Absolute Rotary Encoder Research Articles

A new system for measuring boom displacement in a field crop sprayer

This study proposes an innovative system for measuring the displacement of a sprayer boom’s tips and calculating their velocity and acceleration in the horizontal and the vertical plane. The system measures the length of measuring cables which are attached at the end of a sprayer boom’s tips. Two supports are mounted in the central part of the sprayer boom. Absolute rotary encoders with measuring reels and tension springs are attached to the supports, which enables the system to determine changes in the position of boom arms in two perpendicular directions. The signals generated by each encoder are transmitted to a computer by a rapid data acquisition device, and they are transposed to the indicated parameters. The designed system can be used to measure sprayer boom displacement both in the field and in laboratory experimental tracks.

Absolute Two-Tracked Optical Rotary Encoders Based on Vernier Method

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 the Vernier method are analyzed. One, already discussed in the literature, displays the Vernier scale across the whole circumference (full-Vernier), and the other shows half Vernier traces over the entire perimeter (half-Vernier), which is an original feature. Both the 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 microcontroller units (MCUs). The Vernier encoders are also compared with the state-of-the-art absolute and relative solutions, i.e., incremental, binary, and Gray-code encoders. Experimental tests are carried out to assess the accuracy of the proposed sensors. The investigation shows that: 1) 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; 2) the half-Vernier produces a trusty measurement of the absolute angle and velocity; and 3) can give a reliable position result with less than 30° shaft turn, but it can suffer from marginal performance degradation at low velocities in conjunction with high accelerations. Compared with 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.

Absolute rotary encoder system based on optical sensor for angular measurement

A goniometer is a device used to measure the angular range of motion of various human joints and muscle groups, such as the elbow, knee or waist. However, the majority of mechanical goniometers are heavy, provide inaccurate measurements and are affected by dust or stains. Electronic and optical fiber-based goniometers demonstrate better capability than their mechanical equivalents; however, due to their higher costs and complicated setup requirements, their usage is not viable. Optical-based encoder patterns were GC-ARE previously proposed and discussed in some studies. Such optical-based encoder patterns achieve the same angular resolution as traditional Gray code encoder patterns with many shortcomings, such as a high error rate and low tolerance, which arise as a result of the encoding method. This paper presents a design for a reliable and non-intrusive phase shift code absolute rotary encoder (PSC-ARE), which is based on an optical sensor, providing a low-cost, high-precision absolute rotary encoder system. An inexpensive optical mouse sensor is used to capture the code image and the phase shift code transforming time-domain data into frequency domain, which is used to decode the corresponding absolute angle. The PSC-ARE proposed in this study shows a performance improvement over conventional designs owing to the reduced interference from dust and other environmental particles and provides lower sensitivity to calibration errors. Furthermore, the proposed design is not only more compact and portable than the traditional goniometer, and it can also provide a longer lifespan as no stepper motor is included. Finally, the proposed design demonstrates high tolerance to “unintentional defocus” effects and noise effects.

Machine learning-based method for linearization and error compensation of a novel absolute rotary encoder

The main objective of this work is to develop a miniaturized, high accuracy, single-turn absolute, rotary encoder called ASTRAS360. Its measurement principle is based on capturing an image that uniquely identifies the rotation angle. To evaluate this angle, the image first has to be classified into its sector based on its color, and only then can the angle be regressed. Inspired by machine learning, we built a calibration setup, able to generate labeled training data automatically. We used these training data to test, characterize, and compare several machine learning algorithms for the classification and the regression. In an additional experiment, we also characterized the tolerance of our rotary encoder to eccentric mounting. Our findings demonstrate that various algorithms can perform these tasks with high accuracy and reliability; furthermore, providing extra-inputs (e.g. rotation direction) allows the machine learning algorithms to compensate for the mechanical imperfections of the rotary encoder.

