Automatic control of myoelectric hand using inertial measurement unit

Abstract

To provide a control system of a prosthetic hand capable of horizontal maintenance control.SOLUTION: Provided is a control system for a prosthetic hand including three servo motors, a processor, and a myoelectric potential sensor, in which the processor operates the servo motors to enable grasping of an object and a horizontal maintaining operation of the prosthetic hand when a voltage from the myoelectric potential sensor is equal to or greater than a predetermined value, and the processor operates the servo motors to release the grasping of the object and a horizontal maintaining operation of the prosthetic hand when the voltage from the myoelectric potential sensor is less than the predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to automatic control of a myoelectric prosthetic hand using an inertial measurement unit. [Background technology]

[0002] The background to this invention is that the operation of a myoelectric prosthetic hand is performed by analyzing the myoelectric potential generated when the user exerts force on a muscle, so it is ideal to be able to obtain clear signals from multiple muscles. However, many people who use myoelectric prostheses have weakened muscles in their residual limbs, and there are also individual differences, so it is often difficult to obtain signals near the residual limb, or clear signals cannot be obtained. In such cases, signals from areas unrelated to the arm, such as the pectoral muscles or oblique abdominal muscles, are used, making it difficult to control the force, etc.

[0003] Search content: J-PlatPat simple search Keywords: Inertial Measurement Unit, Attitude Control, 16 results Keyword prosthetic arm 1500 results Using a simple search, we identified the contents of the patents that were closest to our invention from the 1,516 hits using the above keywords. Patent document 1 (JP 2021-123118 A) discloses an invention that uses an inertial measurement unit to perform posture control, but the present invention differs in that it is applied to prosthetic limbs. In Patent Document 2 (JP Patent Publication No. 2015-80480), a rotation sensor is used to control the arm movement to operate the prosthetic hand, but this is only used for the grasping movement of the prosthetic hand, while the present invention differs in that it is used to control the wrist joint, which does not require operation by the user. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-123118 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-080480 Summary of the Invention [Problem to be solved by the invention]

[0005] We have invented a myoelectric prosthetic hand that allows delicate movements even for people with physical disabilities who have difficulty controlling their strength, with simple operations that do not require adjustment of force.The prosthetic hand of this invention also allows the user to maintain horizontality while grasping an object. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a prosthetic hand control system comprising three servo motors, a processor, and an electromyography sensor, wherein the processor operates the servo motors so as to enable grasping of an object and keeping the prosthetic hand horizontal when the voltage from the electromyography sensor is equal to or greater than a predetermined value, and the processor operates the servo motors so as to release grasping of the object and keeping the prosthetic hand horizontal when the voltage from the electromyography sensor is less than the predetermined value. [Effects of the Invention]

[0007] The prosthetic hand is equipped with control using an inertial measurement unit, allowing for delicate movements with minimal input. The prosthetic hand of the present invention can also maintain horizontality while grasping an object. Other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows an explanation of the components constituting a myoelectric prosthetic hand according to one embodiment of the present invention. [Figure 2] FIG. 2 shows the coordinate axis settings for posture calculation in a myoelectric prosthetic hand according to one embodiment of the present invention. [Figure 3] FIG. 3 shows the myoelectric prosthetic hand of one embodiment of the present invention in use. [Figure 4] FIG. 4 shows a block diagram for controlling a myoelectric prosthetic hand according to one embodiment of the present invention. [Figure 5] FIG. 5 shows a flowchart of the myoelectric prosthetic hand according to one embodiment of the present invention. [Figure 6] FIG. 6 shows data displaying the acquired posture and the target posture in the myoelectric prosthetic hand of one embodiment of the present invention. [Figure 7] FIG. 7 shows the state of use of the myoelectric prosthetic hand according to one embodiment of the present invention, showing grasping of an object. [Figure 8] FIG. 8 shows the state of the myoelectric prosthetic hand according to one embodiment of the present invention when in use, showing the release of the grip of an object. DETAILED DESCRIPTION OF THE INVENTION

