Servo accelerometer

Abstract

This suppresses short circuits between electrodes that detect capacitance. [Solution] The problem is solved by a servo accelerometer that detects the displacement of a pendulum by capacitance, where the inertial force generated in the pendulum and the Lorentz force generated by the current flowing through the torque coil wrapped around the torque cup and the magnetic field passing through the yoke are in equilibrium, and the pendulum is equipped with a thin film electrode 10d for detecting capacitance, the yoke is equipped with electrode surfaces 15e and 16e that detect capacitance and are paired with the thin film electrode 10d, and the surface of the thin film electrode 10d is equipped with a polymer insulating layer 40 made of polymer material.

Description

Technical Field

[0001] The present invention relates to a servo accelerometer using a pendulum.

Background Art

[0002] Conventionally, a servo accelerometer has been put on the market, which includes a yoke unit forming a magnetic circuit and a pendulum that swings with an input acceleration. The yoke unit is composed of a permanent magnet that generates magnetic flux, a pole piece through which the magnetic flux passes inside, and a yoke. The pendulum is composed of a weight portion whose displacement occurs due to acceleration, a hinge that suspends the weight portion, and a support portion that suspends the weight portion via the hinge. A torquer cup around which a torquer coil is wound is fixed to the surface of the weight portion, and it swings together with the weight portion under acceleration. The displacement of the weight portion is detected as the capacitance generated in the gap between the electrodes formed on the weight portion and the yoke unit, etc., and a current converted and amplified into a voltage is supplied to the torquer coil. The displacement of the weight portion is controlled to zero by the magnetic field in the magnetic gap of the yoke unit and the Lorentz force (restoring force) generated by the current flowing through the torquer coil. Since the restoring force at this time balances with the inertial force, the acceleration can be detected from the torquer coil current.

[0003] During the operation of the servo accelerometer shown in Patent Document 1, the electrode provided on the surface of the weight portion faces the electrode on the surface of the yoke unit. Before the accelerometer starts up or when an acceleration exceeding the displacement control function is input, the weight portion may approach the yoke unit, and the electrode provided on the surface of the weight portion may short-circuit with the electrode provided on the surface of the yoke unit. Then, the circuit for detecting the displacement of the weight portion may malfunction, and the servo accelerometer may malfunction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] This suppresses short circuits between electrodes that detect capacitance. [Means for solving the problem]

[0006] To solve the above problems, the servo accelerometer of the present invention is a servo accelerometer in which the inertial force generated in a pendulum and the Lorentz force generated by the current flowing through the torque coil wrapped around the torque cup and the magnetic field passing through the yoke are in equilibrium, and the displacement of the pendulum is detected by capacitance, characterized in that the pendulum is provided with a thin film electrode for detecting capacitance, the yoke is provided with an electrode surface that detects capacitance and is paired with the thin film electrode, and the surface of the thin film electrode is provided with a polymer insulating layer made of a polymer material. [Effects of the Invention]

[0007] This suppresses short circuits between electrodes that detect capacitance. [Brief explanation of the drawing]

