Absolute Two-Tracked Optical Rotary Encoders Based on Vernier Method

Abstract

Driving synchronous machines requires early and accurate knowledge of the absolute position of the rotor; current solutions based on resolvers, sin-cos or absolute encoders are complex, bulky and costly. Hence, in this work two variants of absolute rotary encoder based on Vernier method are analyzed. One, already discussed in the literature, displays the Vernier scale across the whole circumference (full-Vernier), the other shows half Vernier traces over the entire perimeter (half-Vernier), which is an original feature. Both implementations are characterized by only two tracks and as many sensors: the proposed conditioning algorithms provide the absolute angular position as a function of the time delays between the wave edges generated by the two traces, thus being of easy implementation on low-cost MCUs. The Vernier encoders are also compared with state-of-the-art absolute and relative solutions, i.e. incremental, binary and Graycode encoders. Experimental tests are carried out to assess the accuracy of the proposed sensors. The investigation shows that (i) the full-Vernier cannot provide, in practice, a reliable estimate of the direction of rotation and of the actual angular sector without resorting to a third sensor; (ii) the half-Vernier produces a trusty measurement of the absolute angle and velocity and (iii) can give a reliable position result with less than 30°shaft turn, but (iv) it can suffer from marginal performance degradation at low velocities in conjunction with high accelerations. Compared to the Gray encoder, the half-Vernier provides a simpler and more compact hardware for a given resolution, similar to that of an incremental encoder, at the expense of a small accuracy reduction at low speed.

A Novel Angle Segmentation Method for Magnetic Encoders Based on Filtering Window Adaptive Adjustment Using Improved Particle Swarm Optimization

“…Then, the angle values of the combined encoder are sorted from small to large and are shrunk by a factor of 6 25 . Meanwhile, the angle deviation of the two types of encoders changes accordingly.…”

“…On the other hand, improving the precision and accuracy of encoders, the feedback element of the control system offers another approach to enhancing the control precision of the control system [5]. Among numerous encoders, rotary encoders are widely applied [6][7][8] and photoelectric encoders and magnetic encoders are the most common. Although the photoelectric encoder has high detection accuracy, the volume it requires increases with higher accuracy, and it cannot be used in harsh environments with pollution, vibration, and other factors [9,10].…”

Belt conveyor speed detection based on fiber-optic Sagnac interferometer vibration sensor

“…In order to ensure the safe operation of the belt conveyor, the detection of overspeed and speed control is required. The existing belt conveyor speed is detected by the method of a Photoelectric encoder [4][5][6], a Hall Speed Sensor [7][8][9], and magnetoelectric speed sensors [10][11][12], the core of which is the Photoelectric encoder. Measurement errors can easily be produced due to * Author to whom any correspondence should be addressed.…”