively, predefined). For example, the gait state may include a stance and a swing. The swing indicates a state in which a foot is away from the ground. A gait state of a left leg of the user may include a left stance (LSt) and a left swing (LSw), and a gait state of a right leg of the user may include a right stance (RSt) and a right swing (RSw). 
     In a finite-state machine (FSM), a gait cycle of such gait states or phases may be mapped in advance. For example, 0% of the gait cycle may be mapped at a point in time at which a stance starts, 60% of the gait cycle may be mapped at a point in time at which a swing starts, and 100% of the gait cycle may be mapped at a point in time immediately before a next stance starts. 
     According to an example embodiment, the stance and the swing may be more elaborately classified into a plurality of states. The stance may be classified into, for example, an initial contact, a weight bearing, a middle stance, a terminal stance, and a pre-swing. In addition, the swing may be classified into, for example, an initial swing, a middle swing, and a terminal swing. However, the classification of the stance and the swing is not limited to the example classification described in the foregoing, and the stance and the swing may be differently classified according to examples. 
       FIG. 4  is a diagram illustrating an example of a transition in gait state according to at least one example embodiment. 
     Referring to  FIG. 4 , according to a general gait mechanism, a gait state of each of both legs may include a stance and a swing, and the stance and the swing may occur alternately for walking. 
     A gait state  410  of a right leg according to a change  400  in the right leg by walking may include a right stance and a right swing. Here, the stance may include a weight bearing, a middle stance, and a terminal stance. However, examples are not limited to the illustrated example. A gait state  420  of a left leg according to a change (not shown) in the left leg with respect to the change  400  in the right leg may include a left stance and a left swing. 
     When muscular strength of an ankle of a user weakens due to aging or a disease, the user may experience inconvenience when walking. For example, when a leg starts swinging, a tip of a foot of the leg needs to be raised, but if not the swinging leg may hit the ground. That is, in such a case of a foot drop, there may be a risk of a fall. To prevent such a risk, an angle of the ankle may need to be adjusted based on a progression of a gait state or phase or a change in the gait state or phase. Thus, a wearable device may be provided to those who may have difficulty in adjusting an angle of an ankle themselves due to reduced muscular strength of the ankle. The wearable device may be worn around an ankle of a user and output an assistance torque based on a value sensed in association with walking or gait of the user. The assistance torque may be used to adjust an angle of the ankle of the user. 
     Although the example embodiment described above relates to assisting or supporting an ankle, the example embodiment may also be similarly and substantially applied to assisting or supporting a hip joint or a knee. 
       FIG. 5  is a diagram illustrating an example of a trajectory of an ankle joint angle with respect to a gait cycle according to at least one example embodiment. 
     Referring to  FIG. 5 , when a user walks according to a general gait mechanism, an ankle joint angle of the user may change as shown in a trajectory  500 . Although an ankle joint angle may change even in the same gait state based on a stride and a walking speed, trajectories of an ankle joint angle with respect to one gait cycle may develop in a similar pattern. The trajectory  500  may have an illustrated range of changes in a progression of a gait cycle. The range of changes may include weight bearing  510 , middle stance  520 , terminal stance  530  and swing  540 . 
     However, the illustrated trajectory  500  may not be shown in an ankle joint angle of a leg of a patient who may experience inconvenience with the leg. Here, when the ankle joint angle of the leg from which the patient may experience inconvenience is adjusted such that the ankle joint angle of the leg has the trajectory  500 , a gait mechanism of the patient may be improved. 
     Although a trajectory of an ankle joint angle has been described above with reference to  FIG. 5 , the foregoing description may be similarly and substantially applied to a hip joint ankle and a knee joint. 
       FIG. 6  is a diagram illustrating an example of a trajectory of an ankle torque with respect to a gait cycle according to at least one example embodiment. 
     Referring to  FIG. 6 , what is to be described hereinafter with reference to  FIG. 6  may be applied to a case in which the wearable device  100  operates in an assistance mode in which the wearable device  100  assists a user wearing the wearable device  100  in walking. A case in which the wearable device  100  operates in an exercise mode will be described in detail with reference to  FIGS. 7 through 21 . 
     When a user walks according to a general gait mechanism, an ankle torque to be output by an ankle joint of the user may change as shown in a trajectory  600 . A positive value of the ankle torque may increase an ankle joint angle, for example, enabling plantar flexion. A negative value of the ankle torque may decrease the ankle joint angle, for example, enabling dorsiflexion. 
     According to an example embodiment, a first portion  610  of the trajectory  600  of the ankle torque that corresponds to a segment after a push-off occurs may be an assistance torque value for the dorsiflexion to prevent a foot drop. The assistance torque value for the dorsiflexion may be a negative value. 
     A patient who may experience inconvenience with his/her leg may not generate a sufficient assistance torque himself/herself, and thus the patient may wear a wearable device on the leg from which the patient experiences inconvenience to receive the assistance torque. The wearable device may output the assistance torque through a driver and adjust an ankle angle. Here, the assistance torque for adjusting the ankle angle may need to be output at a desirable timing so that the user may not experience inconvenience. For example, a relatively high assistance torque for increasing the ankle angle may need to be provided at a time at which the leg performs a push-off. For example, the timing may be determined by directly determining a gait state of the leg from which the patient experiences inconvenience. For another example, the timing may be determined by indirectly determining a gait state of the leg based on a gait state of the other normal leg from which the patient does not experience inconvenience. 
     Hereinafter, a structure of the motor driver circuit  112  included in the driver  110  that enables the wearable device  100  to operate in an exercise mode that does not require use of the battery  150  will be described in detail with reference to  FIGS. 7 through 10 . 
       FIGS. 7 through 10  are diagrams illustrating an example of a motor driver circuit of a wearable device according to at least one example embodiment. 
     Referring to  FIG. 7 , the motor driver circuit  112  is an H-bridge circuit and includes a plurality of switches, for example, a first switch  710 , a second switch  720 , a third switch  730 , and a fourth switch  740 . The motor driver circuit  112  is connected to the motor  114 . 
     For example, when the first switch  710  and the fourth switch  740  are closed and the second switch  720  and the third switch  730  are open under the control of the processor  142 , a closed loop including the battery  150  may be formed. Thus, power may be provided to the motor  114  from the battery  150 . In such an example, the motor  114  may rotate in a first direction. 
