Ground reaction force

The friction coefficient is defined as the tangential force acting on a sliding body to the ground reaction force. For rubbers this is a function of the ground pressure. Its dependence has been discussed sufficiently in the literature where it was shown that this is important for soft rubbers on smooth surfaces [2,3], but is of little influence for tire compounds on roads which are always sufficiently rough for the load dependence to be small if not completely absent [4,5]. 

The 3-D ground reaction force vector, the vertical ground reaction torque and the point of application of the ground reaction force vector (i.e., center of pressure) are measured with force platforms embedded in the walkway. Force plates with typical measurement surface dimensions of 0.5 x 0.5 m are comprised of several strain gauges or piezoelectric sensor arrays rigidly mounted together. 

The dynamic distributed load that corresponds to the vertical ground reaction force can be evaluated with the use of a flat, two-dimensional array of small piezoresistive sensors. OveraU resolution of the transducer is dictated by the size of the individual sensor ceU. Sensor arrays configured as shoe insole inserts or flat plates offer the clinical user two measurement alternatives. Although the currently available technology does afford the clinical practitioner better insight into the quahtative force distribution patterns across the plantar surface of the foot, its quantitative capabiKty is limited because of the challenge of caKbration and signal drift (e.g., sensor creep). 

Musculographics, the developers of SIMM, also produce a component as part of the SIMM suite specifically directed toward gait analysis that provides ground reaction force vectors and color-highlighted... 

Force platforms are used to resolve the load a subject applies to the ground. These forces and moments are measured about X, Y, and Z axes specific to the force platform. In general, the orientation of the force platform axes will differ from the orientation of the reference axes of the object-space. This is illustrated schematically in Fig. 5.14. Thus, it is necessary that the ground reaction forces be transformed into the appropriate reference system before they are used in subsequent calculations. For example, the ground reaction forces acting on the foot should be transformed into the foot coordinate system, if ankle joint forces and moments are expressed in an anatomically meaningful reference system (i.e., about axes of the ACSfooi). 

A. P. Arya, A. Lees, H. C. Nirula, and L. Klenerman (1995), A biomechanical comparison of the SACH Seattle and Jaipur feet using ground reaction forces, Prosthet. Orthot. Int. 19 37-45. 

Fig. 3. Energy pulse generated by heel strike. Shown is the vertical ground reaction force at "heel strike"...

Figure 8. (a) An irregular building-soil interaction model before and after deformation (Wu etal, 2001), (b) Top-view of floor equipped with MTMD (c) Top-view of foundation with ground reaction forces... 

The instrumented platform will measure the vertical ground reaction force while the wearable accelerometer subsystem will measure the relevant joint kinematics. The datalogging system consists of signal conditioning circuitry. Finally, the computer system was used to store and analyse gait parameters collected by the system. Fig. 1 shows the overview setup of the proposed system. 

There are two different sensor subsystems namely, the wireless wearable accelerometer subsystem, and instrumented platform. The function of wireless wearable accelerometer subsystem is to measure joint kinematics and instrumented platform to quantify the vertical ground reaction forces of human movement. 

An instrumented platform of 0.81 mX 0.81 mX 0.019 m in size was built. Total of eight (8), 38.1cm Interlink Electronics Force Sensing Resistors (FSR) were used to collect vertical ground reaction forces of human movement. Fig. 3 shows the completed prototype of the subsystem. 

Prosthetic Foot Design The Significance of the Normalized Ground Reaction Force... 

Keywords— Prosthetic foot, graph, ground reaction force. 

Gait kinematics and kinetics such as simulated joint angles and torques, muscle force, and experimental ground reaction forces are presented as below. 

The experimental ground reaction forces of PPRP subject are greater than the ground reaction forces of healthy subject. The qualitative comparison showed a longer contact time for PPRP subject. The maximal peak force happened at the heel strike phase during the contact between the foot and the ground. Furthermore, the heel off and toe off phases are not occurred for PPRP subject (Fig. 5). 

Fig. 5 Experimental ground reaction forces healthy vs. PPRP subjects...

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