Practical Aspects of Ultrasonic Rotary Encoder—Probe Placing, Real-Time Operation, and Automotive Bench Test

The operational principle of an ultrasonic rotary encoder was investigated in order to examine the sensitivity of the measurement to the placement of the sensor probe. Ultrasound was sent to the moving blades attached to a rotating signal plate, and its amplitude and frequency were modulated by the blades. The sensor detected the modulated ultrasound, and the angle, speed, and angular velocity of the rotational motion were derived from the amplitude and frequency demodulation. Bragg's law of diffraction was adopted to explain how the mechanical motion affected the sound wave, and the diffraction was experimentally investigated. The moving blades examined were made of aluminum, cast iron, or plastic, all of which modulated the amplitude and frequency of the ultrasound, as predicted by the theory. Thus, the ultrasonic sensing method proposed is independent of the material of the rotating bodies, while the conventional magnetic method requires ferromagnetic material that tends to be heavy. The signal processing for the rotary encoder functions was implemented in a microcontroller to realize real-time operation and to build a stand-alone sensor. The sensor was tested on an automotive powertrain bench, and the result of rotation speed measurement agreed well with the reference result obtained from the instrumentation sensors in the test bench.

I. Introduction

Rotary encoders or rotational motion sensors are widely used in industrial and automotive control systems. Although they have been in use for decades, new approaches to build them are still being investigated, applying, for instance, optical [1], magnetic [2], capacitive [3], magneto-optical [4], and piezoelectric [5] methods. These studies are intended to improve the performance of the sensor and add new features to it. Fleming [6], [7] showed that automotive control systems employ a number of rotational motion sensors and require improved performance. The automotive sensors often carry different names referring to their functionality. Crank angle sensors in automotive powertrains, for example, measure the rotation angle of an engine’s crankshaft and its revolving speed, and provide the fuel and spark timings for engine management systems. The gear speed sensors used in the transmission mechanism detect essential information for the power-shift control of automotive powertrains. Wheel speed sensors are commonly used for vehicle speed sensing, as well as advanced braking controls. For these automotive rotation measurements, magnetic sensors based on the magnetoresistive effect are predominantly used because of their robustness against harsh environments, such as wide temperature ranges and dusty air.