[0008] [Figure 1] This is an exploded perspective view showing the configuration of a servo accelerometer according to the embodiment. [Figure 2] This is a cross-sectional view showing the configuration of a servo accelerometer according to an embodiment. [Figure 3] This is a diagram showing the front view of the pendulum in Example 1. [Figure 4] This is a diagram showing the back of the pendulum in Example 1. [Figure 5] This is a schematic cross-sectional view showing the positional relationship between the polymer insulating layer and the electrode surface in Example 1. [Figure 6] This is a schematic cross-sectional view showing the state in which the polymer insulating layer is in contact with the electrode surface in Example 1. [Figure 7] This is a schematic cross-sectional view showing the positional relationship between the polymer insulating layer and the electrode surface in Example 1. [Figure 8]It is a schematic cross-sectional view showing a state where the polymer insulating layer is sufficiently inside from the end of the weight portion and the thin film electrode is close to the electrode surface. [Figure 9] It is a schematic cross-sectional view showing the positional relationship between the polymer insulating layer and the electrode surface in Example 1. [Figure 10] It is a schematic cross-sectional view showing a method of wet etching of quartz glass. [Figure 11] It is a schematic cross-sectional view showing the positional relationship between the polymer insulating layer and the electrode surface in Example 1. [Figure 12] It is a diagram showing a method of creating corners of a polymer insulating layer having a rectangular or chamfered or R shape. [Figure 13] It is a schematic cross-sectional view showing the positional relationship between the polymer insulating layer and the electrode surface in Example 2. [Figure 14] It is a schematic cross-sectional view showing a state where the polymer insulating layer in Example 2 contacts the electrode surface. [Figure 15] It is a view showing the front of the oscillator in Example 3. [Figure 16] It is a schematic cross-sectional view showing the positional relationship between the polymer insulating layer and the electrode surface in Example 3.

Best Mode for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the present invention will be described. FIG. 1 shows the configuration of an embodiment of a servo accelerometer according to this invention, and is an exploded perspective view of the components. FIG. 2 shows a cross-sectional view of the servo accelerometer. The servo accelerometer is a device in which disk-shaped or cylindrical parts are stacked, and the central axes of these part groups coincide. Each part is assembled for each of the oscillator 1, yoke units 2 and 3, and each assembly is fixed by a seal band 23.

[0010] The acceleration detection axis 30 is along the central axis of the servo accelerometer. In the following description, the name indicating the direction is such that the direction of viewing the oscillator 1 from the yoke unit 3 is the front side, and the direction of viewing the oscillator 1 from the yoke unit 2, which is the opposite direction, is the back side.

[0011] The pendulum 1 has Torca cups 13 and 14 fixed to the surface of the pendulum base 10, and Torca coils 11 and 12 fixed to the outer circumference of Torca cups 13 and 14. Methods of fixing Torca cups 13 and 14 include bonding with epoxy adhesive, mechanical fixing using screws, and joining using welding. Suitable materials for Torca cups 13 and 14 are non-magnetic and lightweight materials such as aluminum alloy, titanium alloy, and resin materials. Torca coils 11 and 12 are assemblies of metal wire wound around the outer circumference of Torca cups 13 and 14, and the material of the core requires high conductivity, so copper, copper alloy, aluminum, and aluminum alloy are suitable. The outer circumference of the metal wire has an insulating layer such as polyurethane, polyester, or polyesterimide, and further on the outer circumference there is a fusion layer mainly of polyvinyl butyral, polyamide, or polyester. After the metal wire is wrapped around the outer circumference of the Torca cups 13 and 14, the shape of the Torca coils 11 and 12 is fixed by the adhesion of adjacent fusion layers. Methods for adhering the fusion layers include applying a solvent or softening and melting by heating.

[0012] The configuration of yoke units 2 and 3 is described below. One end of yokes 15 and 16 is closed by circular yokes 17 and 18, while the other end, the open end face, is in contact with the base 10 of the pendulum. Pole pieces 19 and 20 are positioned at the center of the holes in the open end faces of yokes 15 and 16, and cylindrical permanent magnets 21 and 22 are in contact with pole pieces 19 and 20 and housed inside yokes 15 and 16. In this configuration, magnetic flux passes through each component, and a magnetic circuit is formed by yoke units 2 and 3. An annular magnetic gap is formed between the inner circumferential surface of the open end of yokes 15 and 16 and the outer circumferential surface of pole pieces 19 and 20. After the assembly of the servo accelerometer, torque coils 11 and 12 are housed in the magnetic gap, and the magnetic field passes through the torque coil. The seal band 23 is then fixed to the outer circumference of yokes 15 and 16 using adhesive or the like.