[0009] To enable people to quickly master the operation of myoelectric prosthetic hands, which are difficult to master, we invented a control system using an inertial measurement unit to automate some of the movements. In particular, we implemented a system that specializes in control of maintaining the hand in a horizontal or arbitrary position. The inertial measurement unit is less affected by the environment and is completely independent of the user, so there is no need for user-specific calibration, which requires specialized knowledge. This makes it possible to reduce the time required for adjusting the prosthetic hand, which is part of the training process. Furthermore, to automate some of the movements of a myoelectric prosthesis, it is necessary to position the prosthesis so that it assumes a posture calculated by a motion planner or similar. In this case, it is important to maintain a constant posture, primarily horizontal control, so that the prosthesis operates at an accurate position and angle without being affected by external disturbances such as the swaying of the arm wearing it. For this reason, the present invention developed posture control, which is the basis for automating various movements. One of the reasons why myoelectric prosthetic hands are difficult to operate is that the majority of currently popular myoelectric prosthetic hands are operated using proportional control, which requires delicate adjustment of force. Therefore, in this invention, the user's myoelectric potential is used to distinguish the type of movement using a threshold rather than proportional control, and the delicate adjustment of movement that was performed using proportional control in conventional myoelectric prosthetic hands is now controlled using an inertial measurement unit. There are several types of prosthetic hands to suit the position of the user's residual limb, but this invention was developed with the forearm prosthetic hand in mind. Also, because this invention is about control, it does not include a socket for attaching it to the arm residual limb. [Example]

[0010] He invented a myoelectric prosthetic hand that can be easily operated by minimizing electromyographic control. With existing myoelectric prosthetic hands, the amount of muscle force applied directly affects the speed and grip strength of the prosthetic hand, so it is necessary to adjust the amount of force applied in order to use it effectively. In contrast, our invention measures whether muscle force is above a certain level and allows operation based on only two settings: high and low myoelectric potential. Muscles exhibit high myoelectric potential when exerted force, and low myoelectric potential when released. Furthermore, to simplify operation while still maintaining the same or greater range of motion than existing devices, we incorporated additional inertial measurement unit control. The inertial measurement unit integrates gyro, accelerometer, and geomagnetic sensors and can measure posture. Because it is difficult to perform motions that require adjustment based solely on myoelectric potential, the system uses myoelectric potential to select the type of motion (e.g., opening or closing the hand, turning wrist angle control on or off, etc.). The microprocessor and inertial measurement unit then automatically control the selected motion (e.g., opening and closing the hand within a certain grip strength, maintaining a constant wrist angle, etc.) without user intervention. There are many actions that require the use of a prosthetic hand, but this time we focused on posture control, specifically holding an object horizontally. This action is necessary when holding tableware during meals, and is useful in everyday life. In addition, it is necessary to maintain a constant posture when performing other, more complex actions (such as buttoning or writing), so it also serves as the foundation for other actions.

[0011] FIG. 1 shows an explanation of the components constituting a myoelectric prosthetic hand according to one embodiment of the present invention. The prosthetic hand in Figure 1 is composed of multiple wrist joint servo motors and multiple finger servo motors. In this example, it is composed of three wrist joint servo motors and three finger servo motors. Reference symbol a in Figure 1 denotes the servo motor for the wrist joint, which moves so that the wrist of the prosthetic hand rotates on the X-axis shown in Figure 2. In Figure 1, b is the servo motor for the wrist joint, which moves the Z axis of the joint. In Figure 1, c is the servo motor for the wrist joint, which moves the Y axis of the joint. d in Figure 1 is a finger servo motor that switches the position of the thumb to the same side as the back of the prosthetic hand or the opposite side. In Figure 1, e is a finger servo motor that moves the index finger and middle finger. In Figure 1, f is a finger servo motor that moves the ring finger and little finger. g in Figure 1 is a microprocessor, which is connected to all sensors and servo motors. The symbol h in Figure 1 is an inertial measurement unit (IMU), which combines a gyro, acceleration sensor, and geomagnetic sensor to measure posture. It is housed inside the prosthetic arm. In Figure 1, i is a myoelectric potential sensor, which is attached to the skin near the muscles used for operation. For example, it can be attached to one arm (for example, any part of the biceps), the pectoral muscles, or the oblique abdominal muscles. The voltage output from the sensor is high when the myoelectric potential is high, i.e., when the muscles are tense, and is low when the myoelectric potential is low, i.e., when the muscles are relaxed. Parts such as a socket for attaching to the arm stump may be added to the rear left part of Figure 1.

[0012] FIG. 2 shows the coordinate axis settings for posture calculation in a myoelectric prosthetic hand according to one embodiment of the present invention. In this embodiment, for convenience of explanation, the X, Y, and Z axes are defined as shown in FIG. Figure 2 shows all servo motors at 0°. The range of motion of the servo motor on the X axis (a in FIG. 1) in this embodiment is, for example, from −90° to 90°, with clockwise rotation being positive and counterclockwise rotation being negative. The range of motion of the servo motor on the Y axis (b in FIG. 1) in this embodiment is, for example, from −70° to 90°, with clockwise rotation being positive and counterclockwise rotation being negative. The range of motion of the servo motor on the Z axis (c in FIG. 1) in this embodiment is, for example, from −25° to 55°, with counterclockwise rotation being positive and clockwise rotation being negative.

