DE19534146A1 - Stepper-motor driven pointer instrument with timer unit for vehicle instrument panel - Google Patents

Abstract

An actual setting detector determines each time an instantaneous setting (theta p) of the pointer, if the timer (15) completes the downwards counting of the set time (Ts). A differential computing unit (16) computes a difference between the target setting (theta M), which is computed by the target setting computer (14) and the instantaneous setting (theta p), which is determined by the actual setting detector (13). An interval computer unit (16) computes the set time based on the difference (theta). The computer unit (16) enters the set time in the timer (15). The time set is shorter the respectively greater the difference is, and the time set is greater, the smaller the respective difference is. A pulse generator (10) supplies each time a pulse, if the timer (15) completes the downwards counting of the set time.

Description

Field of the Invention

The present invention relates to a Display device with a pointer by a stepper motor is driven.

State of the art

When using a stepper motor to drive the Pointer of a measuring instrument installed in a vehicle must be the frequency of one placed on the stepper motor Pulse signal corresponding to changes over time Input signal can be changed in a suitable manner. Such Frequency changes should allow for a steady display through the pointer is done as gently as possible, simultaneously but also proceed sufficiently quickly that the pointer as close as possible to the changes in the input signal to be displayed possible follows.

A stepper motor rotates in steps, namely one step per drive pulse, from a current angular position to an adjacent angular position. Thus, the smooth change of pointer and the rapid change in frequency of a driving pulse train are two opposite requirements, and it is quite difficult to meet both requirements at the same time. Fig. 9 shows changes in the angular position Θ _{M of} the pointer of a tachometer in the event that the vehicle speed initially increases slowly, then increases rapidly and gradually reaches a constant value. This tachometer works on the same principle as conventional tachometers. That is, a central processor unit (CPU) calculates e.g. B. from a pulse signal received from a sensor as a characteristic value for the vehicle speed, the vehicle speed. The CPU then calculates the difference between the angular position of the pointer corresponding to a new vehicle speed and the angular position Θ _P to which the pointer is currently aligned. If the difference is significant, the CPU causes the stepper motor to rotate a number of steps corresponding to the difference.

A stepper motor has a characteristic torque curve over the frequency, as z. B. is shown in Fig. 10. The curve determines a minimum available torque and a maximum frequency that can be applied to the motor to achieve a smooth and quick response to changes in the input signal. This curve reveals that a minimum time T _A (= 1 / fa) is required to drive the stepper motor by one step.

At the end of successive short time periods T, the CPU calculates a difference θ between θ _M and θ _P as follows:

θ = θ _M -θ _P (1)

Then the number N of pulses required to drive the stepper motor from θ _P to θ _M is calculated as follows:

N = θ / θ₀ (2)

where θ₀ is the angle by which the stepper motor moves Impulse turns.

In this way, a sequence of N pulses is output to the stepper motor, for example - as shown in FIG. 8A - a pulse after each time T _A within the time interval T. However, in FIG. 8A, N pulses at the beginning of the time interval T output, and towards the end of the time interval T no more pulse is output. This means that in the final phase of the time interval T the pointer does not move at all. Such a distribution of drive pulses over time T is detrimental to a gentle movement of the pointer.

Japanese Utility Model Laid-Open No. 64-6556 suggests that drive pulses be applied to the stepper motor in the manner shown in Fig. 8B. According to Fig. 8B, each of the N pulses outputted within a respective period of T / N to the stepping motor. It should be noted that the first pulse is output at a time T / 2N after the start of the time interval T so that the pulses are more evenly distributed over the time interval T. This even pulse distribution improves to a certain extent the continuity of the pointer movement. However, the following relationship must be satisfied between the time period T and the value T _A :

(T / N) T _A (3)

and taking into account the fact that the first pulse is output at a time T / 2N after the beginning of the time interval T, the following relationship is obtained from Fig. 8B and equation (3):

T 2T _A (4)

In other words, the time interval T cannot be shorter than 2T _A.

