Abstract
To provide stroke patients with good rehabilitation training, the rehabilitation robot should ensure that each joint of the limb of the patient does not exceed its joint range of motion. Based on the machine vision combined with an RGB-Depth (RGB-D) camera, a convenient and quick human-machine interaction method to measure the lower limb joint range of motion of the stroke patient is proposed. By analyzing the principle of the RGB-D camera, the transformation relationship between the camera coordinate system and the pixel coordinate system in the image is established. Through the markers on the human body and chair on the rehabilitation robot, an RGB-D camera is used to obtain their image data with relative position. The threshold segmentation method is used to process the image. Through the analysis of the image data with the least square method and the vector product method, the range of motion of the hip joint, knee joint in the sagittal plane, and hip joint in the coronal plane could be obtained. Finally, to verify the effectiveness of the proposed method for measuring the lower limb joint range of motion of human, the mechanical leg joint range of motion from a lower limb rehabilitation robot, which will be measured by the angular transducers and the RGB-D camera, was used as the control group and experiment group for comparison. The angle difference in the sagittal plane measured by the proposed detection method and angle sensor is relatively conservative, and the maximum measurement error is not more than 2.2 degrees. The angle difference in the coronal plane between the angle at the peak obtained by the designed detection system and the angle sensor is not more than 2.65 degrees. This paper provides an important and valuable reference for the future rehabilitation robot to set each joint range of motion limited in the safe workspace of the patient.
Highlights
According to the World Population Prospects 2019 (United Nations, 2019), by 2050, one in six people in the world will be over the age of 65 years, up from one in 11 in 2019 (Tian et al, 2021)
To accurately describe the motion of human lower limb joints in the sagittal plane and the hip joint in the coronal plane, the human hip joint is simplified as two rotation pairs, which rotates around the parallel axis, such as the sagittal axis and the coronal axis, respectively
For the hip joint range of motion in the coronal plane, the sagittal plane is taken as the zero-reference plane, and the angle between the plane containing the human thigh and calf and the zero reference plane is taken as the hip joint range of motion θH1 in the coronal plane, in which the outward expansion direction is set as the forward direction of the joint range of motion
Summary
According to the World Population Prospects 2019 (United Nations, 2019), by 2050, one in six people in the world will be over the age of 65 years, up from one in 11 in 2019 (Tian et al, 2021). According to the characteristics of stroke and human limb movement function, it mainly uses the mechanical factors, based on the kinematics, sports mechanics, and neurophysiology, and selects appropriate functional activities and exercise methods to train the patients to prevent diseases and promote the recovery of physical and mental functions (Gassert and Dietz, 2018; D’Onofrio et al, 2019; Cespedes et al, 2021). Lokomat is designed as the most famous lower limb rehabilitation robot that has been carried out in many clinical research (Lee et al, 2021; Maggio et al, 2021; van Kammen et al, 2021). It is mainly composed of three parts: gait trainer, suspended weight loss system, and running platform. In terms of the humanmachine interaction of rehabilitation robots, it is very important to determine the setting of limb safe workspace of the patient and especially setting safety protection at the control level
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