Systems and methods for controlling a powered prosthetic joint

Abstract

Powered joints (e.g., knee, ankle, etc.) can modulate the impedance / position controller based on the thigh velocity. The higher the thigh velocity is, the more assistance received by the user receives; and the lower the thigh velocity is, the higher the resistance received by the user. Additionally or alternatively, the impedance / position controller may enter a thigh tracking control mode in response to the thigh angle exceeding a threshold.

Description

OSSUR.237WO PATENTSYSTEMS AND METHODS FOR CONTROLLING A POWERED PROSTHETIC JOINTBACKGROUNDField

[0001] The present application relates to features associated with a control system for managing operation of a powered prosthetic device, in particular relating to impedance control.Description of the Related Art

[0002] In contrast to traditional hinges or passive mechanisms used in lower- limb prosthetic devices, powered actuators have the capacity to generate net positive mechanical power. The generation of power allows the lower-limb prosthetic devices to more closely match the human lower-limb joint characteristics. A few types of joint actuation mechanisms for prosthetic devices are known in the art. Usually, joint actuation mechanisms form part of a prosthetic device and include a housing for an actuator. The actuator can include a motor and a shaft in communication with a reducer, which communicates with an output to cause the joint to rotate about an axis thereof. Actuation mechanisms can provide measurement of the torque applied to the joint by an external force, which can be either from a prosthetic user or the motor of the actuator.

[0003] An impedance controller for orthotic and prosthetic devices can include an equilibrium trajectory generator that receives locomotion data regarding the locomotion of a user, a dynamic trajectory compensator that generates one or more control parameters based on the locomotion data and one or more physiological characteristics of the user, and a dynamic gain tuner that adjusts the one or more control parameters based on a gain scaling factor that is calculated using a measured deflection point and an expected deflection point. The adjusted control parameters are used to control movement of an actuator of an orthotic or prosthetic device.SUMMARY

[0004] The present disclosure includes embodiments of prosthetic joint with a control system that may not rely on determination of every gait activity and / or subphase state of a user. The prosthetic joint control embodiments disclosed herein may provide more generalized and / or less complicated thresholds for impedance control, and more intuitive and / or continuous control. In some embodiments, using the powered knee jointas an example, a thigh velocity may be used to change the behavior of the knee joint by starting in a stand-up or sit down activity, which in turn may be achieved by changing the control parameters of an impedance controller.

[0005] For purposes of this summary, certain aspects, advantages, and novel features are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular aspect. Thus, for example, those skilled in the art will recognize the disclosures herein may be carried out in a manner that achieves one or more advantages taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0006] In some aspects, the present disclosure includes a powered prosthetic lower limb device including: a shank structure and a knee joint positioned between a shank structure and an adjacent prosthetic portion or a limb segment of a user. The knee joint may include a powered actuator configured to rotate the shank structure relative to the adjacent prosthetic portion or the limb segment of the user. The device may further include a control system in communication with the powered actuator. The control system may be configured to receive a reading from an inertial measurement unit (IMU) and calculate an angle of the knee joint, the shank structure, or the adjacent prosthetic portion or the limb segment. Based at least in part on the angle, the control system may be configured to perform an interpolation function of control parameters of impedance control between: fumbling around and resistance to rotate the knee joint, or fumbling around and assistance to rotate the knee joint. The control system may be further configured to output a torque of the actuator based on the interpolated control parameters.

[0007] In some aspects, the control system may be further configured to determine an angular velocity based on the angle.

[0008] In some aspects, in response to the angular velocity being zero or greater than zero, the control system may be configured to interpolate the control parameters between fumbling around and assistance to rotate the knee joint; and in response to the angular velocity being less than zero, the control system may be configured to interpolate the control parameters between fumbling around and resistance to rotate the knee joint.

[0009] In some aspects, the device may further include the IMU, wherein the IMU may be at the knee joint.

[0010] In some aspects, the device may further include the IMU, wherein the IMU may be at the shank structure.

[0011] In some aspects, the knee joint may be positioned between the shank structure and the adjacent prosthetic portion and the IMU may be located at the adjacent prosthetic portion.

[0012] In some aspects, the angle calculated may be the angle of the adjacent prosthetic portion or the limb segment.

[0013] In some aspects, the interpolation function may be bounded.

[0014] In some aspects, the interpolation function may be unbounded.

[0015] In some aspects, the interpolation function may be linear.

[0016] In some aspects, the interpolation function may be non-linear.

[0017] In some aspects, the control system may be further configured to interpolate one or more of the control parameters using one or more interpolation functions.

[0018] In some aspects, the control parameters may include one or more of: proportional gain, derivative gain, mass gain, desired position set-point, and / or desired velocity set-point.

[0019] In some aspects, the shank structure may include a distal connector configured to be coupled to a powered prosthetic ankle, wherein the impedance control of the device may be synced with impedance control of the powered prosthetic ankle.

[0020] The present disclosure relates to a powered prosthetic lower limb device including: a shank structure and a knee joint positioned between a shank structure and an adjacent prosthetic portion or a limb segment of a user. The knee joint may include a powered actuator configured to rotate the shank structure relative to the adjacent prosthetic portion or the limb segment of the user. The device may further include a control system in communication with the powered actuator. The control system may be configured to receive a reading from an inertial measurement unit (IMU) and calculate an angle of the knee joint, the shank structure, or the adjacent prosthetic portion or the limb segment. In response to the angle exceeding a threshold, the control system may be configured to determine a target knee joint position based at least in part on the angle. The control system may be further configured to output a torque of the actuator based at least in part on the target knee joint position. The target knee joint position may be one of control parameters of impedance control of the knee joint.

[0021] In some aspects, the threshold may be a negative value.

[0022] In some aspects, the angle exceeding the threshold may include the angle being more negative than the negative value.

[0023] In some aspects, the negative value may be -45°.