The above-mentioned device according to the prior art Technology offers a steady hand movement, but points following shortcomings.

• (a) The difference θ is calculated for each T, therefore the reaction is delayed at all points on the curve shown in FIG. 9.
• (b) The pulse frequency changes from one time interval T to another. Therefore, the smooth movement of the pointer is lost when the signal changes abruptly, as shown at A in Fig. 9.
• (c) Extending the time T aggravates the above defects (a) and (b).
• (d) Time T cannot be shorter than 2T _A , as shown in equation (4).

The input signal supplied to the stepper motor can have varied timelines, so it's pretty difficult to determine a value for the time interval T that best possible for all types of changes in the input signal is applicable. Thus, a quick response and a gentle movement of a pointer may not be compatible, and the smoothness of the pointer movement is after the procedure the state of the art is inadequate, in each case according to given time T a difference θ is calculated and then in Time intervals that correspond to the calculated difference θ, Drive impulses are output.

Summary of the invention

An object of the present invention is Specification of a display device with pointer, in which the Movement of a pointer runs smoothly and the reaction quickly is. A display device with a pointer has a through a stepper motor driven pointer.  

An input signal supplied to the device is converted into an angular position of a pointer. When the magnitude of the input signal changes, a target position θ _{M is} calculated and the current position θ _{P is} detected. A check is carried out to determine whether the difference θ is significant. If it is significant, then a drive pulse is output to the stepper motor. A time T _{s is also} calculated, which represents a waiting time until the next determination of θ. The larger θ, the shorter the time T _s . The smaller θ, the longer the time T _s . In this way, the time interval T _s between adjacent drive pulses supplied to the stepper motor is changed in close association with changes in the input signal, so that the frequency of the drive pulses changes smoothly. If the difference θ is zero or less than a predetermined small value, no drive pulse is output. If the difference is very small, a fixed time T1 can be used instead of the time T _s .

Brief description of the drawings

Features and further objects of the invention emerge from the Description of the preferred embodiments with reference on the accompanying drawings; show in it

Fig. 1A and 1B basic inventive arrangements;

Fig. 2 shows the arrangement of a first embodiment of the invention;

FIGS. 3 and 4 are flow charts for illustrating the operation of the first embodiment of the invention;

Fig. 5 shows the arrangement of a second embodiment of the invention;

FIGS. 6 and 7 are flow charts for illustrating the operation of the second embodiment of the invention;

Figs. 8A to 8B, the operation of conventional means, and 8C, the operation of the invention.

Fig. 9 shows the operating characteristics illustrates a pointer according to the prior art on the one hand and of a pointer according to the invention on the other hand; and

Fig. 10 illustrates the frequency-torque characteristic of a stepper motor.

Description of the preferred embodiment Mode of operation

An input signal supplied to the device is converted into an angular position of a pointer. As soon as the size of the input signal changes, a target position θ _{M is} calculated and the current position θ _{P is} detected. A check is made as to whether the difference θ is significant. If it is significant, then a drive pulse is output to the stepper motor. A time T _{s is also} calculated, which represents a waiting time until the next determination of θ. The larger θ, the shorter the time T _s . The smaller θ, the longer the time T _s . In this way, the time interval T _s between adjacent drive pulses supplied to the stepper motor is changed in close association with changes in the input signal, so that the frequency of the drive pulses changes smoothly. If the difference θ is zero or less than a predetermined small value, no drive pulse is output. If the difference is very small, a predefined time can be used instead of the time T _s .

First embodiment

The invention is described below by way of examples with reference to the drawings. Fig. 2 is a block diagram showing a general structure of a first embodiment of the invention. FIGS. 3 and 4 are flow charts illustrating the operation of the first embodiment.