     For another example, when the second switch  720  and the third switch  730  are closed and the first switch  710  and the fourth switch  740  are open under the control of the processor  142 , a closed loop including the battery  150  may be formed. Thus, power may be provided to the motor  114  from the battery  150 . In such an example, the motor  114  may rotate in a second direction which is opposite to the first direction. 
     Referring to  FIG. 8 , the motor driver circuit  112  may be controlled such that a closed loop including the battery  150  is formed. The battery  150  may provide power to the motor  114 . The motor  114  may rotate in a direction corresponding to a direction of a current. For example, when the wearable device  100  operates in an assistance mode, the processor  142  may control the motor driver circuit  112  such that the closed loop including the battery  150  is formed. 
     Dissimilar to what is described above with reference to  FIGS. 7 and 8 , the motor driver circuit  112  may also be controlled such that the battery  150  is excluded. Such an example will be described hereinafter with reference to  FIGS. 9 and 10 . The example of controlling the motor driver circuit  112  as described hereinafter with reference to  FIGS. 9 and 10  may be used when an operation mode of the wearable device  100  is an exercise mode. 
     Referring to  FIG. 9 , the processor  142  may block an electrical connection between the battery  150  and the motor  114  by opening the first switch  710  and the second switch  720 . In an exercise mode, the first switch  710  and the second switch  720  may remain opened. In the exercise mode, a lower driver circuit including the third switch  730  and the fourth switch  740  connected to the motor  114  may only be controlled. 
     The processor  142  may apply control signal  1  to the third switch  730  and apply control signal  2  to the fourth switch  740  such that a control state of the motor driver circuit  112  changes between a first control state and a second control state. Here, control signal  1  and control signal  2  may be in a form of a PWM in which a high value and a low value repeatedly alternate and have a duty ratio. The duty ratio may indicate a connection ratio. In a case in which one period is T and a time for which a high value is maintained in one period T is t H , the duty ratio is t H /T. Although the outputting of control signals  1  and  2  by the processor  142  is described herein, examples are not limited thereto. For example, the processor  142  may output a single control signal, and the output control signal may be divided by a separate circuit. Control signals obtained through the dividing may be applied to the third switch  730  and the fourth switch  740 , respectively. 
     For example, when control signals  1  and  2  are high values, a (+) terminal and a (−) terminal of the motor  114  may be connected to be in an equipotential state. That is, in the first control state, the (+) terminal and the (−) terminal of the motor  114  may be electrically connected to have the same potential or voltage. 
     In the first control state, the motor  114  may form a closed loop with the ground without an electrical connection with the battery  150 . Thus, the first control state may also be referred to as a closed loop state of the motor  114  free of the electrical connection with the battery  150 . 
     When a user moves in the first control state, the motor  114  disposed around a corresponding joint of the user may rotate by the movement of the joint of the user. By such a rotation, an electromotive force or a potential difference may occur in the motor  114 . The terminals of the motor  114  in the first control state may be in the equipotential state, and thus a rotation resistance may be generated in the motor  114  to reduce the generated electromotive force. This rotation resistance may be provided to the user as a resistance force. 
     For example, when control signals  1  and  2  are low values, the (+) terminal and the (−) terminal of the motor  114  may be electrically opened. In the second control state, there is no electrical connection to the motor  114 . Thus, the second control state may also be referred to as an open loop state of the motor  114 . 
     When a user moves in the second control state, the motor  114  may rotate by the movement of the user. In the second control state, the (+) terminal and the (−) terminal of the motor  114  may be electrically opened, and thus an electromotive force may not occur in the motor  114  and the resistance force may not be output. That is, back-drivability of the motor  114  may increase, and a frictional force by a gear ratio may only be felt or experienced by the user as the resistance force. 
     Based on the high values and the low values of control signals  1  and  2  may repeat according to a PWM signal, and thus the control sate of the motor driver circuit  112  may be switched repeatedly between the first control state and the second control state. 
     The processor  142  may adjust a magnitude of the resistance force by controlling a duty ratio of each of control signals  1  and  2 . For example, when a time for which a high value is maintained increases in a period of each of control signals  1  and  2  (that is, a time for which a low value is maintained decreases), a ratio of the motor  114  operating in the first control state in a period of each of control signals  1  and  2  may increase compared to a ratio of the motor  114  operating in the second control state in a period of each of control signals  1  and  2 . Thus, an intensity of the resistance force to be output to the user may increase. In contrast, when a time for which a high value is maintained decreases in a period of each of control signals  1  and  2  (that is, a time for which a low value is maintained increase), a ratio of the motor  114  operating in the second control state in a period of each of control signals  1  and  2  may increase compared to a ratio of the motor  114  operating in the first control state in a period of each of control signals  1  and  2 . Thus, an intensity of the resistance force to be output to the user may decrease. 
     In the exercise mode, the wearable device  100  may output a resistance force without providing power of the battery  150  to the motor  114 , and it is thus possible to consume less power of the battery  150  and increase an available time for using the wearable device  100 . When power of the battery  150  is provided to the motor  114 , the motor  114  may malfunction. However, in the exercise mode, the power of the battery  150  may not be provided to the motor  114 , and thus a potential malfunction of the motor  114  may be prevented and the safety of the wearable device  100  may be improved further. 
     Referring to  FIG. 10 , the motor driver circuit  112  may be controlled not to include the battery  150 . The battery  150  may be electrically disconnected from the motor  114 . Based on a connection state of the motor driver circuit  112 , the motor  114  may generate an electromotive force (in a case in which the connection state corresponds to a closed loop) by an external force or may not generate the electromotive force (in a case in which the connection state corresponds to an open loop). 
       FIG. 11  is a flowchart illustrating an example of a method of providing a resistance force according to at least one example embodiment. 
     Operations  1110  through  1180  to be described hereinafter with reference to  FIG. 11  may be performed by the wearable device  100 . Although the wearable device  100  is described above as being worn on a lower body of a user, examples of the wearable device  100  are not limited thereto. For example, the wearable device  100  may be worn on an upper body of a user. For another example, the wearable device  100  may be worn throughout a whole body of a user. 
     Referring to  FIG. 11 , in operation  1110 , the wearable device  100  receives, from a user, an operation mode that controls the wearable device  100 . The operation mode may include an exercise mode and an assistance mode, and the received operation mode may be the exercise mode or the assistance mode. 
     For example, the user may transmit the operation mode to the wearable device  100  through a user terminal connected to the wearable device  100  through a wireless network. The wearable device  100  may receive the operation mode through a communication module. The wireless network may include, for example, a cellular network, a Bluetooth network, a WiFi network, and the like, but examples are not limited thereto. 
