Absolute Encoder Research Articles

An Adaptive Linear-Neuron-Based Third-Order PLL to Improve the Accuracy of Absolute Magnetic Encoders

Absolute magnetic encoders (AMEs) use two magnets: a ring multipolar magnet (MPM) generating high-resolution and improving the accuracy for the encoder, and a bipolar magnet in the center calculating the number cycle of MPM signals. The phase outputs of these AMEs are tracked from the sinusoidal signals of the MPM. However, these sine/cosine signals are disturbed by amplitude differences, offsets, phase-shift, harmonic components, and random noise. In order to solve this problem, this paper presents an adaptive linear neuron based on a third-order phase-locked loop (ALN-PLL) to improve the accuracy of AMEs. The proposed approach consists of two main parts: The first part is an ALN algorithm that uses the phase feedback of the third-order PLL in order to build the mathematical model of input signals, and then reject the disturbances. The second part is a third-order PLL that is designed based on a dominant pole approximation algorithm. The proposed PLL can reduce noise and eliminate dc-error during the phase step, frequency step, and frequency ramp. The simulation and experimental results demonstrate the effectiveness of the proposed approach.

Design of a Pneumatic Actuated Ankle-Foot Orthosis which has Talocrural and Subtalar Joint.

As aging progresses, risk of falls in elderly people increases due to the decreasing the range of motion (RoM) of eversion and the weakening of the plantar flexor. Balance training is performed to reduce the risk of falls and powered ankle-foot orthosis (PAFO) can be utilized in this process. The elderly can conduct training on the narrow roads or on the rugged ground with assistance on rotation of eversion and propulsion by PAFO. However, existing PAFOs were developed just by considering the talocrural joint which make the rotation of sagittal plane of ankle which is called by plantar flexion and dorsiflexion. So, we developed the 2 Degree of Freedom (DoF) PAFO which has the Talocrural and Subtalar joints for frontal plane rotation which is called inversion and eversion. We established the coordinate system and calculated the spatial formulas for talocrural and subtalar joint based on anatomical data. Developed PAFO has the pneumatic artificial muscle (PAM) as an actuator which is controlled by solenoid valve with PWM methods, light-weight 3D printed body and knee orthosis for interfacing with wearer in three area which are thigh, shank and foot. The total weight of developed PAFO is 2. 14kg and it can be 1. 44kg without the weight of knee orthosis (0.7kg). Measurement sensors for PAFO were the absolute encoders to measure the angle of talocrural and subtalar joint, tensile loadcell to measure the magnitude of force from PAM, pressure sensor to measure the pressure of PAM and FSR sensor to judge the phase of the gait cycle. The results of the paper show the validation of design, kinematics and functional capacity for human subject experiments with proportional myoelectric control (PMc) of developed PAFO.

An improved high-precision subdivision algorithm for single-track absolute encoder using machine vision techniques

In order to achieve high-precision and robust measurement for a single-track absolute encoder, an improved subdivision algorithm based on machine vision technology is proposed. First, the composite subdivision algorithm combining RANdom SAmple Consensus and least square estimation is introduced. Second, the proposed algorithm is proved to be high-precision and effective to remove fault error from signal noise and spot by simulation. Finally, real test results show that the algorithm output angle stably achieves precision within 2.5 arc-seconds and accuracy up to 1.6 arc-seconds. Research results provide a high-precision and robust subdivision algorithm that is improved by modern machine vision technology of RANdom SAmple Consensus and it can be applied in the field of absolute angle sensor in the future.

Absolute Encoder-Based Dual Axis Tilt Sensor

In this paper, an optical type dual axis tilt sensor is demonstrated for the measurement of surface inclination in the range of ±90°. The proposed sensor measured the surface tilt by tracking a pendulum motion in two different axes. Unlike the traditional tilt sensor, the proposed concept used an absolute encoder for sensing the pendulum motion. This newly designed encoding track (named as index and code track) is attached separately with two pendulum blocks. As the encoder tracks are used a gray color coded pattern instead of binary code, hence the pendulum position is encoded as the variant intensity of gray colors. Thus, during the inclination of the sensor, a pair of optical trans-receiver reads the pendulum position by capturing the track information’s as well as transformed it into the variant intensity of lights. Furthermore, a simple signal processing circuit has been used for calibrating the light intensity as measured surface inclination. The static behavior of the proposed sensor has been observed in laboratory conditions and found satisfactory performance in the above-mentioned measured range.

