Yoshio Inoue

Novel approach to ambulatory assessment of human segmental orientation on a wearable sensor system

A new method using a double-sensor difference based algorithm for analyzing human segment rotational angles in two directions for segmental orientation analysis in the three-dimensional (3D) space was presented. A wearable sensor system based only on triaxial accelerometers was developed to obtain the pitch and yaw angles of thigh segment with an accelerometer approximating translational acceleration of the hip joint and two accelerometers measuring the actual accelerations on the thigh. To evaluate the method, the system was first tested on a 2 degrees of freedom mechanical arm assembled out of rigid segments and encoders. Then, to estimate the human segmental orientation, the wearable sensor system was tested on the thighs of eight volunteer subjects, who walked in a straight forward line in the work space of an optical motion analysis system at three self-selected speeds: slow, normal and fast. In the experiment, the subject was assumed to walk in a straight forward way with very little trunk sway, skin artifacts and no significant internal/external rotation of the leg. The root mean square (RMS) errors of the thigh segment orientation measurement were between 2.4 degrees and 4.9 degrees during normal gait that had a 45 degrees flexion/extension range of motion. Measurement error was observed to increase with increasing walking speed probably because of the result of increased trunk sway, axial rotation and skin artifacts. The results show that, without integration and switching between different sensors, using only one kind of sensor, the wearable sensor system is suitable for ambulatory analysis of normal gait orientation of thigh and shank in two directions of the segment-fixed local coordinate system in 3D space. It can then be applied to assess spatio-temporal gait parameters and monitoring the gait function of patients in clinical settings.

A Wearable Ground Reaction Force Sensor System and Its Application to the Measurement of Extrinsic Gait Variability

Wearable sensors for gait analysis are attracting wide interest. In this paper, a wearable ground reaction force (GRF) sensor system and its application to measure extrinsic gait variability are presented. To validate the GRF and centre of pressure (CoP) measurements of the sensor system and examine the effectiveness of the proposed method for gait analysis, we conducted an experimental study on seven volunteer subjects. Based on the assessment of the influence of the sensor system on natural gait, we found that no significant differences were found for almost all measured gait parameters (p-values < 0.05). As for measurement accuracy, the root mean square (RMS) differences for the two transverse components and the vertical component of the GRF were 7.2% ± 0.8% and 9.0% ± 1% of the maximum of each transverse component and 1.5% ± 0.9% of the maximum vertical component of GRF, respectively. The RMS distance between both CoP measurements was 1.4% ± 0.2% of the length of the shoe. The area of CoP distribution on the foot-plate and the average coefficient of variation of the triaxial GRF, are the introduced parameters for analysing extrinsic gait variability. Based on a statistical analysis of the results of the tests with subjects wearing the sensor system, we found that the proposed parameters changed according to walking speed and turning (p-values < 0.05).

A wearable force plate system for the continuous measurement of triaxial ground reaction force in biomechanical applications

The ambulatory measurement of ground reaction force (GRF) and human motion under free-living conditions is convenient, inexpensive and never restricted to gait analysis in a laboratory environment and is therefore much desired by researchers and clinical doctors in biomedical applications. A wearable force plate system was developed by integrating small triaxial force sensors and three-dimensional (3D) inertial sensors for estimating dynamic triaxial GRF in biomechanical applications. The system, in comparison to existent systems, is characterized by being lightweight, thin and easy-to-wear. A six-axial force sensor (Nitta Co., Japan) was used as a verification measurement device to validate the static accuracy of the developed force plate. To evaluate the precision during dynamic gait measurements, we compared the measurements of the triaxial GRF and the center of pressure (CoP) by using the developed system with the reference measurements made using a stationary force plate and an optical motion analysis system. The root mean square (RMS) differences of the two transverse components (x- and y-axes) and the vertical component (z-axis) of the GRF were 4.3 ± 0.9 N, 6.0 ± 1.3 N and 12.1 ± 1.1 N, respectively, corresponding to 5.1 ± 1.1% and 6.5 ± 1% of the maximum of each transverse component and 1.3 ± 0.2% of the maximum vertical component of GRF. The RMS distance between the two systems CoP traces was 3.2 ± 0.8 mm, corresponding to 1.2 ± 0.3% of the length of the shoe. Moreover, based on the results of the assessment of the influence of the system on natural gait, we found that gait was almost never affected. Therefore, the wearable system as an alternative device can be a potential solution for measuring CoP and triaxial GRF in non-laboratory environments.

Imitation Control for Biped Robot Using Wearable Motion Sensor

In conventional imitation control, optical tracking devices have been widely adopted to capture human motion and control robots in a laboratory environment. Wearable sensors are attracting extensive interest in the development of a lower-cost human-robot control system without constraints from stationary motion analysis devices. We propose an ambulatory human motion analysis system based on small inertial sensors to measure body segment orientations in real time. A new imitation control method was developed and applied to a biped robot using data of human joint angles obtained from a wearable sensor system. An experimental study was carried out to verify the method of synchronous imitation control for a biped robot. By comparing the results obtained from direct imitation control with an improved method based on a training algorithm, which includes a personal motion pattern, we found that the accuracy of imitation control was markedly improved and the tri-axial average errors of x-y- and z-moving displacements related to leg length were 12%, 8% and 4%, respectively. Experimental results support the feasibility of the proposed control method.

