A method for correcting wearing error of exoskeleton equipment

Abstract

The present invention discloses a method for correcting errors in wearing an exoskeleton device, including performing IMU self-calibration when the wearer of the exoskeleton device is standing upright; performing lower limb lying correction when the wearer of the exoskeleton device is lying flat; and converting the Euler angles measured by the IMU into quaternion form when the wearer of the exoskeleton device is exercising normally, and correcting the quaternion using the recorded angular velocity vector, and converting the compensated Euler angles according to the corrected quaternion as the final joint angle to complete the error correction of wearing the exoskeleton device. The present invention accurately measures the joint angles of the wearer without the aid of external equipment, and provides accurate motion information feedback for the exoskeleton device or rehabilitation monitoring equipment.

Description

Technical Field

[0001] The present application belongs to the field of motion detection technology, and specifically relates to a method for correcting wearing errors of an exoskeleton device. Background Art

[0002] In recent years, with the gradual development of science and technology and the significant improvement of the national medical and health level, wearable exoskeleton devices have developed rapidly in the fields of health care, medical rehabilitation and sports fitness. When working normally, the exoskeleton device needs to accurately obtain the wearer's joint movement as reference information for the exoskeleton controller or for analyzing the wearer's movement, rehabilitation, etc.

[0003] Among all wearable motion measurement solutions, inertial measurement units (hereinafter referred to as IMUs) have become the main sensors due to their low cost, good portability, fast dynamic response, and no restrictions on usage scenarios. However, there are several problems when using IMUs to monitor joint motion angles: (1) As described in patent application publication numbers CN110522458A and CN108852360A, almost all products using IMUs directly or indirectly require that the sensor must be fixed in a standard plane (generally parallel or perpendicular to the sagittal plane of the human body). However, the human body is not a regular geometric body. Especially when it comes to motion measurement of multiple joints such as the hip and knee, it is impossible to ensure that the axis of the IMU can be completely along the direction of human motion when the device is worn; (2) The IMU uses Euler angles as the output of posture measurement. However, the Euler angle representation using only three parameters is not a global, non-singular rigid body motion description method. Moreover, due to the problems of "universal joint lock" and complex periodicity of Euler angles, using Euler angles to represent the motion angles of joints is not so intuitive. Especially when the problem described in (1) exists, using Euler angles to describe human motion posture becomes very unintuitive.

[0004] Based on the problems existing in the use of IMU, some corresponding solutions have been proposed in the prior art. For example, the patent document with the patent application publication number CN111166346A describes a device that uses only an angular velocity sensor to detect human motion, and according to the characteristics of the lower limb movement of the human body, the movement angle of the knee joint can be measured without any requirements for wearing. However, the method described in the patent needs to be optimized offline first, and the movement axis is obtained by analyzing the human motion data, and then the real-time angle is solved. The complexity is high and the solution is time-consuming. For example, the patent document with the patent application publication number CN110646014A describes a method for IMU wear calibration based on a human joint position capture device. This method can be used directly online, but it is necessary to calibrate the wearing deviation of the IMU with the help of a human joint position capture device other than the skeleton, which increases the complexity of the equipment and requires data conversion calculations between devices. Summary of the invention

[0005] The purpose of this application is to provide a method for correcting the wearing error of an exoskeleton device, which can accurately measure the joint angles of the wearer without the aid of external equipment and provide accurate motion information feedback for the exoskeleton device or rehabilitation monitoring equipment.

[0006] In order to achieve the above purpose, the technical solution adopted by this application is:

[0007] A method for correcting wearing errors of an exoskeleton device, wherein the exoskeleton device is equipped with an IMU, and the method for correcting wearing errors of the exoskeleton device comprises:

[0008] Step 1: Perform IMU self-calibration with the wearer of the exoskeleton device standing upright;

[0009] Step 2: Perform lower limb lying correction when the wearer of the exoskeleton device is lying flat, including:

[0010] Step 2.1, detecting whether the wearer meets the lower limb lying flat correction condition, wherein the lower limb lying flat correction condition is: the wearer lies flat on a horizontal surface with the toes facing upward and remains stationary for at least 2 seconds;

[0011] Step 2.2: If it is detected that the wearer does not meet the lower limb lying correction condition, return to step 2.1 to continue the detection; otherwise, execute step 2.3;

[0012] Step 2.3: Get the acceleration value a measured by IMU x and a y ;

[0013] Step 2.4: According to the acceleration value a x and a y Calculate the angle α between the IMU installation plane and the human body sagittal plane;

[0014] Step 2.5: Calculate and obtain the angular velocity vector ω based on the angle α obtained in step 2.4 V , the calculation formula is as follows:

[0015]

[0016] Where Δt represents the sampling time of the IMU in seconds, and the angular velocity vector ω V The unit of is radians per second;

[0017] Step 3: When the wearer of the exoskeleton device is in normal motion, convert the Euler angles measured by the IMU into quaternion form, and use the recorded angular velocity vector ω V The quaternion is corrected, and the compensated Euler angle is converted according to the corrected quaternion as the final joint angle to complete the error correction of the exoskeleton device.