[0024] In some aspects, determining the target knee joint position may include multiplying the angle by an angle gain.

[0025] In some aspects, determining the target knee joint position may further include adding an offset angle.

[0026] In some aspects, the control system may be further configured to, based at least in part on the angle, perform interpolation of the control parameters of impedance control between: fumbling around and resistance to rotate the knee joint, or fumbling around and assistance to rotate of the knee joint. The control system may be further configured to output the torque to the actuator based in part on the interpolated control parameters.

[0027] In some aspects, the device may further include the IMU.

[0028] In some aspects, the control system may be further configured to determine an angular velocity based on the angle.

[0029] In some aspects, in response to the angular velocity being zero or greater than zero, the control system may be configured to interpolate the control parameters between fumbling around and assistance to rotate the knee joint; and in response to the angular velocity being less than zero, the control system may be configured to interpolate the control parameters between fumbling around and resistance to rotate the knee joint.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] These and other features, aspects, and advantages of the present disclosure are described with reference to the drawings of certain embodiments, which are intended to schematically illustrate certain embodiments and not to limit the disclosure.

[0031] Figure 1 illustrates a powered lower limb prosthetic device according to an embodiment disclosed herein.

[0032] Figure 2A illustrates a block diagram of certain hardware components of a powered prosthetic device.

[0033] Figure 2B illustrates a block diagram of certain hardware components of a powered prosthetic device (e.g., a lower-limb device).

[0034] Figure 3A illustrates a control process according to an embodiment disclosed herein.

[0035] Figure 3B illustrates a control process according to an embodiment disclosed herein.

[0036] Figure 4 illustrates a control process according to an embodiment disclosed herein.

[0037] Figure 5 illustrates an example graph showing certain parameters of a prosthetic knee device as the user repeats sit-stand activities.

[0038] Figure 6A illustrates graphically a linear unbounded interpolation function of control parameters for impedance control.

[0039] Figure 6B illustrates graphically a linear bounded interpolation function of control parameters for impedance control.

[0040] Figure 6C illustrates graphically a non-linear bounded interpolation function of control parameters for impedance control.

[0041] Figure 7 illustrates an ankle control process according to an embodiment disclosed herein.

[0042] Figure 8 illustrates a block diagram of the control systems of a prosthetic knee device and a prosthetic ankle device working together to provide impedance control.DETAILED DESCRIPTION

[0043] Although several aspects, examples, and illustrations are disclosed below, it will be understood by those of ordinary skill in the art that the system, methods, and devices described herein extend beyond the specifically disclosed aspects, examples, and illustrations and includes other uses of the system, methods, and devices and obvious modifications and equivalents thereof. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner simply because it is being used in conjunction with a detailed description of certain specific aspects of the disclosure. In addition, aspects of the disclosure can comprise several novel features and no single feature is solely responsible for its desirable attributes or is essential to practicing the system, methods, and devices herein described.

[0044] The present disclosure includes embodiments of powered joints (e.g., knee, ankle, etc.) that can provide impedance and / or position control based on a phase estimation from a limb angle (e.g., thigh angle, shank angle, etc.). In some embodiments, the control system disclosed herein may interpolate control parameters of an impedance controller based on whether a thigh angular velocity is above or below 0. The control parameters for impedance control (e.g., variable gain impedance control) may include but are not limited to any one or more of the following: proportional gain, derivative gain, mass gain, desired position set-point, and / or or desired velocity (e.g., angular velocity) set-point. In some embodiments, the control system disclosed herein may enter a thigh tracking control mode in response to the thigh angle exceeding a threshold. An impedance controller can come in various forms. In addition to its basic formulation, an impedance controller(e.g., variable gain impedance controller) may include breaking feedback transfer function and / or energy injection feedforward function. Details of impedance controllers are described in U.S. PatentNos. 9,808,357B2 (see, e.g., Figures 5, 7, and 9), issued November 7, 2017, and 9,060, 884B2, issued June 23, 2015, the disclosure of each of which is incorporated herein by reference and should be considered part of the specification.

[0045] The powered joints disclosed herein may provide a control system that does not require defining a gait activity or subphase state of the user and transitioning between the gait activity states. For control based on system states in existing powered knee joints, the control map may include eight to ten (or more) different gait activities, such as slow walk, fast walk, stairs up, yield, sit, standby, stand-up, and stairs down. Each activity may have its one or more enter and exit conditions as well as set of gains / parameters for the impedance or position controller. It can be difficult to generalize these enter and exit conditions for the entire user population. As a result, not all the users’ gait activities and / or transitions between gait activities may be detected using these enter and exit conditions. The control system and / or control scheme in the embodiments disclosed herein require more generalized and / or less complicated thresholds. In some embodiments, the control system and / or control scheme in the embodiments disclosed herein does not need to determine whether the user is sitting down, standing up, walking, ascending or descending stairs or a slope, and / or the like.

[0046] The powered joints disclosed herein offer more intuitive, more continuous, and / or smoother transitions between activities. Existing prosthetic knee devices may require a user to enter an intermediate defined state before entering the desired activity, or may allow a gait activity state to be entered only via a selected groups of defined gait activities. Existing prosthetic knee devices also may be limited in their responses to a user switching to a different activity or phase without completing the current activity or phase. For example, in existing prosthetic knee devices, the user cannot transition between sit-down and stand-up without entering the sit activity state. Users may not always understand what is missing when trying to enter a new activity. For example, the users may start stair ascent on the prosthetic leg (similar to being midway between sitting and standing), and think they are doing something wrong because the existing powered knee devices may not provide the assistance to get their bodies up as expected. In other words, existing prosthetic knee devices may be limited in their abilities to enter control of a new phase when the user is in the middle of a current state. For example, the user may be moving around in a kitchen or another place where the user may be ambulating, but notprogressing in a particular direction, e.g., walking half a step and walking back, turning around, midway between sitting and standing, etc. (also referred to as “fumbling around” in the present disclosure). In some embodiments, fumbling around may include movements with which the user is not making forward progression (with consecutive steps going forward), or backward progression (with consecutive steps going backward). In some embodiments, fumbling around may include not in any of the defined states of existing knee control schemes, including but not limited to those existing devices disclosed herein. The control system disclosed herein may advantageously adapt when the user is fumbling around. For example, several embodiments of the control system disclosed herein may allow users to stop mid-air in the process of sitting down (with the knee device providing resistance) and decide to stand up by the knee device providing the necessary assistance to stand up.