A pointer 12 is attached to the axis of rotation of a stepper motor 10 and points to markings on the graduated scale 11 when the stepper motor 10 rotates. The stepper motor 10 rotates by the angle θ₀ every time it is supplied with a drive pulse via an input / output circuit 19 . A target computing unit 14 calculates - e.g. B. due to a speed pulse signal of a vehicle - an angular position to which the pointer should move. The angular position calculation is carried out every time the time counter 15 counts down to zero. The time counter 15 is designed as a down counter. An actual position detection element 13 detects the current angular position to which the pointer is currently pointing and sends the determined current angular position to an input / output circuit 20 . The actual position detection element 13 can take any shape as long as it detects the angular position of the axis of the stepping motor 10 . The actual position detection element 13 can be replaced by an actual position counter 23 , as shown in FIG. 5. A pulse generator 17 supplies the stepper motor 10 with pulses which are required to drive the stepper motor 10 so that it rotates from the current position into a target position. An interval calculator 16 calculates a time interval Ts, which is predetermined for the time counter 15 , on the basis of the difference between the current position and the target position of the stepping motor 10 . A microprocessor or CPU 21 receives and transmits signals and data between the circuit parts 13 to 20 , respectively, in order to carry out the necessary calculation and control processes.

In the first embodiment, a sensor (not shown) outputs a pulse each time a vehicle has traveled a distance unit, so that the pointer indicates the vehicle speed based on the speed pulses. The speed pulses are fed to an input / output circuit 18 . The stepper motor 10 rotates by a minimum angle θ₀ every time it is supplied with a drive pulse via the input / output circuit 19 .

The operation of the target computing unit 14 is explained below with reference to FIG. 4. The target computing unit 14 starts an interrupt subroutine as shown in FIG. 4 each time a speed pulse is supplied to it from the sensor via the input / output circuit 18 . In step S11, a time interval t between the last received pulse and the just received pulse is calculated. The program then proceeds to step S12, in which a target position θ _{M is} calculated using the following equation:

θ _M = K _B / t (5),

where KB is a constant.

That is, the CPU 21 calculates a speed of the vehicle based on the time interval t between adjacent pulses which have been supplied via the input / output circuit 18 to derive a target position θ _{M of} the pointer 12 corresponding to the calculated vehicle speed. The CPU 21 then stores the calculated value _{M M} in step S13, thereby completing the interrupt subroutine.

Although a target position is calculated in the first exemplary embodiment on the basis of a time interval t between successive pulses, a value of the target position θ _M averaged over a certain period of time can also be calculated from a corresponding plurality of speed pulses.

The operation of the first embodiment will now be described with reference to FIG. 3.

In step S1 it is checked whether the time counter 15 has counted downwards from a value T to zero. If the answer is no, the program waits until the answer is yes. If it is YES, then the program proceeds to step S2, in which the interval calculator 16 reads the target position θ _M from the memory and receives the current position θ _{P of} the pointer from the actual position detector 13 via the input / output circuit 20 . Then the interval calculator 16 calculates a difference θ based on the values θ _M and θ _P as follows:

θ = θ _M -θ _P (6)

The values for θ _M and θ _P are rounded so that θ is a multiple of θ₀. In step S3 it is checked whether θ is zero, ie:

| Θ | = 0 (7)

Equation (7) indicates that there is no change in the input signal supplied to the device. Thus, the program proceeds to step S4, in which the CPU gives the time counter 15 a predetermined short time T 1, and after a time T 1, the CPU checks the value again in steps S1 to S3. The use of a relatively small value for T 1 enables the device to react to changes in the input signal without too much delay, even if a difference θ occurs during the time T = T 1.

In step S5, the interval calculator 16 calculates a new value T _s for the time T as follows:

T _s = | K _A / Θ | (8th)

where K _{A is} a constant.

The larger the value θ, the smaller the value T _s . In other words, if the input signal (ie the vehicle speed) changes abruptly, the drive pulses are output at shorter intervals. This enables the pointer to closely follow the changes in the input signal.