[0018] Several optional methods are also provided below, but they are not intended to be additional limitations on the above-mentioned overall solution, but are merely further supplements or preferences. Under the premise that there are no technical or logical contradictions, each optional method can be combined with the above-mentioned overall solution separately, and multiple optional methods can also be combined.

[0019] Preferably, the acceleration value a x and a y Calculate the angle α between the IMU installation plane and the human body sagittal plane, including:

[0020] If the exoskeleton device is worn on the outside of the wearer's lower limbs, the angle α is calculated as:

[0021]

[0022] If the exoskeleton device is worn on the front of the wearer's lower limbs, the angle α is calculated as:

[0023]

[0024] Wherein, the angle α is in radians.

[0025] Preferably, the Euler angles measured by the IMU are converted into quaternion form, and the recorded angular velocity vector ω is used V Correct the quaternion and convert the corrected quaternion into the compensated Euler angle as the final joint angle, including:

[0026] Step 3.1: Convert the Euler angles measured by the IMU into quaternion form as follows:

[0027]

[0028] Where q is a quaternion, ψ, θ, φ are Euler angles;

[0029] Step 3.2: Substitute the quaternion q and the angular velocity vector ω V Substitute the following formula:

[0030]

[0031] In the formula, is the angular velocity vector ω V The four-element form of is the corrected quaternion;

[0032] Step 3.3: Calculate the compensated Euler angle based on the corrected quaternion.

[0033] The exoskeleton device wearing error correction method provided by the present application first obtains the degree of inclination of the IMU sensor installation plane relative to the human body's sagittal plane, and then eliminates the deviation of the angle data transmitted by the IMU at the numerical level. In the process of correcting the deviation, no external measuring instrument is required. The wearer only needs to perform a two-step process of standing calibration and lower limb lying calibration to accurately measure the wearer's hip extension / flexion, abduction / adduction, and knee extension / flexion and other joint angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart of the exoskeleton device wearing error correction method of the present application;

[0035] Figure 2 This is a top view of the exoskeleton device of this application. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0038] At present, when wearing exoskeleton devices, there is a problem that the axis of the IMU cannot be guaranteed to be completely along the direction of human movement, nor can it be guaranteed that the installation plane of the IMU is completely in line with the human anatomical plane. When the above deviations occur when the device is worn, the Euler angles given by the IMU cannot intuitively reflect the movement angles of the hip and knee joints along a certain axis. However, whether in the field of power-assisted control or rehabilitation monitoring, people are generally interested in the movement angles of the lower limbs along a specific axis, and need to obtain precise angles about the specific axis, which leads to major problems in the application of current exoskeleton devices.

[0039] In response to the above problems, in one of the embodiments, a method for correcting the wearing error of an exoskeleton device is provided. When there is a deviation in the wearing of the IMU device, the wearing deviation of the IMU is corrected without the aid of external equipment, thereby accurately measuring the movement angles of the wearer's hip and knee joints along a specific movement axis, and providing accurate movement information feedback for the exoskeleton assist device or rehabilitation monitoring device.

[0040] like Figure 1 As shown, the exoskeleton device wearing error correction method in this embodiment includes:

[0041] Step 1: Perform IMU self-calibration with the wearer of the exoskeleton device standing upright.

[0042] IMU self-calibration refers to the calibration procedure that comes with the inertial measurement unit (IMU) currently on the market, which is mainly used to eliminate the deviation of the gyroscope and accelerometer. You can start the corresponding calibration procedure according to different models of IMU. The calibration procedure that comes with IMU is not described in detail here.

[0043] In the IMU self-calibration when the wearer is standing upright, the judgment of the upright state can be actively triggered or passively triggered. The active triggering, for example, detects the state of the wearer and actively triggers the IMU self-calibration when the upright state is met. The passive triggering, for example, receives a trigger to perform IMU self-calibration after the wearer switches to the upright state.

