Rotary Optical Encoders Research Articles

Smartphone-Based Wearable Gait Monitoring System Using Wireless Inertial Sensors

This paper presents a wearable virtual reality system with a wireless network of inertial sensors for lower limb monitoring. The system comprises seven sensor nodes sending data wirelessly to a master node. The information is then collected, organized, and sent to a screening device via a serial interface. An application executed either on a smartphone or a personal computer features an avatar which represents the received data and mimics the sensed movements of the patient, providing online feedback during and after the execution of a therapy. The data resulting from the therapy execution can be uploaded to a web server to facilitate the assessment and decision-making by health professionals. A pendulum featuring a rotary optical encoder is used for sensor functional behavior validation. In addition, the orientation angles measured by the proposed system are compared with respect to measurements from the motion analysis software Kinovea. The delay between the patient's body movement and the avatar is 33 ms, which is acceptable for visual feedback. This system is portable, inexpensive and enables a patient to complete physical therapy sessions at home or anywhere, with the advantage of enabling visual feedback through an avatar during rehabilitation therapy and allowing the reproduction of a therapy session for further analysis.

A calibration method for rotary optical encoder temperature error in a rotational inertial navigation system

A rotary optical encoder is an important component in a rotational inertial navigation system (RINS). It is used to form a closed-loop motor control system and calculate the system attitude. The system performance will be affected by the encoder’s error. Ín addition to the installation errors, the working temperature variants can lead to encoder error. Therefore, in this paper we propose a method to calibrate and compensate the temperature errors of rotary optical encoders. First, an independent testing mechanism with position limitation and a rotatable platform is designed and produced to verify the temperature influence on encoders. Then, the temperature error of the rotary optical encoder used in RINS is calculated by a gyroscope whose sensitive axis is parallel to the same motor axis. The method is verified by a self-researched single-axis RINS. According to the experimental results, the measurement accuracy is increased by more than 47.9% compared to the traditional method.

Calibration of rotary encoders with different interfaces by means of a dynamic goniometer

Rotary optical encoders are widely used in all areas of industry, robotics, and special equipment. The accurate measurement of their characteristics is a necessary task for their successful implementation. We attempt to find a unified approach to determining the accuracy of rotary encoders. The proposed approach is based on statistics and code reliability, which characterizes the probability that the measured code corresponds to the specified code. To determine the code reliability, one has to measure the turn angle with a goniometric device and compare the measured values with the encoder codes. The paper considers the dynamic goniometer for determining the error of absolute angle encoders, which allows for highly accurate measurements in a wide range of rotation rates. The measurement is made at certain moments of time, depending on the electrical interface of the encoder. In the case of a parallel interface, the time points are determined by the moment when the encoder code changes. This data collection allows for obtaining a general population. In the case of an encoder, with the sequential approach to reading the code, it is not possible to obtain the general population in a wide range of rotation rates. We analyze the above-mentioned case in detail and present experimental data obtained with a dynamic goniometer and the results of code reliability calculations.

On-line angle self-correction strategy based on a cobweb-structured grating scale

Installation eccentricity of the grating scale is the main source of error for rotary optical encoders in practical applications. In this paper, an on-line angle self-correction strategy for rotary optical encoders is proposed. Firstly, the eccentricity error model is described, which explains the numerical relationship between the eccentricity error and the eccentric parameters including eccentric distance and eccentric angle. Then, a bioinspired cobweb-structured grating scale is adopted as the measurement standard of the rotary optical encoder. This grating scale allows the rotary optical encoder to sense the rotary angle and the radial displacement simultaneously. The eccentric parameters can be determined in real time from the rotary angle and the radial displacement information. Thus, the measured rotary angle can be on-line corrected by applying the eccentric parameters to the eccentricity error model. The feasibility and effectiveness of the proposed strategy have been confirmed from the experimental results.

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.

A novel optical rotary encoder with eccentricity self-detection ability.

