Showing papers on "Piezoelectric sensor published in 1989"

Ultrasonic load indicating member, apparatus and method

Abstract: A method of measuring the load in a member subjected to longitudinal stress, a load measuring device and a fastener tightening device using the method of measuring, a load indicating member and a load indicating fastener for use in conjunction with the method of measuring, a method of making the load indicating fastener, a method of tightening the load indicating fastener and a transducer for instrumenting a load bearing member are each disclosed and claimed. A thin piezoelectric sensor consisting of a piezoelectric film sandwiched between two thin electrodes is permanently mechanically and acoustically coupled to the upper surface of a member and is used to determine the length, tensile load, stress, or other tensile load dependent characteristic of the member by ultrasonic techniques.

Robot gripper control system using PVDF piezoelectric sensors

Abstract: A novel robot gripper control system is presented that uses PVDF (polyvinylidene fluoride) piezoelectric sensors to damp exerted force actively. By monitoring the current developed by the PVDF sensor, an output proportional to the rate of change of the force exerted by the gripper is obtained. The signals from the PVDF sensor and strain-gauge force sensor are arranged in a proportional and derivative control system for the control of force. The control system was tested on an instrumented Rhino XR-1 manipulator hand. The capabilities of the control system are analyzed and are verified experimentally. The results for this particular gripper indicate that the additional sensory feedback can decrease the force step response rise time by 88% while maintaining a monotonic zero-overshoot response. The inclusion of the rate feedback increases the damping ratio of the dominant poles while maintaining the step response rise time. >

Development of a light-weight robot end-effector using polymeric piezoelectric bimorph

Abstract: The development of a lightweight piezoelectric end-effector (multifinger type) for robotic applications is reported. The fundamental configuration of each finger is a simple piezoelectric bimorph structure made of a piezoelectric polyvinylidene fluoride material. Injection of a controlled high voltage into the finger can induce a deformation in a prescribed direction. Depending on the applied voltage, the effector can hold an object from outside or inside. The theoretical predictions are verified by the experimental and finite-element simulation results. This end effector is designed for lightweight objects such as electronic chips, and for high-precision (or even micro-precision) operation. Gripping force can always be enhanced by injecting higher voltage. Coordinating the applied voltage in two fingers can also compensate the position offset if misalignment exists in the setup. >

Integrated distributed sensing and active vibration suppression of flexible manipulators using distributed piezoelectrics

Abstract: Structural oscillation of flexible robot manipulators would severely hamper their operation accuracy and precision. This article presents an integrated distributed sensor and active distributed vibration actuator design for elastic or flexible robot structures. The proposed distributed sensor and actuator is a layer, or multilayer of piezoelectric material directly attached on the flexible component needed to be monitored and controlled. The integrated piezoelectric sensor/actuator can monitor the oscillation as well as actively and directly constrain the undesirable oscillation of the flexible robot manipulators by direct/converse piezoelectric effects, respectively. A general theory on the distributed sensing and active vibration control using the piezoelectric elements is first proposed. An equivalent finite element formulation is also developed. A physical model with distributed sensor/actuator is tested in laboratory; and a finite element model with the piezoelectric actuator is simulated. The distributed sensing and control effectiveness are studied.

Dust monitors and dust monitoring

Abstract: A dual monitor comprises a piezoelectric sensor in the form of a quartz crystal and an electrode system thereon. An exposure device in the form of a dust discriminator is provided to expose the piezoelectric sensor at least periodically to a stream of a gas which may contain dust or other organic or inorganic particulate material whose presence in or absence from the gas is to be monitored. The gas of said stream consists primarily of air. An electronic monitoring device is provided coupled to the electrode system of said piezoelectric sensor to monitor variations in the resonant frequency of said piezoelectric sensor induced by the aggregation of dust or other particulate material on said piezoelectric sensor.