[0044] Step 2: Perform lower limb lying correction when the wearer of the exoskeleton device is lying flat.

[0045] The purpose of IMU calibration when the wearer is lying flat is to obtain the inclination angle of the IMU installation plane relative to the human body sagittal plane (the longitudinal section that divides the body into left and right parts) as the basis for the compensation of the joint angle data obtained by the IMU later. The purpose of deviation correction is achieved by solving the Euler angle in a way that the IMU is installed in a plane parallel to the human body sagittal plane.

[0046] According to the wearing condition of the exoskeleton device, this embodiment defines the state where the exoskeleton device is worn on the outer side of the lower limb of the human body and parallel to the sagittal plane of the human body as the correct wearing state, that is, at this time, effective motion angle data can be obtained after IMU self-calibration. The outer side of the lower limb is understood as the outer side of the lower limb, that is, the side opposite to the two legs is the inner side of the lower limb, and the side opposite to the two legs is the outer side of the lower limb.

[0047] In this embodiment, the lower limb coordinate system is referred to as the b system, x b The axial direction is defined as the direction perpendicular to the coronal plane of the human body (the longitudinal section that divides the body into the front and back parts) and pointing to the back of the human body. b The axis is located in the coronal plane of the human body and is b The axis is vertical and points to the right side of the body, z b The axis is determined according to the right-hand rule (the right-hand rule used in the definition of the three-dimensional coordinate system). The IMU coordinate system is s system, z s Axis and z b parallel and pointing in the same direction, x s With x b Located in the cross section of the human body with an angle of α, y s The axis is determined according to the right-hand rule. And the IMU installation plane is taken to be parallel to the x s Axis and perpendicular to y s axis.

[0048] like Figure 2 As shown, this embodiment is worn on the left lower limb of the human body and surrounds the left lower limb from the outer side. b The error correction method of the present application is illustrated by taking an exoskeleton device with an axis deflected in the negative direction (after deflection, it is still considered to be worn on the outer side of the lower limb) as an example.

[0049] Specifically, in this embodiment, the lower limb lying flat correction specifically includes the following steps:

[0050] Step 2.1, check whether the wearer meets the lower limbs lying flat correction condition. In order to ensure the correction effect, the lower limbs lying flat correction condition in this embodiment is set as: the wearer lies flat on a horizontal surface with the toes facing upward and remains stationary for at least 2 seconds.

[0051] If the exoskeleton device is worn on the outer side of the left lower limb of the human body, then when detecting whether the lower limb lying flat correction conditions are met, the detection can be based on the gyroscope and IMU of the exoskeleton device. If the gyroscope data has not changed and the IMU of the knee joint and the IMU of the hip joint simultaneously meet the requirements that the collected acceleration vector is parallel to the vector [-1,0,0] and this is maintained for at least 2 seconds, it is considered that the lower limb lying flat correction conditions are met.

[0052] However, considering that the exoskeleton device may be worn tilted during actual application, in order to more accurately determine whether the lower limbs lie flat correction conditions are met, it can be set to directly receive the satisfaction signal input by the user. When the satisfaction signal is received, it is determined that the lower limbs lie flat correction conditions are met, otherwise the lower limbs lie flat correction conditions are not met.

[0053] Step 2.2: If it is detected that the wearer does not meet the lower limbs lying flat correction condition, return to step 2.1 to continue the test; otherwise, go to step 2.3. Since the lower limbs lying flat correction is a necessary calibration step, if the wearer's posture does not meet the condition, the test will be re-executed until the condition is met.

[0054] Step 2.3: Get the acceleration value a measured by IMU x and a y When the wearer is stationary on the ground, the acceleration value a x is the local gravitational acceleration along x s Component of the axis, acceleration value a y is the local gravitational acceleration along y s The weight of the axis.

[0055] It is easy to understand that when the wearer is in motion or not stationary relative to the ground, the acceleration applied to the IMU is not necessarily the local gravity acceleration, so the acceleration value a x is the acceleration actually applied to the IMU along x s Component of the axis, acceleration value a y is the acceleration actually applied to the IMU along the y axis s The weight of the axis.

[0056] Step 2.4: According to the acceleration value a x and a y Calculate the angle α between the IMU installation plane and the human body sagittal plane (radians):

[0057]

[0058] Step 2.5: Calculate the angular velocity vector ω based on the angle α obtained in step 2.4 V And record. Angular velocity vector ω V The calculation formula is as follows:

[0059]

[0060] Where Δt represents the sampling time of the IMU in seconds, and the angular velocity vector ω V The unit is radians per second.