Very large values of θ lead to very small values of K _A / θ, and in such a case the value T _{s is set} to T _A. Very small values of θ lead to very large values of T _s . Too large a value for T _s prevents the device from responding quickly to changes in the input signal when a difference θ occurs while the time counter is counting down a large amount of time T = T _s . To solve this problem, the time counter 15 can be set in step S6 to achieve a better response to a finite predetermined value T₀ if T _{s is} much larger than T₀. The program then proceeds to step S6, in which the time counter 15 is given a new value for Ts, after which the time counter 15 begins to count down.

In step S7, the pulse generator 17 outputs a drive pulse to the stepper motor 10 via the input / output circuit 19 . The drive pulse is accompanied by a logic high flag (flag) when the difference θ is a positive value and a logic low flag (flag) when the difference θ is a negative value, so that the stepper motor converges to the flag bit (Flag) rotates corresponding direction. The order of steps S6 and S7 can be interchanged.

In the first exemplary embodiment, steps S1 to S7 and S11 to S13 are carried out repeatedly, so that a drive pulse is output at the end of each cycle and the cycles are of different durations. The pulse train as a whole looks like that shown in Fig. 8C. The entire pulse train follows smooth and rapid gradual and abrupt changes in the input signal, while in the prior art the pulses are concentrated in the first part of the time interval T or the frequency of the pulse train changes in steps from time interval T to time interval T.

If the values θ _M and θ _{P are} not rounded, it can be checked in step S3 instead of the check = 0 whether θ <(₀₀ / 2) applies.

If the target position θ _{M changes} abruptly by a large amount, the following relationship applies to the rate of change dθ _P / dt of the current position θ _P :

dθ _P / dt = θ₀ / T _s = (θ _M -θ _P ) θ₀ / K _A (9)

Equation (9) can be rewritten as follows:

r = θ _M {1-exp (-θ₀ / K _A )} (10)

Equation (10) states that the current position θ _P exponentially approaches a final value θ _M and thus shows a smooth and fast response.

Second embodiment

A second embodiment will now be described with reference to FIGS. 5 to 7. Fig. 5 shows a general structure of the second embodiment. FIGS. 6 and 7 are flow charts for the second embodiment.

It is 5 Referring to FIG. the second embodiment differs from the first by a time counter A with the reference symbol 22 , an actual position counter 23 and a difference calculator 24 . The time counter A 22 repeatedly counts down briefly, for example starting from a minimum duration that is required to drive the stepping motor 10 . As described below with reference to FIG. 6, the actual position counter 23 counts up or down each time, depending on the direction of rotation of the stepper motor 10 , when the pulse generator 17 outputs a drive pulse to the stepper motor 10 . In other words, the actual position counter 23 counts up by one when the pulse is for clockwise rotation of the stepper motor and downwards when the pulse is for counterclockwise rotation of the stepper motor. Thus, the actual position counter 23 always contains a count that indicates the distance of the pointer from the zero position.

The target arithmetic unit 14 executes the subroutine shown in Fig. 4 just as in the first embodiment to calculate θ _M and then update the value for θ _M in the memory.

The mode of operation of the target computing unit 14 is described below with reference to FIG. 7. The difference calculator 24 executes the interrupt subroutine shown in FIG. 7 every time the time counter A 22 has counted down to zero. In step S21, the CPU reads the value of θ _M and proceeds to step S22, in which the CPU reads a counter reading NP from the actual position counter 23 to calculate θ _M as follows:

θ _P = N _P × θ₀ (11)

where θ₀ denotes the angle around which the stepper motor per drive pulse rotates.

In step S23, a difference θ is calculated as follows:

θ = θ _M -θ _P (12)

In step S24, the CPU stores the difference value θ calculated in step S23 in the memory (not shown) to complete the interrupt subroutine. As mentioned above, each time the counter A 22 counts down to zero, the difference calculator 24 calculates a new value of the difference θ.