Design and Development of a Reduced Form-Factor High Accuracy Three-Axis Teslameter

A novel three-axis teslameter and other similar machines have been designed and developed for SwissFEL at the Paul Scherrer Institute (PSI). The developed instrument will be used for high fidelity characterisation and optimisation of the undulators for the ATHOS soft X-ray beamline. The teslameter incorporates analogue signal conditioning for the three-axes interface to a SENIS Hall probe, an interface to a Heidenhain linear absolute encoder and an on-board high-resolution 24-bit analogue-to-digital conversion. This is in contrast to the old instrumentation setup used, which only comprises the analogue circuitry with digitization being done externally to the instrument. The new instrument fits in a volumetric space of 150 mm × 50 mm × 45 mm, being very compact in size and also compatible with the in-vacuum undulators. This paper describes the design and the development of the different components of the teslameter. Performance results are presented that demonstrate offset fluctuation and drift (0.1–10 Hz) with a standard deviation of 0.78 µT and a broadband noise (10–500 Hz) of 2.05 µT with an acquisition frequency of 2 kHz.

Design and Workspace Analysis of a Parallel Ankle Rehabilitation Robot (PARR).

The ankle rehabilitation robot is essential equipment for patients with foot drop and talipes valgus to make up deficiencies of the manual rehabilitation training and reduce the workload of rehabilitation physicians. A parallel ankle rehabilitation robot (PARR) was developed which had three rotational degrees of freedom around a virtual stationary center for the ankle joint. The center of the ankle should be coincided with the virtual stationary center during the rehabilitation process. Meanwhile, a complete information acquisition system was constructed to improve the human-machine interactivity among the robot, patients, and physicians. The physiological motion space (PMS) of ankle joint in the autonomous and boundary elliptical movements was obtained with the help of the RRR branch and absolute encoders. The natural extreme postures of the ankle complex are the superposition of the three typical movements at the boundary motions. Based on the kinematic model of PARR, the theoretical workspace (TWS) of the parallel mechanism was acquired using the limit boundary searching method and could encircle PMS completely. However, the effective workspace (EWS) was smaller than TWS due to the physical structure, volume, and interference of mechanical elements. In addition, EWS has more clinical significance for the ankle rehabilitation. The PARR prototype satisfies all single-axis rehabilitations of the ankle and can cover most compound motions of the ankle. The goodness of fit of PMS can reach 93.5%. Hence, the developed PARR can be applied to the ankle rehabilitation widely.

On the Rotor Stator Interaction Effects of Low Specific Speed Francis Turbines

The rotor stator interaction in a low specific speed Francis model turbine and a pump-turbine is analyzed utilizing pressure sensors in the vaneless space and in the guide vane cascade. The measurements are analyzed relative to the runner angular position by utilizing an absolute encoder mounted on the shaft end. From the literature, the pressure in the analyzed area is known to be a combination of two effects: the rotating runner pressure and the throttling of the guide vane channels. The measured pressure is fitted to a mathematical pressure model to separate the two effects for two different runners. One turbine with 15+15 splitter blades and full-length blades and one pump-turbine with six blades are investigated. The blade loading on the two runners is different, giving different input for the pressure model. The main findings show that the pressure fluctuations in the guide vane cascade are mainly controlled by throttling for the low blade loading case and the rotating runner pressure for the higher blade loading case.

