METHOD OF MANUFACTURING FLUIDIC ANGULAR RATE SENSOR

Abstract: A method of manufacturing a fluidic angular rate sensor of the type that fine wires such as tungsten wires are tensely spread over the heads of two pairs of metal supports which are mounted on a ceramic disc having fluid passage apertures, includes the steps of: plating a gold on the wires and fixedly spreading the wires over the metal supports by means of thermocompression bonding or the like; and heating the wires in a predetermined atmo­ sphere which allows the plated gold to be removed and the wires to be crystalized.

Description: The present invention relates to a fluidic angular rate sensor to be mounted on a moving object such as an automobile, an airplane or the like to detect its location by measuring an angular rate, without using an auxiliary signal sent from the external, e.g., radio waves sent from a stationary satellite. According to a conventional manufacturing method, two pairs of metal supports are mounted on a ceramic disc which has fluid passage apertures. Fine tungsten or molybdenum wires are tensely spread over the respective metal supports. In this case, very fine wires are used to obtain a high sensitivity and detect a small angular rate. Such very fine wires cannot be bonded to the metal supports by means of, e.g., spot welding. Instead, ultrasonic bonding has been used wherein a gold is metal-plated on the wires and the heads of the metal supports to allow tight contact therebetween, and thereafter gold balls are used to ultrasonically bond the tensely spread wires to the metal supports (Patent of Japan, Vol. 7, No. 117 (P-198) 1262, 21st May 1983). The operating principle of the fluidic angular rate sensor having the sensitive element as above is as follows. Specifically, the sensor mounted on a vehicle or the like is adjusted such that the wires of the sensor are aligned perpendicular to the plane of angular rate sensitivity. A helium gas is jetted out from a nozzle. In this condition, if there is no angular rate, the helium gas goes straight ahead and equally contacts the two wires to maintain the same temperature condition and hence the same resistance value of the two wires. If there exists an angular rate, the helium gas is biased to one direction so that one of the wires is cooled more than the other to cause a temperature difference and hence a difference in resistance. The angular rate is measured based on this resistance difference. The sensitive sensor made by the above-described conventional manufacturing method, however, has the following problems. First, since gold is metal-plated on the wires, a relatively large resistance temperature coefficient of, e.g., tungsten lowers, resulting in a degraded sensitivity. The resultant temperature coefficient is dependent upon the thickness of the plated gold. Therefore, the temperature coefficient may vary with a manufacture lot so that a correct measurement of angular rate is not possible without adjusting the temperature coefficient of each lot. Second, since the wires are tensely spread over the metal supports, this tension remains as residual stresses which become a cause of age variations in resistance values of the wires. Thus, a long term stable measurement of angular rate becomes impossible, thus causing frequent maintenances. The residual stresses are present also in the plated gold so that the age variations become more complicated to the degree that the variations cannot be compensated in practice. In addition to the above problems, the wires, e.g., tungsten wires made only by a wiredraw process have the structure of fiber state. Therefore, by supplying an electric power to a mounted sensor, the wires are heated to undergo re-crystalization which causes variations in resistance. To solve the above problems, the present invention provides a method of manufacturing a fluidic angular rate sensor of the type that fine wires such as tungsten wires are tensely spread over the heads of two pairs of metal supports which are mounted on a ceramic disc having fluid passage apertures, comprising the steps of: plating a gold on said wires and fixedly spreading said wires over said metal supports by means of thermocompression bonding or the like; and heating said wires in a predetermined atmosphere of atmospheric pressure or less, which allows said plated gold to be removed and said wires to be crystalized. The foregoing and other objects, features and advantages of the present invention will become more apparent from the subclaims and the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings. Figure 1 is a schematic view showing the heating process constituting the main part of an embodiment of a method of manufacturing a fluidic angular rate sensor according to the present invention; Figure 2 is an enlarged view showing the structure of a wire prior to undergoing the heating process; Figure 3 is an enlarged view showing the structure of the wire after undergoing the heating process; Figure 4 is a schematic view showing the heating process of second and third embodiments of the method according to the present invention; Figure 5 is a schematic view showing the heating process of a fourth embodiment of the method according to the present invention; Figure 6 is a perspective view showing a sensitive element constituting the main part of a conventional fluidic angular rate sensor; Figure 7 is a perspective enlarged view showing the detail of the sensitive element and Figure 8 illustrates the operating principle of a fluidic angular rate sensor. The conventional fluidic angular rate sensor shown in Figure 6 was described in detail in the above introductory part of the specification. Figure 6 illustrates the following parts: sensitive element 1, ceramic disc 12, fluid passage apertures 12a, tungsten or molybdenum wires 14, metal supports 13. The present invention will now be described in detail with reference to the accompanying drawings. To understand the invention easily, elements identical to those conventional ones are designated by using the same reference numerals, and the description same as the conventional one is partially omitted. Referring to Figure 1, a sensitive element generally designated by reference numeral 1 is is formed using the method similar to a conventional one. The sensitive element 1 is mounted on a chamber 4 and sealed therein with the wires 14 being connected to a power supply 3 via leads 2. An air exhaust device 5 coupled to the chamber 4 is then operated to exhaust air and attain a high vacuum smaller than 1.5 pascal. Next, the power supply 3 is turned on to supply electric power to the wires 14. This heating process continues for a time sufficient to heat the plated gold 14a to a temperature allowing the plated gold 14a to be evaporated and removed from the wires 14. With the heating process, the plated gold 14a is removed and the material forming the wires 14 is completely exposed. The power supply 3 is controlled such that the temperature of the wires 14, e.g., tungsten wires becomes greater than 1500 °C to carry out a secondary re-crystalization of tungsten. Figure 2 is a flying spot electron micrograph showing the tungsten wire 14 prior to undergoing the heating process. As seen from Figure 2, the structure of the wire presents fiber state as of bamboo fibers. Whereas the structure of the wire after the heating process presents re-crystalization as shown in Figure 3 and is converted into a more stable state. Figure 4 illustrates the second embodiment of the method of manufacturing a fluidic angular rate sensor according to the present invention. Connected to the chamber 4 are an air exhaust device 5 and a gas cylinder 8 containing inert gas such as nitrogen gas. The air exhaust device 5 and the gas cylinder 8 can be operated interchangeably by respective stop valves 6 and 7. A sensitive element 1 is mounted on the chamber 4 and sealed therein. Thereafter, the stop valve 6 of the air exhaust device 5 is released to start operating the device and exhaust air. After closing the stop valve 6, the stop valve 7 of the gas cylinder 8 is released to fill inert gas in the chamber. As the pressure of the inert gas becomes high, the evaporation temperature of the plated gold 14a (melting point of gold is above 1070 °C at an atmospheric pressure) will also rise, thus requiring a higher temperature at the heating process. Consequently, the pressure of the inert gas is preferably maintained lower than the atmospheric pressure. Then, the wires 14 are subjected to the heating process similar to the first embodiment by supplying electric power to the wires 14 from the power supply 3. In the third embodiment which is not shown because the embodiment configuration is the same as Figure 4, reductive gas such as hydrogen is used in the gas cylinder 8. After the heating process similar to the second embodiment the same advantageous effects were obtained. Further, a mixture of inert gas and reductive gas may be used, which also showed the same effects. Referring to Figure 5 which illustrates a further embodiment of this invention, instead of the power supply 3, a laser beam device 9 is used. The heating process for the wires 14 is conducted using laser beams generated by the laser beam device 9. In this case, the heating process can be carried out under relatively uniform conditions, without considering variations in diameter of the wire with plated gold which cause variations in generated temperature, a change in resistance value which occurs as the plated gold 14a is evaporated gradually, or the like. In the above embodiments, it is apparent that the wires 14 are subjected to re-crystalization so that residual stresses at the tensely spread wires 14 over the metal supports 13 are lightened and that the plated gold 14a is removed. The sensitive element 1 thus formed is mounted on a case and assembled into a fluidic angular rate sensor as in a conventional manner. As appreciated from the foregoing description of this invention, after the wires are tensely spread, the plated gold thereon is evaporated and removed therefrom. In addition, the heating process for the wires, e.g., tungsten wires is conducted at the temperature that the material can undergo the re-crystalization. Therefore, the temperature coefficient becomes near that of, e.g., tungsten because of removal of the plated gold, thus resulting in high sensitivity. Further, the stresses caused by the tension of the wires are lightened. Therefore, age variations of the resistance of the wire are eliminated so that long term stable angular rate measurement is possible without adjustments and with simple maintenance. Furthermore, tungsten wires, for example, made only by a wiredraw process have the structure of fiber state. Therefore, by supplying an electric power to a mounted sensor, the wires are heated to undergo re-crystalization which causes variations in resistance. However, the present invention has practically eliminated the above age variations. With the above advantageous effects, the practical utilization of the fluidic angular rate sensor is enhanced.