The operation of the second embodiment will now be described with reference to FIG. 6. The steps S1 to S7 according to FIG. 6 are similar to those described in connection with FIG. 3.

In step S2, the interval calculator 16 reads the difference θ from the memory (not shown) in the difference calculator 24 .

In step S8, the actual position counter 23 counts up when the difference θ is a positive value and downwards when the difference θ is a negative value.

Although the second embodiment uses the actual position counter 23 , this can be replaced by an actual position detection element 13 , as shown in FIG. 2.

Claims (8)

1. Display device with a pointer ( 12 ) driven by a stepper motor ( 10 ) and the following further features:
a time counter ( 15 , 22 ) which is designed to count down from a predetermined time (T _s );
a target computing unit ( 14 , 14 ) configured to calculate a target position (θ _M ) of the pointer each time the time counter ( 15 , 22 ) completes the countdown of the timing (T _s );
an actual position detection element ( 13 , 23 ) which is designed to detect an instantaneous position (θ _P ) of the pointer each time the time counter ( 15 , 22 ) completes the countdown of the time specification (T _s );
a difference calculation unit ( 16 , 24 ) for calculating a difference (θ) between the target position (θ _M ), which is calculated by means of the target position calculation unit ( 14 , 14 ), and the current position (θ _P ), which is calculated from the actual Position detection element ( 13 , 23 ) is detected;
an interval arithmetic unit ( 16 ) for calculating the timing based on the difference (θ), the interval arithmetic unit ( 16 ) entering the timing into the time counting device ( 15 ) and the greater the difference, the shorter the timing and the greater the timing , the smaller the difference; and a pulse generator ( 17 ) configured to supply the stepping motor ( 10 ) with a pulse each time the time counter ( 15 , 22 ) completes the countdown of the timing. 2. Device according to claim 1, wherein the pulse generator ( 17 ) supplies the stepper motor ( 10 ) together with the pulse train a first signal when the stepper motor is to be rotated in a first direction, and the stepper motor ( 10 ) together with the pulse train supplies second signal if the stepper motor is to be rotated in a second direction. 3. Device according to claim 2, in which the actual position detection element ( 13 , 23 ) counts pulses output by the pulse generator ( 17 ), the actual position detection element ( 13 ) counting up when the stepper motor rotates in the first direction and counts down when the stepper motor is to be rotated in the second direction and the current position (θ _P ) is derived from a count of the actual position detector ( 13 ). 4. Device according to claim 1 or 2, wherein the pulse generator ( 17 ) stops the output of drive pulses to the stepper motor when the difference (θ) is below a predetermined value (θ₀ / 2). 5. Device according to claim 1 or 2, wherein the interval computing unit ( 16 ) sets the time counter ( 15 ) instead of the default time to a predetermined time (T₁) when the difference (θ) is below a predetermined value (θ₀ / 2) . 6. The device of claim 1 or 2, wherein the pulse generator ( 17 ) stops outputting drive pulses to the stepper motor when the difference (θ) is zero. 7. Device according to claim 1 or 2, wherein the interval computing unit ( 16 ) sets the time counter ( 15 ) instead of the default time to a predetermined time (T₁) when the difference (θ) is zero. Counting 8. Device according to one of claims 1 to 7, wherein the time counting means (15, 22) a second time counting means (22) which is formed, starting from a predetermined fixed timing downward; in which
the target position computing unit ( 14 ) is designed to calculate the target position (θ _M ) of the pointer each time the second time counter completes the countdown of the predetermined fixed time;
the actual position detection element ( 23 ) is designed to detect the current position (θ _P ) of the pointer each time the second time counter ( 22 ) completes the countdown of the predetermined fixed time; and
the difference computing unit ( 24 ) is designed to calculate the difference (θ) on the basis of the current position and the target position.