Imu calibration system

Abstract

The present invention relates to a system for the calibration of inertial measurement units (IMUs) for use in medical engineering, in particular for gait analysis, e.g. for the adaptation of medical orthoses. The calibration system according to the invention comprises a hollow body with receiving devices for the IMUs, and drive units which allow a targeted rotation of the sphere about two different spatial axes.

Description

[0001] IMU -Kai i brieru ngssystem

[0002] The present invention relates to a system for calibrating inertial measurement units (IMU) for use in medical technology, in particular for the analysis of gait, e.g. for the adaptation of medical

[0003] 5 technical orthoses.

[0004] It is known that orthoses can be used to improve gait in people with movement disorders, e.g., after strokes. Such orthoses are described, for example, in EP 2922506 B1 (Orthopunkt AG). Precise gait analysis is a prerequisite for adjusting the orthosis. For this purpose, too, there are a variety of systems that analyze a person's gait using optical methods, for example. The "gold standard" is the VICON system, which uses at least six cameras and is very complex to prepare and analyze. Recently, a sensor-based gait analysis system (WO 2022 / 058974 A1, MOWA Healthcare AG) was introduced that analyzes gait using so-called inertial measuring units, which are attached to the affected person's extremities.By analyzing movement, particularly angular acceleration relative to the gravitational field, a precise analysis of gait can be performed, providing crucial data for orthotic adjustment. It has been found that the IMUs used for the system described in WO 2022 / 058974 A1 must be calibrated prior to use. During this calibration, the IMUs must be specifically aligned along the spatial axes and rotated. Such calibration is currently performed manually, which is a lengthy and laborious process.

[0005] Devices with which calibration is possible are known from the prior art, such as JP200626680A or WO2022249292A1, which, however, still have disadvantages. In particular, the devices described therein can only calibrate one IMU per run. Furthermore, the IMUs are rotated around all three spatial axes during calibration, which is time-consuming. The present invention relates to a calibration system for IMUs that automatically enables the calibration of multiple IMUs within a very short time. The calibration system according to the invention initially contains a hollow body with mounting devices for the IMUs.

[0006] Typically, several IMUs are used for gait analysis in clinical settings. Typically, six IMUs are attached to the extremities. In some cases,

[0007] In some cases, up to eight IMUs can be used. In other cases, four IMUs are sufficient. For more advanced motion analyses, up to 21 IMUs can be used. The hollow body described here thus contains mounting devices for the desired number of IMUs. The hollow body is preferably designed to accommodate at least four IMUs, particularly preferably six to eight IMUs. Appropriately enlarged hollow bodies can also accommodate up to 21 IMUs; alternatively, calibration can also be performed by calibrating three times, each with seven IMUs.

[0008] In production, significantly more than 21 IMUs can be calibrated in a single run. However, simultaneous calibration of very large quantities5 (e.g., more than 100) in a single run is impractical, as the time required to load the fixture would then be significantly longer than the time required for calibration.

[0009] The hollow body is preferably spherical and consists of two half-shells with retaining elements. The retaining elements can be magnetic closures. Pins inserted into corresponding openings on the opposite side can also be used. Another alternative is to create a screw connection using appropriate threads in the half-shells. The hollow body can also have a different geometry, but a spherical design has been found to provide the best results to avoid imbalance. The retaining devices contained in the sphere must be designed to prevent movement of the IMUs within the sphere during the calibration process described below.

[0010] The device according to the invention further comprises drive units that enable targeted rotation of the sphere around the various spatial axes. This can be achieved, for example, by an arrangement according to Figure 1. Here, the sphere is mounted on a disc-shaped base plate. A motor can rotate the sphere vertically.

[0011] A horizontal rotation axis is formed orthogonally to this. For this purpose, another motor is arranged horizontally, equipped with a holding device. Using a corresponding actuator (linear motor), the holding device can be pressed against the sphere and released again. By controlling the motor, the sphere can be rotated around a horizontal axis.

[0012] For the intended purpose, it is essential that the rotational movement of the mo¬

[0013] 5 tors is fully transferred to the sphere, both for vertical and horizontal rotation. For this purpose, the corresponding holding elements are provided with a non-slip surface, for example, made of rubber or a similar material.

