Information Acquisition of Laser Tracker Incremental Encoder Based on FPGA

Signal acquisition technology for photoelectric encoder based on FPGA

The majority of encoder signal process circuits only support one type of the specific photoelectric encoder, either absolute encoder or incremental encoder. In order to realize the compatibility for both two types of encoders simultaneously, a novel encoder signal process circuit based on FPGA is presented in this paper. Firstly, a series of universal functions are analyzed and demonstrated. On this basis, the approaches on multiplexing interfaces is designed and verified by simulation. Importantly, the compatibility is solved by multiplexing pins of the IC chip in terms of the hardware interface. As for the software interface, FPGA internal signal acquisition and processing programs deal with the different encoder protocols. Finally, two different types of encoders are concurrently connected to the circuit for system testing. The result indicates that the real-time angular position curve is smooth and the measured angle value is accurately displayed on the host computer. Consequently, the stability and compatibility are successfully proven. Besides, those expensive dedicated interface circuits could be replaced by the proposed circuit, as well as the costs can be significantly reduced. The circuit is ideal for applications requiring high resolution and fast data acquisition in industrial control fields.

The photoelectric encoder is a kind of encoder that uses high-precision metrology grating as the detection element to convert the input angular position information into corresponding digital signals through the photo-electric conversion device. It has the advantages of high resolution and wide measuring range, so it is widely used in precision angle measuring devices and high-precision speed regulating systems. In this study, an incremental photoelectric encoder is used, and a receiving system of vertical incidence is chosen, covering a photocell receiving circuit and an infrared circuit. The signal acquisition device of the photoelectric encoder is further designed, that is, the weak photoelectric signal is captured and transformed into an electrical signal that can be recognized by the microprocessor after amplification and adjustment, and then the signal is processed and transmitted. In the test, the signal output of the photoelectric encoder is simulated first. The results reveal that the theoretical output voltage of the drive is 3.5 V, and the peak of the actual output signal is 7.2 V, which meets the design requirements. The designed photoelectric encoder signal device is used with the charge coupled device (CCD) camera to capture the track image. The single-camera and dual-camera tests are carried out respectively. The speed of the bearing vehicle is adjusted to 0.6 m/s~1.2 m/s, and the velocity of the vehicle is adjusted timely. The findings show that the signal device of the photoelectric encoder +CCD camera can be triggered in real-time with the different speeds of the vehicle, and obtain relatively clear images of the track surface and its image of the fastener.

In this paper, we present the use of the laser tracker to aid the alignment of a Swing Arm Profilometer (SAP) and measure the length of the swinging arm, thus calibrating the operating radius of the SAP. The measurement uncertainty analysis is given. A laser tracker is used to align the SAP to ensure the path of the probe head passes through the rotary axis of the rotary table. By building the coordinate system by laser tracker measurement on the rotary table and measuring the swinging arc of the arm, we can determine whether the swinging path of the probe head passes through the rotary axis of the rotary table and perform the corresponding adjustment if necessary. A laser tracker is also used to measure the arm length, i.e. the length between the probe's ball centre and the rotation axis of the swinging arm. By placing a retroreflector or the tracker ball on the swinging arm and scanning the swinging path of the arm using the laser tracker, we can acquire the data of an arc and fit to determine the length of the probe head center to rotation axis of swinging arm, thus giving accurate SAP calibration data.

In order to evaluate the task specific measurement uncertainty of laser tracker, based on the analysis of the uncertainties of the laser tracker system(LTS) ,the Monte-Carlo(MC) method is proposed and applied, and it's principle and steps are described. We have measured the flatness of the marble table with a laser tracker and a CMM, and compared with the MC uncertainty simulation. The results of the MC method and laser tracker measurements are in well agreement with each other, so we conclude that the MC methods could be used in the evaluation of the task-specific measurement uncertainty of laser tracker.