[0013] The permanent magnets 21 and 22 are neodymium, samarium cobalt, alnico magnets, etc. magnetized in the thickness direction, and the yokes 15 and 16, the circular yokes 17 and 18, and the pole pieces 19 and 20 are made of soft magnetic materials. The permanent magnets 21 and 22, the circular yokes 17 and 18, and the pole pieces 19 and 20 are fixed by an adhesive respectively, and the yokes 15 and 16 and the circular yokes 17 and 18 are joined by laser welding.

[0014] Fig. 3 shows a front view of the pendulum 1, and Fig. 4 shows a rear view of the pendulum 1. The weight portion 10a of the tongue-shaped pendulum 1 is located within the frame of the support portion 10b which is a cylindrical frame body. The support portion 10b is fixed to the yokes 15 and 16 via the fixing portions 10f arranged at symmetric positions on both surfaces of the support portion 10b. The weight portion 10a is suspended from the support portion 10b by a hinge 10c arranged between the fixing portions 10f. When an acceleration occurs in the direction of the acceleration detection axis 30, the thin hinge 10c elastically deforms with respect to the support portion 10b, and the weight portion 10a performs a rotational motion (reciprocating rotation).

[0015] A manufacturing method for the weight portion 10a, the support portion 10b, and the hinge 10c will be described. A substrate with a desired thickness and surface accuracy is manufactured by cutting out a plate from a base material of metal or glass material and polishing it. The surface of the pendulum 1 serves as a reference for the positions of the torque cups 13 and 14 and the yokes 15 and 16. Therefore, the higher the surface accuracy of the pendulum surface, the higher the assembly accuracy of each component. Next, the shapes of the weight portion 10a, the support portion 10b, and the hinge 10c are manufactured by removing a part of the base material by cutting, wet etching, laser, etc.

[0016] The surface of the weight portion 10a is provided with a thin-film electrode 10d (not shown), and the surface of the thin-film electrode 10d is provided with a polymer insulating layer 40. The electrode surfaces 15e and 16e on the surfaces of the yokes 15 and 16, and the thin-film electrode 10d on the surface of the weight portion 10a opposite to them, function as electrodes for two capacitors. The displacement of the weight portion 10a caused by the input acceleration changes the capacitance between the electrodes, and the difference is detected as a voltage, which is differentially amplified by a servo amplifier (not shown). A servo current based on the capacitance difference is then supplied to a pair of torque coils 11 and 12. This electrical signal detecting capacitance and the servo current flow to the servo amplifier via the thin-film electrode 10d, thin-film wiring 10e formed on the surfaces of the hinge 10c and support portion 10b, metal wire 24, and terminal 25.

[0017] The torque coils 11 and 12 are subjected to a Lorentz force by the magnetic field and servo current formed by the yoke units 2 and 3. When acceleration is applied in a direction perpendicular to the plane of the pendulum base 10 (acceleration detection axis 30), the accelerated weight 10a is displaced. However, by controlling the servo current so that the displacement is zero, the inertial force acting on the pendulum and the Lorentz force are balanced. At this time, the magnitude of the servo current directly corresponds to the magnitude of the acceleration along the acceleration detection axis 30, making it possible to detect acceleration.

[0018] (Example 1) Figure 5 is a schematic diagram showing the servo accelerometer cut at AA' in Figure 3 and some components extracted to illustrate the positional relationship between the thin film electrode 10d and the electrode surfaces 15e and 16e. The thin film electrode 10d is positioned opposite the electrode surfaces 15e and 16e, and a polymer insulating layer 40 is provided on the surface of the thin film electrode 10d. During operation of the servo accelerometer, the position of the weight portion 10a is controlled to be midway between the electrode surfaces 15e and 16e. On the other hand, before the sensor operates or when it receives acceleration exceeding its control capacity, the thin film electrode 10d and the electrode surface 15e may come into close proximity, as shown in Figure 6. If the thin film electrode 10d and the electrode surfaces 15e and 16e come into contact, the electrodes may short-circuit, causing the circuit that detects capacitance to malfunction and potentially making it impossible to control the position of the weight portion 10a. The polymer insulating layer 40 can suppress short circuits between the thin film electrode 10d and the electrode surfaces 15e and 16e.

