Angular velocity sensor

Abstract: An angular velocity sensor according to the present invention, wherein an internal temperature of the sensor body is sensed by a temperature sensor and adjusted to be equal to a preset value; an offset value is obtained from an output of the angular velocity sensor at the preset internal temperature with no angular velocity acting thereon and an angular velocity signal at the preset internal temperature is compensated for the obtained offset value; and also an angular velocity detection signal obtained before the internal temperature reaching to the preset value is compensated for an offset value determined on the base of a value readout from a memory table storing therein characteristic offset values varying with the internal temperature of the sensor body.

Description: BACKGROUND OF THE INVENTION The present invention relates to an angular velocity sensor which is capable of sensing an angular velocity acting on the sensor body to generate an electrical detection signal. Generally, there are mainly used two types of angular velocity sensors: one is of a gas flow type which is intended to detect a deflection of gas flow by the use of a temperature sensing element when an angular velocity acting on the sensor body, and the other is of piezoelectric type which is intended to sense a change in resonant frequency of a pair of piezoeltctric elements. Both temperature sensing element and piezoelectric element may vary their characteristics with temperature and time to cause an error of angular velocity measurement. This means that with no rotational motion being applied to the sensor body an error output is produced due to a deviation of characteristics of paired temperature sensing elements or piezoelectric elements and therefore it must be cut off from the angular velocity detection signal. Previously, since the offset output varies depending upon a change of the internal temperature of the angular velocity sensor, the sensor body is forcibly heated in such a way that its internal temperature detectable by the temperature sensing element may be constantly kept at the preset value, and thereby an angular velocity detection signal is compensated for a value corresponding to the offset caused at the preset temperature. However, the above-mentioned solution to control the temperature by heating the sensor body by the use of a heater causes such a problem that the compensation of the angular velocity detection signal can not be performed for the time necessary to rise the internal temperature of the sensor body to the preset value. An angular velocity sensor with temperature control is disclosed in JP-A-63 081 269. SUMMARY OF THE INVENTION In view of the foregoing, the present invention was made to provide an angular velocity sensor which is capable of performing the offset compensation of an angular velocity detection signal immediately from the beginning of temperature control to rise the internal temperature of the sensor body and keep constantly at the preset value. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a block diagram showing a practical construction of an angular velocity sensor embodying the present invention. Fig. 2 is a plan view showing an example of construction of a gas flow type angular velocity sensor. Fig. 3 shows a deflected state of a gas flow when an angular velocity is applied to the angular velocity sensor body. Fig. 4 shows an example of resistance bridge electric circuit consisting of a pair of heat wires. Fig. 5 shows an representative temperature-resistance characteristic of each of paired heat wires. Fig. 6 shows a rising characteristic of an internal temperature of the sensor body. Fig. 7 shows a characteristic of an offset value depending on temperature rising in a sensor body. Fig. 8 shows an offset-temperature characteristic at the time of temperature rising. Fig. 9 shows a characteristic of offset changing state for a period from the beginning of temperature rising to the time of final stabilization of temperature at the preset value. Fig. 10 is a flow chart showing a proceding process of offset compensation during a period from the initiation of temperature rising to the time of final stabilization of the temperature at the preset value. In the drawings, 1 is a signal processing device, 2 is a sensor body, 3 is a heater driving circuit, 4 is a speed sensor, 5 is a non-volatile memory, 15 is a pumping chamber, 18 is a nozzle port, 21a, 21b are heat wires, 24 is a thermostat, 25 is a heating wire and 26 is a temperature sensing element. DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to achieve the above-mentioned purposes, the present invention provides an angular velocity sensor which includes a table containing therein a series of preset values of temperature-related offsets, and which for the period of temperature rising in its body reads out of the table a series of offset values corresponding to the temperature rising in its body and compensate angular velocity detection signals for the corresponding offset values. Furthermore, the present invention is also directed to provide an angular velocity sensor which is capable of constantly