[0047] In some embodiments, the control system disclosed herein may advantageously provide swing thigh tracking, for example, when users need to climb differently heighted stairs or curbs. The thigh tracking control mode may allow the users to adjust the height using the angle of the thigh (or hip flexion). In some embodiments, the control system disclosed herein may allow users to step on a box using their prosthetic leg and get assistance to raise their bodies when they extend their hip. After having gotten up on the box with both legs, the users can flex the hip to lower their bodies again so they can reach the ground on the other side with their unamputated leg.

[0048] Figure 1 illustrates a prosthetic device 100 according to an embodiment disclosed herein. The prosthetic device 100 may include a shank portion 102 and a joint mechanism 104. The prosthetic device 100 may include a lower limb prosthetic. The prosthetic device 100 may include a prosthetic knee. Accordingly, the shank portion 102 may include a lower leg and the joint mechanism 104 may include a knee joint.

[0049] The shank portion 102 may extend between a proximal end 106 and a distal end 108. The shank portion 102 may include a shank structure 110 and a cover 112 positioned over the shank structure 110. The shank portion 102 may include a distal connector 114 at the distal end 108 of the shank portion 102. The distal connector 114 may couple the prosthetic device 100 to a prosthetic ankle and / or a prosthetic foot thereto. The joint mechanism 104 may be positioned at the proximal end 106 of the shank portion 102. The joint mechanism 104 may include a prosthetic connector 116. The prosthetic connector 116 may be connected to another adjacent prosthetic portion, such as a common socket, (not shown) that is mountable to a limb segment (e.g., leg stump) of a user. The jointmechanism 104 may be positioned between the shank portion 102 and the prosthetic portion and / or the limb (e.g., leg stump) of the user.

[0050] The j oint mechanism 104 may include an actuator for rotating the shank portion 102 relative to the prosthetic portion and / or the limb (e.g., leg stump) of the user. In some embodiments, the actuator may be controlled by a control system of the prosthetic device 100. In some embodiments, the control system may control the actuator using impedance control.

[0051] Figure 2A illustrates a block diagram 250 of example hardware components (e.g., the building blocks) for a processor-controlled powered prosthetic device, which may include the prosthetic knee 100, a prosthetic foot with a powered ankle, or otherwise. The control system disclosed herein may include a processor 201, which may be in communication with the actuator 214 at the joint mechanism. The control system may include a memory 202 and / or wireless communication 203. The processor 201 may be in operational communication with the memory 202, where information for the system operation can be stored and retrieved. The processor 201 may manage the wireless communication module 203 to exchange information with external devices, such as mobile phones or tablets, where various types of applications can be used to retrieve information from the powered prosthetic device, trigger specific functions, or provide new data to be stored in the memory 202. The processor 201 and the actuator 214 may be powered by a battery 204 located in the prosthetic device. In some embodiments, the actuator may include a torque sensor 211, which may provide measurements to the processor 201. The prosthetic device disclosed herein may further include an inertial measurement unit (IMU) 209. The IMU may be located on the joint mechanism. Alternatively, the prosthetic device disclosed herein may not include an IMU, but the processor 201 may be in communication with an IMU located on the adjacent prosthetic portion coupled to the prosthetic connector disclosed herein. In some embodiments, the prosthetic device may include other sensor(s) 216, including but not limited to an angle sensor, a ground contact sensor, or any other sensor disclosed herein. The sensors disclosed herein may be functionally connected with the processor 201. The processor 201 may retrieve the information from the connected sensors and further process it based on the definition of the detection and control processes.

[0052] Figure 2B illustrates a block diagram 200 of example hardware components (e.g., the building blocks) for a processor-controlled powered prosthetic knee 100. Any of the features of the block diagram 200 may be incorporated into the block diagram 250 and any of the features of the block diagram 250 may be incorporated into theblock diagram 200. The powered prosthetic knee 100 may use a brushless DC motor 205 combined with a harmonic drive 206 and a compliant transmission element 210. Alternatively, or in addition, the powered prosthetic knee 100 may use one or more AC motors and / or brushed motors. The processor 201 may connect most of the other building blocks together. The processor 201 may operate in such a way as to create a cohesive ensemble from the individual components and modules. The processor 201 is in operational communication with a memory 202, where information for the correct system operation can be stored and retrieved. Additionally, or alternatively, the processor 201 manages the wireless communication module 203 to exchange information with external devices, such as mobile phones or tablets, where various types of applications can be used to retrieve information from the powered prosthetic knee 100, trigger specific functions, or provide new data to be stored in the memory 202.

[0053] The powered prosthetic knee 100 may include a battery 204 to power the electronic components, such as the various sensors 207, 208, 209 and 211, the processor 201, and the motor 205. Various types of battery technologies can be used to power the control system of the powered prosthetic knee 100. Additionally, the powered prosthetic knee 100 may use secondary type battery technologies to reduce the operating costs of these devices by allowing the battery to be recharged, as well as reduce the environmental impact related to the device’s operation.