Miniaturized Optical Encoder with Micro Structured Encoder Disc

A novel optical incremental and absolute encoder based on an optical application-specific integrated circuit (opto-ASIC) and an encoder disc carrying micro manufactured structures is presented. The physical basis of the encoder is the diffraction of light using a reflective phase grating. The opto-ASIC contains a ring of photodiodes that represents the encryption of the encoder. It also includes the analog signal conditioning, the signal acquisition, and the control of a light source, as well as the digital position processing. The development and fabrication of the opto-ASIC is also described in this work. A laser diode was assembled in the center on top of the opto-ASIC, together with a micro manufactured polymer lens. The latter was fabricated using ultra-precision machining. The encoder disc was fabricated using micro injection molding and contains micro structures forming a blazed grating. This way, a 10-bit optical encoder with a form factor of only 1 cm3 was realized and tested successfully.

An anti-spot, high-precision subdivision algorithm for linear CCD based single-track absolute encoder

To improve precision performance of angular sensor, in this paper, research is performed on subdivision technology for a single-track absolute photoelectrical encoder. Firstly, a robust subdivision algorithm is proposed by means of processing a feature matrix of measurement which is created from multiple grating lines’ image. Secondly, simulation of anti-noise and anti-spot is established to prove that the proposed algorithm is robust theoretically. Finally, the algorithm is applied in a photoelectrical encoder for real tests, experiment result shows that the subdivision algorithm proposed in this paper is more accurate and adaptive than the traditional way. To reduce a negative precision effect caused by noises and spots, it measures angle according to multiple grating lines by assigning different weights, making those grating lines deeply noised with lower weight, and higher weight with minor noise, thus the overall accuracy is improved. With the proposed subdivision algorithm, test encoder’s standard deviation of error can be increased to 1.6″ and precision achieves up to ±0.9″.

Rotational Speed Control of Brushless Dc Motor Using Genetic Algorithm Optimized PD Controller

Controlling the rotational speed of brushless DC (BLDC) motor is an essential task to improve the transient and the steady state performances under loaded condition. Rotational speed control of BLDC motor using genetic algorithm optimized proportional-derivative (PD) controller to form what the so-called the genetic algorithm-PD (GA-PD) controller is proposed in this paper. Control system is realized in a microcontroller namely a 16MHz Atmega2560 with an absolute encoder as a position sensor. The effectiveness of the GA-PD controller is tested under constant and varying step functions with the Ziegler-Nichols-PD (ZN-PD) controller as a benchmark. Experimental results show that the GA-PD controller has slower speed than the ZN-PD controller, but the latter has overshoot and small oscillations during its steady state condition as a consequent of having a fast rise time.

Development of Absolute Magnetic Rotary Encoder with Eccentric Rotation

Development of Absolute Magnetic Rotary Encoder with Eccentric Rotation

Development of shape memory alloy actuator integrated flexible poly-ether-ether-ketone antenna with simultaneous beam steering and shaping ability

Active control of antenna radiation by mechanical reconfiguration has large potential applications in space as well as in ground segment. Such reconfigurable antenna primarily has two functionalities: beam steering and beam shaping. While previous research has shown individual control of these functions; we have developed a suitable antenna actuation system which takes care of both the functionalities. To demonstrate our concept, we have fabricated a 1-m diameterC-band flexible reflector of poly-ether-ether-ketone using precisely machined aluminum mold. A periphery feed structure is connected to the center of the reflector by a goose-neck-shaped supporting frame. Next, we have designed and developed a smart control-disk containing two types of shape memory alloy actuator-based self-locking devices. A group of actuators are used for locking/unlocking the rotational degree of freedom of the antenna; while the other group generates deformation of antenna at the desired direction. An 8-bit absolute encoder is installed with each locking device to sense and feedback the displacement of a control point. We have achieved a controllable deflection up to 25 mm with a precision of 0.3 mm with this system. A directional precision of [Formula: see text] is also achieved simultaneously. Presently, we have developed eight such actuation points on the disk to control the shape of the antenna. For numerical simulation of the structural deformation and study of the radio frequency pattern, finite element analysis is carried out using ABAQUS, and the far-field radiation pattern corresponding to the deformed shape is obtained. The electromagnetic patterns are analyzed using geometric optics technique. Finally, a methodology of achieving surface coordinates for desired radiation pattern is presented. The study provides useful insights into the design of flexible and reconfigurable antenna system.