[0019] As shown in Figure 6, the polymer insulating layer 40 and the electrode surfaces 15e and 16e tend to be in point contact or line contact, so the impact energy received by the polymer insulating layer 40 tends to concentrate in one area. Polymer materials have superior impact resistance compared to other materials because they attenuate impact energy through their molecular structure and dissipate it as heat. On the other hand, in the acceleration sensor described in Patent Document 2, the insulating layer of the electrode is made of silicon oxide. Brittle materials such as silicon oxide are weak against impact and are therefore unsuitable for servo accelerometers where point contact or line contact is likely to occur.

[0020] When detecting the capacitance between the thin film electrode 10d and the electrode surfaces 15e and 16e, an electric field is generated between the thin film electrode 10d and the electrode surfaces 15e and 16e. As shown in Figure 6, when the thin film electrode 10d and the electrode surfaces 15d and 16d approach each other via the polymer insulating layer 40, the electric field generated in the polymer insulating layer 40 increases, which may cause dielectric breakdown. Polyparaxylylene (hereinafter also referred to as parylene) is a polymer material with excellent impact resistance and dielectric strength, making it suitable as a material for the polymer insulating layer 40. In addition, parylene has a higher abrasion index compared to general polymer materials, resulting in fewer particles being generated from the polymer insulating layer 40 upon contact with the electrode surfaces 15d and 16d. In addition to these characteristics, parylene HT (a product name manufactured by Nippon Parylene LLC) has excellent heat resistance and can withstand continuous use at 350°C. A polymer insulating layer 40 made of parylene HT is suitable for servo accelerometers that require high-temperature resistance of 200°C or higher, such as sensors used in oil drilling machines.

[0021] In a pair of electrodes consisting of a thin film electrode 10d and electrode surfaces 15e and 16e, the difference in thickness between the two polymer insulating layers 40 on the surface of the thin film electrode 10d results in a difference in capacitance obtained from the two pairs of electrodes, which can cause bias errors in the servo accelerometer. Since there are limits to correcting bias errors by electrical circuits, the difference in capacitance is preferably within 5%, and more preferably within 1%. The present invention eliminates variations between film formations and reduces the difference in thickness between the polymer insulating layers 40 by simultaneously depositing the two polymer insulating layers 40.

[0022] The method for producing a polymer insulating layer 40 will be explained using parylene as an example. By a vapor deposition polymerization process, the parylene raw material is thermally decomposed into a gaseous monomer and attached to the surface of a thin film electrode 10d. Then, a thin film of parylene is formed on the surface of the thin film electrode 10d by polymerization of the monomers. Since the gaseous monomer adheres uniformly to the substrate, the thickness of the parylene film tends to be uniform even if the attachment locations differ. The variation is within 5%, and the difference in the average thickness of the two polymer insulating layers 40 on the surfaces of two thin film electrodes 10d is within 1%. By partially irradiating the unwanted parts of the parylene film formed on the surface of the thin film electrode 10d with high-energy oxygen plasma to remove them, a polymer insulating layer 40 with the desired shape is formed.

[0023] A gas-filled gap exists between the thin-film electrode 10d and the electrode surfaces 15e and 16e, allowing charge to accumulate between the electrodes. Since polymer materials have a higher dielectric constant than gases, variations in the thickness of the polymer insulating layer 40 tend to increase the difference in capacitance between the two pairs of electrodes. Parylene HT has a dielectric constant of approximately 2.1, which is lower than other parylene materials, so a polymer insulating layer 40 composed of parylene HT is likely to contribute to suppressing bias errors.