Piezoelectric actuator driving apparatus

Abstract: Disclosed is a piezoelectric actuator driving apparatus in which a piezoelectric element used to operate as an electro-mechanical transducer is suitably charged and discharged so that the piezoelectric element can make a predetermined amount of mechanical displacement. In the apparatus, the energy of electric charge causing expansion of the piezoelectric element is controlled by a plurality of pulse signals. Each of these pulse signals acts to store electric charge having a predetermined amount of energy in a capacitor, so that the amount of electric charge stored in the capacitor increases with the increase in the number of the pulse signals. After the total amount of the energy of the electric charge stored in the capacitor attains a predetermined value sufficient to cause expansion of the piezoelectric element, the electric charge stored in the capacitor is supplied to the piezoelectric element. Thus, even when a high speed response and high energy are demanded for controlling the amount of expansion of the piezoelectric element, this demand can be readily dealt with. On the other hand, when the electric charge stored in the piezoelectric element is discharged, voltages applied to the piezoelectric element and the primary and secondary windings of a transformer are controlled so as to prevent deterioration of the piezoelectric element.

Operating characteristics and comparison of photopyroelectric and piezoelectric sensors for trace hydrogen gas detection. II. Piezoelectric quartz‐crystal microbalance sensor

Abstract: A 6‐MHz piezoelectric quartz‐crystal microbalance coated with palladium electrodes has been used under STP gas flow‐through conditions to detect hydrogen adsorption at low concentrations (<5% in nitrogen) where anomalous behavior has been observed due to interferences from other ambient or impurity gases (mainly O2). A systematic study showed that a concentration of 0.4% hydrogen produced no frequency shift in the sensor due to counterbalancing effects from other gases. Thus sensor sensitivity limits were established at 0.5% hydrogen, which is ca.∼200 times lower than the photopyroelectric (P2E) sensor (part I). The hydrogen selectivity of the piezoelectric sensor was found to be inferior to that of the P2E device.

Vehicle deceleration warning piezo-sensor

Abstract: A vehicle deceleration warning apparatus for use in a vehicle having brake lights, a floorboard and an accelerator pedal, the system including a piezoelectric sensor element (150) con­nected to one of the accelerator pedal or the floorboard for outputting a first signal when subjected to appropriate stress conditions, a contact element connected to the other of the accel­erator pedal or the floorboard for contacting the piezoelectric sensor means (150) in a manner which is dependent upon the rate of release of the accelerator pedal and causing the sensor means (150) to output the first signal in response thereto, and a circuit element connected to the brake lights and to the piezoelectric sensor means (150) for analyzing the first signal produced by the piezoelectric sensor means (150) and for actuating the brake lights (70) in response to the analysis when the first signal is above a predetermined threshold.

Torque sensor having a spoked sensor element support structure

Abstract: Piezoelectric sensor devices are attached across pairs of circularly arranged spokes arrayed on the periphery of an annular ring. The sensor devices each include a preloaded steel ball mounting arrangement for mounting a piezoelectric sensor element. A first circular interface plate on one side of the sensor structure attaches to alternate ones of the spokes, and a circular interface plate on the opposite side of the same diameter as the first interface plate attaches to the remaining spokes.

Transducer to detect force which is applied to machine tool when machining workpiece and its attaching structure

Abstract: A cutting load or a cutting resistance which is applied to a machine tool is detected by using a transducer having a film sheet type piezoelectric sensor. A detection output of the transducer is converted into a voltage signal by a charge amplifier. The transducer is attached to the portion of a feed nut which is moved in the axial direction by a screw shaft, and the cutting load is applied to the transducer. On the other hand, the transducer may be assembled in the portion of the bearing which supports the feed screw shaft so as to detect the cutting load which is applied to the screw shaft. Further, the transducer may be assembled integrally with the tool holder. In order to prevent a drift which occurs in the output of the charge amplifier since a constant assembly load is applied to the transducer having the piezoelectric sensor, two transducers are provided so that the cutting loads are applied in opposite directions to the transducers and the inverted output of one of two charge amplifiers is added to the output of the other charge amplifier.