A mobile force plate system and its application to quantitative evaluation of normal and pathological gait

In clinical applications, the quantitative analysis of gait variability using kinematic and kinetic characterizations can be helpful to medical doctors in monitoring patient recovery status. A high-speed camera system and a stationary force plate can only accurately measure complete ground reaction force (GRF) and body orientations during a few steps, but data on successive gait measurements including three-dimensional (3D) force and motion in different environments is really desired by clinical researchers and doctors. We have developed a mobile force plate and 3D motion analysis system (M3D) by integrating small triaxial force sensors and 3D inertial sensors for estimating multi-axial GRF and orientations of feet during successive gait movements. In order to verify the measurements of the developed system, we used a stationary force plate as a reference measurement system to simultaneously measure the triaxial GRF and center of pressure (CoP) when a subject was required to wear the M3D. Static and dynamic test experiments were implemented to validate the triaxial force measurement of the M3D. Experimental results verify that the developed system can be used to measure the triaxial force with acceptable precision (error: less than 6.4% of maximum measurement force). An application trial was carried out to analyze normal gait and paralysis gait using the M3D. Quantitative differences between gaits were analyzed, based on the results of the vertical component of GRF and medial-lateral directional angular flexions of the feet.

New method for assessment of gait variability based on wearable ground reaction force sensor

In this paper, a new quantitative method of analyzing gait variability using a developed wearable ground reaction force (GRF) sensor system is presented. The design of the sensor system is based on the use of five small 3-axial sensors distributed on the underside of a shoe, so that in human dynamics analysis this system can continuously measure vertical pressure force and bio-directional friction forces referring to anterior-posterior friction force and mediolateral friction force. Compared to existing spatio-temporal evaluation methods using traditional force plates or instrumented treadmills, the new method was developed based on measurements of ambulatory or wearable force sensor which can continuously measure ground reaction force in various environments not limited to the laboratory environment. The area of the center of pressure (CoP) distribution on the foot-plate and the average coefficient of variation of the 3-axial GRF, which correlate strongly with the distribution of CoP, are suggested parameters for quantifying gait variability. To certify the effectiveness of these parameters, we conducted an experimental study on a group of volunteer subjects who walked under a designed experimental protocol.

A master-slave control system with energy recycling and force sensing for upper limb rehabilitation robots

An innovative bilateral master-slave control method for an upper limb rehabilitation robot system which can afford training for hemiplegic patients is introduced. The system consists of two identical motors with the master motor working in the generating state and the slave motor working in the electromotion state. Based on hemi-disabled characteristic of hemiplegic patients, the healthy limb is used to operate the master motor to generate electric energy, which in turn powers the slave motor to rotate and support impaired limb in motion imitation, thus realizing rehabilitation training. An experimental prototype with energy supplement control was developed. The appropriate amount of energy is provided for the master-slave closed-loop circuit to compensate the inside energy loss, and further to achieve good motion tracking performance. Test experiments were conducted and the results confirm that the proposed system is capable of achieving motion tracking, energy recycling, and force sensing without force sensors. Thus, this master-slave control system has a great potential for application in rehabilitation robot systems.

Synchronous imitation control for biped robot based on wearable human motion analysis system

To achieve accurate and efficient interaction with humans, robot training is indispensable to make robot cooperate with different host. We are focusing on development of a human motion analysis system to real-time measure body segment orientations. Imitation control was applied on a biped robot based on measurements of the developed wearable sensor system. Experimental study was implemented to verify the synchronous imitation control method proposed for the biped robot, and verification results proved the feasibility of the proposed control method. Through comparing results obtained from direct imitation control method and improved method based on training algorithm considering the personal motion pattern, we found that the imitation control accuracy was markedly improved, and the three-axial average errors of x- y- and z- moving displacements related to leg length were 12%, 8% and 4% respectively.

Design of low-cost tactile force sensor for 3D force scan

A new 3D tactile sensor was proposed for measuring tri-axial ground reaction force distribution. Pressure sensitive electric conductive rubber (PSECR) and smart pectinate circuits were used to design the pressure sensing cells in the 3D force sensor, making it possible to implement a low-cost, compact and light sensing matrix which is highly sensitive in measuring force distribution. Moreover, to address the application for measurements of human touch force, we adopted the elastic rubber as the sensor input component to realize a comfortable human-sensor interface. A compact electrical hardware system including amplifiers module, conditioning circuits and a micro-computer controller and wireless modules was developed to sample sensor outputs into personal computer for data processing. Calibration experiments were conducted, in which a smart 3-axial force sensor (Tec Gihan, Japan) was used as the verification measurement device.

A wearable force plate system to successively measure multi-axial ground reaction force for gait analysis

A stationary force plate can only accurately measure complete ground reaction force (GRF) during no more than one stride, but the data of a successively measured multi-axial GRF in different environments is desired not only for researchers on gait analysis but also for clinical doctors. A wearable force plate system was developed by integrating small triaxial force sensors and 3D inertial sensors for estimating multi-axial GRF under free-living environments. In order to verify measures of the developed system, we adopted a combination system including a stationary force plate and an optical motion analysis system as a reference system that simultaneously measured triaxial GRF and the center of pressure (CoP) when a subject was required to wear the wearable system. The RMS difference and standard deviation of the two transverse components (x-axis and y-axis) and the vertical component (z-axis) of the GRF was 4.3±0.9N, 6.0±1.3N, and 12.1±1.1N respectively, corresponding to 5.1±1.1% and 6.5±1% of the maximum of each transverse component, and to 1.3±0.2% of the maximum vertical component of GRF. The RMS distance between the two systems CoP traces was 3.2±0.8mm, corresponding to 1.2±0.3% of the length of the shoe. Based on the experimental results, we can conclude that the wearable system as an alternative device can be used to measure CoP and triaxial GRF with an acceptable accuracy in non-laboratory environments.