[0014] Using the two drives, the sphere can, in principle, be moved around all three spatial axes. To rotate around the third spatial axis, the horizontal fixation must be released, the sphere rotated vertically by 90°, and then re-fixed horizontally by pressing the actuator. However, it has surprisingly been found that rotation around two axes is sufficient for the calibration process: Rotation around the z-axis (perpendicular to the Earth's surface) is not required.

[0015] It goes without saying that the rotation of the sphere must occur with low friction and avoid any imbalance. A person skilled in the art can select the necessary components based on their specialist knowledge without having to resort to inventive steps. The calibration system according to the invention can also be implemented with other elements. The decisive factor is the ability to precisely align the sphere along at least two spatial axes.

[0016] For calibration, the IMUs are first inserted into the holders inside the hollow body, the hollow body is closed, and inserted into the calibration system. The individual IMUs automatically transmit the measurement data electromagnetically to a receiving station, e.g., via Wi-Fi or Bluetooth.

[0017] During calibration, the IMUs are first aligned along the x- and y-axes. Repeated measurements have been found to be advantageous. Typically, 10 to 50, preferably approximately 30, different orientations are attempted, and the respective transmitted measurement values ​​from the IMUs are saved. The hollow body with the IMUs is then rotated. The rotational movements also occur around the aforementioned x- and y-axes. Both positive and negative rotation directions are set. The rotation speed is 2 to 20 revolutions per minute, typically approximately 10 revolutions per minute.

[0018] Surprisingly, it has been found that calibration of several IMUs at the same time is possible, although the acceleration forces during the rotations

[0019] 5 vary from IMU position to IMU position. IMUs closer to the shell edge experience higher centrifugal forces at the same angular velocity than IMUs closer to the center of the sphere.

[0020] All measured data is transmitted electromagnetically (e.g., via Wi-Fi) to the receiving system, where it is evaluated. Calibration is performed by comparing the movement data between the IMUs with the preset movement data. The calibration process takes approximately 3 to a maximum of 10 minutes. Typically, the entire process is completed in less than 5 minutes.

[0021] The figures show an exemplary embodiment of the invention. 5 Figure 1 shows the structure of the system with a sphere and a horizontal and a vertical rotation axis for rotating the sphere as a sectional view (a) and a top view (b).

[0022] For vertical rotation, the sphere rests on a ball bearing on a turntable (see below). For horizontal rotation, the sphere can be clamped using an actuator / linear motor. Horizontal rotation is achieved via a motor drive on the horizontal axis. For low-friction rotation in the horizontal direction, a suitable ball bearing is mounted on the turntable on which the sphere rests.

[0023] Figure 2 shows an example of the details of the horizontal drive. 5 Figure 3 shows an example of the details of the vertical drive.

[0024] Figure 4 shows an exemplary embodiment of the opened sphere with holding device and magnetic and pin-shaped fixing elements.

Claims

Claims 1. Calibration system for calibrating inertial measurement units (IMUs), comprising a holding device for at least four IMUs, a horizontal drive for rotating the holding device about the horizontal axis, a vertical drive for rotating the holding device about the vertical axis, a receiving unit for receiving data from the IMUs, and an electronic control of the drive system by means of a microcontroller and corresponding software; an electronic evaluation unit for evaluating the measurement data and calibrating the IMUs by means of a microcontroller and corresponding software.

2. Calibration system for calibrating Inertial Measurement Units (IMUs), comprising a spherical hollow body with internal holding devices for at least 4 IMUs and at least one closable opening, a horizontal sphere holder, wherein the horizontal sphere holder has at least one linear actuator and wherein the contact point between the sphere holder and the sphere is formed by a non-slip, elastic material, wherein the horizontal sphere holder allows horizontal rotation about the horizontal axis of rotation by means of a controlled motor, a vertical sphere holder, wherein the vertical sphere holder has at least one actuator and wherein the contact point between the sphere holder and the sphere is formed by a non-slip, elastic material, wherein the vertical sphere holder allows vertical rotation about the vertical axis of rotation by means of a controlled motor,a receiving unit for receiving data from the IMUs and an electronic control unit for the drive system using a microcontroller and corresponding software; an electronic evaluation unit for evaluating the measurement data and calibrating the IMUs using a microcontroller and corresponding software.

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