Eccentricity error is the main error source of optical rotary encoders. Real-time detection and compensation of the eccentricity error is an effective way of improving the accuracy of rotary optical encoders. In this paper, a novel rotary optical encoder is presented to realize eccentricity self-detection. The proposed encoder adopts a spider-web-patterned scale grating as a measuring standard which is scanned by a dual-head scanning unit. Two scanning heads of the dual-head scanning unit, which are arranged orthogonally, have the function of scanning the periodic pattern of the scale grating along the angular and radial directions, respectively. By this means, synchronous measurement of angular and radial displacements of the scale grating is realized. This paper gives the details of the operating principle of the rotary optical encoder, developing and testing work of a prototype. The eccentricity self-detection result agrees well with the result measured by an optical microscope. The experimental result preliminarily proves the feasibility and effectiveness of the proposed optical encoder.

Use of rotary optical encoder for firing detection in a spark ignition engine

Abstract Detection of spark ignition engine firing is an important parameter to understand proper and improper combustion inside the engine cylinder. The engine firing can be detected by direct measurement of in-cylinder pressure by using piezo-electric sensor. However, the cost of the sensor is really high. Therefore, in this paper, engine firing has been detected by analysis of instantaneous angular speed (IAS) signal from output shaft measured by cheap device like rotary encoder. The direct short time Fourier transform (STFT) is unable to detect engine firing clearly as the signal contains various frequencies (rotational frequency and its harmonics) other than engine firing frequency. Therefore, an algorithm has been developed based on complementary ensemble empirical mode decomposition (CEEMD) and followed by STFT and applied on IAS signal to detect engine firing. Moreover, a comparative study has been performed between laser vibrometer signal and IAS signal to understand the efficacy of these signals.

UAV Testbed Training Platform development using Panda3d

Purpose– The paper aims to report the development of an Unmanned Aerial Vehicle (UAV) Testbed Training Platform (TTP). The development is to enable users to safely fly and control the UAV in real time within a limited (yet unconstrained) virtually created environment. Thus, the paper introduces a hardware–virtual environment coupling concept, the Panda3D gaming engine utilization to develop the graphical user interface (GUI) and the 3D-flying environment, as well as the interfacing electronics that enables tracking, monitoring and mapping of real-time movement onto the virtual domain and vice verse.Design/methodology/approach– The platform comprises a spring-shuttle assembly fixed to a heavy aluminium base. The spring supports a rotating platform (RP), which is intended to support UAVs. The RP yaw, pitch and roll are measured by an inertial measurement unit, its climb/descend is measured by a low cost infrared proximity sensor and its rotation is measured by a rotary optical encoder. The hardware is coupled to a virtual environment (VE), which was developed using the Panda3D gaming engine. The VE includes a GUI to generate, edit, load and save real-life environments. Hardware manoeuvres are reflected into the VE.Findings– The prototype was proven effective in dynamically mapping and tracking the rotating platform movements in the virtual environment. This should not be confused with the hardware in loop approach, which requires the inclusion of a mathematical model of the hardware in a loop. The finding will provide future means of testing navigation and tracking algorithms.Research limitations/implications– The work is still new, and there is great room for improvement in many aspects. Here, this paper reports the concept and its technical implementation only.Practical implications– In the literature, various testbeds were reported, and it is felt that there is still room to come up with a better design that enables UAV flying in safer and unlimited environments. This has many practical implications, particularly in testing control and navigation algorithms in hazardous fields.Social implications– The main social impact is to utilise the concept to develop systems that are capable of autonomous rescue mission navigation in disaster zones.Originality/value– The authors are aware that various researchers have developed various testbeds, at different degrees of freedom. Similarly, the authors are also aware that researchers have used game engines to simulate mobile robots or sophisticated equipment (like the VICON Motion Capture System) to measure to perform complex manoeuvres. However, the cost of this kind of equipment is very high, autonomous movements are planned in restricted environments and tested systems are only autonomous in certain setups. However, the idea of mapping the dynamics of an avatar flying object onto a 3D-VE is novel. To improve productivity and rapid prototyping, this paper proposes the use of commercially available game engines, such as the Panda3D, to create virtual environments.

Near field diffraction of cylindrical convex gratings

We analyze the field produced by a cylindrical convex diffraction grating at the Fresnel regime for several kinds of light sources, including a monochromatic quasipunctual source, finite size, and polychromatic sources. These results can help one understand the functioning of rotary optical encoder technology. A decrease in the self-image contrast is produced for finite nonpunctual sources. In addition, the polychromaticity of the source affects the smoothness of the self-images, making them quasicontinuous from a certain distance from the grating forward. Finally, we experimentally validate the obtained analytical predictions.

