There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Starting from human ?sense of touch,? this paper reviews the state of tactile sensing in robotics. The physiology, coding, and transferring tactile data and perceptual importance of the ?sense of touch? in humans are discussed. Following this, a number of design hints derived for robotic tactile sensing are presented. Various technologies and transduction methods used to improve the touch sense capability of robots are presented. Tactile sensing, focused to fingertips and hands until past decade or so, has now been extended to whole body, even though many issues remain open. Trend and methods to develop tactile sensing arrays for various body sites are presented. Finally, various system issues that keep tactile sensing away from widespread utility are discussed.

Tactile Sensing—From Humans to Humanoids

A review of 3D/2D registration methods for image-guided interventions

1. We studied quiet stance investigating strategies for maintaining balance. Normal subjects stood with natural stance and with feet together, with eyes open or closed. Kinematic, kinetic and EMG data were evaluated and cross-correlated. 2. Cross-correlation analysis revealed a high, positive, zero-phased correlation between anteroposterior motions of the centre of gravity (COG) and centre of pressure (COP), head and COG, and between linear motions of the shoulder and knee in both sagittal and frontal planes. There was a moderate, negative, zero-phased correlation between the anteroposterior motion of COP and ankle angular motion. 3. Narrow stance width increased ankle angular motion, hip angular motion, mediolateral sway of the COG, and the correlation between linear motions of the shoulder and knee in the frontal plane. Correlations between COG and COP and linear motions of the shoulder and knee in the sagittal plane were decreased. The correlation between the hip angular sway in the sagittal and frontal planes was dependent on interaction between support and vision. 4. Low, significant positive correlations with time lags of the maximum of cross-correlation of 250-300 ms were found between the EMG activity of the lateral gastrocnemius muscle and anteroposterior motions of the COG and COP during normal stance. Narrow stance width decreased both correlations whereas absence of vision increased the correlation with COP. 5. Ankle mechanisms dominate during normal stance especially in the sagittal plane. Narrow stance width decreased the role of the ankle and increased the role of hip mechanisms in the sagittal plane, while in the frontal plane both increased. 6. The modulation pattern of the lateral gastrocnemius muscle suggests a central program of control of the ankle joint stiffness working to predict the loading pattern.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7793.1999.915ad.x

Feedforward ankle strategy of balance during quiet stance in adults

This study shows that center-of-pressure (COP) traces that closely resemble physiologically measured COP functions can be produced by an appropriate selection of model parameters in a simple feedback model of the human postural control system. Variations in the values of stiffness, damping, time delay, and noise level determine the values of 15 sway measures commonly used to characterize spontaneous sway. Results from model simulations indicate that there is a high degree of correlation among these sway measures, and the measures cluster into three different groups. Only two principal components accounted for about 92% of the variation among the different sway measures analyzed. This model can be used to formulate hypotheses regarding the cause of postural control deficits reported in the literature. This is accomplished using a multidimensional optimization procedure to estimate model parameters from a diverse set of spontaneous sway measures. These model parameters describe physiologically meaningful features of the postural control system as opposed to conventional sway measures that provide only a parametric description of sway. To show the application of this method, we applied it to published data of spontaneous sway from elderly subjects and contrasted it to the data of young healthy subjects. We found that modest increases in stiffness and damping and a fairly large increase in noise level with aging could account for the variety of sway measures reported in the literature for elderly subjects.

A new interpretation of spontaneous sway measures based on a simple model of human postural control

To identify characteristics of a sensory feedback path of a posture control system without external disturbances, the maximum likelihood identification method was applied to data of an antero-posterior sway during quiet stance. A subject stood on a force plate and the sway angle of a body (input) was measured by a position sensor camera and the ankle joint moment (output) was measured by the force plate. Using data of 500 input-output pairs sampled every 0.1 s, parameters of the sensory feedback path were estimated and frequency response functions were calculated. These showed derivative characteristics that are necessary for stabilization of the posture control system. Gain characteristics under the closed eyes condition tended to be greater than those under the open eyes condition.

Maximum Likelihood Identification of a Posture Control System

By means of a servocontrolled force plate, pseudorandom acceleration disturbances were imposed upon a standing subject. By measuring and processing the responses of a subject, we computed the frequency-response functions of the posture-control system. The experimental results are discussed from a viewpoint of control engineering.

Responses of the posture-control system to pseudorandom acceleration disturbances.

A capacitive transducer is developed which continuously measures the vertical component of foot forces during walking. The transducer is shaped like an insole and consists of two subtransducer units, the front and rear. The outputs of the two units are summed to give the total force exerted by the foot. Each unit has a multilayered structure. The basic layer is a 2 mm Neoprene sponge sheet sandwiched by two 50 μm copper foils. They as a whole form a capacitor. The other two layers are a driving shield and static shield, which minimise the effect of stray capacitance and power-line noise, respectively. The transducer is thin (3·8 mm), light (90 g) and flexible and so does not hinder the natural gait pattern. It can be attached to the sale of the shoe easily by elastic bands and Velcro straps. The accuracy of the transducer is well within ±10 per cent of the full scale. An error analysis is made to clarify the change in sensitivity owing to a localised foad. The results are used to compensate for the inherent nonlinearity of the transducer units.

Capacitive transducer for continuous measurement of vertical foot force.

A modified back-propagation method to avoid false local minima

Control of the standing posture of humans involves at least two distinct modes of operation to restore the body balance in the sagittal plane: the ankle strategy and the hip strategy. The objective of the study was to estimate the contribution of vestibular, visual and somatosensory feedbacks to these distinct strategies. The body dynamics was described as the motion of two linked rigid segments that represented the legs and the rest of the body. The posture controller received the inclination angles of the two body segments as inputs and regulated the moments around the ankle and hip joints. The controller had four feedback paths that were characterised by transfer functions connecting the two inputs and the two outputs. To evoke the distinct strategies, the floor conditions were varied by narrowing the support surface under the feet. A continuous pseudo-random external disturbing force was applied to the waist and the thigh independently. The inclination angles of the body segments and the ground reaction force were measured, and the transfer functions of the controller were estimated with the maximum-likelihood system identification procedure. Six healthy male adult subjects participated in the experiment. When the hip strategy became evident under the narrow support surface conditions, the transfer function relating the leg inclination angle and the ankle joint moment decreased its DC gain (16%), whereas the other three transfer functions increased the gains (20-140%) (ANOVA, p < 0.05). Based on a criterion for simplicity in the modification of the posture controller, these changes suggest a new hypothesis that, when posture control becomes difficult, the central nervous system selectively activates the somatosensory feedback paths from the hip joint angle to the moments around the ankle and hip joints.

Akimasa Ishida

Papers

Maximum Likelihood Identification of a Posture Control System

Responses of the posture-control system to pseudorandom acceleration disturbances.

Capacitive transducer for continuous measurement of vertical foot force.

A modified back-propagation method to avoid false local minima

Human standing posture control system depending on adopted strategies.