Joint torque

Low-back injury risk assessment See Chaffin et al. 1999 Joint torques, postures Suitable... 

Fatigue analysis Rohmert 1973a, b Laurig 1973 Joint torques, strength equations Suitable... 

Joint torque (/((/>)) dependence on a joint angle. The nonlinear function relating torque and joint angle is simulated by a quadratic curve, F = oq + i 0 + The torque generated can not be negative for any angle, so... 

Normalized joint torque g(p)) dependence on the angular velocity. The normalized joint torques vs. joint angular velocities can be modelled piecewise linear ... 

Resistive joint torque Soft tissue, passive stretching of antagonistic muscles, and ligaments introduce nonKnearities, which can be modeled as ... 

Physics-based methods are implemented when direct analysis of the system or its resources is feasible. With regard to the human system, such methods are commonly applied in biomechanical analysis where unknown parameters, such as joint torque, are derived from known characteristics, such as segment lengths and reaction forces, based on estabhshed physical laws and relationships. 

Physical motion is common to most situations in which the human functions and is therefore fundamental to the analysis of performance. Parameters such as segment position, orientation, velocity, and acceleration are derived using kinematic or dynamic analysis or both. This approach is equally appropriate for operations on a single joint system or linked multibody systems, such as is typically required for human analysis. Depending on the desired output, foreword (direct) or inverse analysis may be employed to obtain the parameters of interest. For example, inverse dynamic analysis can provide joint torque, given motion and force data while foreword (direct) dynamic analysis uses joint torque to derive motion. Especially for three-dimensional analyses of multijoint systems, the methods are quite complex and are presently a focal point for computer implementation [Allard et al., 1994]. 

In this chapter we have examined forward and inverse dynamics approaches to the study of human motion. We have outlined the steps involved in using the inverse approach to studying movement with a particular focus on human gait. This is perhaps the most commonly used method for examining joint kinetics. The forward or direct dynamics approach requires that one start with knowledge of the neural command signal, the muscle forces, or, perhaps, the joint torques. These are then used to compute kinematics. 

J. P. Dewald and R. F. Beer (2001), Abnormal joint torque patterns in the paretic upper limb of subjects with hemiparesis. Muscle and Nerve 24 273-283. 

A similar relationship exists for the joint torque (force) vector, r, as shown below ... 

By definition, the projection of f2 wito 02 is the joint torque (force) vectw, T2. Again, the unknown constraint fwces at the added joint int 2) have been eliminated. The juDjection, Jj" f2, may be recognized as the external force term from the dynamic equation for the one-link manipulate. Equation 3.9. 

As in the single closed chain case, the open-chain terms, (qt)open and (Xik)open, are completely defined for each chain given the present state genial joint positions and rates, qt and qt, the applied graeral joint torques/forces in the free directions, n, and the motion of the supprat surface. Any appropriate open-chain Direct Dynamics algorithm may be used to calculate these terms. Because the general joint positions are known, fit and Aj are also defined. The efficient computation of fit and for a single serial-link chain was discussed in detail in Chapter 4. 

Single-axis arm designed with an ultrasonic motor basic active/passive joint torque control... 

In the joint torque control mode, the torque acting at the joint is actively controlled by a PI controller designed as... 

Joint torque control result by using Equation 3.3... 

In the passive joint torque control mode, an external force given to the arm can be absorbed smoothly. Here, a stiffness control, a compliance control and an impedance control are considered by using the inner servo system given by Equation 3.2. 

Joint torque manually controlled by an operator, In which the force is given by the operator s fingers... 

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