Adaptive feedforward control of a collaborative industrial robot manipulator using a novel extension of the Generalized Maxwell-Slip friction model

Collaborative industrial robots often use strain-wave transmissions which display a highly nonlinear behavior. In particular, the friction torque depend on the load torque and the hysteresis characteristics were recently found to depend on the joint angular position.This paper presents a novel extension of the Generalized Maxwell-Slip friction model to describe said phenomena in a combined framework. The method overcomes the discontinuity around zero velocity of existing models. Experiments on the Universal Robots UR5e manipulator show superior performance in terms of torque prediction accuracy and tracking performance of the proposed method.An adaptive feedforward friction compensator is proposed based on the extended Generalized Maxwell-Slip friction model to compensate the time-variations of the Coulomb and viscous friction due to, respectively, wear and mispredictions of the lubricant temperature. The adaptive estimator relies on the sensing hardware readily available in the joints of the Universal Robots manipulators, i.e. two absolute rotary encoders; one at each side of the transmission, current sensing for the electric actuator, and a temperature sensor. Results show a considerable reduction of the torque prediction error and tracking error.

Optimizing the De-Bruijn Code of Rotary Optical Encoders Preventing From the Photocurrent Blooming

The De-Bruijn sequences could provide appropriate circular arrangements to achieve a single-track absolute rotary optical encoder in the servo motor application. One example used popularly is the maximum length sequences. High-resolution single-track encoders need a sensor array to obtain the position signal simultaneously. Nevertheless, the individual photocurrents would interference by other adjacent photocurrents, like the photocurrent blooming. The circumstances would increase the bias noise for the digital binarization. The concept in this article would try to find the optimal De-Bruijn sequences to reduce the photocurrent blooming interference intrinsically without signal process remodification. Three different types of the 9-bits codes, the adjacent De-Bruijn code, the quarter De-Bruijn codes, and the optimal De-Bruijn codes, are analyzed, manufactured, and experimented in the actual encoders. Based on the open-factor of the eye-diagram, the adjacent De-Bruijn code has 0.328 and would be the worse signal quality in De-Bruijn sequences. The quarter De-Bruijn codes have 0.386 of the open-factor with 17.7% improvement to adjacent De-Bruijn code. Finally, the optimal De-Bruijn codes have 0.436 of the open-factor with 32.9% improvement to the traditional M-code. The fact would mean the possible ability of 3-bits progress from 9-bits of adjacent De-Bruijn code to 12-bits of the optimal De-Bruijn codes under the same signal-to-noise ratio.

Proof of concept of a novel absolute rotary encoder

Rotary encoders are used in many applications that require monitoring or controlling mechanical systems such as robots. Typically, small rotary encoders have poor resolution; this is unfortunate for applications such as robotics in medical surgery procedures. For example, in an articulated robotic endoscope, miniaturization is mandatory and, when automation is desired, high accuracy to track the shape and pose of the device is required; small (few millimeters) and accurate (few hundred arcsec) rotary encoders are thus needed.Previously, we introduced a novel concept of a miniaturizable angular sensor, called ASTRAS (Angular Sensor for TRAcking System). This was presented as a basic element of a tracking system for articulated endoscopes. The principle of measurement of ASTRAS is based on processing a shadow image cast by a shadow mask onto an image sensor. The characterization of the first prototype of ASTRAS was very promising, however, its angular range of about ±30 degrees was too limiting for many practical applications.In this work, we present an extension of the concept mentioned above to a rotary encoder that can measure one full rotation of 360 degrees thus the name is ASTRAS360. Its working principle bases on encoding the shadow image using colored light to distinguish different angular sectors. The identification of the sector corresponds to a coarse angular measurement, which is afterward refined using the same technique as in ASTRAS. We implemented this concept, realizing a prototype and an algorithm to calculate the angle from the shadow image. The experiments demonstrated the validity of this concept and showed encouraging results with a precision of ∼0.6 arcsec and 6σ-resolution of 3.6 arcsec corresponding to 19 bits.

Design and development of robotic end-effector position measuring device

Robot end-effector position measurement is very essential to determine the error between the commanded position and actual position reached by the robot end-effector. This also ensures the error with which the robot end-effector traces the commanded path. Conventionally position measuring devices like laser trackers, coordinate measuring machine and other non-contact-based position measuring devices are widely used to measure the position of the end-effector due to their high accuracy and precision, even though they are very expensive. This paper presents a cost effective solution for the measurement of position of robot end-effector. An end-effector position measuring device is designed and developed in spherical coordinate system using two absolute rotary encoders and a draw-wire sensor. A mathematical model for the end effector position measuring device is developed to determine the position of the end-effector with respect to a reference coordinate system using 3D homogeneous transformation approach. End-effector position measuring device is tested for ABB IRB 1600 for numerous poses and for a straight line path. The newly developed end-effector position measuring device is found to be capable of measuring the end effector position with an accuracy of 2 mm and hence can be implemented in calibration of industrial robots.

