Patent Application
20070169550
Not applicable
Not applicable
The present invention generally relates to education and demonstration, and to measuring and testing. More specifically it relates to a sophisticated, low-cost, integrated-circuit-electrostatic (ICE), plug-on sensor for electronically sensing motion involved in the behavior testing and health monitoring of educational structural models sensibly demonstrating eneraction—what makes the world and sensors work.
Various types of physical models have been employed for ages to help teach science and technology, and to explore reality. Applying modem technology, many such educational models now employ computers displaying signals from electronic sensors to facilitate learning and teaching. Among the multitude of structural models and sensors available today, obvious wants and needs still exist for new and improved sensors to demonstrate and explore sensing and communicating, gravimetric calibration, the behavior testing and health monitoring of things, including sensors, and eneraction. Related science and technology experiments tend to integrate rather fragmented knowledge and experience back into a unified whole.
Eneraction, a new word, explains how the world and sensors work—how sensors and senses structurally sense and communicate? Eneractively, through transfers of energy: physical, mental, and spiritual, forces of nature and man move and bend things, trigger and power events, and sense and communicate information. Likewise, eneractively, through transfers of mechanical and electrical energy, forces deflecting elastic sensor structures transfer physical phenomena into electrical signals. Sensors are not mystical devices.
Knowledge gained physically testing models extends by analogy to mental and spiritual realms. For example, through transfers of energy, physically force moves objects, mentally feeling stimulates thought, and spiritually, spirit inspires action. Moreover, ancient wisdom encourages us to test all things, and retain what is good.
Industrial sensors are usually too big and expensive for use on desktop, educational, structural models. Although some modern semiconductor strain gage and MEMS (Micro-Electro-Mechanical Systems) type sensors are now being used on educational models, they present complex cabling and mounting problems. In another field, acoustics, small electret microphones employing popular ICP (integrated circuit piezoelectric) technology operating over flexible, two-wire cables to make similar low-level measurements. Modified, these modern marvels show promise for motion sensing, but present other problems. They are sensitive to humidity and moisture, and need to be sealed and vented. Enlarged internal passages reduce damping, and sluggish behavior.
Because of the mass of the elastic diaphragm material, such microphones are inherently sensitive to motion. Adding mass to the diaphragm increases the acceleration sensitivity, and adapts them for use on structural models. But, finding practical ways to permanently attach the mass to the diaphragm, environmentally seal the assembly, sufficiently vent, and conveniently install has stymied development.
Although the polarized capacitor sensing element in electret microphones is a simulated piezoelectric crystal, popular ICP technology when used with microphones ought to be more generally termed ICE (Integrated Circuit Electrostatic). ICP is a subclass of ICE. Like electret capacitors, piezoelectric quartz crystals are electrostatic in nature. ICP technology involves an isolation amplifier inside the sensor operating over two ordinary wires. One wire carries both signal and power, creating a bias voltage on the output. The other wire is ground.
Thus, a want and need exists for a low cost, high sensitivity, easy to mount, flexibly cabled, sealed, ICE, educational accelerometer, which the present invention addresses.
Accordingly, most of the above wants and needs are met by the present invention of a modified, popular, commercial, electret microphone sealed in a thin vinyl cap, and embedded in a hard rubber housing having a hole for mounting by plugging onto an oversize mating post on the test object.
Modifications include carefully attaching a small mass to the central part of the microphone diaphragm with a silicone adhesive that remains flexible and withstands elevated temperatures, and drilling holes in the microphone casing to enlarge internal cavities. Filling with wax or a sealant the open end of the plastic cap where the wires protrude hermetically seals the assembly. The outside diameter of the plastic cap of the microphone assembly the snugly fits in a central round hole in the cylindrical housing. The two flexible wires for electrical connection to external signal and power conditioning circuitry protrude through a small hole in one end of the housing, and are gripped by its wall.
For quick, easy installation and removal, the central hole in the elastic housing also snuggly fits and grips an oversize mating post protruding from the test subject. Residual stresses in the elastic housing firmly press and hold the mating interface surfaces together in intimate contact, ensuring faithful transmission of motion, and accurate alignment of the sensitive, cylindrical axis of the accelerometer normal to the mounting surface.
The popular, low-cost, electret microphone, now produced by the millions for toys and cell phones, incorporates a built-in ICP type isolation amplifier that operates over two flexible wires from a computer expanded to display electronic signals, like an oscilloscope.
For a differential sensor with improved linearity and sensitivity operating over three wires, two modified microphone capsules are assembled face to face in a common plastic cap, with their seismic masses adhesively connected to form a single unit,
Structural behavior of both the microphone assembly and the housing is adequate for measurements on existing swing, free-fall, and beam type educational structural models. First resonances are above 1000 Hertz. During calibration, the sensor faithfully follows a square wave of known, one g, input motion, with a rise time of less than three milliseconds, and no appreciable signal decay over a 50 millisecond time interval.