[0024] In parylene film deposition using a vapor deposition polymerization process, the temperature rise of the weight portion 10a is limited to room temperature or a few degrees. Compared to other film deposition methods, the residual stress caused by heat is small, resulting in less deformation of the weight portion 10a due to film deposition. For example, if an insulating layer is created using a silicon oxide film, which tends to generate large residual stresses, the weight portion 10a shown in Figure 5 will bend into a convex shape relative to the upper or lower side in the figure. This changes the rotational motion of the weight portion 10a, which reflects acceleration, from an ideal state, potentially reducing the accuracy of the servo accelerometer. The parylene polymer insulating layer 40 contributes to maintaining sensor accuracy in the servo accelerometer.

[0025] For example, as shown in Figure 7, extending the thin film electrode 10d to the end of the weight portion 10a increases the surface area of ​​the thin film electrode 10d, and the capacitance stored between the electrodes increases. As the voltage converted from the capacitance increases, the signal-to-noise ratio of the detection circuit against noise increases, and the sensor resolution tends to improve. On the other hand, if the area of ​​the thin film electrode 10d is sufficiently inward from the end of the weight portion 10a, as shown in Figure 8, the end of the weight portion 10a will stop in contact with the electrode surface 16e, so the thin film electrode 10d and the electrode surface 16e will not short-circuit even without the polymer insulating layer 40. However, since the area near the end face of the weight portion 10a cannot be used as the thin film electrode 10d, the capacitance between the electrodes decreases. By providing the polymer insulating layer 40, it becomes possible to extend the thin film electrode 10d to the end of the weight portion 10a, thereby improving the sensor resolution.

[0026] The pendulum shown in Figure 9 has a weight portion 10a made of quartz glass, on which a thin film electrode 10d is attached, and on which a polymer insulating layer 40 is attached. In addition, the yokes 15 and 16 and electrode surfaces 15e and 16e, which are positioned opposite the thin film electrode 10d, are made of Invar alloy. The coefficient of linear expansion of quartz glass is 0.5 × 10⁻⁶. -6 The temperature is around / K, which is about 1 / 10th of that of typical commercial metals. Because the dimensional change of the weight portion 10a in response to temperature changes is small, the motion state of the weight portion in response to acceleration is easily maintained, which contributes to expanding the temperature range in which the servo accelerometer can be used.

[0027] The coefficient of thermal expansion of Invar alloy is 1 to 2 × 10⁻⁶. -6The temperature is around / K, and the difference with quartz glass is small, making it difficult to impart strain to the pendulum support part 10b due to temperature changes. If deformation occurs in the support part 10b, it may cause a decrease in sensor performance or malfunction. If stress is applied to the hinge 10c due to the deformation of the support part 10b, the correspondence between the displacement of the weight part 10a and the input acceleration changes, and the difference from the original relationship becomes an error. Alternatively, the weight part 10a may be pressed against the yokes 15 and 16 by the hinge 10c and become immobile. If the force (fixed load) received from the yoke is reduced to reduce the amount of deformation of the support part 10b, the static friction force generated between the fixed part 10f and the yokes 15 and 16 decreases, and when the servo accelerometer is subjected to a radial impact, the positions of the pendulum 1 and the yoke units 2 and 3 may shift, which may cause the accelerometer to malfunction. Thus, by using quartz glass and Invar alloy as structural materials, it is possible to suppress malfunctions of the servo accelerometer and a decrease in sensor accuracy.

[0028] This document describes a method for manufacturing a pendulum made of quartz glass. First, a thin film pattern 42 resistant to hydrofluoric acid is formed on both sides of a quartz glass plate 41. The pair of thin film patterns 42 formed on both sides are symmetrical with respect to the center of the plate's thickness. By immersing this sample in hydrofluoric acid, the quartz glass dissolves (is etched) from the areas where there is no thin film pattern 42. By etching from both sides, hinges and through-holes are formed, and as shown in Figure 10, a projection 44 is formed at the center of the end face of the quartz glass plate 41 at the end of the through-hole 43. Finally, by removing the thin film pattern 42, the through-hole 43 is completed. Compared to machining, wet etching does not increase the surface roughness of the processed surface as much, so it is possible to create a hinge 10c with excellent impact resistance.