     For another example, the user may input the operation mode through the input interface  146  of the wearable device  100 . The input interface  146  may include, for example, a physical button for receiving an input of the user, a software button formed based on a touch panel, a display and an indicator for outputting a state of the wearable device  100 , and the like. The indicator may be, for example, a light-emitting diode (LED), but examples are not limited thereto. 
     A plurality of dynamic modes that control the wearable device  100  may be provided in advance in the wearable device  100 . 
     For example, the wearable device  100  may control an operation of the wearable device  100  through a control algorithm. The control algorithm may be an algorithm that outputs a control value corresponding to an input including, for example, an input from the user and an input from the sensor  120 , the IMU  130 , and the like. For example, the control algorithm may operate based on a control table indicating an output value corresponding to input values. 
     For another example, the wearable device  100  may control an operation of the wearable device  100  based on a neural network corresponding to each operation mode rather than through a control algorithm. The neural network may be an artificial neural network, and be trained in advance through machine learning. The neural network may be, for example, a convolutional neural network (CNN), a recurrent neural network (RNN), a deep neural network (DNN), and a combination thereof, but examples are not limited thereto. 
     In response to an input being received, the neural network may output a result for the input. For example, when an angle of a joint is input, a neural network trained with the assistance mode may determine a gait state corresponding to the angle and calculate an assistance torque value for the joint. For another example, when an angle of a joint is input, a neural network trained with the exercise mode may determine a gait state corresponding to the angle and calculate and output a resistance level for the joint. In this example, the resistance level to be calculated may vary based on an exercise level set by the user. For example, when a higher exercise level is set, a higher resistance level may be calculated. 
     In operation  1120 , the wearable device  100  measures an angle of a joint of the user using the sensor  121 . The sensor  121  may be an angle sensor, and measure an angle of at least one of a hip joint, a knee joint, or an ankle joint. Alternatively, respective angles of a plurality of joints may be measured. The angles of the joints that are simultaneously measured may form a joint angle set with respect to a certain time. The joint angle set may be used to determine a level of a gait cycle of the user. For example, a leg pose of the user may be determined based on a hip joint angle, a knee joint angle, and an ankle joint angle. In addition, the joint angle set may additionally include an angular acceleration calculated based on a variation in the same joint angle. 
     Although the hip joint, the knee joint, and the ankle joint are described herein as examples, the foregoing description may also be applied to other joints including, for example, a shoulder joint, an elbow joint, and a wrist joint. 
     Although operation  1120  is illustrated as being performed between operations  1110  and  1130 , operation  1120  may be performed continuously as long as power is provided to the sensor  121 . The sensor  121  may generate data including, for example, a joint angle, on a preset period. That is, the joint angle may be measured successively and continuously. 
     In operation  1130 , the processor  142  of the wearable device  100  determines whether the operation mode is the exercise mode or the assistance mode. When the operation mode is the exercise mode, a resistance force may be provided to the user. When the operation mode is the assistance mode, an assistance force may be provided to the user. To provide the resistance force to the user, operations  1140  through  1160  may be performed. To provide the assistance force to the user, operations  1170  and  1180  may be performed. 
     Although it is described that the operation mode is determined in operation  1130 , whether the operation mode is the assistance mode may be determined in operation  1130  and then whether the operation mode is the exercise mode may be determined when the operation mode is determined not to be the assistance mode. Alternatively, whether the operation mode is the exercise mode may be determined in operation  1130  and then whether the operation mode is the assistance mode may be determined when the operation mode is determined not to be the exercise mode. 
     According to an example embodiment, when the user walks, the exercise mode may be applied in the entire gait state, or selectively applied in a certain gait state. For example, the exercise mode may be applied only in a swing state between a stance state and the swing state as the user chooses. Here, to determine a current gait state of the user, the angle of the joint of the user may be used. 
     In operation  1140 , when the operation mode is the exercise mode, the processor  142  of the wearable device  100  determines the resistance level for the joint based on the measured angle of the joint. For example, through the control algorithm, a resistance level for an input of a joint angle may be determined. For another example, a resistance level may be output by inputting a joint angle to a neural network determined based on the operation mode. 
     The resistance level refers to a level or magnitude of a resistance force the user may feel or experience. For example, when the user desires to receive the same resistance force for an entire gait motion (or a running motion), the same resistance level may be determined for the entire gait motion. For another example, when the user desires to receive a different resistance force for a certain state or phase of a gait mechanism (e.g., a swing state), a level of a gait cycle of the user may be determined based on a joint angle (e.g., a joint angle set) and a resistance level corresponding to the determined level of the gait cycle may be determined. The level of the gait cycle may change in real time, and thus the resistance level to be determined may change in real time. 
     According to an example embodiment, a resistance force profile generated in advance may indicate a trajectory of a resistance level with respect to an entire gait cycle. Based on the resistance force profile with respect to the entire gait cycle, a resistance level corresponding to a level of a current gait cycle may be determined. 
     The resistance profile may be adjusted by the user. For example, the user may adjust a resistance level of at least a portion of the resistance force profile through the input interface  146  of the wearable device  100  or a user terminal connected to the wearable device  100 . That is, the user may adjust a resistance level of at least a portion of the resistance force profile to set an exercise method desired by the user. The resistance force profile will be described in detail with reference to  FIG. 12 . 
     Here, a neural network for each operation mode may be pretrained by a manufacturer of the wearable device  100 . In addition, the neural network may be additionally trained, for example, fine-tuned, by the user of the wearable device  100 . For example, the user may input feedback on a current output of the neural network to the wearable device  100 , and the processor  142  may additionally train the neural network such that the feedback is reflected. For example, to train the neural network, backpropagation or reinforcement learning may be used, but examples are not limited thereto. 
     According to an example embodiment, the resistance level may be determined based on a position and an angle of a joint of the user. For example, a target pose of a left leg of the user may be set in advance, and a resistance level may be determined based on a difference between the target pose and a current pose of the user. In this example, when the difference between the target pose and the current pose is great, the resistance level may be determined to be small. In contrast, when the difference between the target pose and the current pose is small, the resistance level may be determined to be great. In addition, when the current pose corresponds to the target pose, a maximum resistance level may be provided to the user. 
     For example, in a case in which a pose of lifting a thigh by a preset or greater angle is set as the target pose, a resistance level may be greater when the user lifts the thigh higher, and the user may feel or experience a strongest resistance force from the target pose. 