A new goniometer for X-ray powder diffractometry and its setting are described. The diffraction angles are easily and quickly measured with high accuracy (10−3°θ), even if experiments require the use of some large or heavy device such as a cryostat or furnace. An original mechanical design allows a direct measurement of the angular position, 20, of the receiving slit, by means of an incremental (10−3°) photoelectric encoder. Three independent stepping motors, for the θ and 2θ scans and the sample translation, allow one to define with a very good reproducibility the `zero' goniometer position. Diagrams of Pb3O4 and Pb(NO3)2 have been recorded in continuous scanning (0.05° θ/min): differences between θ of the two diffraction lines recorded on each side of the goniometer do not exceed ±2 × 10−3°, and reproducibility of measurements is better than +1 × 10−3°. Sensitivity of angular measurements is very good; it is proved by studying, in the range 9–40° (θ), the thermal expansion of Pb(NO3)2 between 273 and 291 K. Moreover, use of a large radius (500 mm) and of a set of undivergent slits improves angular resolution, principally for θ<20°, which is very important for molecular-compound studies: an example is given showing diffraction line splitting due to a monoclinic triclinic phase transition.

The signal acquisition system (SAS) operated by battery is designed in this paper. SAS includes signal acquisition and statistics function based on movement joints of basketball player. SAS is a recording of the electrical activity of the brain and pulse from the scalp and the recorded waveforms provide insights into the dynamic aspects of brain activity. The amplified SAS signals are digitized by an A/D converter. The digitized signal is transmitted to PC by a wireless serial port or stored in secure digital memory card. Experimental result shows that the system could implement the acquisition and storage of the foot compressive mechanical characteristics signals efficiently. This system would be of benefit to all involved in the use of SAS for sports training.

Identification and Kinematic Calculation of Laser Tracker Errors

Laser trackers are widely used to measure kinematic tasks such as tracking robot movements.Common methods to evaluate the uncertainty in the kinematic measurement include approximations specified by the manufacturers, various analytical adjustment methods and the Kalman filter. In this paper a new, real-time technique is proposed, which estimates the 4D-path (3D-position + time) uncertainty of an arbitrary path in space. Here a hybrid system estimator is applied in conjunction with the kinematic measurement model. This method can be applied to processes, which include various types of kinematic behaviour, constant velocity, variable acceleration or variable turn rates. The new approach is compared with the Kalman filter and a manufacturer's approximations. The comparison was made using data obtained by tracking an industrial robot's tool centre point with a Leica laser tracker AT901 and a Leica laser tracker LTD500. It shows that the new approach is more appropriate to analysing kinematic processes than the Kalman filter, as it reduces overshoots and decreases the estimated variance. In comparison with the manufacturer's approximations, the new approach takes account of kinematic behaviour with an improved description of the real measurement process and a reduction in estimated variance. This approach is therefore well suited to the analysis of kinematic processes with unknown changes in kinematic behaviour as well as the fusion among laser trackers.

In this paper, we used Lab VIEW development platform, designed a virtual signal acquisition and analysis system based on the soundcard. In addition we studied the signal acquisition performance of it. This system has functions of signal acquisition, analysis, waveform display and storage. It is easy to use with good interface, and function appending is available on user requirement. It offers a kind of DAQ solution with low cost. It has broad application prospect, can be extended to the field of speech recognition, ambient noise monitoring and laboratory measurement etc.

Most measurement and control systems of combines use digital tubes or LCD as their monitor, which has some problems like low brightness, poor functional expansion and over-occupy port resources. In this paper, a signal acquisition and failure alarm system of combine harvester is designed, based on touch screen technology. The system uses MCU as the main control unit to receive forward speed signal and rotational speed signals of threshing cylinder, transport grain auger and conveyor pan. It handles the signal data, makes judgments, and sends the signal data to the touch screen through serial communication. Some functions like parameters display, parameters setting and faults alarm are set in the touch screen. The system is applied to Taihu Star TH988 combine harvester and had rice harvest tests. The results show that it has good human-computer interaction and improves stability and accuracy, hardware structure and electrical design simplified.