[0029] The protrusions 44 on the weight portion 10b, created by wet etching, may chip due to impact from contact between the weight portion 10a and the yoke. Small fragments of detached quartz glass may then become lodged between the weight portion 10a and the yoke, potentially obstructing the movement of the weight portion 10a. By covering the protrusions 44 with a polymer insulating layer 40, the separation of quartz glass fragments from the weight portion 10a can be suppressed.

[0030] If the corners 40a of the polymer insulating layer 40 that come into contact with the electrode surfaces 15e and 16e are chamfered or rounded as shown in Figure 11, the contact area between the corners 40a and the electrode surfaces 15e and 16e becomes larger compared to a rectangular shape. The stress applied to the polymer insulating layer 40 by contact with the electrode surfaces 15e and 16e is reduced, and damage to the polymer insulating layer 40 can be suppressed. A method for creating the chamfered or rounded corners 40a of the polymer insulating layer will be explained using Figure 12. Figure 12(a) shows a sample in which a curved photoresist pattern 46 is formed on the surface of a polymer film 45. When the photoresist pattern 46 and the polymer film 45 are etched by irradiating them with oxygen plasma using a reactive ion etching apparatus, the sample becomes as shown in Figure 12(b). In the photoresist pattern 46 in Figure 12(a), areas with a small thickness are removed as the oxygen plasma irradiation progresses, and the surface of the polymer film 45 in those areas is etched, creating a chamfered or rounded shape. Then, when the resist pattern 46 is removed, the corner portion 40a of the polymer insulating layer, which has a chamfered or R-shaped form as shown in 12(c), is completed.

[0031] (Example 2) Figure 13 shows one embodiment of the polymer insulating layer 40. The polymer insulating layer 40 is provided on the outer periphery of the thin film electrode 10d, but not on the inner periphery of the electrode film. By reducing the area of ​​the polymer insulating layer 40, the weight is reduced, and the restoring force required for the input acceleration is reduced, thus obtaining a servo accelerometer that can operate with low current. As shown in Figure 14, the inner periphery of the weight portion 10d is less likely to come into contact with the electrode surfaces 15e and 16e compared to the outer periphery, so by placing the polymer insulating layer 40 only on the outer periphery, it is possible to effectively suppress short circuits between the electrode film and the electrode while suppressing an increase in the weight of the weight portion.

[0032] (Example 3) Figure 15 shows one embodiment of the polymer insulating film. Two or more polymer insulating layers 40 are provided on one surface of the thin film electrode 10d, and the layer has a shape that radiates outward from the central axis of the pendulum 1 and is arranged symmetrically with respect to the central axis. Figure 16 shows a schematic cross-sectional view in which the servo accelerometer is cut at the BB' cross-section of Figure 15 and some components are extracted. Due to the rotational motion of the weight portion 10a, the thin film electrode 10d approaches the electrode surface 15e or electrode surface 16e, but the weight portion 10a stops when the polymer insulating layer 40 comes into contact with the electrode films 15e and 16e, so the distance between the thin film electrode 10d and the electrode films 15e and 16e is kept constant, and short circuits of the electrodes are unlikely to occur.

[0033] There is a gap between the electrode surfaces 15e and 16e and the thin-film electrode 10d or the polymer insulating layer 40. When the weight portion 10a rotates around the center of the hinge, the weight portion 10a experiences damping resistance due to the viscosity of the gas filling the gap. Generally, as the damping resistance increases, the thermomechanical noise (Brownian noise) due to thermal vibrations of the surrounding gas also increases.