     To determine a resistance level, a damping control technology to which a muscle model is applied may be used. When resistance levels determined through the damping control technology change in sequential order, a sense of resistance the user may feel or experience against a change in exercise load may be reduced. 
     According to a biological muscle model (e.g., a hill-type muscle model developed in medical engineering) that is generally known, when a stimulus signal is input to muscle, the input stimulus signal may be amplified in proportion to a force generated by the muscle (which is positive feedback), and muscular strength (or a force) amplified by the stimulus signal may have a relational expression by a length of the muscle and a contraction speed of the muscle. 
     When the muscle is contracted most and when the muscle is stretched most, there may not be a great force. However, when the muscle has an appropriate length, the muscle may have strongest power. A force generated based on a speed at which the length of the muscle changes may be greater when the speed of the change increases. 
     A relationship between the length of the muscle and the muscular strength of the muscle based on the length of the muscle may be in a form of a normal distribution. A relationship between the muscle stretching speed and the muscular strength of the muscle based on the muscle stretching speed may be in a form of a sigmoid. 
     The user may be familiar with a change in a physical movement based on the stretching of the muscle and the magnitude of the corresponding strength or force. Thus, when a resistance level corresponding to the magnitude of the force exhibited in response to the change in the physical movement is provided to the user, the user may also become familiar with a resistance force (or an exercise load) provided by the resistance level and a change in the resistance force based on a change in the resistance level. 
     The wearable device  100  may calculate a physical movement of the user based on a position and an angle of a joint of the user. In the exercise mode, the processor  142  of the wearable device  100  may calculate the physical movement and the magnitude of the corresponding force by the movement, based on the position and the angle of the joint of the user, and calculate a control level based on the calculated magnitude of the force. 
     In operation  1150 , the processor  142  of the wearable device  100  determines a ratio between a time for which the motor driver circuit  112  is controlled to be a closed loop and a time for which the motor driver circuit  112  is controlled to be an open loop, based on the resistance level. Here, the ratio between the time for which the motor driver circuit  112  is controlled to be the closed loop and the time for which the motor driver circuit  112  is controlled to be the open loop may also be referred to as a connection ratio. For example, the connection ratio of the motor driver circuit  112  corresponding to the resistance level may be determined. The connection ratio of the motor driver circuit  112  may indicate a ratio at which the motor driver circuit  112  is controlled to be the closed loop (e.g., the first control state) or the open loop (e.g., the second control state) while energy is controlled not to be provided to the motor  114  from the battery  150 . For example, based on a closed loop state, the connection ratio being 0.5 may indicate that the closed loop state is controlled to be 50% and an open loop state is controlled to be 50% in a set (or, alternatively, a preset) period. When the resistance level changes, the connection ratio may be dynamically adjusted. 
     For example, the connection ratio may be implemented using a PWM. However, examples are not limited to the foregoing example, and various methods may be applied to adjust a connection state of the motor driver circuit  112 . When the PWM is used to control the connection ratio, the connection ratio determined in operation  1150  may be represented by a PWM having a certain duty ratio. The PWM having the duty ratio may be set (or, alternatively, preset) such that a desired resistance force is provided to the user. By the PWM having the duty ratio, the motor driver circuit  112  may be controlled to be the closed loop (first control state) or the open loop (second control state). For example, the processor  142  may control the motor driver circuit  112  to be the closed loop or the open loop by controlling an operation of each of switches in the motor driver circuit  112  using the PWM. 
     When the motor driver circuit  112  is the closed loop, the motor  114  may operate as a generator, and back-drivability of the motor  114  may decrease by dynamic braking. When the back-drivability decreases, a resistance force the user may feel or experience may increase. In contrast, when the motor driver circuit  112  is the open loop, the back-drivability of the motor  114  may increase, and only a frictional force by a gear ratio may be experienced by the user as a resistance force. 
     A desired back-drivability may be obtained by adjusting an open-closed state ratio of the motor driver circuit  112  based on the connection ratio. For example, the resistance force to be provided to the user may be adjusted by the ratio at which the motor driver circuit  112  is controlled to be the closed loop or the open loop within a uniform and repetitive time interval of the PWM, and the resistance force may increase when the ratio of the time for controlling the motor driver circuit  112  to be the closed loop increases. 
     In operation  1160 , the processor  142  of the wearable device  100  controls the motor  114  through the motor driver circuit  112  based on the determined connection ratio. The motor driver circuit  112  may include at least one switch (e.g., the first to fourth switches  710 - 740 ) to be controlled based on the connection ratio, and the motor driver circuit  112  may be controlled to be the closed loop or the open loop by the switch. When the exercise mode is set as the operation mode of the wearable device  100 , energy of the wearable device  100  may not be provided to the motor  114 . For example, electric energy stored in the battery  150  of the wearable device  100  may not be provided to the motor  114 . In this example, although the electric energy is not provided to the motor  114 , the back-drivability of the motor  112  may be controlled by controlling the motor driver circuit  112  to be the closed loop or the open loop, and thus the resistance force may be adjusted by the controlled back-drivability. 
     When the user does not move, the motor  112  may not operate as the generator. When the motor  112  does not operate as the generator, the resistance force may not be generated and provided to the user. That is, the resistance force that is generated based on the back-drivability of the motor  112  may only occur when the user moves. 
     When the motor  112  operates as the generator, the battery  150  of the wearable device  100  may be charged based on energy generated by the generator. That is, while the wearable device  100  is operating in the exercise mode, the energy of the battery  150  of the wearable device  100  may be consumed considerably less, but charged instead. When the wearable device  100  operates in the exercise mode, the wearable device  100  may continue operating even when energy is not supplied from outside. 
     Operations  1140  through  1160  described above may be performed when the operation mode of the wearable device  100  is set as the exercise mode. Operations  1170  and  1180  to be described hereinafter may be performed when the operation mode of the wearable device  100  is set as the assistance mode. 
     In operation  1170 , when the assistance mode is received as an input from the user, the processor  142  of the wearable device  100  calculates an assistance torque value for the joint based on the measured angle of the joint. For example, the assistance torque value for the input joint angle may be determined through the control algorithm. For another example, the assistance torque value may be output by inputting the joint angle to the neural network determined based on the operation mode. 
     According to an example embodiment, the processor  142  may determine a gait state or phase, or a progression of a gait cycle, of the user based on the angle of the joint, and determine an assistance torque value corresponding to the determined gait state or the determined progression of the gait cycle. For example, when the number of joints to be measured increases, a more accurate gait state or a more accurate progression of a gait cycle may be determined. 