[0054] Embedded sensors may be integrated in the basic components of the system hardware. The embedded sensors may be used as input sources for implementing the various control loops and intent management functions. In some embodiments, the powered prosthetic knee 100 may use a ground contact sensor 208 to monitor the interaction between the user wearing the prosthetic or orthotic device 100 and the immediate environment. Various constructions can be adopted to implement the ground contact sensor 208, such as, but not limited to, loadcells, optical displacement sensors, strain gauges, magnetic displacement sensors, inductive displacement sensors, capacitive displacement sensors, pressure sensors, and piezoelectric load sensors. In one non-limitative embodiment of a ground contact sensor system, a ground contact sensor array can be used to provide sensing capabilities to segregate between heel load and toe load due to sensor mechanical properties and use of a sensor array.

[0055] In some embodiments, a load sensor assembly may be located at a distal end of the prosthetic device 100 near the distal connector. The load sensor assembly may have one or more load sensors (e.g., one load sensor, five load sensors, seven load sensors,more than seven load sensors, or any number in between). The locations of the sensors may represent different load-bearing areas of the prosthetic device 100. Any number of sensors (e.g., one sensor, two sensors, three sensors, more than three sensors, or any number in between) may be used to represent different load-bearing areas, and that some of the load sensors may represent multiple load-bearing areas (e.g., the posterior-lateral area / portion of a prosthetic or orthotic foot).

[0056] The powered prosthetic knee 100 may integrate one or more IMUs 209 to measure the kinematics of the user’s residual limb or the prosthetic device. In some embodiments, the powered prosthetic knee 100 may include a knee position sensor 207 or another type of sensor that can be used to measure knee joint kinematics directly, which are the result of the interaction between the user, the environment, and the actuator of the powered prosthetic knee 100. In some embodiments, the powered prosthetic knee 100 may have a knee angle sensor (e.g., encoder).

[0057] In some embodiments, the actuator of the powered prosthetic knee 100 may include the brushless DC motor 205, the harmonic drive 206, and a compliant transmission element 210 (or a different type of transmission element). The actuator may alternatively be separated from and work together with the brushless DC motor 205, the harmonic drive 206 transmission and the transmission element 210 to control the powered prosthetic knee 100. In some embodiments, the brushless DC motor 205 may be functionally connected to and controlled by the processor 201 based on the outcome of the data processing performed in firmware.

[0058] In some embodiments, the powered prosthetic knee 100 may include a torque sensor 211 that may directly measure the interactions occurring between the prosthetic device and the user, providing a direct measure of the system kinetics. The sensors disclosed herein may be functionally connected with the processor 201. The processor 201 may retrieve the information from the connected sensors and further process it based on the definition of the detection and control processes.

[0059] Additional details of the hardware and software components of the powered prosthetic device embodiments disclosed herein are described in U.S. Patent Publication No. 2024 / 0207073 Al, the disclosure of the entirety of which is incorporated herein by reference and should be considered part of the specification.

[0060] Several embodiments of the present disclosure may provide stand behavior control, which may include using thigh angle (or other angles such as knee angle, shank angle, etc.) to determine how much assist / resi stance the user requires from the knee.In some implementations, the user or a certified prosthetists Orthotists (CPO) may select how much stair ascent or stand up assistance the user needs and how much sit-down resistance the user needs via a mobile app. Depending on the thigh angular velocity (or another velocity as disclosed herein) on the prosthetic device, the control system of the device can calculate the assistance (positive torque value), and resistance (negative torque value) needed. The control parameters of the impedance controller of the knee device may be interpolated between a set of fixed values defined for assistance (e.g., stair ascent, stand up, etc.), fumbling around, and resistance (e.g., sit-down activities). When no angular thigh movement is measured, the control system may set the control parameters to fumbling around. The control system may provide more assistance to the user in response to a more positive angular thigh movement, with interpolation between fumbling around and assistance to obtain more assistance control parameters. The control system may provide more resistance to the user in response to a more negative angular thigh movement, with interpolation between fumbling around and resistance to obtain more resistance control parameters. The interpolation can be linear or non-linear, bounded or non-bounded. In some embodiments, the interpolation may have a dead-band around 0 7s angular thigh velocity. In some embodiments, the interpolation may include a maximum velocity (e.g., a positive maximum velocity or a negative maximum velocity, with the maximum defining the amplitude of the velocity regardless of the direction). Using the stance behavior control may advantageously allow users to feel more in control and allow the knees to respond more naturally and smoothly to the users’ movements. The user can sit down and stand up without any fixed control triggers or entry / exit conditions. In one implementation, the stance behavior control can allow a user to squat (e.g., in a more natural fashion).

[0061] Figures 3A-3B illustrate processes for providing impedance control according to several embodiments of the present disclosure. In Figures 3A and 3B, shown in step 302, the control system (which may be a control system of any prosthetic device, such as a knee joint, an ankle joint, etc.) may receive new IMU sensor values. In some embodiments, other sensor values may be used. In some embodiments, the IMU sensor may be located on the joint (e.g., the knee joint). In some embodiments, the IMU sensor may be located on the shank structure. In some embodiments, the IMU sensor may be located on the adjacent prosthetic portion coupled to the proximal connector of the joint. The sampling rate for the IMU sensor may vary between about 30 Hz to about 1,000 Hz, or about 40 Hz to about 800 Hz, or about 50 Hz to about 500 Hz, or about 60 Hz to about 140 Hz, or about 70 Hzto about 130 Hz, or about 80 Hz to about 120 Hz, or about 90 Hz toabout 110 Hz, or about 100 Hz, or any frequency within any range defined by those values. In other embodiments, the measurements may be from a different sensor, e.g., an angle sensor.

[0062] At step 304 of Figures 3 A and 3B, the control system may calculate an angle from the IMU sensor. In some embodiments, the angle may be thigh angle. In some embodiments, the angle may be knee angle. In some embodiments, the angle may be shank angle. In some embodiments, the thigh angle value may be determined from the knee angle and / or the shank angle.