Design and development of robotic end-effector position measuring device

Robot end-effector position measurement is very essential to determine the error between the commanded position and actual position reached by the robot end-effector. This also ensures the error with which the robot end-effector traces the commanded path. Conventionally position measuring devices like laser trackers, coordinate measuring machine and other non-contact-based position measuring devices are widely used to measure the position of the end-effector due to their high accuracy and precision, even though they are very expensive. This paper presents a cost effective solution for the measurement of position of robot end-effector. An end-effector position measuring device is designed and developed in spherical coordinate system using two absolute rotary encoders and a draw-wire sensor. A mathematical model for the end effector position measuring device is developed to determine the position of the end-effector with respect to a reference coordinate system using 3D homogeneous transformation approach. End-effector position measuring device is tested for ABB IRB 1600 for numerous poses and for a straight line path. The newly developed end-effector position measuring device is found to be capable of measuring the end effector position with an accuracy of 2 mm and hence can be implemented in calibration of industrial robots.

A Research On Rice Transplanter Fitted with Seedling Number Counting Device

Rice is the staple food for a large portion of the world’s population, therefore breeding improved high yielding varieties is important in the achievement of food security. An important factor in an experimental plot is quantifying the number of seedlings planted for experimenting on rice breeding, seed breeding, soil fertility and other tests. A research was carried out on a PZ-60D high-speed rice seedling transplanter fitted with a seedling number counting device based on Hall sensor, in order to analyse the marginal signal count at various transplanting speeds. The seedling counting system is divided into two parts: a counting signal acquisition device and a counting display device, the hall sensor generates the signal which is then displayed on a counting relay. To synchronize the counter signal and transplanting claws, an absolute rotary encoder was used to determine the angle of push point and transplanting claws stop position, and a logic analyzer was used to process the encoder signal into a data form readable on a computer. The installation position of counting device on the transplanting shaft was within the range of 143 ~ 202 degree. Both transplanter idle running test and field test showed that the counter device works accurately.

偏心構造を利用した小型かつ高性能な磁気式アブソリュートエンコーダの開発

偏心構造を利用した小型かつ高性能な磁気式アブソリュートエンコーダの開発

Study on array of photo-detector based absolute rotary encoder

Absolute rotary encoder is an electromechanical device which indicates the absolute position of an object. In this paper, a low cost absolute rotary encoder is presented. Proposed encoder measures the rotational position of a moveable object with accuracy of ±1° and resolution of 0.1°. Here, Encoder disc does not carry any binary or gray coded positional information, instead of that it acts as a positional pointer over the array of photo-detector based circular track. The one forth segment of fiber glass disc is kept transparent and rest portion is covered up by a semi-transparent layer. The disc is placed between the circular track and a light source. A marker at the centre of transparent portion indicates the angular position of the object. Now during the rotation of disc along with the object, high intensity of light is passed through the disc’s transparent portion compared to the semi-transparent portion and impinged over a fixed circular track. Thus according to the variation of light intensity over the track surface area, absolute angular position of object is determined by analyzing the variation of photo-detector’s output. In order to proof of this concept, an experimental prototype has been designed, developed and tested.

A Novel Approach of an Absolute Encoder Coding Pattern

This paper presents a novel approach of an absolute rotary and linear optical encoder codding patterns. The concept is based on the analysis of 2-D images to find a unique sequence that allows to unambiguously determine an angular shaft position. The adopted coding method allows to achieve a very high data density for specified number of tracks on the code pattern disc. Encoders based on the proposed solution enable the production from readily available and inexpensive components. Nevertheless, encoders retain high measuring accuracy and high dependability obtained in the classical approach. The optical device and a design of processing system is proposed. Finally, the feasibility of the pattern coding method is further proved with encoder prototype.

Using the image acquisition capabilities of the optical mouse sensor to build an absolute rotary encoder

In this paper, the optical mouse sensor is proposed as the main sensor of an absolute rotary encoder. The image acquired by the optical sensor is used to read a positioning binary code printed on an internal rotary surface to obtain the absolute rotary position. The two-dimensional image matrix acquisition is more robust than the single reading point approach used in other absolute rotary encoders (with only one pixel) where the position must be coded using random sequence codes. Additionally, the low cost of the optical sensor facilitates the development of inexpensive absolute rotary encoders.