obtaining an optimum offset value to be used for compensation of the angular detection signal with due consideration of variation of offset value with ageing of the sensor. Referring now to the drawings, an embodiment of the present invention will be described in detail as follows: Fig. 2 shows an example of a body construction of a gas flow type angular velocity sensor embodying the present invention. As shown in Fig. 2, a casing 8 is a cylinder which has one closed end and the other open end with a flange 9. The casing 8 has three inwardly raised and lengthwise elongated strips evenly spaced from each other at its inner cylindrical surface to form a gas passage 10 in the axial direction between the raised strips and a body portion 11 abutting against the raised strips of the casing 8. The body portion 11 placed in the casing 8 is composed of a holder 12, a neck portion 13 and a cylinder 14. The holder 12 serves to seal gas filled in the casing 8. A pumping chamber 15 is formed in the holder 12 to accommodate therein a diaphragm pump composed of piezo plate 16. By the action of this pump the gas is pumped into the gas passage 10 through a discharging hole 17. The gas supplied into the gas passage 10 is forced to be injected in a laminar flow into a sensor room 20 formed in a cylindrical portion 14 through a nozzle hole and a plural number of gas flow rectifying holes 19 formed around the nozzle hole, and then it passes through a pair of heat wires in a front part of the sensor room and returns into the pumping chamber 15, wherefrom the gas is pumped out again into the gas passage 10 to repeat the above-mentioned circulation. The flange 9 of the casing 8 supports a circuit board 22 whereon a resistance bridge circuit, an amplifier, an electric power supply circuit and so on are mounted. In Fig. 2, numeral 23 designates a supporting cylinder for supporting the sensor body. As shown in Fig. 3, a pair of heat wires 21a and 21b are arranged symmetrically about axis line 0-0 of the nozzle hole 18. The gas injected into the gas passage through the nozzle hole 18 goes straight along the axis 0-0 to evenly attack the heat wires 21a and 21b giving even radiations to them while no lateral angular velocity "ω" being applied to the sensor body. When a lateral angular velocity "ω" acts on the sensor body, the gas flow injected into the gas passage through the nozzle hole 18 is deflected to one side by an angle corresponding to the acting force as shown with a dotted line in Fig. 3, thereby an amount of deflection "ε" of the gas flow from the axis line 0-0 is produced at the place of the heat wires 21a and 21b and therefore the gas flow contacts much more with the heat wire 21a to produce a difference of the heat radiations given to the respective heat wires 21a and 21b. A signal corresponding to a difference between temperature sensitive outputs of two heat wires 21a and 21b due to the radiation difference is taken out through the resistance bridge circuit (refer to Fig. 4) formed together with the paired heat wires 21a and 21b and the amplifier, and it is used for determining therefrom a direction and a magnitude of the angular velocity "ω" acting on the sensor body by its polarity and amplitude respectively. It is possible to determine a change of movable direction of movable body by integrating the detected values "w" of angular velocity for the time of movement of the movable body. Fig. 4 shows an example of a resistance bridge circuit comprising standard resistances "Ra" and "Rb" with known resistivity, a stabilized voltage supply unit "E" and an amplifier "AMP". In thus constructed gas flow type angular velocity sensor, since it is hardly difficult to make a pair of heat wires 21a and 21b to be of the same resistance-temperature characteristic, the paired heat wires may have different characteristics as shown in Fig. 5. Accordingly, the bridge circuit may be unbalanced due to a change of temperature in the sensor body and/or ageing even with no angular velocity acting on the sensor body and thereby it produces an output causing an error included in an angular velocity detection signal. To avoid this, as shown in Fig. 2, the sensor body is placed in a thermostat 24 and forcibly heated by heating wires 25 spirally wound around the casing 8 and the supporting cylinder 23 under such a temperature control that internal temperature of the sensor body detected by a temperature sensing element 26 is constantly maintained at the preset value. The angular velocity sensor keeping temperature therein at the preset value rewrites its memory with a new output as an offset value at every time when the movable body stops and compensates its angular velocity detection signal outputted while the movable body moves by the use of the offset value stored in the memory. By applying the above-mentioned offset compensating means it becomes possible to precisely detect an angular velocity "ω" as the movable body changes its moving direction with no affection of external temperature change and ageing. Thus constructed angular velocity sensor according to the present invention is also provided with such a offset compensation means that since