A SIMPLE SYSTEM FOR THE ONLINE DETECTION OF SKIP/LOOP STITCHES IN SINGLE NEEDLE LOCKSTITCH SEWING MACHINES

Abstract In single needle lockstitch sewing machines, the needle thread consumption of 10 normal stitches for a fabric with a particular number of layers at a particular stitches per unit length is manually measured kept as a reference value. If the value of needle thread consumed per stitch is very small, the length of thread consumed per 10 stitches is used as a comparing value. The actual thread consumed for every 10 stitches is measured online by a rotary optical encoder sensor by converting the angular movement into the linear movement of the thread and continually compared with the reference value. If the online measured length is more or less a buzzer sounds to indicate the variation. The counting of every stitch formed is undertaken by a proximity sensor by sensing the protrusion in the hand wheel of the machine, which rotates once for every rotation.

Self-imaging with curved gratings

We analyze the near field behavior of binary amplitude gratings which present a curved profile. This configuration has an important application in rotary optical encoders. This kind of encoders is used to measure the angular displacement between two different parts of the devices. To our knowledge, its behavior in the near field has not been analyzed yet. We have found that Talbot effect is produced but the period of the self-images and Talbot distances change as we separate from the grating. We have fabricated a curved grating and have performed the experiment to corroborate the behavior theoretically found. This fact could be useful in systems that use Talbot effect to measure displacements, since the mechanical tolerances grow.

Measurement of the Vacuum Arc Plasma Force

The axial force carried by the expanding plasma plume from 50-250-A copper and aluminum vacuum arcs was measured using a pendulum whose axle was equipped with a rotary optical encoder. It was found that the force was a linear function of current. The electrode geometry was varied to find the maximum force. At maximum, the average forces per unit current were 21.4 dyn/A for aluminum cathodes and 36.1 dyn/A for copper cathodes. The Cu ion current fraction was measured to be 8.6%.

An automated image alignment system for the scanning electron microscope

AbstractWe have developed an automated image alignment system for the scanning electron microscope (SEM). This system enables specific locations on a sample to be located and automatically aligned with submicron accuracy. The system comprises a sample stage motorization and control unit together with dedicated imaging electronics and image processing software. The standard SEM sample stage is motorized in the X and Y axes with stepping motors which are fitted with rotary optical encoders. The imaging electronics are interfaced to beam deflection electronics of the SEM and provide the image data for the image processing software. The system initially moves the motorized sample stage to the area of interest and acquires an image. This image is compared with a reference image to determine the required adjustments to the stage position or beam deflection. This procedure is repeated until the area imaged by the SEM matches the reference image. A hierarchical image correlation technique is used to achieve submicron alignment accuracy in a few seconds. The ability to control the SEM beam deflection enables the images to be aligned with an accuracy far exceeding the positioning ability of the SEM stage. The alignment system may be used on a variety of samples without the need for registration or alignment marks since the features in the SEM image are used for alignment. This system has been used for the automatic inspection of devices on semiconductor wafers, and has also enabled the SEM to be used for direct write self‐aligned electron beam lithography.

A flexible multiple mobile robots system

Optimal performance of a manufacturing layout consisting of several mobile robots performing specific transportation tasks is addressed. A synergistic approach based on decentralized path planning, heuristic-algorithm-based navigation, and localized collision avoidance is presented. A comprehensive, flexible multiple mobile robots system (MMRS) consisting of standard patterns, a local controller, and individual mobile robots is described. The mobile robots are capable of performing their own path planning and collision avoidance by means of ultrasonic sensors, standard patterns, and rotary optical encoders. Specially designed algorithms for the mobile robot and local controller are presented. To ensure greater flexibility in designing the layout, the MMRS was interfaced with a specially designed CAD subsystem. Simulations using varying numbers of robots were performed on a sample layout that was designed using the CAD subsystem. The results of the simulation illustrate the validity of the approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Modular System for Transmission Error Measurement

A modular system of electronics for measuring transmission error with standard rotary optical encoders is described. The system can work flexibly with an overall speed range of the order of a 1000 to 1 by changing the order of the modules and will respond correctly to speed variations in both input and output of a synchronous drive such as a gear, chain or toothed belt drive.