Incremental photoelectric encoders inevitably have undesirable factors such as quantization errors, manufacturing defects and wear and aging, which bring noise to the speed estimation. The previous speed measurement methods of motor rotors all use the differential method. The differential method amplifies the noise and introduces a time delay to the controller, which are extremely detrimental to the controller design. This article aims to use Nonlinear differential tracker (NDT) to estimate the rotor speed of a DC servo motor without increasing hardware resources, and to provide reliable speed feedback information for the controller. Given the rotor position information of the motor, this method can quickly track the derivative of the input position signal, avoiding the problem of noise amplification caused by other methods, and the algorithm is simple and easy to implement on a microprocessor. Simulation and experimental results verify that this method can effectively reduce noise interference and provide relatively smooth speed estimation information with less jitter. It is of great significance to the design of the control system.KeywordsNonlinear differential trackerSpeed estimateSuppress noiseDSP28335

PurposeDevices for step estimation are body-worn devices used to compute steps taken and/or distance covered by the user. Even though textiles or clothing are foremost to come to mind in terms of articles meant to be worn, their prominence among devices and systems meant for cadence is overshadowed by electronic products such as accelerometers, wristbands and smart phones. Athletes and sports enthusiasts using knee sleeves should be able to track their performances and monitor workout progress without the need to carry other devices with no direct sport utility, such as wristbands and wearable accelerometers. The purpose of this study thus is to contribute to the broad area of wearable devices for cadence application by developing a cheap but effective and efficient stride measurement system based on a knee sleeve.Design/methodology/approachA textile strain sensor is designed by weft knitting silver-plated nylon yarn together with nylon DTY and covered elastic yarn using a 1 × 1 rib structure. The area occupied by the silver-plated yarn within the structure served as the strain sensor. It worked such that, upon being subjected to stress, the electrical resistance of the sensor increases and in turn, is restored when the stress is removed. The strip with the sensor is knitted separately and subsequently sewn to the knee sleeve. The knee sleeve is then connected to a custom-made signal acquisition and processing system. A volunteer was employed for a wearer trial.FindingsExperimental results establish that the number of strides taken by the wearer can easily be correlated to the knee flexion and extension cycles of the wearer. The number of peaks computed by the signal acquisition and processing system is therefore counted to represent stride per minute. Therefore, the sensor is able to effectively count the number of strides taken by the user per minute. The coefficient of variation of over-ground test results yielded 0.03%, and stair climbing also obtained 0.14%, an indication of very high sensor repeatability.Research limitations/implicationsThe study was conducted using limited number of volunteers for the wearer trials.Practical implicationsBy embedding textile piezoresistive sensors in some specific garments and or accessories, physical activity such as gait and its related data can be effectively measured.Originality/valueTo the best of our knowledge, this is the first application of piezoresistive sensing in the knee sleeve for stride estimation. Also, this study establishes that it is possible to attach (sew) already-knit textile strain sensors to apparel to effectuate smart functionality.

With the prosperous development of electronic science and technology, electrical logging technology has been widely used in the process of oil exploitation. Seismoelectric logging is one of the many electrical logging methods, which has some unique advantages compared with other logging methods. At present, there are a lot of theoretical research on the seismoelectric logging at home and abroad, but due to some engineering problems has not been solved, practical instrument is not yet come into being. The acquisition of seismoelectric signal is one of the most difficult problems in the practical application. In this paper, a set of seismoelectric signal acquisition system based on SPI bus is designed to solve this problem. Experiment show that the system basically meets the demand of signal acquisition in seismoelectric logging

We have developed a metrology system that is capable of measuring rough ground and polished surfaces alike, has limited sensitivity to the nominal surface shape, and can accommodate surfaces up to 8.4 m in diameter. The system couples a commercial laser tracker with an advanced calibration technique and a system of stability references to mitigate numerous error sources. This system was built to guide loose abrasive grinding and initial polishing of the off-axis primary mirror segments for the Giant Magellan Telescope (GMT), and is also being used to guide the fabrication of the Large Synoptic Survey Telescope primary and tertiary mirrors. In addition to guiding fabrication, the system also works as a verification test for the GMT principal optical interferometric test of the polished mirror segment to corroborate the measurement in several low-order aberrations. A quantitative assessment of the system accuracy is presented, along with measurement results for GMT, including a comparison to the optical interferometric test of the polished surface.8