WO1990001169A1

WO1990001169A1 - Device for measuring and recording acceleration data

Info

Publication number: WO1990001169A1
Application number: PCT/HU1988/000053
Authority: WO
Inventors: Levente SZÉKELY; Gábor RÁCZ; Károlyné OTTA
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-07-26
Filing date: 1988-07-26
Publication date: 1990-02-08
Anticipated expiration: 1991-01-26

Abstract

Apparatus for measuring and recording acceleration primarily for use in automotive vehicles which comprises one or two acceleration sensors, each of them comprising a mass (12) arranged on a cross beam (11) mounted on a rotatable frame (10) with a coil (20) thereon similar to those used generally in moving coil instruments, a planar element (13) is attached to the end of the cross member (11) which protrudes into the sensing area of the optical sensor (15) and the output of the optical sensor (15) is connected to an amplifier, and the coil (20) carried on the frame (10) is connected into the output circuit of the amplifier, furthermore the output of the amplifier is coupled to a voltage controlled oscillator connected to a microprocessor.

Description

DEVICE FOR MEASURING AND RECORDING ACCELERATION DATA

The invention relates to a device for measuring and recording acceleration data, primarily for use in auto¬ motive vehicles for the purpose of measuring and dis¬ playing vehicle acceleration and, if required, for storing the' measured values .

There are several known methods available for the measurement of acceleration and deceleration. The possibi¬ lities of such measurements are limited when acceleration is to be sensed within an accelerating object, e.g. inside a moving motor vehicle. A known way is e.g. to measure the differential quotient of speed. This method is, however, unsuitable to furnish satisfactory results because of the inertia and inaccuracy of speedometers. In many cases the knowledge of a component of acceleration in a given direc- tion (e.g. forward-reverse) is insufficient, since values of acceleration in other directions and their absolute magnitudes are also required.

In commercial traffic the required data are recorded by means of tachographs. From tachograph records, however, no sufficiently accurate conclusions can be drawn concerning magnitude and direction of accelerations or decelerations , just in cases considered as being most critical. Not only data of vehicle travel are measured and indicated by the tachograph, but these are recorded in a permanent way. Therefore, it has been a long standing requirement raised in practice to measure acceleration and deceleration data of a vehicle, not only by their magnitude, but by their direction as well, further to record the measured data.

In an accelerometer described in U.S. patent No. . 95.815 a coil wound on a core is placed in the magnetic field of three precisely spaced hard magnets. The core has a hollow design and it surrounds the magnet located in the middle. The coil is mounted to one end of a pivoted arm supported in bearings permitting rotation of the arm about an outer axis arranged parallel to the magnetic field. The other end of the pivoted arm is a plate placed parallel to said axis. The magnetic field produced by the current passed through the coil is linked up with the permanent magnetic field of the magnets, thus a force arises therebetween. The differential quotient of this force is proportional with the component of the acceleration in a predetermined direction.

In column 3 of the above patent specification reference is made to the operation of the accelerometer connected into the closed loop circuit of the set-up.

The distance between the plate placed parallel to the magnetic field and a fixed point is measured by means of an infrared distance meter, and a current signal propor- tional to the distance is led through the coil. Construc- tionally, this arrangement has three main deficiencies. As first of these the extreme sensitivity of the assembly to the arrangement of the magnetic circuits and to the assumed spatial position of the coil should be mentioned. The second problem results from the limitations of distance measuremen .

Accuracy of infrared distance measurement and the time requirement of such measurement is questionable. In a fed- back analogue system both the time delay and inaccuracy of the feedback signal affect the reliability of the feedback loop. The time problem associated with acceleration measure¬ ments is due to the proneness of feedback-type regulation systems to swings and self-oscillations. There are too many derived characteristics in the loop rendering the system unstable .

Due to the size, cost and technical limitations outlined above, that system is less suitable for measuring and record¬ ing accelerations in automotive vehicle operation.