temperature characteristic of offset values for the period from the beginning of supplying the heating wires 25 with current to the time when the temperature in sensor body reaching to the preset value is reproducible, the offset values variable with temperature while the movable body moves straightly or stops with no angular velocity acting on the sensor body are previously written in the table (memory) wherefrom the offset value corresponding to the temperature detected by the temperature sensing element 26 is read out to compensate the angular velocity detection signal outputted before the internal temperature of the angular velocity sensor body rises to the preset value. Fig. 7 shows the characteristic of the signal offset as a function of time for rising temperature to the preset value. Fig. 8 shows the characteristic of the signal offset as a function of temperature when the last rising to the preset value. Consequently, the angular velocity sensor according to the present invention can precisely detect any angular velocity "ω" of the medium with a change in the direction of movement of the movable body for the period from the moment of starting the conduction of the heat wires to the moment of getting the temperature in the sensor body at the preset value by compensating for temperature and time-varying offset by the use of the table. Fig. 1 shows an example of construction of an embodiment of the present invention. In Fig. 1, a signal processing device 1 composed of a microcomputer, which, by reading therein a temperature detection signal T from the temperature sensing element 26 mounted in the angular velocity sensor body 2, generates a control signal CS to control a driving circuit 3 of the heating wires 25 so as to adjust the detected temperature to the preset value. The signal processing device 1 also reads therein a speed detection signal "v" from a speed sensor 4 for detecting a moving speed of the movable body to detect whether the movable body moves or stops, and by reading therein a output signal T of the angular velocity sensor and a temperature detection signal T at the time of its stoppage makes the table of offset values and stores said table in a non-volatile memory 5. At every time when the movable body stops after the internal temperature reaching to the preset value the signal processing device 1 determines an offset value from the output signal T and rewrite the stored offset value with the obtained value in the memory 5. Furthermore, the signal processing device 1 read out of the table-memory 5 the offset value corresponding to the temperature detection signal T at the time of temperature rising and also the offset value after the temperature reaching to the preset value and generates a angular velocity signal T' compensated for the offset value by subtracting the offset value from the angular velocity detection signal T obtained from the angular velocity sensor body 1 when the movable body moves. The present invention also provides that since the offset value is stabilized with its gently sloping characteristic immediately before the internal temperature of the sensor body reaches to the preset value T₂ as shown in Fig. 6 to 8, the temperature-varying offset data are gathered more frequently for a certain period just before sensor body obtains the preset temperature, so as to enrich the compensation table to be stored in the memory. More practically speaking, in case of presetting the temperature T₂ at 70°C the temperature-varying offset values is sampled at every 0.5°C for the period of temperature rising up to 65°C at a relatively sharp slope of the characteristic curve and at every 0.1°C for the period of temperature rising over 65°C to 70°C at a gentle slope of characteristic curve. Adoption of the above-mentioned means for making the compensation table makes it possible to carry out precise compensation for offset of the angular velocity sensor according to its practical temperature rising characteristic. According to the present invention, such a provision is also made to allow the data processing device 1 to rewrite the table stored in the memory 5 with offset data newly obtained from outputs of the angular velocity sensor at temperatures detected by the temperature sensing element 26 when the movable body stops in process of temperature rising to the preset value, thus assuring compensation for any change of the offset characteristics of the angular velocity sensor with time at corresponding temperatures. If the stopping time of the movable body is so short to make sampling only in a limited range of temperature rising, the data processing device rewrites a corresponding part of the table. To assure higher reliability of the data, said partial restoring is carried out in such a way that a given proportion of a difference between the preceding (stored) value and the newly obtained value is determined and is added to or subtracted from the newly obtained value and the calculation result is written as a new offset value in the table with erasing the preceding value at the same time. In this case it is possible, for example, to obtain a mean value of preceding and present offset