[0061] Step 3: When the wearer of the exoskeleton device is in normal motion, convert the Euler angles measured by the IMU into quaternion form, and use the recorded angular velocity vector ω V The quaternion is corrected, and the compensated Euler angle is converted according to the corrected quaternion as the final joint angle to complete the error correction of the exoskeleton device.

[0062] In order to avoid the singularity problem caused by Euler angle solution, quaternion is used to correct the angle obtained by IMU solution in the angle compensation stage. Therefore, the process of compensating Euler angle in this embodiment is as follows:

[0063] Definition of quaternions is as follows:

[0064]

[0065] In the formula, q0 represents the scalar part of the quaternion, q represents the vector part of the quaternion, q=[q0 q1 q2 q3] T When quaternions represent the rotation of a rigid body, its dynamic equation has an analytical solution, and the discrete form is as follows:

[0066]

[0067] in, is the symbol for quaternion multiplication, q ω =[0,ω T ] T is the four-component quantity expression of the IMU rotation angular velocity ω, q(t) represents the quaternion at time t, q(t+Δt) represents the quaternion at time t+Δt, and Δt represents the sampling time of the IMU. Here, the exponential operation of the quaternion can be simply calculated according to the mapping formula between the rotation vector and the quaternion, let:

[0068]

[0069] Then the following mapping is established:

[0070]

[0071] In order to correct the wearing deviation of the device, we must correct the original quaternion (the quaternion converted from the Euler angle uploaded by the IMU). This embodiment proposes the following quaternion correction formula based on the calculation principle of the quaternion:

[0072]

[0073] In the formula, q represents the original quaternion, represents the corrected quaternion, is the angular velocity vector ω V In the four-element form, we only need to replace the angular velocity vector ω calculated in formula (2) V Bring in The corrected quaternion can be obtained from the calculation formula. Symbol ω V The subscripts in represent virtual meanings and are used to distinguish the IMU rotation angular velocity from the angular velocity vector.

[0074] Therefore, when the wearer performs hip or knee joint exercises or rehabilitation treatment, the specific steps for correcting the Euler angles measured by the IMU are:

[0075] Step 3.1: Convert the Euler angles measured by the IMU into quaternion form as follows:

[0076]

[0077] Where q is a quaternion, ψ, θ, ψ are Euler angles, ψ is the heading angle, θ is the pitch angle, and φ is the roll angle.

[0078] Step 3.2: Substitute the quaternion q and the angular velocity vector ω V Substituting into equation (7) we can get the corrected quaternion.

[0079] Step 3.3, convert the corrected quaternion to obtain the compensated Euler angle. The quaternion can be converted into Euler angle according to the following formula:

[0080]

[0081] The corrected Euler angles will be able to accurately and directly reflect the movement angles of the hip and knee joints along a specific axis.

[0082] It should be noted that the present embodiment is worn on the left lower limb of the human body and is surrounded by the outer side of the left lower limb. b An exoskeleton device with an axis deflected in the negative direction is used as an example for explanation, but this does not limit the error correction method of the present application to be applicable only to this wearing method.

[0083] The error correction method of the present application is applicable to any wearing method of the limbs, wherein the above-mentioned wearable device is worn on the left lower limb of the human body and is encircled from the outer side of the left lower limb by z b The error correction method of the exoskeleton device with negative deflection of the axis is used as the basic correction method, wherein the exoskeleton device is worn on the left lower limb of the human body and starts from the outer side of the left lower limb around the z b The error correction method when the axis is deflected in the positive direction is the same as the basic correction method; it is worn on the right lower limb of the human body and starts from the outer side of the right lower limb around z b The error correction method when the axis is deflected in the positive / negative direction is the same as the basic correction method.

[0084] There is also a more common way to wear exoskeleton equipment, which is to wear it on the front of the wearer's lower limbs. Therefore, the state of wearing the exoskeleton equipment on the front of the human lower limbs and parallel to the human coronal plane can also be defined as the correct wearing state, that is, at this time, after IMU self-calibration, valid motion angle data can be obtained. The front of the lower limb is understood as the side of the lower limb located on the wearer's face. When the exoskeleton equipment is worn on the front of the human lower limb, it may also be worn tilted, that is, there is a situation of tilting around the z direction from the front of the lower limb. b In the case of positive / negative deflection of the axis, when the exoskeleton device is worn on the front of the lower limb of the human body in the correct wearing state or in the wearing state of tilt, the error correction method is different from the basic correction method only in the formula for calculating the angle α. The other steps or formulas are the same, and the formula for the angle α in this case is:

[0085] The error correction method proposed in this application is applicable to any wearing mode of the exoskeleton device on the lower limbs of the human body. Whether the exoskeleton device is worn on the outer side or the front of the lower limb can be measured and determined by an external sensor, or can be directly input by the wearer.