[0063] At step 306 of Figures 3 A and 3B, the control system may calculate a velocity (e.g., angular velocity) from the angles calculated at step 304. In some embodiments, the thigh velocity may be determined by calculating the differences between the thigh angle values. The velocity may be a thigh velocity or knee velocity. In other embodiments, the velocity may be a shank velocity (e.g., when the control system is controlling an ankle joint). In some embodiments, the control system may filter the velocity, e.g., thigh velocity, to improve sensor measurement accuracy and / or reliability. In some embodiments, the filter may remove jerky movements that may be introduced as the user is moving about (e.g., jerky thigh motion that can create jerky torque commands, which in turn causes jerky thigh motion and that may destabilize the system). In some embodiments, the filter may be a low pass filter. In one implementation, the filter may include a 10 Hz filter. In other embodiments, other low-pass filter frequencies may be implemented. For example, the cut-off frequency may range from about 2 Hz to about 20 Hz, or about 5 Hz to about 15 Hz, or any cut-off frequency within a range defined by those values. In one embodiment, the filter is a Butterworth second order low-pass filter with a cut-off frequency of 10 Hz.

[0064] At step 308 of Figure 3A, the control system may, based on the velocity calculated in step 306, interpolate control parameters of an impedance controller between fumbling around and assistance from the actuator (that is, net positive torque values) or between fumbling around and resistance from actuator (that is, net negative values). In the present disclosure, the positive torque values may refer to net positive torque values and the negative torque values may refer to net negative torque values, which may take into account a force asserted by the user on the actuator. As disclosed herein, one example of when assistance is helpful is when the user is standing up (e.g., from a sitting position, a deep squat position, or a slight squat position). One example of when resistance is helpful is when the user is sitting down (e.g., from a sitting position, a deep squat position, or aslight squat position). In the present disclosure, the control system can directly control the knee joint between when the user is fumbling around and standing up (that is, moving the thigh angle to a 0 degree position), and when the user is fumbling around and sitting down (that is, moving the thigh angle to about a 90 degree position or a different angle for a different heighted chair). If the user is initially in the process of standing up from a sit- down state, but changes her mind and decides to sit down again, the user does not need to first complete the stand-up movement (moving the thigh angle to about 0 degree) before the control system can control the actuator to provide resistance to sit down. Vice versa, if the user is initially in the process of sitting down from a standing state, but changes her mind and decides to stand up again, the user does not need to first complete the sit down movement (moving the thigh angle to back to about 90 degree or another angle depending on the height of the seat) before the control system can control the actuator to provide assistance to stand up.

[0065] The control parameters for impedance control (e.g., variable gain impedance control) may include but are not limited to any one or more of the following: proportional gain, derivative gain, mass gain, desired position set-point, and / or desired velocity (e.g., angular velocity) set-point, or any other parameters disclosed herein (including the parameters disclosed in the patents incorporated herein by reference).

[0066] Figure 3B illustrates one embodiment of the interpolation between when the user is fumbling around and needing assistance, and when the user is fumbling around and needing resistance (i.e., one implementation of step 308 in Figure 3A). At decision step 310, the control system can determine whether the velocity (e.g., thigh velocity) calculated at step 306 is greater than or equal to zero. If true, at step 312, the controller can interpolate the control parameters between fumbling around and assistance (e.g., stair ascent activities, standing up etc.). The control system can use the velocity to calculate a ratio by dividing the velocity by the maximum velocity. The maximum velocity may include, e.g., 50 deg / s, 100 deg / s, 150 deg / s, 200 deg / s, 250 deg / s, or any maximum velocity within a range defined by these values. If false, at step 314, the control system can interpolate the control parameters between fumbling around and resistance (e.g., stair descent activities, sit-down activities, etc.). The control system can use the velocity to calculate a ratio by dividing velocity by the maximum velocity. The maximum velocity may include, e.g., -50 deg / s, -100 deg / s, 150 deg / s, -200 deg / s, -250 deg / s, or any maximum velocity within a range defined by these values.

[0067] As shown in Figures 3 A and 3B, at step 316, the control system may use the interpolated control parameters in the impedance controller to determine the torque value of the actuator, which may be output to the actuator. In some embodiments, the interpolated control parameters may be used in the impedance controller with a given delay / ramp up to create a smoother transition between activities. The delay can be, for example, about 50 ms to about 200 ms, or about 60 ms to about 150 ms, or about 80 ms to about 120 ms, or about 100 ms, or any duration within a range defined by those values.

[0068] In some embodiments, during swing phase, if the thigh is raised higher (larger negative value) than a set threshold, the control system of a prosthetic knee joint disclosed herein can enter thigh position tracking and calculate a target knee position apos (e.g., an angular position) using the equation: apos = aoffset + G*(<j>thigh)

[0069] where aoffset is an offset angle and G is a thigh angle gain. This swing thigh tracking mode can be used when users are entering stair ascent where the thigh angle is usually greater than the set threshold. The set threshold can be a negative value, for example, from about -30° to about -60°, or about -35° to about -55°, or about -40° to about -50°, or about -45°. In some embodiments, the offset angle may range from about -5° to about 5°, or about -3° to about 3°, or about -1° to about 1°, or about 0. To exceed the set threshold, the thigh is more negative (that is, being negative with a greater absolute value) than the negative value of the set threshold. In some embodiments, the thigh angle gain may range from about 14 to about 4 / 3, or about 1 / 3 to about 114, or about 2 / 3 to about 1, or any other gain within a range defined by those values.

[0070] Figure 4 illustrates a swing thigh tracking mode according to an embodiment of the present disclosure. At step 402, the swing thigh tracking mode may be initially activated (or with the offset angle and / or the thigh angle gain reduced). The swing thigh tracking mode can be disabled when the user enters the stance phase. Alternatively, the offset angle and / or the thigh angle gain can be adjusted below the values set for when the thigh angle is more negative than the set threshold. In one example, the thigh angle gain may be reduced from 1 to 1 / 3 or 14, or any gain value within this range.