[0013] Figure 3 shows the state of use of a myoelectric prosthetic hand according to one embodiment of the present invention. Figure 3 shows the prosthetic hand grasping an object j while maintaining a constant horizontal position. In this embodiment, a prosthetic hand that can be worn on one arm will be described. The principle that makes such control possible will be explained below. The principle of control is that the posture of the myoelectric prosthetic hand is measured by an inertial measurement unit, and the difference between the target posture (hereinafter referred to as the "target posture") (an example is the posture shown in Figure 3) and the acquired posture is used as the tilt of the myoelectric prosthetic hand. The motor is then operated by the amount of tilt to control the tip of the prosthetic hand to the target posture. Here, an example of the tip of the prosthetic hand in this embodiment is the fingers of the prosthetic hand, and an example of the target posture in this embodiment is horizontal. Therefore, an example of the target posture of the tip of the prosthetic hand in this embodiment is a posture in which the fingers (longitudinal direction) of the prosthetic hand are horizontal (with respect to the ground). By grasping an object while maintaining such a target posture, the object can be held stably. For example, if the object in Figure 3 is a cup filled with water, control can be achieved so that the cup does not tilt and the water does not spill, even when the entire prosthetic hand is moved. Attitude calculation is performed using the coordinate axis settings shown in Figure 2. The attitude quaternion obtained from the inertial measurement unit is Q q , the attitude quaternion of the target attitude is P q Then, the differential quaternion D, which is the motor movement amount, q teeth,

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[0014] FIG. 4 shows a block diagram for controlling a myoelectric prosthetic hand according to one embodiment of the present invention. In this embodiment, it is composed of a microprocessor, a myoelectric potential sensor, an inertial measurement unit, a motor driver, and a plurality of servo motors. The microprocessor controls the myoelectric potential sensors, the inertial measurement unit, and the motor drivers, and manages the processing and input / output of the necessary signals and data. The myoelectric potential sensor amplifies the minute myoelectric potential and transmits it to a microprocessor as an analog signal. The inertial measurement unit communicates with the microprocessor and transmits attitude values. The motor driver drives the servo motor. Multiple servo motors operate each part of the prosthetic hand. To control the angle of the tip of the prosthetic hand, three servo motors (Fig. 1a, b, c) were installed so that the wrist could be driven on three axes, just like a human, and three servo motors (Fig. 1d, e, f) were installed so that the three pairs of fingers could be driven: the index finger and middle finger, the ring finger and little finger, and the thumb.A microprocessor (Fig. 1g) was installed at the base of the prosthetic hand, and it used an inertial measurement unit (Fig. 1h) to calculate the amount of motor movement to maintain horizontality, and switched operations using signals from an electromyography sensor (Fig. 1i).

[0015] FIG. 5 shows a flowchart of the myoelectric prosthetic hand according to one embodiment of the present invention.

