ABSTRACT
For the dynamic shaft, the dynamic torque Md and the torsion angle ϕ have the following relationship [5]:
M J d dt
C d dt
GI ld
P+ 1 6
2 2+ 2
2 ϕ ϕ ϕ (2)
1 INTRODUCTION
Shaft dynamic torque measurement has important effects on testing transmission performance of mechanical equipments and calculating shaft power. However, the shaft is typically stiff which will result in very small strains or displacements under the effect of torque. So even small disturbance in the measurement can contribute a great error. Because of the inherent vibration and eccentric motion of shaft, narrow testing space and the measurements are easily affected by the factors such as temperature, smoke, electromagnetic, making the high precision measurement of the shaft dynamic torque very difficult. A lot of researches have been conducted both at home and abroad, and the principle of the method is also varied. The existing studies of shaft torque measurement can be divided into two categories, one is the study of torque sensitive materials and related detection device design. When a torque is imposed on the shaft, the stress and strain changes, the corresponding physical parameters of sensitive material attached to the shaft will change. By measuring the changes, the torque can be calculated. Stress and strain sensitive materials commonly used in engineering torque measurement are ferromagnetic materials, piezoelectric materials, light elastic materials, metal strain materials, etc [1-4]. These methods often need to attach sensitive materials on the surface of shaft, not real non-contact measurement in a strict sense. Besides, these materials are easily affected by external environment, and the measuring devices are also more complex. Another method is to measure the relative torsion angle of two shaft sections, it usually converts angular displacement into phase difference values of two measurable signals, through optical, Figure 1. Geometric relationship of shaft angle.
