Simple virtual slip force sensor for walking biped robots

This paper presents a novel simple Virtual Slip Force Sensor (VSFS) for a walking biped. Bipeds walking stability is critical and they tend to lose it easily in real environments. Among the significant aspects that affect the stability is the availability of the required friction force which is necessary for the robot not to slip. In this paper we propose the use of the virtual sensor to detect the slip force. The design structure of the VSFS consists of two steps, in the first step it utilizes the measured acceleration of the center of mass (CoM) and the ZMP signals in the simple linear inverted pendulum model (LIPM) to estimate the position of the CoM, and in the second step the Newton law is employed to find the total ground reaction force (GRF) for each leg based on the position of CoM. Then both the estimated force and the measured force from the sensors assembled at the foot are used to detect the slip force. The validity of the proposed estimation method was confirmed by simulations on 3D dynamics model of the humanoid robot SURALP while walking. The results are promising and prove themselves well

Experimental Estimation of Slipping in the Supporting Point of a Biped Robot

When developing a gait cycle on a low-friction surface, a biped robot eventually tends to slip. In general, it is commonto overcome this problem by means of either slow movements or physical adaptations of the robot at the contact pointwith the walking surface in order to increase the frictional characteristics. In the case of slipping, several types ofsensors have been used to identify the relative displacement at the contact point of the supporting leg with the walkingsurface for control purposes. This work is focused on the experimental implementation of a low-cost force sensor as ameasurement system of the slipping phenomenon. It is shown how, supported on a suitable change of coordinates,the force measurement at the contact point is used to obtain the total displacement at the supporting point due to thelow-friction conditions. This is an important issue when an accurate Cartesian task is required

Effect of floor condition on pig gait

Unhealthy legs and claws in pig production are a persistent problem, a primary reason for which seems to be inappropriate floor properties in the pig pen. Inadequate frictional properties or low coefficient of friction (COF) may result in slippery floors and slip injuries to pigs. This thesis presents basis of design criteria for pig house floors with the aim of minimising the number of claw disorders. Parameter values were determined by pig gait studies in a gait analysis laboratory, where the pigs walked a straight or a curved test aisle. The gait was recorded by a force plate and a perpendicularly placed digital video camera as the pigs walked the test aisle. The specific aims of the four studies included in the thesis were to: 1) characterise pig gait and describe the effect of clean and fouled floor conditions for pigs walking a line on solid concrete, walking a curve on solid concrete and walking a curve on rubber mat; 2) determine the utilised COF (UCOF) of the walking pigs and compare it with measured dynamic COF (DCOF); and 3) analyse pig slip in different floor conditions. A set of parameter values characterising pig gait in clean and fouled concrete floor conditions were obtained by kinematic and kinetic methods. The data showed that pigs walking a straight line adapted their gait to fouled floor conditions. Pigs were able to adapt to walking a curve in clean floor conditions but the observed adaptation was not enough for safe walking in fouled floor conditions, where UCOF exceeded DCOF. Walking a curve on fouled rubber mat gave better traction and reduced forward and backward slips by over 50% compared with walking a curve on fouled concrete. The discrepancy between UCOF and measured DCOF observed in the studies could be due to the friction measuring device underestimating the actual risk of slipping and falling in fouled floor conditions, especially when walking a curve. Additional studies are needed to provide pig producers with more detailed information, e.g. guidelines for required COF values in pig pen situations where the required motion and speed of motion are determined. An appropriate data set for COF measurements at farm level can bring safer and more slip-resistant floor solutions in the future

Effect of concrete slats, three mat types and out-wintering pads on performance and welfare of finishing beef steers

peer-reviewedBackground The objective was to investigate the effect of placing mats on concrete slatted floors on performance, behaviour, hoof condition, dirt scores, physiological and immunological variables of beef steers, and to compare responses with animals on out-wintering pads. Continental crossbred beef steers [n = 360; mean (±SD) initial live weight 539 kg (42.2)] were blocked by breed and live weight and randomly assigned to one of five treatments; (1) Concrete slats alone, (2) Mat 1 (Natural Rubber structure) (Durapak Rubber Products), (3) Mat 2 (Natural rubber structure) (EasyFix), (4) Mat 3 (modified ethylene vinyl acetate (EVA) foam structure) and (5) Out-wintering pads (OWP’s). Results Animals on the OWPs had a greater (P  0.05) as the other treatments. Animals on the OWPs had reduced lying percentage time compared with all the other treatments. Dry matter (DM) intake was greater for animals on the OWPs compared with all the other treatments. Carcass weight, kill out proportion, carcass fat score, carcass composition score, FCR and physiological responses were similar (P > 0.05) among treatments. No incidence of laminitis was observed among treatments. The number of hoof lesions was greater on all mat types (P < 0.05) compared with concrete slats and OWP treatments. Dirt scores were greater (P < 0.05) for animals on OWPs when measured on days 42, 84, 105, 126 and 150 compared with animals on slats. Conclusions Under the conditions adopted for the present study, there was no evidence to suggest that animals housed on bare concrete slats were disadvantaged in respect of animal welfare compared with animals housed on other floor types. It is concluded that the welfare of steers was not adversely affected by slats compared with different mat types or OWPs