The object of the invention is to fulfill the above requirement and to provide an apparatus capable of measuring both the acceleration and deceleration and storing these data with sufficient reliability. To achieve this object an accelero eter has been devised which is sensitive to a predetermined component of the acceleration only which falls in one direction and which can provide the output in the form of an electrical signal. This accelerometer i.e. acceleration sensor comprises a frame pivotally mounted in a magnetic field, a coil wound around the frame, a cross beam rigidly mounted to said frame, a mechanical mass fixed to said cross beam, a planar element attached to and preferably arranged normal to the cross beam and an optical detector, the sensing zone of the detector is partially covered by the planar element, and the optical detector comprises a photo-sensitive transistor connected to a high-gain amplifier, said coil is coupled to the output circuit of the amplifier, a compensating capacitor is inserted between an intermediate point of the amplifier and a ground potential, the output of the amplifier is coupled to the control input of a voltage controlled oscillator the output of which is connected to a frequency counter, furthermore the apparatus comprises a micro¬ processor generating an acceleration signal in response to the output of the counter, a memory associated with said microprocessor and a display unit controlled by the output of said microprocessor. A preferable embodiment of the apparatus according to the invention is suitable for determining the direction of the acceleration as well which comprises a pair of identical acceleration detectors of the above design with sensing directions perpendicular to each other, respective voltage controlled oscillators are coupled to the output of the detectors and a third voltage controlled oscilllator of the same design as the other two is provided having an input coupled to a stabilized direct voltage source and the outputs of the three voltage controlled oscillators are connected to the microprocessor through a multiplexer.

From the point of view of reducing the current consump¬ tion it is of advantage to use a microprocessor suitable for standby mode of operation by providing it with a standby circuit connected to its standby input , one input of said standby circuit is coupled to a switch and an other input is connected to a power supply comprising an internal battery.

The high gain required for the detection can preferably be provided by using a pair of Darlington transistors in the amplifier.

In the optical detector it is advantageous to use a light emitting diode as light source.

The apparatus according to the invention possesses the required sensitivity, it has a low power consumption and in standby state i.e. during standstill of the vehicle or during transportthe data stored therein are safely regained whereby the conditions of acceleration can well be re¬ constructed. The use of a microprocessor offers the possib¬ ility of utilizing several further optional facilities as well.

The apparatus according to the invention will now be described in connection with preferable embodiments thereof and in connection with the attached drawing.

In the drawing:

Fig. 1 shows the basic arrangement of the components of the acceleration sensor according to the invention,

Fig. 2 is the circuit diagram of the circuitry associated with the sensor of Figure 1, and

Fig. 3 is the general block diagram of the apparatus according to the invention.

The setup and operation of the accelerometer will be described with reference to Figures 1 and 2. Frame 10 is provided with a coil, and similar to the known moving coil instruments, it is accommmodated in a homogeneous magnetic field act represented in the drawing, said frame is rota ahly supporτed by two bearings mounted a~ the two ends thereof and it is kept in a given angular position by flat helical springs. The axle of frame 10 is rigidly coupled to cross beam 11 arranged perpendicularly to the axle, and similar to the pointer of a conventional instrument, the frame can rotate in both directions about the axle . At a given distance from the axle a concentrated mass 12 is mounted to the cross beam 11, and a planar element 13 is attached to the projecting end of the cross beam. The planar element 13 protrudes into a U-shaped opening formed by two legs of sensing element 14. The light path of an optical sensor 15 is passed through the opening formed by said legs, and this path is partly intercepted or covered by the planar element 13 when rotated in the opening. The optical sensor 15 consists of a light-emitting diode 16 and light-sensitive transistor 17 shown in Fig. 2. In Figure 2 the schematic diagram of the circuit arrange¬ ment is shown. Light-sensitive transistor 17 is connected to transistor 18, 19 arranged in Darlington connection. Coil 20 wound around the frame 10 is coupled into the collector circuit of the transistor 19- Between the base of the transis tor 19 and earth a compensating capacitor 21 is inserted, by which the upper cutoff frequency of the circuit is set to about 5 Hz. Across emitter resistor 22 of the transistor 19, as it will be explained, a voltage proportional to that component of the force acting on the mass 12 can be measured which is normal to the cross beam 11. This voltage represents the output of the sensor.

In the apparatus according to the invention two sensors and associated circuits as shown in Figures 1 and 2 are used and the sensing directions of these sensors are normal to each other in the horizontal plane. It follows from the desig that the mass 12 can be displaced in tangential direction only since the bearings impede any radial displacement, so that the sensor output is insensitive to radial forces.