[0034] When the weight portion 10a is displaced by acceleration, the end of the weight portion 10a approaches the electrode surface 15e or electrode surface 16e, and the gas filling the gap is compressed or expanded by the polymer insulating layer or thin film electrode 10d and the electrode surfaces 15e and 16e. When compressed, the gas pressure is higher at the center of the weight portion and lower at the outer circumference, so the gas flows from the center to the outer circumference due to the pressure difference, and the opposite is true when the gas expands. In areas where the polymer insulating layer 40 is not present on the surface and the thin film electrode 10d is exposed, the gap becomes larger and the gas flows through more easily. Furthermore, this region is connected in the direction of the center and outer circumference of the pendulum 1 and does not obstruct the flow of gas. This structure suppresses the increase in damping resistance and contributes to reducing Brownian noise.

[0035] Since the polymer insulating layer 40 is arranged symmetrically with respect to the center of the pendulum 1, the damping resistance experienced by the weight portion 10a tends to be point-symmetric within the plane of the weight portion 10a. This suppresses rotational motion caused by non-uniform damping resistance, such as rotational motion in the φ-axis direction shown in Figure 15, and makes it easier to maintain the original rotational motion, thus contributing to maintaining sensor accuracy. [Explanation of symbols]

[0036] 1 pendulum 10. Base of the pendulum 10a Pendulum weight 10b Support part of the pendulum 10c Pendulum hinge Thin film electrodes of a 10d pendulum 10e Thin film wiring formed on the surface of hinges, supports, and weights. 10f Fixing part of the support that is fixed by the yoke 11, 12 Torca Coil 13, 14 Torka Cup 24 metal wires 25 terminals 26 Cover 27 Soldering section 30 Acceleration detection axes 40 Polymer insulating layer 40a Corner of polymer insulating layer 41. Quartz glass plate 42 Thin Film Patterns 43 Penetration section 44 Protrusion 45 Polymer membrane 46 Photoresist Patterns

Claims

1. The inertial force generated in the pendulum and the Lorentz force generated by the current flowing through the torque coil wrapped around the torque cup and the magnetic field passing through the yoke are in equilibrium. A servo accelerometer that detects the displacement of the pendulum by capacitance, The pendulum is equipped with thin-film electrodes for detecting capacitance, The yoke detects capacitance and has an electrode surface that is paired with the thin film electrode, A servo accelerometer characterized by having a polymer insulating layer made of polymer material on the surface of the thin film electrode.

2. The material of the polymer insulating layer is polyparaxylylene. A servo accelerometer according to claim 1.

3. The corners of the polymer insulating layer are chamfered or rounded. A servo accelerometer according to claim 1.

4. The polymer insulating layer is provided on the outer periphery of the thin film electrode, The polymer insulating layer is not provided on the inner circumference of the thin film electrode. A servo accelerometer according to claim 1.

5. The surface of the thin film electrode is provided with two or more polymer insulating layers, The polymer insulating layer has a shape that radiates outward from the central axis of the pendulum, The polymer insulating layer is characterized in that it is arranged symmetrically with respect to the central axis of the pendulum. A servo accelerometer according to claim 1.

6. The material of the pendulum is quartz glass. The material of the yoke is characterized by being an Invar alloy. A servo accelerometer according to claim 1.

7. The thin film electrode is provided with a projection at the center of the adjacent end face of the pendulum, The aforementioned protrusion is characterized by being covered with the polymer insulating layer. The servo accelerometer according to claim 6.

8. The thin film electrodes are provided on the front and back of the pendulum. The displacement of the pendulum is detected by the difference in capacitance detected from each of the thin film electrodes on the front and back sides, The servo accelerometer according to claim 1 or 2, characterized in that the polymer insulating layer is formed on both the front and back surfaces simultaneously on the thin film electrode.

9. The polymer insulating layer is characterized by being formed by a vapor deposition polymerization process. Servo accelerometer according to claim 8

10. The polymer insulating layer is characterized by having a uniform film thickness. Servo accelerometer according to claim 9

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