[0016] In S501, the measurement reference for the inertial measurement unit is determined. The horizontal reference is determined by detecting gravitational acceleration with the acceleration sensor, and the horizontal reference is determined by obtaining the direction with the geomagnetic sensor. From then on, the information from the inertial measurement unit is data obtained by correcting the measurement values ​​of the gyro sensor with the acceleration sensor and geomagnetic sensor. In S502, the attitude at startup is acquired from the inertial measurement unit h and set as the target attitude. Here, the acquired attitude information is a quaternion that represents the attitude obtained from the inertial measurement unit when the hand is lowered or held horizontally, for example. In S503, the microprocessor determines whether the signal voltage of the electromyogram sensor i is equal to or higher than a predetermined threshold value (in this embodiment, 50% of the signal voltage when the user applies maximum force to the muscle of the sensor mounting part) (S402). Here, it is assumed that the signal voltage when applying maximum force (hereinafter referred to as the maximum value) and the signal voltage when completely relaxing the force are measured in advance and recorded in the memory of the microprocessor. Hereinafter, the information processing when the signal voltage of the electromyogram sensor is 50% or higher will be described. The information processing when the signal voltage of the electromyogram sensor is less than 50% will be described later. In S504, the microprocessor acquires the posture from the inertial measurement unit h (S401). In S505, the microprocessor calculates the difference between the target posture and the acquired posture, and performs vibration suppression processing according to the magnitude of the difference. (S404) (see FIG. 6). In S506, the microprocessor converts the difference into the operating angle of the servo motor. In S507, the microprocessor determines whether the servo motors (servo motors a, b, c of the wrist joint) are within the movable range. Here, as an example of the method for determining whether the servo motor is within the movable range, when the angle of the movable range of the motor is 45° to 135°, if the numerical value of the angle for which it is desired to determine whether it is within the movable range is x, it is determined whether 45 < x < 135 holds. If the motor is not within the movable range, the operating angle is corrected so as to be maximized within the movable range of the motor (S508). In S509, the microprocessor commands the angles to the servo motors a, b, c of the wrist joint (S403). In S510, the microprocessor drives the servo motors a, b, c of the wrist joint by PID control (S403, S404). In S511, the microprocessor closes the servo motors d, e, f of the fingers to grasp the object (j) (see FIG. 7). Also, the microprocessor maintains the horizontal of the object grasped in S509. In S512, the microprocessor may wait until the servo motors a, b, c of the wrist joint reach the joint angles for the prosthetic hand to reach the target posture. Thereafter, the process returns to S503 and the above-described processing is carried out.

[0017] The information processing when the signal voltage of the myoelectric potential sensor is less than 50% of the maximum value will be described below. In S513, the microprocessor obtains the attitude from the inertial measurement unit h. In S514, the microprocessor sets the acquired attitude as the target attitude to be used in S505. In S515, the microprocessor maintains the current angles of the servo motors a, b, and c of the wrist joint. In S516, the microprocessor opens the finger servo motors d, e, and f to release the grasped object j. As shown in Figure 8, after the object is released, the horizontal maintenance action is also released. Thereafter, the process returns to S503 and the above-described processing is carried out.

[0018] FIG. 6 shows data displaying the acquired posture and the target posture in the myoelectric prosthetic hand of one embodiment of the present invention. Figure 6 shows an internal view. The two arrows represent the target posture and the acquired posture, respectively. Although the user will not see it, those skilled in the art will be able to understand in what direction the myoelectric prosthetic arm is trying to maintain its angle.

[0019] Although the embodiments of the present invention have been described above, various alternatives, modifications, and variations are possible for those skilled in the art based on the above description, and the present invention includes the various alternatives, modifications, and variations described above within the scope of the present invention. [Explanation of symbols]

[0020] Wrist joint servo motors a, b, c Finger servo motors d, e, f

Claims

1. A control system for a prosthetic hand, comprising three servo motors, a processor, and an electromyography sensor, The processor operates the servo motor when the voltage from the myoelectric potential sensor is equal to or greater than a predetermined value so as to enable grasping of an object and horizontal maintenance of the prosthetic arm; A prosthetic hand control system characterized in that the processor operates the servo motor to release the grip of the object and the horizontal maintenance action of the prosthetic hand when the voltage from the electromyography sensor is below a predetermined value.

2. The control system for the prosthetic hand further comprises an inertial measurement unit; If the attitude quaternion obtained from the inertial measurement unit is Q and the attitude quaternion of the target attitude is P, the differential quaternion R, which is the motor operation amount, is given by: and Convert the difference quaternion R into Euler angles in the X-Z-Y system, and use the converted Euler angles as D. ｅ (θ ｄｉｆｘ , θ ｄｉｆｚ , θ ｄｉｆｙ ) and by applying the elements E to the servo motors of the corresponding rotation axes, it is possible to control the horizontal maintenance operation of the prosthetic arm.

3. The overall magnitude of the gradient T is year, The sigmoid function with the magnitude of this gradient T as a parameter is called the Euler angle D ｅ The control system according to claim 2, wherein the horizontal maintenance operation of the prosthetic arm can be controlled by multiplying each element of the above formula (1) by the above formula (2).

4. Using gains a and b to adjust the influence of the sigmoid function, the following calculation formula is used: Therefore, the Euler angle D ｅ current angle θ ｘ , θ ｚ , θ ｙ and add them to the angle φ commanded to the servo motor. ｘ , φ ｚ , φ ｙ Calculate φ ｘ , φ ｚ , φ ｙ 4. The control system according to claim 3, wherein the horizontal maintenance operation of the prosthetic arm can be controlled by applying the above to the servo motors of the corresponding rotation axes.

5. A program for executing the control system according to any one of claims 1 to 4.

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