Tilt sensor

• US 20010045019A1
• Filed: 02/23/2001
• Published: 11/29/2001
• Est. Priority Date: 02/25/2000
• Status: Active Grant

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Kawamoto, Hiroshi, Takeuchi, Yoshiaki
• Granted Patent: US 6,442,855 B2
• Time in Patent Office: Days
• US Class Current: 33/366.19
• CPC Class Codes: G01C 2009/062 capacitive
• CPC Class Codes: G01C 2009/185 dielectric
• CPC Class Codes: G01C 9/06 Electric or photoelectric indication or reading means
• CPC Class Codes: G01C 9/20 the indication being based on the inclination of the surface of a liquid relative to its container

Abstract

A tilt angle sensor is disclosed that is capable of detecting whether a tilt angle of a reference plane exceeds a predetermined value by means of only one threshold value. Although only one threshold value is used, the tilt angle can be measured with respect to either a clockwise or a counterclockwise direction from the untilted state. A pair of differential electrodes electrically independent of each other are formed in a shape symmetric with respect to upper and lower sections of a printed circuit board. A common electrode plate is mounted opposed to the pair of differential electrodes with a predetermined gap therebetween. The pair of differential electrodes and the common electrode is stored in a closed space formed by the printed circuit board and an oil case. A dielectric liquid is filled into the closed space in such a way that the level of the liquid varies according to the tilt of the reference plane. An output signal corresponding to the difference in capacity between two capacitors formed by associated components is produced as a tilt detection output.

Claims

1. A tilt sensor comprising:

a printed circuit board disposed in a direction normal to a reference plane for measuring a tilt angle;

a pair of differential electrodes mounted on the printed circuit board;

a common electrode plate opposed to the pair of differential electrodes with a predetermined gap formed between said differential electrodes;

a common electrode fixed to the printed circuit board by a terminal formed from the common electrode plate;

a dielectric liquid filled into a closed space in a state where its surface level varies according to the tilt angle of the reference plane;

a signal processing circuit section formed on the printed circuit board, said signal processing circuit section producing an output signal corresponding to a difference in capacity between two capacitors, each capacitor includes the common electrode and a respective differential electrode of said pair of differential electrodes, as a tilt angle detection output,

wherein the pair of differential electrodes are mounted electrically independently of each other in upper and lower regions respectively, wherein said upper and lower regions are divided by a horizontal centerline, said horizontal centerline passing through a center of gravity of said printed circuit board in a direction normal to a direction of gravity when said printed circuit board is in a no tilt condition, and said pair of differential electrodes are formed in shapes symmetrical to said horizontal centerline and a vertical centerline of said printed circuit board, said vertical centerline passing through said center of gravity and normal to said horizontal centerline; and

an oil case for storing the pair of differential electrodes and the common electrode plate and forming said closed space between itself and the printed circuit board.

2. The tilt sensor according to

claim 1

, wherein the dielectric liquid is filled into the closed space to the level of the horizontal centerline.

3. The tilt sensor according to

claim 1

, wherein the signal processing circuit section further comprises:

a buffer circuit for receiving an exterior signal of a predetermined frequency and supplying it to the common electrode;

a first capacity-voltage conversion circuit for rectifying a first capacitor signal taken out of a first capacitor of said two capacitors and converting said first capacitor signal into a first output voltage;

a second capacity-voltage conversion circuit for rectifying a second capacitor signal taken out of a second capacitor of said two capacitors and converting said second capacitor signal into a second output voltage; and

a differential amplifier circuit for producing a differential voltage between the first output voltage and the second output voltage.

4. The tilt sensor according to

claim 1

, wherein the dielectric liquid is filled into the closed space to the level of the horizontal centerline.

5. The tilt sensor according to

claim 1

, wherein said no tilt condition of said printed circuit board occurs when said horizontal centerline is normal with the direction of gravity and said tilt angle is equal to zero degrees.

6. The tilt sensor according to

claim 1

, wherein said pair of differential electrodes includes an upper differential electrode and a lower differential electrode formed of copper foil patterns.

7. The tilt sensor according to

claim 6

, wherein said upper and lower differential electrodes are fan-shaped and have a corresponding open angle S, wherein said open angle S is set according to a desired range of tilt angle to be measured.

