A method to compensate periodic errors by gain tuning ininstrumentation

The method described uses multiprobes without individual probes accuracy calibrations. By simple gain (or sensitivity) tuning, perfect compensation of any arbitrary frequency component of an error is achieved. Online calculations or estimations of the periodic error are not required, and significant improvements are achieved just by initial tuning of the gains of separate probes. In Sections II and III, we first derive a mathematical model of the periodic error and then propose a new method to compensate it. In. Section IV, we derive the minimum number of probes needed to compensate a given number of frequency components of the periodic error, and present two algorithms to calculate the gains for separate probes. In Section V, we show two simulated and one experimental example of periodic error compensation. One of the simulated examples is applied to a rotary type of a sensor and the other to a linear type of a sensor. Minimum number of probes needed to compensate multiple frequency components is also derived. The method is successfully demonstrated on two simulated and one experimental example, where one and two frequency components of a periodic error are perfectly compensated. The method is applicable both to rotary and to linear types of sensors     

Ripple compensation for torque sensors built into harmonic drives

Harmonic drives include a mechanically flexible component which transmits load torque, and therefore, a torque sensor can be built into harmonic drives by cementing strain gages on a flexible component of the gear. However, a periodic sensing error called ripple is generated by deformation of a flexible component during the gear operation. The ripple signal cannot be sufficiently compensated by pairs of strain gages that produce opposite phase signals, because the strain gages cannot be exactly positioned on the desired locations. In this paper, we present a method to compensate the ripple by a new approach of tuning the ripple amplitudes for separate strain gages. The ripple, caused by positioning errors of the strain gages, can be perfectly compensated, and, therefore, the requirement for accurate strain gage positioning is reduced. The method does not need any online calculations, and consequently, the torque signal is not delayed. The minimum number of strain gages needed to compensate a given number of frequency components of a ripple is derived. Some experimental results are shown     

Performance of gain-tuned harmonic drive torque sensor under loadand speed conditions

Addresses the topic of torque sensing by using strain gauges, which are cemented directly onto the flexspline of a harmonic drive gear reducer. Conventionally, two or four strain gauges are used to reduce the ripple signal, which is generated by the gear operation. However, our analysis shows that an odd number of strain gauges is more suitable for the ripple compensation. The method does not need online calculations and reduces the needed accuracy of the strain gauges positioning, so it can be practically implemented. Two techniques to define the gains are presented in the paper. One is based on a mathematical model of the fluctuation signal, and the other employs a heuristic approach. Practical results show effectiveness and usefulness of the proposed method. We present the new method and evaluate its performance under load torque and rotational speed conditions. No significant deterioration of the performance under load torque and at various rotational speeds was confirmed     

Accuracy improvement of built-in torque sensing for Harmonic Drives

Built-in torque sensing for Harmonic Drives is attractive since it maintains mechanical characteristics of the gear while providing detection of the transmitted torque. Torque sensing by using strain gauges has been studied, but is not widely used yet due to a relatively high signal fluctuation, which is generated by the gear operation. Characteristics of the signal fluctuation are analyzed in this paper, and a method to effectively compensate the signal fluctuation is proposed. The signal fluctuation is perfectly compensated by adjustment of the strain gauge sensitivities. A minimum number of strain gauges needed to compensate the signal fluctuation is derived. The experimental result with three strain gauges compensating the basic frequency component of the signal fluctuation is shown