Therefore the primary object of this invention is a low-cost, sensitive, rugged, light weight, flexibly cabled, easy-to-install, accelerometer for sensing the motion of educational structural models during experiments testing the behavior and monitoring the health monitoring of things.
Another object of this invention is a typical sensor to demonstrate how sensors structurally sense and communicate through eneraction—the interactive transfer of energy.
Another object of this invention is an educational accelerometer with flexible wiring to demonstrate free-fall calibration, and dynamic behavior testing of sensors.
Still another object of this invention is a sensor to demonstrate and explain popular, modern, ICP (integrated-circuit-piezoelectric) technology.
The structure of the preferred embodiment of the educational accelerometer and typical test results are illustrated in the following drawings, in which:
Through transfers of energy as force and motion, the sensor capsule 10 structurally senses motion of the test object 30. Transferring energy, when the housing 21 plugs onto a mating post 31 protruding from a test object 30, and is accelerated in a direction normal to the plane of said diaphragm 13, the force required to accelerate mass 14 to follow the motion of housing 21 deflects diaphragm 13, generating an output signal from said ICP microphone assembly 10 representing the acceleration aspect of motion being experienced.
Deflection of the diaphragm 13 changes the capacitance between it and a backup plate 15, which converts into an electrical signal for display on a computer monitor expanded to act like an oscilloscope.
The pre-polarized, electret capacitor 14, 15 acts as a simulated piezoelectric crystal in a typical ICP (integrated-circuit-piezoelectric) system. An ICP isolation amplifier inside the microphone prevents external circuitry from discharging the capacitor and eliminating the signal. When connected to a computer through a data acquisition device, plus 5 volt USB power is supplied through lead 42 and resistor 44 over the signal lead 41. An optional filter capacitor 45 attenuates high frequency electrical noise.
Conveniently installed in a small module or bulge in the cable, resistor 44 and filter capacitor 45 form a typical ICP coupling unit. Standard telephone connector 48 plugs directly into commercially available, low-cost, educational, data acquisition instruments. The flexible, ordinary, two wire cable allows measurements on moving objects without introducing significant spurious cable forces. High level signals obviate the need for shielding in most situations.
The so-called seismic or proof mass 14 in the educational accelerometer is a thin disk of heavy metal material, such as brass, bonded to the center of the elastic diaphragm 13 with a flexible silicone adhesive that can withstand elevated temperatures. Holes 16 drilled through the side of the microphone 10 case enlarge internal passages to reduce air damping, and allow the diaphragm 13 more freedom to move. A small groove or saw slot 19 in the surface of the microphone 11 connects the hole 15 to the end chamber of the plastic cap 12 to equalize static pressure across the diaphragm 13.
The sealing means is a cylindrical plastic cap 12 housing the microphone assembly and having its open end coated and sealed with pliable petrowax 18. The wax 18 also effectively seals the exposed top surface of the electret microphone 11, which, like the ultra high impedance piezoelectric crystal device it simulates, is notoriously sensitive to moisture and humidity.
The housing 21 is a cylindrical body of stiff, hard rubber, elastic material having a hole for mounting, and a cavity containing the modified microphone 11. The mounting hole connects to and grips a mating post 31 protruding from the test object 30. The housing 21 transfers motion of the test object 31 to the microphone assembly 10, aligns the microphone 11 with the test object 31, insulates it against environmental noise and temperature changes, and facilitates installation and removal of the accelerometer. Residual stresses in the hard, elastic housing 12, force and hold mating surfaces in intimate contact. This intimate interface contact ensures faithful transmission of motion between the test object and the sensing element over the frequency range of interest in educational experiments.
Operating over three wires 41,42, 43,
As illustrated in
The sensitive axis of the educational accelerometer is along the central axis of the cylindrical housing 21. Sensors capsules 10 for measuring in other directions can also be embedded in the thick side walls of same elastic housing 21. While the electrostatic, polarized capacitance, electret microphone capsule offers simple cabling, behavior, and cost advantages, the novel, rugged, stiff, elastic housing can also readily accommodate other type miniature accelerometer capsules, such as resistive strain gage, passive capacitive, or MEMS. Such an integrated, rugged, educational accelerometer assembly offers several advantages.
Simple, quick, plug-on installation and removal of light weight, motion sensors equipped with flexible cables and standard telephone connectors is a real advantage for student experimenters and teachers. These features facilitate many traditional and new science and technology experiments, such as swing, bungee-jumper, diving board, Newton's laws, behavior testing, health monitoring, sensing and communicating, gravimetric calibration, and eneraction, which, as mentioned and illustrated, is what makes the world and sensors work.