values and replace the preceding value with the mean value. If the stopping time of the movable body is long enough to make data sampling over the full range of temperature rising, the data processing device unconditionally rewrites the table with the newly obtained data. Application of the above-mentioned means for rewriting the table makes it possible to perform the offset compensation of angular detection signals T by the use of the continuously restored table without being affected by ageing of the angular velocity sensor. When the angular velocity sensor having been in unused state for a long time is operated, the offset values stored in the table may be largely differ from the present data due to the ageing of the angular velocity sensor. Consequently, it is not preferable to directly change compensation values by the new offset value obtained at the first stop of the movable body after temperature in the angular velocity sensor body reached to the preset value since the compensation may be sharply changed by a large amount and the temperature is not yet stabilized at the moment just after the temperature rose to the preset value T₂ and therefore the offset value obtained at that time may be unstable. Therefore, the present invention provides that the data processing device 1 makes the offset compensation of output signals of the angular velocity sensor by using the offset values set in the table at corresponding temperatures for a certain period (of about 30 seconds) necessary for stabilizing the temperature in the angular velocity sensor body at preset value T₂ after the last was obtained, and for a certain buffering period (e.g. of about 3 minutes) after completion of temperature rising (that is, the stabilizing period elapsed) by using an offset value gradually variable with time which is calculated out from the offset values sampled at a given time interval (e.g. of 0.5 seconds) and the earlier offset values stored in the memory so as to ensure gradual reduction of differences between the preceding and the present values. In the above-mentioned case a reduction rate of the difference between the newly obtained offset value 0t and the previously stored offset values Oo is increased at every sampling time so as to get a linear characteristic I of time-varying offset value as shown in Fig. 9. In Fig. 9, t1 is a moment when the temperature reaches to the preset value, t2 is a moment of completion of the temperature rising operation, W1 is a period of the temperature rising and W2 is a buffering period. When the offset value is completely changed over to the preceding offset value Ot at a moment t3, the compensation of signals obtainable thereafter is carried out by the use of said offset value 0o until the movable body stops next. According to the present invention, for a certain period (of about 20 minutes) necessary for putting the angular velocity sensor into completely stabilized operation after the completion of the temperature rising the data processing device 1 performs the offset compensation by the use of a modified offset value which is calculated by that the given proportion of the difference between the present and preceding offset values is added to or subtracted from the present offset value obtained when the movable body stopping. In this case the preceding value stored in the memory 5 is erased off at the time of writing the modified offset value. The proportion of the difference between the preceding and present offset values may be variable with time until the movable body stops. For example, as shown in Fig. 9, when the movable body stops at the first time t4 during the period W3 necessary for bringing the angular velocity sensor into the completely stabilized operating state after completion of the temperature rising, a present offset value O₁ is obtained and 50% of the difference between the value O₁ and the preceding value O ⊘ is added thereto to obtain a modified offset value O₁' for which the angular velocity detection signal is compensated. When the movable body stops next at a time t5, a offset value O₂ is obtained and, in view of a considerable time elapsed from the initial time, 20% of the difference between the value O₂ and the preceding offset value O ⊘ is added thereto to obtain a modified offset value O₂' to be used for compensation of the angular velocity detection signal. When the movable body stops at a time t6 after the period W3, the data processing device 1 gets an offset value O₃ and, assuming that the angular velocity sensor operates in completely stabilized state and therefore the obtained offset value may be finally stabilized one, it directly stores said offset value O₃ in the memory 5 and compensates the angular velocity detection signal for the offset value O₃ stored in the memory 5. Consequently, according to the present invention, it is possible to smoothly change from the offset compensation during temperature rising by the use of the table to the offset compensation by the use of the practical offset values obtainable at every time of the movable body stopping after completion of the temperature rising. Figure 10 shows a flow chart of processing for offset