     For example, the assistance torque value may be determined based on a desired (or, alternatively, a preset) torque profile. However, a method of calculating an assistance torque value is not limited to the foregoing example. 
     In operation  1180 , the processor  142  of the wearable device  100  provides an assistance force to the user by controlling the motor  114  based on the assistance torque value. The wearable device  100  may operate or drive the motor  114  using the battery  150  of the wearable device  100  such that an assistance torque is output, and provide the assistance force to the user by the assistance torque output by the motor  114 . The assistance torque value may indicate a control signal applied to the motor  114 , and the assistance torque may indicate a rotation torque output by the motor  114  based on the assistance torque value. The assistance force may indicate a force the user may feel or experience by the assistance torque. 
     Although the wearable device  100  is described with reference to  FIG. 11  as providing both the exercise mode and the assistance mode to a user, the wearable device  100  may operate only in the exercise mode. In a case in which the wearable device  100  operates only in the exercise mode, operations  1110 ,  1130 ,  1170 , and  1180  described above may not be performed. In addition, the wearable device  100  may not include a battery to provide power to the motor  114 . When the battery is not included, the wearable device  100  may be lightened in terms of weight. 
       FIG. 12  is a diagram illustrating an example of a resistance force profile output from a user terminal according to at least one example embodiment. 
     Referring to  FIG. 12 , the wearable device  100  may be connected to a user terminal  1200  through a wired or wireless network. For example, the wearable device  100  may transmit and receive information associated with the wearable device  100  through an application installed in the user terminal  1200 . The information associated with the wearable device  100  may include, for example, a setting value of the wearable device  100 , an operation state of the wearable device  100 , a device state of the wearable device  100 , and the like. The setting values of the wearable device  100  may include, for example, detailed setting values that are set by a user for an assistance mode or an exercise mode. The operation state of the wearable device  100  may include, for example, a current gait state of the user or a progression of a gait cycle. The device state of the wearable device  100  may include, for example, a residual amount of the battery  150 . 
     Various resistance force profiles associated with the exercise mode may be stored in advance in the wearable device  100  or the user terminal  1200 . For example, the resistance force profiles may be generated in advance to produce different exercise effects. 
     The user may individualize an existing resistance force profile  1210  by adjusting at least a portion  1220  of the resistance force profile  1210  to be a resistance level desired by the user. For example, the portion  1220  may correspond to a swing state, and the user may adjust the resistance level of the portion  1220  such that the resistance level is to be almost minimized in the swing state. For example, the user may adjust the resistance level by touching the portion  1220  through a touch panel of the user terminal  1200  and dragging a trajectory of the selected portion  1220 . 
       FIG. 13  is a flowchart illustrating another example of a method of providing a resistance force according to at least one example embodiment. 
     Operations  1310  through  1380  to be described hereinafter with reference to  FIG. 13  may be performed by the wearable device  100 . 
     Referring to  FIG. 13 , in operation  1310 , the wearable device  100  receives, from a user, an operation mode that controls the wearable device  100 . For a more detailed description of operation  1310 , reference may be made to the description of operation  1110  provided above with reference to  FIG. 11 . 
     In operation  1320 , the wearable device  100  measures an angle of a joint of the user using the sensor  121 . For a more detailed description of operation  1320 , reference may be made to the description of operation  1120  provided above with reference to  FIG. 11 . Operation  1320  may be independently performed with operation  1330  in parallel. 
     In operation  1330 , the wearable device  100  determines whether the operation mode is an exercise mode or an assistance mode. 
     For example, in a case in which the wearable device  100  operates based on a plurality of neural networks, the wearable device  100  may determine a neural network corresponding to the determined operation mode. Based on the determined neural network, subsequent operations may be performed. For example, an exercise mode neural network may be determined for the exercise mode, and an assistance mode neural network may be determined for the assistance mode. When the operation mode is the exercise mode, operations  1340  through  1360  may be performed. When the operation mode is the assistance mode, operations  1370  and  1380  may be performed. 
     Although it is described above that the exercise mode or the assistance mode operates based on its corresponding neural network, examples are not limited thereto. For example, an operation of the wearable device  100  may be controlled through a control algorithm, not such a neural network. 
     &lt;Exercise Mode&gt; 
     In operation  1340 , the processor  142  of the wearable device  100  determines a resistance level for the joint based on the measured angle of the joint. For a more detailed description of operation  1340 , reference may be made to the description of operation  1140  provided above with reference to  FIG. 11 . 
     In operation  1350 , the processor  142  of the wearable device  100  determines a connection ratio of the motor driver circuit  112  corresponding to the resistance level. For a more detailed description of operation  1350 , reference may be made to the description of operation  1150  provided above with reference to  FIG. 11 . 
     In operation  1360 , the processor  142  of the wearable device  100  controls the motor  114  through the connection ratio of the motor driver circuit  112 . For a more detailed description of operation  1360 , reference may be made to the description of operation  1160  provided above with reference to  FIG. 11 . 
     &lt;Assistance Mode&gt; 
     In operation  1370 , the processor  142  of the wearable device  100  calculates an assistance torque value for the joint based on the measured angle of the joint. For a more detailed description of operation  1370 , reference may be made to the description of operation  1170  provided above with reference to  FIG. 11 . 
     In operation  1380 , the processor  142  of the wearable device  100  provides an assistance force to the user by controlling the motor  114  based on the assistance torque value. For a more detailed description of operation  1380 , reference may be made to the description of operation  1180  provided above with reference to  FIG. 11 . 
       FIG. 14  is a diagram illustrating an example of a motor driver circuit of an open loop according to at least one example embodiment. 
     Referring to  FIG. 14 , a motor driver circuit  1400  may be an H-bridge circuit. The motor driver circuit  1400  may have an open or closed state that is determined based on a connection state of switches  1410  through  1440 . The switches  1410  through  1440  may be embodied as, for example, a bipolar junction transistor (BJT) and a metal-oxide-semiconductor field-effect transistor (MOSFET), but examples are not limited thereto. 
     When the motor driver circuit  1400  is in an open circuit state, dynamic braking of the motor  114  may be minimized, and thus back-drivability of the motor  114  may increase. In such a case, the back-drivability may be a frictional force generated by gears connected to the motor  114 . 
       FIGS. 15 and 16  are diagrams illustrating examples of a motor driver circuit of a closed loop according to at least one example embodiment. 