Active control of flexural vibrations in beams

Abstract: The feasibility of using piezoelectric actuators to control the flexural oscillations of large structures in space is investigated. Piezoelectric actuators have the advantage of exerting localized bending moments. In this way, vibration is controlled without exciting rigid body modes in the structure. The actuators are used in collocated sensor/driver pairs to form a feedback control system. The sensor produces a voltage that is proportional to the dynamic stress at the sensor location, and the driver produces a force that is proportional to the voltage applied to it. The analog control system amplifies and phase shifts the sensor signal to produce the voltage signal that drives the driver piezoelectric. The feedback control system is demonstrated to increase the first mode damping in a cantilever beam by up to 85%, depending on the amplifier gain. An analytical model of the control system is developed. The estimated and measured vibration control compare favorably. A simulated free-free beam is fabricated and instrumented with a distribution of piezoelectric sensor/driver pairs. The purpose is to evaluate the damping efficiency of the control system when the piezoelectrics are not optimally positioned at points of high stress in the beam. The control system is found to reduce the overall vibration response to impact by a factor of two.

Dynamics and distributed vibration controls of flexible manipulators; integrated distributed sensing and active piezoelectric actuator

Abstract: An integrated distributed vibration actuator design for elastic flexible robot structures is presented. The proposed distributed sensor and actuator is a layer or multilayer of piezoelectric polymer directly attached to the flexible component needed to be monitored and controlled. The integrated piezoelectric sensor/controller can monitor the oscillation as well as actively and directly constrain the undesirable oscillation of the flexible robot arm by direct/converse piezoelectric effects, respectively. An experimental model and a finite-element simulation are studied, and the effectiveness is evaluated. >

Piezoelectric sensor for foot pressure management

Abstract: The design and fabrication of a piezoelectric sensor which can be used for various pressure measurement applications is discussed. The sensor is 42 mm*19 mm*2 mm, with the piezoelectric film thickness alone being 52 mu m. The sensor is rugged and inexpensive, and it operates with simple, power-efficient electronics. The circuitry used and the problems involved in taking pressure measurements under the bony prominences of the foot are discussed. A major problem is that the sensor does not respond to steady pressures. >

Piezoelectric sensor device

Abstract: A piezoelectric sensor, e.g. for pressure acceleration or displacement measurement, is formed by plasma etching of a quartz crystal blank. The sensor comprises a flexible diaphragm (11) supported around its periphery by an integral rigid annulus (12). Conductive electrodes (13) applied to one surface of the diaphragm define a surface acoustic wave device whose characteristic frequency is determined by displacement of the diaphragm. Use of the sensor in a radio microphone arrangement, e.g. for a cordless telephone, and as an accelerometer, in an inertial guidance system, are mentioned.

Measuring transducer for cutting force or resistance

Abstract: A film type piezoelectric transducer has electrode layers on both sides of a piezoelectric material film. An insulating film section covers the outside of the electrode films of the piezoelectric sensor and is rigidly attached to it. The feeder screw shaft or similar of a machine tool can pass through a hole in the centre of the piezoelectric sensor and of the insulating film section. The transducer is mounted on a nut (28) threaded on the feeder screw shaft (26) of a workpiece table or on a bearing part of the feeder screw.

Piezoelectric sensor comprising at least one pair of flexible sensitive elements of great length

Abstract: A piezoelectric sensor comprising at least one pair of flexible sensitive elements of great length whose respective electrodes are connected in parallel The interconnection is provided by interlacing the sensitive elements so that the two electrodes of each of the flexible sensitive elements are alternately in electric contact with the two electrodes of at least one other sensitive element The sensor may be formed by winding at least one pair of sensitive elements on a support in two spirals of opposite directions with interlacing The chosen assembly method provides both good mechanical strength and simplifies the electric connections because of the multiple electric contacts between the electrodes