[0071] At step 404, the control system (which may be a control system of any prosthetic device, such as a knee joint, an ankle joint, etc.) may receive new IMU sensor values. In some embodiments, other sensor values may be used. In some embodiments, the IMU sensor may be located on the joint (e.g., the knee joint). In some embodiments, the IMU sensor may be located on the shank structure. In some embodiments, the IMUsensor may be located on the adjacent prosthetic portion coupled to the proximal connector of the joint. The sampling rate for the IMU sensor may vary between about 30 Hz to about 1,000 Hz, or about 40 Hz to about 800 Hz, or about 50 Hz to about 500 Hz, or about 60 Hz to about 140 Hz, or about 70 Hzto about 130 Hz, or about 80 Hz to about 120 Hz, or about 90 Hz to about 110 Hz, or about 100 Hz, or any frequency within any range defined by those values. In other embodiments, the measurements may be from a different sensor, e.g., an angle sensor.

[0072] At step 406, the control system may calculate an angle from the IMU sensor. In some embodiments, the angle may be thigh angle. In some embodiments, the angle may be knee angle. In some embodiments, the angle may be shank angle. A thigh angle value may be determined from the knee angle and / or the shank angle.

[0073] At decision step 408, the control system may determine whether the thigh angle measured has met or exceeded the set threshold, as disclosed herein. If true, the control system can enter the swing thigh tracking mode disclosed herein. If false, the control system can return to step 402.

[0074] In some embodiments, the swing thigh tracking mode can be advantageous when the user is stepping over obstacles. The user may need an additional flexion when moving the limb over the obstacles and then additional extension when reaching for the ground on the other side of the obstacles. In some embodiments, the swing thigh tracking mode may allow users to step on a box using their prosthetic leg and get assistance to raise their bodies up when they extend their hip. After having gotten up on the box with both legs, the users can flex the hip to lower their bodies again so they can reach the ground on the other side with their unamputated leg.

[0075] Figure 5 illustrates graphically, as a user is repeating sit-stand activities (with certain amount of fumbling around), example values of gait phase (BASE GAIT PHASE, 500), knee angle (KNEE JOINT ANGLE, 502), and thigh velocity (POWER KNEE THIGH ROT VEL, 504) when the user uses a prosthetic knee device disclosed herein. The gait phase 500 may include indications of whether the prosthesis is loaded or not, which in turn may indicate whether the user is sitting (value 10) or standing (value 0), which is amplified from the 1 (sit) and 0 (stand) control scheme for easier visualization on the graph in Figure 5.

[0076] As shown, at time 0 (x-axis, in ms), the user may start with sitting (value 10). The knee angle 502 may be at about 90° and the thigh velocity 504 may be fluctuation slightly around 0 deg / s. At around 2000 ms, the user may start to stand up (value 0). Theknee angle 502 may drop to about 0°, and the thigh angle (thigh velocity 504) may spike to about 200 deg / s. At around 4000 ms to around 5000 ms, the graph illustrates an example fumbling around, with the knee angle 502 generally plateauing at an angle being between 0° and 90° during that period. In that time period, the thigh velocity 504 may also drop back to zero from round -80 deg / s. The user may have hesitated in the process of sitting down during that time period. The control system disclosed herein may allow the user to do so, e.g., by tracking that the thigh velocity was initially becoming more negative as the user was going to sit down, but returned to zero before the user completed the sit down activity, and then decreased again as the user continued to sit down. As disclosed elsewhere herein, an existing control system that rely on detecting entry / exit conditions and transitions between defined activity states may not allow the user to do so (because the user may need to first completely sit down). At between around 10,000 ms and 12,000 ms, the graphs may illustrate the user completing a sit down activity from a standing up state.

[0077] The interpolation function can be liner or non-linear. Figures 6A-6C illustrate three example interpolation functions, although other suitable interpolation functions may be used. The control system may use any of the interpolation functions. In some embodiments, the control parameters may be determined by more than one interpolation functions. As shown in Figures 6A-6C, the interpolation functions may appear symmetrical between resistance and assistance. However, in several embodiments, the amount of maximum resistance and the amount of maximum resistance may be different, and / or the maximum positive thigh velocity and the maximum negative thigh velocity may be different.

[0078] Figure 6A illustrates graphically a linear, unbounded interpolation function. As shown, the x-axis is the velocity (e.g., thigh velocity, shank velocity, etc.), and the y-axis is the control parameter, which the positive value being assistance (making it easier for the joint to rotate) and the negative value being resistance (making it harder for the joint to rotate). With linear interpolation, the control parameter value is directly proportional to the velocity, with more negative velocity resulting in more resistance and more positive velocity resulting in more assistance. In some embodiments, the control parameter value between a minimum value and a maximum value is directly proportional to the velocity. The ratio (disclosed herein elsewhere as being calculated by dividing the velocity by the maximum velocity value) may dictate where the control parameter value may be between the minimum value and the maximum value. A ratio of 1 (100%) denotes selecting the control parameter value at the maximum and a ratio of 0 denotes selecting theminimum. In linear interpolation, the ratio of 0 may be interpreted as fumbling around. A ratio of 0.5, i.e., 50%, would result in an interpolated point on the graph. For example, in the linear interpolation function, the point at a ratio of 0.5 may be a mean control parameter value between the minimum and maximum values. The interpolation can be non-bounded, such that the user can get more assistance when exceeding the interpolated maximum value.

[0079] Figure 6B illustrates a linear, bounded interpolation function. The graph in Figure 6B is similar to the graph in Figure 6A in terms of the linear relationship. However, in Figure 6B, the control parameter value may have positive and negative limits if the ratio exceeds 1. After the ratio has exceeded 1 , even as the positive velocity continues to increase or the negative velocity continues to decrease, the control parameter value (and the amount of assistance or resistance) may be capped at the respective limits. A bounded interpolation function may advantageously cap the amount of resistance and assistance that have been set by the user and / or the CPO as being required to carry out the necessary activities.