     According to an example embodiment, a closed loop of the motor driver circuit  1400  may be formed to include the battery  150  and the motor  114 . 
     For example, when the switches  1410  and  1440  of the motor driver circuit  1400  are open and the switches  1420  and  1430  of the motor driver circuit  1400  are closed, a current provided to the motor  114  may flow in a first direction  1510 . 
     For another example, when the switches  1410  and  1440  are closed and the switches  1420  and  1430  are open, a current provided to the motor  114  may flow in a second direction  1610 . The second direction  1610  may be a direction opposite to the first direction  1510 . Based on such a current direction, a rotation direction of an axis of the motor  114  may change. 
     These example closed loops may be formed in a case of an assistance mode, and the example current directions  1510  and  1610  may be determined based on a direction of an assistance force to be provided to a user. 
       FIG. 17  is a diagram illustrating an example of a motor driver circuit of a closed loop according to at least one example embodiment. 
     Referring to  FIG. 17 , the motor driver circuit  1400  connected to the motor  114  that is controlled not to use energy of the battery  150  may form a closed loop. That is, in the example of  FIG. 17 , the motor driver circuit  1400  may be a motor driver circuit for an exercise mode that does not use power of the battery  150  and a closed loop circuit connected to the motor  114 . 
     For example, when the switches  1410  and  1430  of the motor driver circuit  1400  are open and the switches  1420  and  1440  of the motor driver circuit  1400  are closed, a closed loop including the motor  114  may be formed. That is, the closed loop may be formed by a lower driver circuit of the motor driver circuit  1400 . The closed loop may be formed in a case of the exercise mode, and dynamic braking of the motor  114  may occur. A user who rotates the motor  114  may feel or experience a resistance force by the dynamic braking. 
       FIG. 18  is a diagram illustrating an example of a motor driver circuit of a closed loop including a braking resistor according to at least one example embodiment. 
     Referring to  FIG. 18 , a motor driver circuit  1800  includes the battery  150 , switches  1810  through  1840  connected to the motor  114 , and a braking resistor  1850 . The switches  1820  and  1840  are closed, and thus a closed loop including the motor  114  may be formed. When the closed loop is formed, a resistance force that may be felt or experienced by a user may be maximized. 
     When a ratio of an open loop state and a closed loop state of the motor driver circuit  1800  is adjusted by a connection ratio, a level of the resistance force may be adjusted. The closed loop state may be maintained to maximize the resistance force, and the open loop state may be maintained to minimize the resistance force. 
     For example, in a state in which the motor driver circuit  1800  is controlled to be the closed loop, the motor  114  may operate as a generator for an external force by the user, and generated energy may be consumed as heat through the braking resistor  1850 . For another example, in the motor driver circuit  1800 , a current which is the energy generated by the motor  114  may flow in a direction from a (+) terminal of the battery  150  to a (−) terminal of the battery  150  by a diode, regardless of a rotation direction of a rotation axis of the motor  114 . Thus, the generated energy may charge the battery  150 . 
       FIG. 19  is a diagram illustrating an example of a motor driver circuit of a closed loop including a resistor according to at least one example embodiment. 
     Referring to  FIG. 19 , a motor driver circuit  1900  obtained by adding an auxiliary path including at least one resistor  1962  and switch  1964  to the motor driver circuit  1400  described above with reference to  FIGS. 14 through 17  may increase electrical stability of a closed loop. 
     In the motor driver circuit  1900  in a closed loop state including the motor  114 , the motor  114  may operate as a generator while rotating by an external force and generate an electromotive force. By the generated electromotive force, there may be a probability that electronic components in the closed loop are damaged. Thus, by adding the resistor  1962  to the closed loop, an internal resistance value of the closed loop may increase, and thus a magnitude of a current generated by the electromotive force may decrease. As the magnitude of the current decreases, the probability that the internal electronic components in the closed loop are damaged may also be reduced. 
       FIG. 20  is a diagram illustrating an example of a motor driver circuit of a closed loop including a brushless direct current (BLDC) motor according to at least one example embodiment. 
     The motor driver circuits  1400 ,  1800 , and  1900  illustrated in  FIGS. 14 through 19  may be connected to a direct circuit (DC) motor. Referring to  FIG. 20 , as another example, a motor driver circuit  2000  may be connected to a BLDC motor  2005 . The BLDC motor  2005  may be connected to three terminals in the motor driver circuit  2000 . In general, compared to a DC motor, a BLDC motor may generate a torque that is great relative to a volume, and may not have a friction generated between a brush and a rotor coil because it does not use a mechanical brush that is used in the DC motor for commuting a current. Since there is no friction between the brush and the rotor coil, the BLDC motor may have a greater durability than the DC motor. 
     For example, when switches  2010 ,  2030 , and  2050  of the motor driver circuit  2000  are open, and switches  2020 ,  2040 , and  2060  of the motor driver circuit  2000  are closed, a closed loop including the BLDC motor  2005  may be formed. The closed loop may be formed with the battery  150  excluded. 
     As a PWM signal is applied to the switches  2020 ,  2040 , and  2060 , a closed loop state and an open loop state of the motor driver circuit  2000  may be controlled. Here, a control ratio may change according to a resistance level. 
     The switch  2020  may control opening and closing of a first terminal (u) of the BLDC motor  2005 . The switch  2040  may control opening and closing of a second terminal (v) of the BLDC motor  2005 . The switch  2060  may control opening and closing of a third terminal (w) of the BLDC motor  2005 . For example, when the same PWM signal is applied to the switches  2020 ,  2040 , and  2060 , a closed loop that is not related to a commutation sequence for the BLDC motor  2005  may be formed. 
     Since the BLDC motor  2005  are connected to the three terminals u, v, and w, it may possible to form a closed loop by determining hall sensor information (e.g., an angle of a rotation axis of a motor) of a rotor and then selectively connecting two switches among the switches  2020 ,  2040 , and  2060  to match the commutation sequence, in order to form an electrical closed loop among the terminals u, v, and w. However, in a case in which the BLDC motor  2005  is controlled to control only back-drivability of the BLDC motor  2005  in an exercise mode, it is possible to form a closed loop by connecting all the switches  2020 ,  2040 , and  2060 , without considering the commutation sequence. In such a case, there is no need to consider the commutation sequence to form the closed loop, a time needed for calculating the commutation sequence may be reduced and a probability of a malfunction of the BLDC motor  2005  may also be reduced. 
