Linear Position Sensor Research Articles

High sensitivity linear position sensor developed using granular Ag–Co giant magnetoresistances

This article describes the sensing material, the fabrication process and the characteristics of a new contactless position sensor. The aim of the proposed sensor is the detection of a linear position using a magnetoresistive thin film based on Ag–Co alloy. The experimental results obtained using permanent magnets as mobile elements are presented and discussed.

Effect of changes in substrate salinity on the elongation of Rosa hybrida L. ‘Kardinal’ stems

Changes in stem elongation rates of Rosa hybrida L. ‘Kardinal’ stems were measured using linear displacement position sensors (LDPS) while plants were exposed to salinized nutrient solutions for 2 or 12 h. Greenhouse-grown plants were acclimated for at least 24 h in a growth chamber before treatment. While in the growth chamber under constant 25 °C and continuous light, plants were automatically irrigated based on substrate moisture tension with half-strength modified Hoagland’s nutrient solution in demineralized water (NS). In the 2 h exposure experiment, a pretreatment irrigation of NS was initiated at 1:00 a.m. and was followed 2 h later by an application of demineralized (deionized) water (DI), NS, or NS with NaCl to increase the solution electrical conductivity (EC) by 1, 2, 4, or 8 dS m −1 (+1, +2, +4, and +8, respectively). A post-treatment irrigation with NS followed after two more hours. The shoot elongation rate (SER) of plants treated with DI increased by 0.30 mm h −1 from 0.95 mm h −1, then returned to the pretreatment rate after the final irrigation. Treatment with NS resulted in a growth rate 0.10 mm h −1 greater than the pretreatment rate. This was unexpected and is probably due to a temperature effect caused by irrigating with cold solution. The +1 treatment had no effect on growth rate, but the higher concentrations resulted in decreases in SER of 0.12, 0.23, and 0.86 mm h −1, respectively. Shoot growth rates of salinized plants returned to or exceeded pretreatment rates after the final leaching irrigation. In a 12 h exposure experiment, the treatment solution was not leached and data was collected for 12 h after the treatment. Treatment with +2, +4, and +8 caused immediate, but temporary reductions in SER. Growth rates then increased and restabilized after 4–6 h. Stems of the +2 and +4 treated plants regained the pretreatment elongation rates, but +8 treated stems only partially recovered at 78% of the pretreatment rate.

Hysteresis compensation in a magnetostrictive linear position sensor

A new linear position sensor (Micrus) has been developed, based on the transmission of ultrasonic signals in a waveguide. Waves are generated at the cursor position by the magnetostrictive effect, and their times of flight to the ends of the waveguide are used to estimate the position of the mobile element. The choice of the generating/transmitting metal for this kind of sensor is discussed. We have found that the magnetic hysteresis inherent to the magnetostrictive phenomenon translates into measurement hysteresis, affecting the performance of the sensor. An explanation of the link between both effects is given, and a compensation technique based in focusing the ultrasonic generation is offered. This compensation technique is tested using an electromagnetic finite element method program and then empirically in the Micrus sensor, with satisfactory results.

Contactless position sensor using magnetic saturation

This paper describes different structures for the realization of a contactless position sensor when restricting to a magnet as the target and an inductance as the sensing element. The principle of measurement is the local saturation of an inductance core by a magnet. A sensor model is explained using Maxwell equations on the magnetic circuit. Some response curves are also presented in order to validate the model. The experimental results obtained on a prototype of linear position sensor are given.

DETERMINATION OF CROSS-GRAIN PROPERTIES OF CLEARWOOD SAMPLES UNDER KILN-DRYING CONDITIONS AT TEMPERATURE UP TO 140° C

ABSTRACT Small specimens of Pinus radiata have been tested to determine the creep strain that occurs during the kiln drying of boards. The samples have been tested over a range of temperatures from 20°C to 140°C. The samples, measuring 150 × 50 × 5 mm, were conditioned at various relative humidities in a pilot-plant kiln, in which the experiments at constant moisture content (MC) in the range of 5-20% MC were undertaken to eliminate mechano-sorptive strains. To determine the creep strain, the samples were brought to their equilibrium moisture content (EMC), then mechanically loaded under tension in the direction perpendicular to the grain. The strain was measured using small linear position sensors (LPS) which detect any elongation or shrinkage in the sample. The instantaneous compliance was measured within 60 sec of the application of the load (stress). The subsequent creep was monitored by the continued logging of strain data from the LPS units. The results of these experiments are consistent with previous studies of Wu and Milota (1995) on Douglas-fir ( Pseudotsuga menziesii ). An increase in temperature or moisture content causes a rise in the creep straw while the sample is under tension. Values for the instantaneous compliance range from 1.7 × 10−3 to 1.28 × 10−7 MPa−1 at temperatures between 20°C and 140°C and moisture content in the range of 5-20%. The rates of change of the creep strains are in the Order of magnitude 10−7to10−8s−1 for these temperatures and moisture contents. The experimental data have been fitted to the constitutive equations of Wu and Miloia (1996) for Douglas-fir to give material parameters for the instantaneous and Creep strain components for Pinus radiata.