Claims: A method of manufacturing a fluidic angular rate sensor of the type that fine wires such as tungsten wires are tensely spread over the heads of two pairs of metal supports which are mounted on a ceramic disc having fluid passage apertures, comprising the step of: plating a gold on said wires and fixedly spreading said wires over said metal supports by means of thermocompression bonding or the like; and being characterized by heating said wires in a predetermined atmosphere of atmospheric pressure or less, which allows said plated gold to be removed and said wires to be crystalized. A method according to claim 1, wherein said heating process internally heats said wires by supplying electric power thereto. A method according to claim 1 or 2, wherein said heating process externally heats said wires by radiating laser beams or the like thereto. A method according to one of claims 1 to 3, wherein said predetermined atmosphere is a vacuum. A method according to one of claims 1 to 3, wherein said predetermined atmosphere is an inert. gas. A method according to one of claims 1 to 3, wherein said predetermined atmosphere is a reductive gas. A method according to one of claims 1 to 3, wherein said predetermined atmosphere is a mixture gas of inert gas and reductive gas.

Inventors: OKAZAKI, KUNIO, SHIRAISHI, MASARU, TAKAHASHI, FUMITAKA, TAKAHASHI, MASAYUKI
Applicants: HONDA MOTOR COMPANY LTD., STANLEY ELECTRIC CO., LTD.
Application year: 1988
Main classification: G01P9
IPC codes: G01P9, G01C19