Absolute Position Coding Method for Angular Sensor-Single-Track Gray Codes.

Single-track Gray codes (STGCs) is a type of absolute position coding method for novel angular sensors, because it has single-track property over traditional Gray codes and mono-difference over linear feedback shift register codes. However, given that the coding theory of STGCs is incomplete, STGC construction is still a challenging task even though it has been defined for more than 20 years. Published coding theories and results on STGCs are about two types of STGC, namely, necklace and self-dual necklace ordering, which are collectively called as k-spaced head STGCs. To find a new code, three constraints on generating sequences are proposed to accelerate the searching algorithm, and the complete searching result of length-6 STGCs is initially obtained. Among the entire 132 length-6 STGCs, two novel types of STGCs with non-k-spaced heads are found, and the basic structures of these codes with the general length n are proposed and defined as twin-necklace and triplet-necklace ordering STGCs. Furthermore, d-plet-necklace ordering STGC, which unifies all the known STGCs by changing the value of d, is also defined. Finally, a single-track absolute encoder prototype is designed to prove that STGCs are as convenient as the traditional position coding methods.

A Novel High-Resolution Optical Encoder With Axially Stacked Coded Disk for Modular Joints: Physical Modeling and Experimental Validation

A novel approach to realize a high-resolution absolute encoder with compact disk size for the application in a light weight robotic arm modular joint is proposed in the present research. First, the high resolution coded disk of the absolute encoder is designed using graph theory-based Hamiltonian cycle. Unlike the traditional 1-D binary coded tracks, the proposed generated code is a 2-D ${n} \times {n}$ matrix code with 0s and 1s as the matrix elements and ${n}$ numbers of uniquely coded tracks. The 2-D matrix code improves the code density of the encoder system by ${2^{n^{2}}}$ compared with that of the traditional 1-D codes ( $2^{n}$ ). Second, the coded tracks are arranged axially along Z-axis to stack the tracks within a constant disk diameter and to avoid the radially divergent track patterns. These combined operations result in a high-resolution absolute encoder with a compact constant disk diameter which is essential to comply with the size constraint of the modular joint. With the proposed designed framework, a prototype with $n = 2$ is manufactured using 3-D printing technology. The designed encoder with two tracks is tested on a rotary system and the absolute angle values are obtained using the unique codes generated by the photosensors installed in the prototype.

Design of an Absolute Shaft Encoder Using Optically Modulated Binary Code

In order to avoid the fabrication of coding pattern over a shaft coupled disk of the binary coded absolute encoder, a new design concept has been presented in this paper. The proposed prototype can encode the binary information by optical modulation principle. Instead of lithographic fabrication, here the pattern code bits are implemented optically through a plurality of infra-red (IR) light emitting diodes (LED). Each LED transmits a bit of information as modulated optical signal and modulation is served by the principle of serial infra red control protocol. During the rotation of an object, a window position of the shaft coupled disk determines which bits’ information will be transmitted. Now, an IR detector of the receiver unit decodes this code by demodulating the transmitted signal. Finally, the absolute position of the object is evaluated from this code by searching a look-up table data. Thus, the receiver unit of the proposed encoder can sense the position of an object remotely without using any additional wireless device. Also, the sensing heads may not be damaged by the rotating disk vibration. The prototype has been tested by using De-Bruijn coding pattern and obtained promising results. Also, the proposed method is equally valid for any binary or gray pattern code.

High-precision absolute linear encoder based on a standard calibrated scale

This paper presents the full research and development cycle of a high-precision absolute linear encoder based on a standard calibrated scale. Already available and used in industry standard scales of invar alloy were employed in the study. The scales have incremental indexes with 1 mm spacing intervals without an absolute code. However, the existing technical task is to measure the absolute position in the range of 2 m with accuracy less than 5 μm. For that, the developed encoder rationally combines magnetic measuring channel for the index numbering and an optical channel for the precise estimation of the encoder position. First, for the development, a simulation was performed to synthesize and analyze an image of an index. This image was used to develop a real-time double-threshold image processing algorithm to estimate the index position. Later the developed image processing algorithm was verified by preliminary testing and supported by a presented three-stage calibration procedure. The final measurements proved that the designed and developed encoder has the accuracy of 1.65 μm (3 standard deviations) at the speed up to 3 m/s. The possibility of use of standard calibrated scales with the presented encoder to solve existing and new industrial tasks forms the value of this paper. A possible use of the existing scales also provides unification and compatibility with conventional metrology equipment.