A self diagnostic system for piezoelectric sensors

Abstract: A technique for determining the mounting conditions of a piezoelectric accelerometer is presented. This technique electrically stimulates the piezoelectric element in the 'diagnostic' frequency band measuring the electrical frequency response characteristics across a capacitive load impedance. The diagnostic frequency band is tipically much higher than the operating bandwidth of the accelerometer. The resonant frequencies of the accelerometer are included in the diagnostic band. By monitoring the shift in these resonant frequencies, via electrical stimulation techniques, certain diagnostic conditions including mounting conditions can be determined. Experimental data from a compression mode accelerometer is used to demonstrate this technique.

Method of manufacturing a flow meter

Abstract: A piezoelectric vortex flow meter for determining the rate of fluid flow through piping including a hermetically sealed bluff body having a vortex generating plate operably associated with a sensing plate. The vortex generating plate is positioned perpendicular to the fluid flow for creating a "vortex street". A pair of piezoelectric sensors are disposed in a pair of recesses formed in the interior of the sensing plate. Sensing surfaces are formed on each side of the sensing plate adjacent the piezoelectric sensors. The sensing surfaces are formed such that the side surfaces of the sensing plate are free from any discontinuities. The vortices created by the vortex generating plate exert a force on the sensing surfaces which transmit a signal porportional to the force exerted, to the piezoelectric sensors. The piezoelectric sensors transform the mechanical energy into electrical energy readily readable with an appropriate electrical circuit.

Safety device for automatically moved window glass of automobile

Abstract: PURPOSE: To prevent a matter from being nipped between window glass and a doorframe and improve the safety by providing a trigger for operating a piezoelectric sensor above the window glass, and reversely rotating an electric motor when the trigger is loaded. CONSTITUTION: A trigger 5 formed preferably as a piezoelectric cable is provided within the seal lip 6 of a seal 7 provided within a doorframe 4 over the whole length of a window glass 3. When the trigger 5 is pressed by a matter pushed up by the glass 3 moving up and loaded, the rotating direction of an electric motor 9 can be reversed by the voltage pulse generated from the piezoelectric cable 5. When a person or matter 8 is nipped between the window 3 and the doorframe 4, the rising motion of the window glass 3 is immediately stopped, and the motion of the window glass 3 is reversed and lowered.

Torque detector for machine tool

Abstract: PURPOSE: To improve the detection sensitivity for the load variation by using a piezoelectric sensor in film sheet form as a torque detector for detecting the torque applied onto a tool in accordance with the cutting resistance or cutting force of a machine tool. CONSTITUTION: A piezoelectric sensor in film sheet form which is prepared by attaching electrode layers 8a and 8b onto the both surfaces of a piezoelectric material layer 7 is used as torque detectors 1a and 1b for machine tool. A motor 2 for revolving a tool such as twist drill is fixed through the piezoelectric sensor, and the driving torque of the tool is detected on the basis of the detection outputs of a pair of piezoelectric sensors. Therefore, even if the driving torque due to a large cutting resistance or force is applied, breakage is prevented by using such piezoelectric sensor, because the rigidity of the detector is high, and even in case of the small cutting force and cutting resistance by the high detection sensitivity, correct detection is permitted. COPYRIGHT: (C)1990,JPO&Japio

Piezoelectric type pressure sensor

Abstract: PURPOSE:To make it possible to detect the distribution of pressure accurately without interference of the other piezoelectric sensors in measurement, by switching sensor elements which are arranged in a matrix pattern through switching means. CONSTITUTION:At first, a transistor 13 which is connected to a control line C1 is made to be a conducting state through a matrix control circuit. Then, the data of sensor elements on a line corresponding to the control line C1 become selectable state through reading lines R1-Rn. Under this state, the reading lines R1-Rn are sequentially switched. The quantity of accumulated electric charge in each corresponding piezoelectric element is measured. Then, the control lines C1-Cn are sequentially switched, and the same measurement is conducted for all the elements 12. Therefore, other elements do not form closed circuits which interfere with the measurement. Thus, the distribution of pressure can be accurately detected.