[0080] Figure 6C illustrates a non-linear, bounded interpolation function. The graph in Figure 6C is similar to the bounded interpolation function in the graph in Figure 6B to the extent that the control parameter value may have positive and negative limits if the ratio exceeds 1. However, the control parameter value may not increase or decrease linearly with the change in the velocity (or the ratio disclosed herein). In one implementation, this non-linear interpolation function may reduce misdetection of standing up when the velocity is close to zero. In that implementation, a greater range of thigh velocity (extending beyond zero) may be interpreted as a sit-down activity or a fumbling around, resulting in a “dead zone” around 0 velocity. Although the user may need more momentum to reach a thigh velocity that may trigger a motion with the non-linear relationship (i.e., the “dead zone” around 0), the non-linear function may allow for more stability in the knee joint. Instead of a linear curve, the relationship may follow a U-shaped curve (in its respective quadrant of the graph) in a higher power (e.g., quadratic or otherwise). In some embodiments, the non-linear relationship may follow any designed curve, e.g. square root, logarithmic, etc.

[0081] In some embodiments, the control system may be a control system of a prosthetic foot with a powered ankle. The control system may include an impedance control for controlling a stiffness of the ankle. In some embodiments, the impedance control may implement an impedance equation for calculating the ankle torque may be T=K*(Pos_des-Pos_act) + D*(Vel_des-Vel_act), where K is stiffness gain, and D isdamping gain, Pos des is the desired ankle position, Pos act is the measured ankle position, Vel des is the desired ankle velocity, and Vel act is the measured ankle velocity. In some embodiments, the measured ankle position and / or measured ankle velocity may be based on the input from the angle sensor. The control system of the ankle joint may use the IMU sensor measurements to interpolate the control parameters of the impedance equation, including but not limited to K, D, Pos des, and Vel des.

[0082] As shown in Figure 7, at step 702, the control system may receive new IMU sensor values. In some embodiments, other sensor values (e.g., angle sensor located at the ankle joint) may be used. In some embodiments, the IMU sensor may be located on the ankle joint. In some embodiments, the IMU sensor may be located on the shank structure. The sampling rate for the IMU sensor may vary between about 50 Hz to about 150 Hz, or about 60 Hz toa bout 140 Hz, or about 70 Hz, or about 130 Hz, or about 80 Hz to about 120 Hz, or about 90 Hz to about 110 Hz, or about 100 Hz, or any frequency within any range defined by those values.

[0083] At step 704, the control system may calculate an angle from the IMU sensor. In some embodiments, the angle may be shank angle. At step 706, the control system may calculate a velocity (e.g., angular velocity) from the angle calculated at step 704. The velocity may be a shank velocity, e.g., angular shank velocity. In some embodiments, the control system may filter the velocity, e.g., shank velocity, to improve sensor measurement accuracy and / or reliability. In some embodiments, the filter may be a low-pass filter. In one implementation, the filter may include a 10 Hz filter. In other embodiments, other low-pass filter frequencies may be implemented. For example, the cutoff frequency may range from about 2 Hz to about 20 Hz, or about 5 Hz to about 15 Hz, or any cut-off frequency within a range defined by those values. In one embodiment, the filter is a Butterworth second order low-pass filter with a cut-off frequency of 10 Hz.

[0084] At step 708, the control system may, based on the velocity calculated in step 706, interpolate control parameters of an impedance controller between assistance and resistance. The higher the shank angular velocity is, the prosthetic foot (e.g., the ankle and / or the flexible foot members of the foot) can become stiffer and more push-off power may be generated during push-off phase. A lower angular velocity may result in less added stiffness in the ankle and / or the flexible foot members during rollover and little to no push- off power.

[0085] As shown in Figure 8, in some embodiments, the knee joint control system 802 and the ankle joint control system 804 may work together to provide impedancecontrol as disclosed herein. The impedance control of the knee joint control system 802 and the ankle joint control system 804 disclosed herein may be synced to collectively produce resistive or assistive controls to improve biomechanical efficiency.

[0086] Although this disclosure has been described in the context of certain embodiments and examples, it will be understood by those skilled in the art that the disclosure extends beyond the specifically disclosed embodiments to other alternative embodiments and / or uses and obvious modifications and equivalents thereof. In addition, while several variations of the embodiments of the disclosure have been shown and described in detail, other modifications, which are within the scope of this disclosure, will be readily apparent to those of skill in the art. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the disclosure. For example, features described above in connection with one embodiment can be used with a different embodiment described herein and the combination still fall within the scope of the disclosure. It should be understood that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another in order to form varying modes of the embodiments of the disclosure. Thus, it is intended that the scope of the disclosure herein should not be limited by the particular embodiments described above. Accordingly, unless otherwise stated, or unless clearly incompatible, each embodiment of this invention may comprise, additional to its essential features described herein, one or more features as described herein from each other embodiment of the invention disclosed herein.

[0087] Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described in this section or elsewhere in this specification unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0088] Furthermore, certain features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations, one or more features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as a subcombination or variation of a subcombination.

[0089] Moreover, while operations may be depicted in the drawings or described in the specification in a particular order, such operations need not be performed in the particular order shown or in sequential order, or that all operations be performed, to achieve desirable results. Other operations that are not depicted or described can be incorporated in the example methods and processes. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the described operations. Further, the operations may be rearranged or reordered in other implementations. Those skilled in the art will appreciate that in some embodiments, the actual steps taken in the processes illustrated and / or disclosed may differ from those shown in the figures. Depending on the embodiment, certain of the steps described above may be removed, others may be added. Furthermore, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Also, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described components and systems can generally be integrated together in a single product or packaged into multiple products.