8. The tilt sensor according to

claim 7

, wherein a predetermined threshold tilt angle value θ

a for said tilt sensor defines said open angle S according to the relationship of S=(90−

θ

a)·

2.

9. The tilt sensor according to

claim 1

, wherein said common electrode plate includes a pair of terminals corresponding to a pair of terminal holes formed on said printed circuit board.

10. The tilt sensor according to

claim 1

, wherein said oil case is bonded to said printed circuit board with bonding means.

11. The tilt sensor according to

claim 2

, wherein said differential electrodes, said common electrode and said oil case are arranged parallel to each other and vertically arranged so that a center of gravity of said common electrode is aligned with a center of gravity of said oil case.

12. The tilt sensor according to

claim 1

, wherein electrostatic shielding plate is mounted on said printed circuit board and covers said oil case and said signal processing section.

13. The tilt sensor according to

claim 2

, wherein said common electrode plate includes through holes for permitting purging of air and filling of dielectric liquid.

14. The tilt sensor according to

claim 12

further comprising a conductive plate fixedly engaged with an outer surface of said oil case, wherein said conductive plate is secured to said printed circuit board with conductive fixing pins through said oil case.

15. The tilt sensor according to

claim 3

, wherein an output voltage of said tilt sensor produced at an output terminal of said tilt sensor is supplied to a control circuit.

16. The tilt sensor according to

claim 15

, wherein said control circuit further comprises a microcomputer including

a CPU;

a system bus,

a program ROM for storing a predetermined threshold tilt value detection program;

a work area RAM; and

I/O ports.

17. A tilt sensor comprising:

a printed circuit board disposed in a direction normal to a reference plane for measuring a tilt angle;

a pair of differential electrodes mounted on the printed circuit board, said differential electrodes are electrically independent of each other;

a common electrode plate opposed to the pair of differential electrodes with a predetermined gap therebetween;

a common electrode fixed to the printed circuit board by a terminal formed from the common electrode plate;

an oil case for storing the pair of differential electrodes and the common electrode plate in a closed space formed by said oil case and the printed circuit board;

a dielectric liquid filled into the closed space in a state where a dielectric liquid surface level varies according to the tilt angle of the reference plane; and

a signal processing circuit section which is formed on the printed circuit board and is capable of producing the output signal of the level corresponding to the difference in capacity between two capacitors, each of said two capacitors includes the common electrode and an electrode from the pair of the differential electrodes, as a tilt detection output,

wherein the pair of differential electrodes are mounted electrically independently of each other in the regions which are divided by a first intersection where a plane parallel to the reference plane intersects the printed circuit board, and are formed in a shape symmetric with respect to the first intersection and each of the pair of differential electrodes is formed in a shape symmetric with respect to a second intersection where a plane normal to the reference plane intersects the printed circuit board;

wherein the dielectric liquid is filled into the closed space to the level of the first intersection; and

wherein the signal processing circuit section comprises;

a buffer circuit for receiving a signal of a predetermined frequency from the outside and supplying it to the common electrode;

a first capacity-voltage conversion circuit for rectifying a signal taken out of a first capacitor constituted by the common electrode and one electrode of the pair of differential electrodes and converting it into voltage;

a second capacity-voltage conversion circuit for rectifying a signal taken out of a second capacitor constituted by the common electrode and the other electrode of the pair of differential electrodes and converting it into voltage; and

a differential amplifier circuit for producing a difference voltage output between the output voltage of the first capacity-voltage conversion circuit and that of the second capacity-voltage conversion circuit.

18. The tilt sensor according to

claim 17

, wherein said differential electrodes, said common electrode and said oil case are arranged parallel to each other and vertically arranged so that a center of gravity of said common electrode is aligned with a center of gravity of said oil case.

19. The tilt sensor according to

claim 18

, wherein said differential electrodes are fan-shaped and have a corresponding open angle S, wherein said open angle S is set according to a desired range of tilt angle to be measured.

20. The tilt sensor according to

claim 19

, wherein a predetermined threshold tilt angle value θ

a for said tilt sensor defines said open angle S according to the relationship of S=(90−

θ

a)·

2.