Load detector using piezoelectric sensor

Abstract: PURPOSE:To eliminate the effect of a drift and thereby to detect a cutting load accurately, by disposing two piezoelectric sensors so that a load applied to one piezoelectric sensor is increased by the cutting load and that a load applied to the other piezoelectric sensor is thereby decreased. CONSTITUTION:Sheet-shaped piezoelectric sensors 1a and 1b are set on a feed screw mechanism which moves a work table or a tool stage of a machine tool. The piezoelectric sensors 1a and 1b are disposed on the opposite sides of a feed nut, for instance, so that a load applied to the sensor 1a is increased in accordance with a cutting load and that a load applied to the sensor 1b is decreased, to the contrary, in accordance with the cutting load. Electric charges generated by the sensors 1a and 1b are amplified by charge amplifier circuits 2a and 2b and converted into voltages. An output of the amplifier circuit 2b is inverted by an inverter circuit 6 and added to an output of the amplifier circuit 2a by an addition circuit 5. Then the charges of the sensors 1a and 1b leak through input impedances of the amplifier circuits 2a and 2b, and therefore a drift to be generated is offset.

Excitation of the Edge Mode Utilizing Piezoelectric Shear Effect

Abstract: The electrical excitation of the edge mode in a thin piezoelectric ceramic strip is studied on the basis of its strain distribution, and a new excitation method utilizing the piezoelectric shear effect is proposed. Applying this method, miniaturized piezoelectric resonators with high electrical impedance and low capacitance ratio are developed for use in the medium frequency range below several megahertz.

Pressure distribution detector

Abstract: PURPOSE:To detect the charge quantity from a piezoelectric type pressure sensor as a digital value without using an A/D converter, by inputting the output of the piezoelectric type pressure sensor to a discharge time measuring means and a data processing means through a sensor element change-over means. CONSTITUTION:The output of a pressure sensor 10 having many piezoelectric sensor elements arranged in a matrix is successively given to a comparator 3 through a change-over circuit 2. The output of the comparator 3 is inputted to an AND gate 5 which in turn inputs the clock pulse corresponding to the discharge time of each piezoelectric sensor element to a counter 7. A data processor 8 calculates the pressure force of the corresponding sensor element of the basis of the count number inputted from the counter 7.

Detector for machine tool and detector fitting structure

Abstract: PURPOSE:To obtain large cutting force and rigidity against cutting resistance and to detect small cutting force and cutting resistance correctly by providing a film sheet-like piezoelectric sensor where an electrode layer is formed on both sides of a piezoelectric material layer, and forming a passing hole in the center thereof. CONSTITUTION:A detector 1 has a piezoelectric material layer 2 using piezoelectric material in the center thereof, and insulating layers 4a, 4b are fixed to the outsides of electrode layers 3a, 3b formed on both sides of the piezoelectric material layer by adhesion or the like. Further, the detector 1 has a passing hole 5 in the center thereof where a feed screw shaft is pierced. The condenser capacity of an electric charge amplifying circuit for taking out detected output is switched to measure extending over a wide range of 1kgf to 1,000kgf, so that resolving power of about 100gf can be accomplished. Thus, large cutting force and rigidity against cutting resistance are attained so as to correctly detect small cutting force and cutting resistance with high detecting sensitivity.

Improvement of Piezoelectric Photoacoustic Imaging Using Two Images at Different Modulation Frequencies

Abstract: A new method is presented to improve piezoelectric photoacoustic imaging. This technique uses two images at different modulation frequencies to cancel the background caused by the coupling condition and the spatially nonuniform sensitivity of the piezoelectric sensor. It is found that the image of an object with sub-surface defects obtained by this technique is much clearer than a conventional image. The obtained photoacoustic image is compared with the ultrasonic image.