The influence of electric-field bending on the nonlinearity of capacitive sensors

Three-layered electrode structures are often employed in multiple-electrode capacitive position sensors. Even when advanced algorithms and well-designed guarding electrodes are used, the electric-field-bending effect is still one of the major contributors to the nonlinearity of capacitive position sensors. In this paper, the effects of electric-field bending on linearities of five capacitive linear-position sensors have been studied based on a physical model of the capacitive sensor. It is shown that the effect of electric-field bending on linearities strongly depends on the sensor structures, and that it is significantly reduced when advanced sensor structures and algorithms are used. The results are very useful for optimizing the sensor structure according to its application.

The novel use of a memory layer in a giant magnetoresistive position sensor design

A linear noncontact position sensor using Co/Cu giant magneto-resistance (GMR) multilayers as the sensing material and incorporating a magnetic memory layer has been designed and modeled. A magnetic head assembly acts as the position locator and the presence of a memory layer makes the throw length unlimited. A numerical model using charge sheets and finite elements has been used to optimize the physical dimensions of the magnetic layers for different magnetic materials and determine their spacing from the Co/Cu GMR sensing material. The output from the sensor has been simulated as the head moves back and forth along the track. These results show that hysteresis in the memory layer can be overcome by optimizing the head design. Using easily available materials, the modeling has shown that a device using second anti-ferromagnetic (AF) peak Co/Cu is realizable. The model has also be used to identify desirable material parameters for potential future engineered materials with the aim of utilizing high GMR first AF peak Co/Cu material in the sensor.

Arc root mobility during contact opening at high current

This paper presents a test system, designed for the investigation of short circuit arcs related to miniature circuit breakers operating in a 240 V, AC supply. An optical fiber imaging system is used to identify arc root motion, with short circuit current up to 6 kA. Two methods are used to measure contact motion, a noncontact linear position sensor, and the optical fiber array. The optical fiber array uses software image processing to identify the position of the arc roots in the arc chamber. The identification of the arc roots allows for a study of the arc immobility at the initial stages of the event. Results are presented on variation of peak current level and arc runner materials on arc root motion for one geometry. The cathode root motion is shown to dominate the event.

On the calibration of position sensors based on magnetic delay lines

Results on the characteristics of three position sensors based on magnetic delay line techniques are illustrated in this paper. These sensors are based on the linear motion of coils or magnets along the length of a magnetic delay line. The uncertainty of the first sensor has been improved up to 40 μm m−1 by applying bias field along its length, while the second cordless sensor has the worst accuracy of 100 μm m−1. The sensitivity of the third position sensor has been determined to be better than 1 μm, provided that it is firmly shielded against ambient magnetic fields. The simplicity of these arrangements makes them interesting for industrial applications, where corded or cordless linear motion position sensors of relatively low cost are required.

Analysis of a linear position sensor with a Hall effect element

The performance characteristics of linear Hall element sensors for non-contact determination of the position of a moveable permanent magnet along a pre-established path are analysed. Simple theoretical expressions suitable for computer modelling of previously described sensors are presented. Practical measurements have verified the theoretical predictions arrived at by simulation means. Having established the validity of the basic formulae predictions of performance for a variety of magnet configurations can now be attempted using superposition principles. As an application, a method of improving the linearity of a simple sensor with a single cylinder magnet by means of shaping the cylinder to a special profile is described. An alternative example is a new high-gradient configuration of a radially symmetric sensor construction on a base of two oppositely magnetized rings.