compensation through the period from the temperature rising to the stabilized operation of the angular velocity sensor. As be apparent from the foregoing description, the angular velocity sensor according to the present invention offers such an advantage that since temperature in the sensor body can be controlled to be always at the preset value by the use of a heating means and an angular velocity detection signal can be precisely compensated for a temperature-varying offset even for the period of temperature rising to the preset value by the use of the table containing the offset data optimally set at corresponding temperatures, the angular velocity acting on the sensor body can be sensed with high accuracy just from the time temperature in the sensor body begins to rise to the preset value. Another advantage of the angular velocity sensor according to the present invention consists in that optimum offset values with due consideration of the possible time-varying characteristic of the sensor can be obtained, thereby the angular velocity detection signal can be precisely compensated for without being affected by the sensor's ageing. The invention as described above can be summarized as follows: An angular velocity sensor according to the present invention, wherein an internal temperature of the sensor body is sensed by a temperature sensor and adjusted to be equal to a preset value; an offset value is obtained from an output of the angular velocity sensor at the preset internal temperature with no angular velocity acting thereon and an angular velocity signal at the preset internal temperature is compensated for the obtained offset value; and also an angular velocity detection signal obtained before the internal temperature reaching to the preset value is compensated for an offset value determined on the base of a value readout from a memory table storing therein characteristic offset values varying with the internal temperature of the sensor body.

Claims: An angular velocity sensor being capable of electrically detecting an angular velocity acting on its body, including a temperature control means for detecting an internal temperature of the sensor body by the use of a temperature sensing element and for adjusting the internal temperature to a preset value; an offset compensating means for obtaining an offset value from an output of the sensor being at the preset temperature therein with no angular velocity acting thereon and for compensating an angular velocity detection signal obtained at the preset temperature in the sensor body for said offset value; and another offset compensating means for reading-out an offset value from a table storing therein offset data in accordance with a temperature detected by the temperature sensing element while the temperature in the angular velocity sensor rising to the preset value and for compensating the angular velocity detection signal for the offset value obtained from the table. An angular velocity sensor as claimed in claim 1, characterized in that temperature-varying offset values is more densely sampled in a certain range of temperature rising immediately before temperature reaching to the preset value. An angular velocity sensor as claimed in claim 1, characterized in that such a means is provided for obtaining offset values varying with temperature from the sensor's output while no angular velocity acting on the sensor body and for rewriting the the table with the obtained values. An angular velocity sensor as claimed in claim 3, characterized in that such a means is provided for obtaining an offset value from an output of the angular velocity sensor in a partial range of temperature rising with no angular velocity acting on the sensor body; calculating a given proportion of a difference between the obtained offset value and the renewably stored offset value in the same temperature range; and rewriting the value stored in the table by the value determined by adding or subtracting the given proportion of the difference to or from the obtained offset value. An angular velocity sensor as claimed in claim 1, characterized in that the sensor body is mountable on a movable body and an offset value is obtainable while the movable body stops. An angular velocity sensor as claimed in claim 5, characterized in that the offset compensation when the temperature in the angular velocity sensor reaching to the preset value is performed by using an offset value previously obtained at the preceding stop of the movable body, and the subsequent offset compensation is performed by using a value determined in such a way that a given proportion of a difference between an offset value newly obtained at subsequent stop of the movable body is added to or subtracted from the previously obtained offset value.

Inventors: IIBOSHI AKIRA, IKEGAMI MASAYUKI, NISHIO TOMOYUKI, TAKAHASHI FUMITAKA, TOMIYAMA SINICHI, TSUCHIDA HIROTATSU, TSUCHIYA RYOICHI, IIBOSHI, AKIRA, IKEGAMI, MASAYUKI, NISHIO, TOMOYUKI, TAKAHASHI, FUMITAKA, TOMIYAMA, SINICHI, TSUCHIDA, HIROTATSU, TSUCHIYA, RYOICHI
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1991
Main classification: G01P9
IPC codes: G01C19, G01C21, G01P9