[0090] For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. Not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0091] Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodimentsdo not include, certain features, elements, and / or steps. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and / or steps are included or are to be performed in any particular embodiment.

[0092] Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

[0093] Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, 0.1 degree, or otherwise.

[0094] Many other variations than those described herein will be apparent from this disclosure. For example, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (for example, not all described acts or events are necessary for the practice of the algorithms). Moreover, acts or events can be performed concurrently, for example, through multi -threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and / or computing systems that can function together.

[0095] It is to be understood that not necessarily all such advantages can be achieved in accordance with any particular example of the examples disclosed herein. Thus, the examples disclosed herein can be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0096] The various illustrative logical blocks, modules, and algorithm steps described in connection with the examples disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure.

[0097] The various illustrative logical blocks and modules described in connection with the examples disclosed herein can be implemented or performed by a machine, such as a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuit or digital logic circuit configured to process computer-executable instructions. In another example, a processor can include an FPGA or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[0098] The steps of a method, process, or algorithm described in connection with the examples disclosed herein can be embodied directly in hardware, in a software module stored in one or more memory devices and executed by one or more processors, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of non-transitory computer-readable storagemedium, media, or physical computer storage known in the art. An example storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The storage medium can be volatile or nonvolatile. The processor and the storage medium can reside in an ASIC.

[0171] The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.

Claims

WHAT IS CLAIMED IS:

1. A powered prosthetic lower limb device, comprising: a shank structure; a knee joint positioned between a shank structure and an adjacent prosthetic portion or a limb segment of a user, the knee joint comprising a powered actuator, wherein the powered actuator is configured to rotate the shank structure relative to the adjacent prosthetic portion or the limb segment of the user; and a control system in communication with the powered actuator, the control system configured to: receive a reading from an inertial measurement unit (IMU); calculate an angle of the knee joint, the shank structure, or the adjacent prosthetic portion or the limb segment; based at least in part on the angle, perform an interpolation function of control parameters of impedance control between: fumbling around and resistance to rotate the knee joint, or fumbling around and assistance to rotate the knee joint; and output a torque of the actuator based on the interpolated control parameters.

2. The device of Claim 1, wherein the control system is further configured to determine an angular velocity based on the angle.

3. The device of Claim 2, wherein: in response to the angular velocity being zero or greater than zero, the control system is configured to interpolate the control parameters between fumbling around and assistance to rotate the knee joint; and in response to the angular velocity being less than zero, the control system is configured to interpolate the control parameters between fumbling around and resistance to rotate the knee joint.

4. The device of any of Claims 1-3, further comprising the IMU, wherein the IMU is at the knee joint.

5. The device of any of Claims 1-3, further comprising the IMU, wherein the IMU is at the shank structure.

6. The device of any of Claims 1-3, wherein the knee joint is positioned between the shank structure and the adjacent prosthetic portion, the IMU being located at the adjacent prosthetic portion.

7. The device of any of Claims 1-6, wherein the angle calculated is the angle of the adjacent prosthetic portion or the limb segment.

8. The device of any of Claims 1-7, wherein the interpolation function is bounded.

9. The device of any of Claims 1-7, wherein the interpolation function is unbounded.

10. The device of any of Claims 1-9, wherein the interpolation function is linear.

11. The device of any of Claims 1-9, wherein the interpolation function is nonlinear.

12. The device of any of Claims 1-11, wherein the control system is further configured to interpolate one or more of the control parameters using one or more interpolation functions.

13. The device of any of Claims 1-12, wherein the control parameters comprise one or more of: proportional gain, derivative gain, mass gain, desired position set-point, and / or desired velocity set-point.

14. The device of any of Claims 1-13, wherein the shank structure comprises a distal connector configured to be coupled to a powered prosthetic ankle, wherein the impedance control of the device is synced with impedance control of the powered prosthetic ankle.

15. A powered prosthetic lower limb device, comprising: a shank structure; a knee joint positioned between a shank structure and an adjacent prosthetic portion or a limb segment of a user, the knee joint comprising a powered actuator, wherein the powered actuator is configured to rotate the shank structure relative to the adjacent prosthetic portion or the limb segment of the user; and a control system in communication with the powered actuator, the control system configured to: receive a reading from an inertial measurement unit (IMU); calculate an angle of the knee joint, the shank structure, or the adjacent prosthetic portion or the limb segment, and in response to the angle exceeding a threshold, determine a target knee joint position based at least in part on the angle; and output a torque of the actuator based at least in part on the target knee joint position, wherein the target knee joint position is one of control parameters of impedance control of the knee joint.

16. The device of Claim 15, wherein the threshold is a negative value.

17. The device of Claim 16, wherein the angle exceeding the threshold comprises the angle being more negative than the negative value.

18. The device of Claim 16 or 17, wherein the negative value is -45°.

19. The device of any of Claims 15-18, wherein determining the target knee joint position comprises multiplying the angle by an angle gain.

20. The device of Claim 19, wherein determining the target knee joint position further comprises adding an offset angle.

21. The device of any of Claims 15-20, wherein the control system is further configured to, based at least in part on the angle, perform interpolation of the control parameters of impedance control between: fumbling around and resistance to rotate the knee joint, or fumbling around and assistance to rotate of the knee joint, wherein the control system is further configured to output the torque to the actuator based in part on the interpolated control parameters.

22. The device of Claim 21, further comprising the IMU.

23. The device of Claim 21 or 22, wherein the control system is further configured to determine an angular velocity based on the angle.

24. The device of Claim 23, wherein: in response to the angular velocity being zero or greater than zero, the control system is configured to interpolate the control parameters between fumbling around and assistance to rotate the knee joint; and in response to the angular velocity being less than zero, the control system is configured to interpolate the control parameters between fumbling around and resistance to rotate the knee joint.

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