Determination of optimal period of absolute encoders with single track cyclic gray code

Low cost and miniaturized rotary encoders are important in automatic and precise production. Presented here is a code called Single Track Cyclic Gray Code (STCGC) that is an image etched on a single circular track of a rotary encoder disk read by a group of even spread reading heads to provide a unique codeword for every angular position and features such that every two adjacent words differ in exactly one component, thus avoiding coarse error. The existing construction or combination methods are helpful but not sufficient in determining the period of the STCGC of large word length and the theoretical approach needs further development to extend the word length. Three principles, such as the seed combination, short code removal and ergodicity examination were put forward that suffice determination of the optimal period for such absolute rotary encoders using STCGC with even spread heads. The optimal periods of STCGC in 3 through 29 bit length were determined and listed.

A 3.2 kHz, 14-Bit Optical Absolute Rotary Encoder With a CMOS Profile Sensor

We have developed a 3.2 kHz, 14-bit optical absolute rotary encoder system using a profile sensor and a slit disc. The profile sensor, which we have designed for this purpose, is a unique CMOS area image sensor aimed at high-speed position detection of X and Y axes. Y axis profile data from the profile sensor is used for recognition of an index code on the slit disc, and X axis profile data is used for position detection of the index code. This combination of two-axis information enables high resolution even with a small number of index codes (64 indexes) and a small amount of digital calculations. Experimental results show that this system can detect rotation with an angular resolution of 14 bits (0.022deg) and a maximum detection speed of 3.2 kHz.

Insertion device operating experience at the Advanced Photon Source

The Advanced Photon Source has 29 insertion devices (IDs) installed in the 7 GeV electron storage ring; 28 of these devices, most of which are 3.3 cm period undulators, use two horizontal permanent magnet structures positioned over a straight vacuum chamber. A support and drive mechanism allows the vertical gap between the magnet structures to be varied, thus changing the x-ray energy produced by the ID [J. Viccaro, Proc. SPIE 1345, 28 (1990); E. Gluskin, J. Synchrotron Radiat. 5, 189 (1998)]. Most of these IDs use a drive scheme with two stepper motors, one driving each end through a mechanism synchronizing the upper and lower magnet structures. Our experience in almost 5 yr of operating this system will be discussed. All of the IDs are in continuous operation for approximately 10 weeks at a time. Reliability of operation is of paramount importance, as access to the storage ring for servicing of a single ID inhibits operation for all users. Our experience in achieving highly reliable ID operation is reviewed. Accuracy of operation and repeatability over time are also vital. To this end, these devices use absolute optical linear encoders with submicron resolution for primary position feedback. Absolute rotary encoders are used as a backup to the linear encoders. The benefits and limitations of each type of encoder, and our experience dealing with radiation and electrical noise are reviewed. The insertion devices operate down to gaps as small as 8.5 mm, with clearance over the vacuum chamber as small as 200 μm. The vacuum chamber has a minimum wall thickness of only 1 mm. A number of levels of safeguards are used to prevent contact between the magnet structure and the vacuum chamber. These safeguards and their evolution after gaining operational experience are presented.

ROC 417 high-resolution absolute rotary encoders are compact

ROC 417 high-resolution absolute rotary encoders are compact

Multi-turn absolute rotary encoders provide digital shaft resolution

Multi-turn absolute rotary encoders provide digital shaft resolution

Precision goniometer equipped with a 22-bit absolute rotary encoder.

The calibration of a compact precision goniometer equipped with a 22-bit absolute rotary encoder is presented. The goniometer is a modified Huber 410 goniometer: the diffraction angles can be coarsely generated by a stepping-motor-driven worm gear and precisely interpolated by a piezoactuator-driven tangent arm. The angular accuracy of the precision rotary stage was evaluated with an autocollimator. It was shown that the deviation from circularity of the rolling bearing utilized in the precision rotary stage restricts the angular positioning accuracy of the goniometer, and results in an angular accuracy ten times larger than the angular resolution of 0.01 arcsec. The 22-bit encoder was calibrated by an incremental rotary encoder. It became evident that the accuracy of the absolute encoder is approximately 18 bit due to systematic errors.