A new capacitive rotary encoder based on analog synchronous demodulation

Rotary encoders, which are mainly used to feedback the angle of the robot arm to the robot controller system, are widely used in industrial and robotic applications. While optical and magnetic rotary encoders are dominant in the market, capacitive rotary encoders are also gaining interest for their simple design, ability to miniaturize and being absolute encoders insensitive to magnetic field variations. In this study, a new economical capacitive rotary encoder based on analog synchronous demodulation is developed. Analog synchronous demodulation technique is used for the first time in the literature as far as known to the authors for capacitive rotary encoders. It is chosen as it is quite robust, simple and economical. A compact mechanical body is developed by 3D printing. After packaging, the sensor is fixed to a motor for testing. The developed encoder shows 2880 pulse/rotation resolution and repeatable output under different temperature environments.

Unambiguous and Reliable Positioning in the vehicle in terms of Functional Safety and Cyber Security

Functional security and agile software development are two modern areas in product development, which initially have very opposite approaches. For example, formal tests are required by the relevant standards for the former, which must be documented very extensively. The agile software development, on the other hand, tries to come to its conclusion with as few documentation and flexible tests as possible. Also, the proof that testing and development are independent of each other for safety-critical projects is difficult in the context of the use of agile methods. However, taking the constraints of functional safety as given and taking advantage of the enormous flexibility of agile software development, e.g. With the use of Scrum, the Daily Team Meetings create new opportunities in product development. In contrast to previous positioning methods for linearly movable axles, a new developed approach for rear axle steering has not been used as an absolute value encoder, but a novel positioning concept has been researched and developed. Functional Safety first! A new safety concept must therefore be developed. The absolute value encoder, usually realized as an optical or magnetic bar-coded sensor, is used reliably but cost-effectively in a large number of systems. In order to save costs as well as space, the development of the new approach to the sensor will be dispensed with and the positioning will be realized via a new concept. The conventional concepts for position determination of axes is an absolute value encoder. However, this is not highly reliable and has no redundancy. With the new safety concept, the exact position of an axis can be determined and output with high accuracy by means of the various safety devices directly after switching on the system. As a result, the sensor system is hardly susceptible to errors. Here, a detailed error analysis has been carried out. Even after system crashes, there are enough detection points, which are constantly detected during normal operation and thus the plausibility check can be restored. The new explored approach allows the steering to work normally even in safe modes. However, the algorithms for protection have to take effect immediately if, for example, an expected index signal does not occur.

Design of Vacuum Compatible Automatic Targets Feeding System

The present paper presents the design of a vacuum compatible automatic targets feeding system (VCATFS) that can be used to introduce targets inside the interaction chambers for accelerators, laser beams and others research plants. As a first application, the system is to be used within the Extreme Light Infrastructure - Nuclear Physics (ELI-NP) project, to load target frames in the interaction chamber without losing the vacuum. The target frames will be inserted and retracted into/from the interaction chamber individually with high accuracy of positioning. Up to three target frames can be used during one experiment. This number of targets is a consequence of several severe spatial constraints where the system will be installed, but for other situations it can be increased. Also, a new technique of moving the target frames is proposed, two horizontal translations in two parallel planes and two vertical translations also in two parallel planes. VCATFS is divided into two main sub-systems: mechanical (includes kinematics, high precision components and systems, vacuum chamber), and a dedicated command and control system (transducers - high accuracy absolute linear encoders, stepper motors and associated electric drives unit, interfaces and proprietary software). Additionally, a dedicated vacuum system was designed. This approach will further be developed as prototype level. This paper will focus on the design of mechanical sub-system, the remaining ones will be the subject of future documents that would be made publicly available in the future.

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.