Effect of Concrete Slats, Three Mat Types and Out-Wintering Pads on Performance and Welfare of Finishing Beef Steers

The objective was to investigate the effect of placing mats on concrete slatted floors on performance, behaviour, hoof condition, dirt scores, physiological and immunological variables of beef steers, and to compare responses with animals on out-wintering pads. Continental crossbred beef steers [n = 360; mean (±SD) initial live weight 539 kg (42.2)] were blocked by breed and live weight and randomly assigned to one of five treatments; (1) Concrete slats alone, (2) Mat 1 (Natural Rubber structure) (Durapak Rubber Products), (3) Mat 2 (Natural rubber structure) (EasyFix), (4) Mat 3 (modified ethylene vinyl acetate (EVA) foam structure) and (5) Out-wintering pads (OWP’s)

Effects of outsole shoe patterns on athletic performance

The focus of this study was to investigate the effects that different basketball shoe outsole tread patterns have on the amount of slip and therefore the performance of the individual while undergoing normal basketball transitions. Tread grooves and therefore patterns must exist on the outsole of a basketball shoe because the chances of contamination and for practical durability. With the existence of so many basketball shoes with varying tread patterns and characteristics it presents the question of whether or not varying patterns affect traction, slip, and therefore athletic performance. This study evaluated the amount of slips of two pairs of basketball shoes with human participants running basketball drills on a hardwood basketball floor at Wartburg College. The results indicated that one shoe with a much more unique tread pattern performed better with fewer slips, and fewer severe slips, especially when considering lateral movements than the other shoe which had a tread pattern with similar tread characteristics to many other currently available market shoes

Appraisal of gloss and slipperiness of resilient floor covering materials

Perhaps man has always been attracted to surfaces which have a high degree of gloss. Within recent years, the resilient floor covering industry has capitalized on this by producing materials which possess a high shine, along with such features as durability, color clarity, and ease of care. The wax manufacturers have made it possible to increase the glossiness of these resilient floor covering materials with polishes especially made to enhance their appearance

Joint friction estimation and slip prediction of biped walking robots

Friction is a nonlinear and complex phenomenon. It is unwanted at the biped joints since it deteriorates the robot’s walking performance in terms of speed and dynamic behavior. On the other hand, it is desired and required between the biped feet and the walking surface to facilitate locomotion. Further, friction forces between the feet and the ground determine the maximum acceleration and deceleration that the robot can afford without foot slip. Although several friction models are developed, there is no exact model that represents the friction behavior. This is why online friction estimation and compensation enter the picture. However, when online model-free estimation is difficult, a model-based method of online identification can prove useful. This thesis proposes a new approach for the joint friction estimation and slip prediction of walking biped robots. The joint friction estimation approach is based on the combination of a measurementbased strategy and a model-based method. The former is used to estimate the joint friction online when the foot is in contact with the ground, it utilizes the force and acceleration measurements in a reduced dynamical model of the biped. The latter adopts a friction model to represent the joint friction when the leg is swinging. The model parameters are identified adaptively using the estimated online friction whenever the foot is in contact. Then the estimated joint friction contributes to joint torque control signals to improve the control performance. The slip prediction is a model-free friction-behavior-inspired approach. A measurement-based online algorithm is designed to estimate the Coulomb friction which is regarded as a slip threshold. To predict the slip, a safety margin is introduced in the negative vicinity of the estimated Coulomb friction. The estimation algorithm concludes that if the applied force is outside the safety margin, then the foot tends to slip. The proposed estimation approaches are validated by experiments on SURALP (Sabanci University Robotics Research Laboratory Platform) and simulations on its model. The results demonstrate the effectiveness of these methods