     For another example, a PWM signal may be applied to each of the switches  2020 ,  2040 , and  2060  to form a closed loop corresponding to a commutation sequence for a state classified based on an angle of a rotation axis of the BLDC motor  2005 . 
       FIG. 21  is a diagram illustrating an example of a driver of a wearable device according to at least one example embodiment. 
     Referring to  FIG. 21 , the driver  110  of the wearable device  100  includes a motor  2110 , a clutch  2120 , and a plurality of gears including a low reduction gear  2130  and a high reduction gear  2140 . From among the gears, different gears may be selected according to an input of a user or a determined resistance level. The clutch  2120  may control driving force transfer by selectively connecting the motor  2110  to one of the gears. 
     A gear ratio may be differently set based on an objective of an operation mode of the wearable device  100 , and thus a magnitude of a resistance force to be provided to the user may be adjusted. 
     Unlike the hip-type wearable device  100  described above with reference to  FIGS. 1A through 1D , a wearable device may be a whole body-type wearable device  1  to be described hereinafter with reference to  FIGS. 22 through 24 . The whole body-type wearable device  1  may be configured to provide a walking assistance torque respectively to a hip joint, a knee joint, and an ankle joint of a user. 
     &lt;Overview of Whole Body-Type Walking Assist Device&gt; 
       FIGS. 22 through 24  are diagrams illustrating an example of a whole body-type wearable device  1  according to at least one example embodiment. 
       FIG. 22  is a front view of the whole body-type wearable device  1 ,  FIG. 23  is a side view of the whole body-type wearable device  1 , and  FIG. 24  is a rear view of the whole body-type wearable device  1 . 
     According to an example embodiment, the whole body-type wearable device  1  may include the driver  110 , the sensor  120 , the IMU  130 , the controller  140 , and the battery  150  that are described above. 
     Referring to  FIGS. 22 through 24 , the whole body-type wearable device  1  may be provided in an exoskeleton structure to be worn on a left leg and a right leg of a user. With the wearable device  1  on, the user may be able to perform various movements, for example, extension, flexion, adduction, and abduction. The extension may indicate a movement or an exercise of stretching joints, and the flexion may indicate a movement or an exercise of bending joints. The adduction may indicate a movement or an exercise of moving legs to be closer to a central axis of a body, and the abduction may indicate a movement or an exercise of stretching legs in a direction receding from a central axis of a body. 
     Referring to  FIGS. 22 through 24 , the wearable device  1  includes a main body portion  10  and a device portion including  20 R and  20 L,  30 R and  30 L, and  40 R and  40 L. 
     The main body portion  10  includes a housing  11  in which various components are embedded. The components to be embedded in the housing  11  may include, for example, a central processing unit (CPU), a printed circuit board (PCB), various types of storage devices, and a power source. Although not illustrated, the whole body-type wearable device  1  may also include the driver  110 , the sensor  120 , the IMU  130 , and the controller  140  that are described above. For example, the main body portion  10  may include the controller  140 , where the controller  140  may include the CPU and the PCB. 
     The CPU may be a microprocessor. The microprocessor may be provided with an arithmetic logic operator, a register, a program counter, an instruction decoder, and/or a control circuit in a silicon chip. The CPU may select a control mode that is suitable for a walking environment, and generate a control signal to control an operation of the device portion. 
     The PCB refers to a board on which a circuit is printed, and the CPU and/or the various storage devices may be installed in the PCB. The PCB may be fixed to an inner side surface of the housing  11 . 
     The various types of storage devices may be embedded in the housing  11 . The storage devices may include a magnetic disk storage device configured to magnetize a magnetic disk surface and store data, and a semiconductor memory device configured to store data using various types of memory semiconductors. 
     The power source embedded in the housing  11  may supply power to the various components embedded in the housing  11  or the device portion. 
     The main body portion  10  further includes a waist support  12  configured to support a waist of the user. The waist support  12  may be provided in a shape of a curved flat surface plate that supports the waist of the user. 
     The main body portion  10  further includes a fixing portion  11   a  configured to fix the housing  11  to a hip portion of the user, and a fixing portion  12   a  configured to fix the waist support  12  to the waist of the user. The fixing portions  11   a  and  12   a  may be embodied by one of a band, a belt, and a strap which are elastic. 
     The main body portion  10  also includes the IMU  130 . For example, the IMU  130  may be provided inside or outside the housing  11 . The IMU  130  may be provided on the PCB provided inside the housing  11 . The IMU  130  may measure an acceleration and an angular velocity. 
     The device portion includes a first structure  20 , a second structure  30 , and a third structure  40  as illustrated in  FIGS. 22 through 24 . 
     The first structure  20  including right  20 R and left  20 L portions may assist or support a movement of a thigh and a hip joint of the user when the user walks. The first structure  20  includes a first driving device including  21 R and  21 L, a first support including  22 R and  22 L, and a first fixing portion including  23 R and  23 L. 
     The driver  110  may include the first driving device including  21 R and  21 L. The description of the driver  110  may be replaced with the description of the first driving device including  21 R and  21 L to be provided hereinafter with reference to  FIGS. 22 through 24 . 
     The first driving device including  21 R and  21 L may be disposed on the hip joint of the first structure  20  including  20 R and  20 L, and generate a rotational force of different magnitudes in a certain direction. The rotational force generated in the first driving device including  21 R and  21 L may be applied to the first support including  22 R and  22 L. The first driving device including  21 R and  21 L may be set to rotate within a motion range of a hip joint of a human body. 
     The first driving device including  21 R and  21 L may operate based on a control signal provided by the main body portion  10 . The first driving device including  21 R and  21 L may be embodied by one of a motor, a vacuum pump, and a hydraulic pump, but examples are not limited thereto. 
     A joint angle sensor may be provided around the first driving device including  21 R and  21 L. The joint angle sensor may detect an angle by which the first driving device including  21 R and  21 L rotates on a rotation axis. The sensor  120  may include the joint angle sensor. 
     The first support including  22 R and  22 L may be physically connected to the first driving device including  21 R and  21 L. The first support including  22 R and  22 L may rotate in a certain direction by the rotational force generated from the first driving device including  21 R and  21 L. 
     The first support including  22 R and  22 L may be provided in various shapes. For example, the first support including  22 R and  22 L may be provided in a shape in which nodes are connected with each other. A joint may be between the nodes, by which the first support including  22 R and  22 L may be bent within a certain range. For another example, the first support including  22 R and  22 L may be provided in a shape of a rod. In this example, the first support including  22 R and  22 L may be formed with a flexible material that may be bent within a certain range. 