Figure 3 shows the general block diagram of the apparatus according to the invention. The apparatus is mounted in a small portable casing and it comprises a first acceleration detector 23 for sensing accelerations in direction x and a second acceleration detector 24 for sensing y-direction accelerations. The outputs of the acceleration detectors 23 and 24 are connected to the inputs of voltage-controlled oscillators 25 and 27, respectively. For providing a stabilized detection a third voltage-controlled oscillator 26 of identical design is used, the input of which is driven by a constant voltage obtained from a voltage divider consisting of a resistor R and a Zener diode Z. Each of the outputs of the three voltage-controlled oscillators 25, 26, 27 is connected to a separate input terminal of multiplexer 28 which has an output coupled to frequency counting input of microprocessor 29 ensuring sufficient intelligence for the apparatus. The microprocessor 29 can be implemented e.g. by the microprocessor of INTEL type 8051. This type of the microprocessor is preferable, since it comprises four 8-bit ports, any bit thereof can equally be input or output, it comprises a complete series-duplex type asynchronous data transmission unit in which the dai^a transmission rate can be varied freely, it is provided furthermore with a so-called standby mode in which the set of stored data can be preserved at very low power consumption. The microprocessor is equipped with two internal timer units, and in addition to these facilities the microprocessor 29 comprises all units required for fulfilling a processor function.

The output terminals of the microprocessor 29 are coupled to a display 30 which .comprises preferably sixteen LEDs . Inputs RxD of the microprocessor 29 receive through line coupling unit 31 signals of input terminals 32, whereas outputs TxD are connected to output terminal 34 through line coupling unit 33-Input terminals 32 and output terminals 34 may be connected to lines having loop currents of 20 milliamp

The apparatus is provided with a rechargeable battery 35, a power supply 36 coupled thereto, a standby circuit 37, a switch 38, a pair of charging terminals 39 connectable to an external power source ensuring external charging and a sensing terminal 40 which leads out the actual output voltage of the battery 35- The operation of the apparatus according to the invention is as follows.

Let the vehicle be assumed as accelerating and the acceleration is tangential to the circular path of dis- placement of the mass 12 shown in Figure 1 as indicated by arrow N. The apparatus is placed previously in the vehicle and it is calibrated as well. The accelerating force acting on the mass 12 tends to move the cross beam 11 angularly out of its position. Due to this angular displacement of the cross beam 11 the light-sensitive transistor 17 will be covered by the planar element 13 to a smaller extent, thus the quantity of light falling thereon increases, its output current increases and this increased current is amplified by the transistors 18, 19, whereby the current flowing through the coil 20 also increases. This increased current provides a magnetic field which tends to turn the cross beam 11 in a sense opposed to the force brought about by the acceleration. If the current gain of transistors 18, 19, i.e. the overall loop gain of the closed regulation circuit is sufficiently high then the angular position of cross beam 11 will not change to a noticeable extent under the effect of the accelerating force but the current flowing in the coil 20 will be proportional to the accelerating force. The voltage across the emitter resistor 22 follows this current. The high frequency components resulting from the swings and vibrations of the vehicle are filtered out by the capacitor 21 and this low-pass characterictic provide s for the stability of the regulating circuit. With accelerating forces not fully coinciding with the direction of the arrow N, the voltage signal obtained will be proportional to the component of such forces falling in the direction of the arrow N. Since, in addition to acceleration detector 23 shown in Figure 1, a further acceleration detector 24 with normal sensing direction is also used, the two voltage outputs will vectorially determine the actual direction of the force as well. The microprofesscr requires that these analogue voltage signals be converted in digital form.

This is done by means of the voltage controlled oscillators 25 and 27 connected to these voltage outputs. The output frequencies of the voltage controlled oscillators 25 and 27 are proportional to the input voltage signals. The multiplexer 28 cyclically couples the outputs of the respective voltage controlled oscillators 25, 26 and 27 to the frequency counting input of the microprocessor 29- By means of a clock available in the microprocessor 29 and with the use of a suitable program the number of cycles occurring within a unit of time is cyclically measured, and this number is the digital representation of the sensed accelerations .

As it is known, the long—term frequency stability of voltage controlled oscillators is poor. For compensating this behaviour the voltage controlled oscillator 26 fed from the stable voltage is used. If the output frequency of this reference ocsillator changes, then microprocessor 29 adjusts the base-frequency used for digitalization in accordance with the changes in the frequency of the oscillator 26, i.e. any change caused by thermal or other effects will not appear in the digitalized acceleration signal output.

The microprocessor 29 obtains separate information concerning the magnitudes of the two mutually normal components.