[0086] The case where the exoskeleton device is worn on the upper limbs of the human body is the same as the case where the exoskeleton device is worn on the lower limbs of the human body, and will not be repeated in this embodiment.

[0087] In addition, since the IMU in the exoskeleton device can be of any model, and the coordinate axes of the coordinate system of the IMUs of different models may be different, their coordinate axes can be analyzed relative to the IMU installation plane. s The y axis is parallel to the IMU installation plane. s The axis is perpendicular to the IMU installation plane. When the coordinate axis of the IMU is transformed, the axis parallel to the IMU installation plane is equivalent to the x in this application. s Axis, that is, the acceleration component on this axis is referred to as a in this application x Calculate and take the axis perpendicular to the IMU installation plane as equivalent to the y axis in this application. s Axis, that is, the acceleration component on this axis is referred to as a in this application y The calculation can be performed, so the error correction method of the present application is applicable to exoskeleton devices with any IMU model.

[0088] This embodiment significantly reduces the difficulty of wearing the exoskeleton device. The existing technology requires that the IMU installation plane must be strictly kept within the human anatomical plane during the wearing stage, or requires the addition of additional calibration equipment, or requires offline complex calculations, which increases the complexity of using the device. The method provided in this embodiment only requires the wearer to bind the exoskeleton device to the lower limbs of the human body in a normal wearing manner, and no correction operation is required during the wearing process. After the wearing is completed, only a simple correction procedure needs to be executed to achieve accurate hip and knee joint motion angle measurement. It is especially suitable for the use of current devices that use IMUs for motion angle measurement.

[0089] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for correcting wearing error of an exoskeleton device, wherein the exoskeleton device is equipped with an IMU, characterized in that: The exoskeleton device wearing error correction method comprises: Step 1: Perform IMU self-calibration with the wearer of the exoskeleton device standing upright; Step 2: Perform lower limb lying correction when the wearer of the exoskeleton device is lying flat, including: Step 2.1, detecting whether the wearer meets the lower limb lying flat correction condition, wherein the lower limb lying flat correction condition is: the wearer lies flat on a horizontal surface with the toes facing upward and remains stationary for at least 2 seconds; Step 2.2: If it is detected that the wearer does not meet the lower limb lying correction condition, return to step 2.1 to continue the detection; otherwise, execute step 2.3; Step 2.3: Get the acceleration value a measured by IMU x and a y ; Step 2.4: According to the acceleration value a x and a y Calculate the angle α between the IMU installation plane and the human body sagittal plane; Step 2.5: Calculate and obtain the angular velocity vector ω based on the angle α obtained in step 2.4 V , the calculation formula is as follows: Where Δt represents the sampling time of the IMU in seconds, and the angular velocity vector ω V The unit of is radians per second; Step 3: When the wearer of the exoskeleton device is in normal motion, convert the Euler angles measured by the IMU into quaternion form, and use the recorded angular velocity vector ω V The quaternion is corrected, and the compensated Euler angle is converted according to the corrected quaternion as the final joint angle to complete the error correction of the exoskeleton device.

2. The exoskeleton device wearing error correction method according to claim 1, characterized in that: According to the acceleration value a x and a y Calculate the angle α between the IMU installation plane and the human body sagittal plane, including: If the exoskeleton device is worn on the outside of the wearer's lower limbs, the angle α is calculated as: If the exoskeleton device is worn on the front of the wearer's lower limbs, the angle α is calculated as: Wherein, the angle α is in radians.

3. The exoskeleton device wearing error correction method according to claim 1, characterized in that: The Euler angles measured by the IMU are converted into quaternion form, and the recorded angular velocity vector ω is used V Correct the quaternion and convert the corrected quaternion into the compensated Euler angle as the final joint angle, including: Step 3.1: Convert the Euler angles measured by the IMU into quaternion form as follows: Where q is a quaternion, ψ, θ, φ are Euler angles; Step 3.2: Substitute the quaternion q and the angular velocity vector ω V Substitute the following formula: In the formula, is the angular velocity vector ω V The four-element form of is the corrected quaternion, is the quaternion multiplication operator symbol; Step 3.3: Calculate the compensated Euler angle based on the corrected quaternion.

Images