     The first fixing portion including  23 R and  23 L may be provided in the first support including  22 R and  22 L. The first fixing portion including  23 R and  23 L may fix the first support including  22 R and  22 L to the thigh of the user. 
       FIGS. 22 through 24  illustrate that the first support including  22 R and  22 L is fixed on an outer side of the thigh of the user by the first fixing portion including  23 R and  23 L. When the first driving device including  21 R and  21 L operates and the first support including  22 R and  22 L rotates, the thigh to which the first support including  22 R and  22 L is fixed may also rotate in a same direction as a rotation direction in which the first support including  22 R and  22 L rotates. 
     The first fixing portion including  23 R and  23 L may be embodied by one of a band, a belt, and a strap which are elastic, or by a metal material.  FIG. 22  illustrates the first fixing portion including  23 R and  23 L as a chain. 
     The second structure  30  including right  30 R and left  30 L portions may assist or support a movement of a calf and a knee joint of the user when the user walks. The second structure  30  including  30 R and  30 L includes a second driving device including  31 R and  31 L, a second support including  32 R and  32 L, and a second fixing portion including  33 R and  33 L. 
     The second driving device including  31 R and  31 L may be disposed on the knee joint of the second structure  30  including  30 R and  30 L, and generate a rotational force of different magnitudes in a certain direction. The rotational force generated in the second driving device including  31 R and  31 L may be applied to the second support including  32 R and  32 L. The second driving device including  31 R and  31 L may be set to rotate within a motion range of a knee joint of a human body. 
     The driver  110  may include the second driving device including  31 R and  31 L. Here, what has been described above in relation to a hip joint with reference to  FIGS. 1A through 1D  may be similarly and substantially applied to the knee joint. 
     The second driving device including  31 R and  31 L may operate based on a control signal provided by the main body portion  10 . The second driving device including  31 R and  31 L may be embodied by one of a motor, a vacuum pump, and a hydraulic pump, but examples are not limited thereto. 
     A joint angle sensor may be provided around the second driving device including  31 R and  31 L. The joint angle sensor may detect an angle by which the second driving device including  31 R and  31 L rotates on a rotation axis. The sensor  120  may include the joint angle sensor. 
     The second support including  32 R and  32 L may be physically connected to the second driving device including  31 R and  31 L. The second support including  32 R and  32 L may rotate in a direction by the rotational force generated from the second driving device  31 R and  31 L. 
     The second fixing portion including  33 R and  33 L may be provided in the second support including  32 R and  32 L. The second fixing portion including  33 R and  33 L may fix the second support including  32 R and  32 L to the calf of the user.  FIGS. 22 through 24  illustrate that the second support including  32 R and  32 L is fixed on an outer side of the calf of the user by the second fixing portion including  33 R and  33 L. When the second driving device including  31 R and  31 L operates and the second support including  32 R and  32 L rotates, the calf to which the second support including  32 R and  32 L is fixed may also rotate in a same direction as a rotation direction in which the second support including  32 R and  32 L rotates. 
     The second fixing portion including  33 R and  33 L may be embodied by one of a band, a belt, and a strap which are elastic, or by a metal material. 
     The third structure  40  including right  40 R and left  40 L portions may assist or support a movement of an ankle joint and related muscles of the user when the user walks. The third structure  40  including  40 R and  40 L includes a third driving device including  41 R and  41 L, a foot support including  42 R and  42 L, and a third fixing portion including  43 R and  43 L. 
     The driver  110  may include the third driving device including  41 R and  41 L. Here, what has been described above in relation to a hip joint withe reference to  FIGS. 1A through 1D  may be similarly and substantially applied to the ankle joint. 
     The third driving device including  41 R and  41 L may be disposed on the ankle joint of the third structure  40  including  40 R and  40 L, and operate based on a control signal provided by the main body portion  10 . Similar to the first driving device including  21 R and  21 L or the second driving device including  30 R and  30 L, the third driving device including  41 R and  41 L may be embodied by a motor. 
     The foot support including  42 R and  42 L may be disposed at a position corresponding to a sole of a foot of the user, and physically connected to the third driving device including  41 R and  41 L. 
     The third fixing portion including  43 R and  43 R may be provided in the foot support including  42 R and  42 L. The third fixing portion including  43 R and  43 L may fix the foot of the user to the foot support including  42 R and  42 L. 
     The units and/or modules described herein may be implemented using hardware components and software components. For example, the hardware components may include microphones, amplifiers, band-pass filters, audio to digital convertors, and processing devices. A processing device may be implemented using one or more hardware device configured to carry out and/or execute program code by performing arithmetical, logical, and input/output operations. The processing device(s) may include a processor, a controller and an arithmetic logic unit, a digital signal processor, a microcomputer, a field programmable array, a programmable logic unit, a microprocessor or any other device capable of responding to and executing instructions in a defined manner. The processing device may run an operating system (OS) and one or more software applications that run on the OS. The processing device also may access, store, manipulate, process, and create data in response to execution of the software. For purpose of simplicity, the description of a processing device is used as singular; however, one skilled in the art will appreciated that a processing device may include multiple processing elements and multiple types of processing elements. For example, a processing device may include multiple processors or a processor and a controller. In addition, different processing configurations are possible, such a parallel processors. 
     The software may include a computer program, a piece of code, an instruction, or some combination thereof, to independently or collectively instruct and/or configure the processing device to operate as desired, thereby transforming the processing device into a special purpose processor. Software and data may be embodied permanently or temporarily in any type of machine, component, physical or virtual equipment, computer storage medium or device, or in a propagated signal wave capable of providing instructions or data to or being interpreted by the processing device. The software also may be distributed over network coupled computer systems so that the software is stored and executed in a distributed fashion. The software and data may be stored by one or more non-transitory computer readable recording mediums. 
     The methods according to the above-described example embodiments may be recorded in non-transitory computer-readable media including program instructions to implement various operations of the above-described example embodiments. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. The program instructions recorded on the media may be those specially designed and constructed for the purposes of example embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of non-transitory computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROM discs, DVDs, and/or Blue-ray discs; magneto-optical media such as optical discs; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory (e.g., USB flash drives, memory cards, memory sticks, etc.), and the like. Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. The above-described devices may be configured to act as one or more software modules in order to perform the operations of the above-described example embodiments, or vice versa. 
     A number of example embodiments have been described above. Nevertheless, it should be understood that various modifications may be made to these example embodiments. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.