A smart capacitive absolute angular-position sensor

Abstract This paper describes a novel low-cost smart accurate capacitive absolute angular-position sensor with high accuracy and high resolution (18 bits r.m.s.). One of the novelties of this sensor is that, for each measurement, it uses all 24 segment electrodes along the circumference, each of them ranging from 0 to 0.3 pF. The capacitance values between these electrodes have a lot of redundancy with respect to the position to be measured. The electronic processing uses this redundancy to compensate for mechanical errors in the sensor in order to obtain an accurate measurement and to reduce the mechanical demands on the sensor. This novel approach can also be applied directly to capacitive absolute linear-position sensors. A simple and cheap oscillator is used to measure the various sensor capacitances. The oscillator converts the analog capacitance information into the time domain and is directly digitized by a microcontroller, eliminating the need for an expensive AD converter.

STEM ELONGATION IN `CARA MIA' ROSES

Stem length of cut flower roses is one of the primary determinants of the sales price. Thus knowledge of the process of shoot elongation is useful in optimization of rose production. In this study shoot elongation was investigated by continuously logging `Cara Mia' rose shoot length using linear displacement position sensors (LDPS). Under natural conditions, elongation was found to occur mainly at night. The objective of this study was to investigate the role of environmental factors on rose stem elongation and to determine whether the process was related to an endogenous circadian rhythm or the absence of light. Measurements were made under various photoperiodic conditions (0, 8, 10, 12 and 24 hours night) and various temperature regimes. Under alternating light/dark regimes, regardless of photoperiod, shoot elongation rates follow a cyclical pattern with maximum values during dark periods and lower rates during periods of light. The elongation rate declined abruptly with the beginning of the light, suggesting that phytochrome activity might be responsible for this cessation of elongation. Under continuous light and constant temperature, the cyclical behavior was also observed, although the amplitude of the rhythm was smaller than under continuous light.

Method and apparatus for using ultrasonic energy for moving microminiature elements

A micromotor device for moving a micro-miniature element along a predetermined path comprises a membrane supported on a substrate having an upper planar surface for supporting the element to be moved and a lower surface. An ultrasonic transducer attached to one membrane surface is supplied with electrical power to produce ultrasonic energy and thereby cause a flexural wave action in the membrane. The membrane may be comprised of a layer of piezoelectric material in one embodiment or an electrically insulating amorphous material which utilizes an electrostriction phenomenon in another embodiment. The generated flexural wave action produces linear movement of one or more microelements on a membrane for a variety of applications. Control of the moving elements may be maintained using a linear position sensor which includes a circuit for producing feedback control signals.

An integrated position sensor using JFETs as a buffer for PSD output signal

Abstract A novel compact integrated linear position sensor has been developed. The sensor chip, fabricated by bipolar IC technology, includes a PSD and its peripheral circuitry. In order to eliminate the dependence of the position signal on light intensity, the difference of the two output currents of the PSD was divided by their sum using a simple conversion circuit of a differential pair of NPN transistors. JFET buffers were incorporated to reduce conversion error caused by the input current of the transistors. A leakage current canceller with an optically shielded PSD was also integrated on the same chip. The output characteristics were measured and the nonlinearity was less than 1% over the temperature range −20-+100 °C.

Linear motion sensor using the Doppler effect with magnetostatic waves

Observation of the Doppler shift of magnetostatic waves and a new linear velocity and position sensor based on this effect are reported. The sensor consists of a magnetostatic surface-wave delay line in which one transducer is allowed to move along the direction of propagation. Position and velocity are indicated by the phase and Doppler shift of the transmitted signal, respectively. These effects are much larger than would be observed with ordinary electromagnetic waves at the same frequency owing to the shorter wavelengths of magnetostatic waves.

A low cost high resolution optical position sensor

A fast high-resolution analog position sensor that provides real-time analog output corresponding to the position of the centroid of a diffuse optical source focused on its surface, is described. Theoretical performance equations are presented. Linear and two-dimensional position sensors have been fabricated and tested to verify the basic theory. Analytic results for system static transfer function and transient response are presented and verified experimentally for a 3- mu m p-well CMOS process. The main component sensitivities are identified and verified using computer-aided modeling techniques. >

Laser range finder based on synchronized scanners

A new geometrical arrangement is proposed to improve performances of optical triangulation. Two scanners in synchronization allow a linear position sensor to be used for surface topography measurement. Besides a large increase in speed of measurement (approximately megahertz), the new geometry allows considerable reduction of the optical head size compared with usual geometries, so the shadow effects are reduced proportionally. It also provides a means to obtain a very large field of view without compromising on resolution. Geometrical analysis and experimental results are presented.