Experience has shown that for recording conditions of acceleration of normal automotive vehicles it is sufficient to cathegorize the acceleration e.g. in one of sixteen possible ranges. The 16 ranges can equally express component absolute or resulting values and appropriate sense values can also be associated therewith. This classification is carried out by the microprocessor 29 by using the digitalized data and by utilizing suitable programs. The actual category is always indicated by the display 30. It is of advantage to perform the evaluation and to make logging in regular periods, e.g. in every half second and only in cases when acceleration signal appears at all.The acceleration values above he giver, category are entered into the memory of microprocessor 23. together with the time pulses issued by the internal clock, the signals being accessible not only at site through observing the display 30, but also at the vehicle depot by reading the memory. On finishing the trip the apparatus is set standby mode by means of the switch 38, whereby the content of the memory is preserved at a current consumption being by 3 orders of magnitude lower than in normal opera¬ tion.The standby state will become activated also when the output voltage of the storage battery 38 drops below a permisssible critical value. Preservation of the memory content will thereby be ensured. The stored data can be read out from the memory through output terminals 34, and the reception of access codes at input terminals 32 can also be a condition of establishing a data transmission link. Otherwise the data traffic takes place in standard codes .

The calibration of the apparatus according to the invention can be performed by utilizing normal gravitational acceleration. If the apparatus is suitable for sensing acceleration in the horizontal plane, one can bring the two sensing directions, one after the other, into the vertical plane by turning the casing of the apparatus by 90 . The program of the microprocessor 29 ensures that the digital value corresponding to a definite fractional part of normal gravitational acceleration is taken as basis for calibration. The sensitivity can be modified by selecting said fractional value correspondingly.

By arranging the apparatus according to the invention into a vehicle information can be obtained and records can be taken on the conditions of acceleration prevailed in the course of vehicle movement which permits the reconstruction of possible dangerous situations or accidents by reading out the data stored in the memory. In the knowledge of the acceleration data the driver will have access to information he could not have acquired by the use of a tachometer or a tachograph. The increased requirements of commercial vehicle traffic render the knowledge of these data important and necessar

Claims

1. Apparatus for the measurement and recording of acceleration comprising an acceleration sensor and a display indicating the sensed value of the acceleration or a range characteristic thereto, said acceleration sensor comprises magnetic poles formed of permanent magnets, a coil placed into the magnetic field between said magnetic poles, a mechanical supporting member holding said coil, said member pivoted around an axis and a circuit for sensing the position of said supporting member, c har ac t e r i z e d in that said member supporting the coil (20) being a frame

(10) placed into the magnetic field and said axis of rotation being normal to the magnetic field, a cross beam

(11) is arranged outside of said magnetic field and being rigidly coupled to said frame (10), a material mass (12) is fixed on said cross beam (11) at a point away from said axis, and a planar element (13) is attached to said cross beam (11) at a remote end region which is substantially normal to said beam, said position sensing circuit comprises an optical sensor (14) with a sensing zone partly covered by the plane of the planar element (10) , and a light-sensitive transistor (17) connected to a high-gain multitransistor amplifier, said coil (20) is coupled to the output circuit of said amplifier, a compensating capacitor (21) is connected between an intermediate point of said amplifier and an earth potential, a voltage-controlled oscillator (25) is coupled to the output of the amplifier and the output thereof is connected to a frequency counter, the apparatus comprises a microprocessor (29) for generating an acceleration signal in response to the output of said counter, a memory is associated with said microprocessor and said display (30) is coupled to the output of said microprocessor (20).

2. The apparatus as claimed in claim 1, c h a r a c ¬ t e r i z e d by comprising a pair of acceleration sensors (23, 24) of identical design, having respective sensing directions normal to each other, each of said sensors beir.Ξ. associated with a respective voltage-controlled oscillator (25, 27), a third voltage-controlled oscillator (26) iden¬ tical with the other two is provided an input fed from a stabilized voltage source, and the outputs of the three voltage-controlled oscillators (25, 26, 27) are connected through a multiplexer (28) to said microprocessor (29).

3. The apparatus as claimed in claims 1 or 2, c harac t e ri z e d in that the microprocessor (29) is designed to comprise a standby mode of operation having a standby input coupled to a standby circuit (17), a first input thereof is coupled to a switch (38), and a second input is coupled to a power supply (36) comprising an internal battery (35).

4. The apparatus as claimed in claim 1, c h a r a c - t e r i z e d in that said amplifier being formed by two transistors (18, 19) arranged in Darlington circuit.

5. The apparatus as claimed in claim 1, c h a r a c ¬ t e r i z e d in that a light-emitting diode (26) is used as light source in said optical sensor (14).