DE19534146B4 - Display device with a pointer driven by a stepper motor - Google Patents

Abstract

Display device with
a pointer (12) driven by a stepper motor (10);
at least one time counter (15) into which a value can be entered, which counts down to zero from this value and thereby generates a corresponding waiting time (T _s );
a target position computing unit (14), from which the target position (Θ _M ) of the pointer (12) can be calculated after the waiting time (T _s );
an actual position detection element (13; 23), from which after the waiting time (T _s ) the actual position (Θ _P ) of the pointer (12) can be detected;
a difference computing unit (16; 24), from which the difference (Θ) between the desired position (Θ _M ) and the actual position (Θ _P ) of the pointer (12) can be calculated;
an interval computing unit (16), from which the value to be counted down to generate the waiting time (T _s ) can be calculated as a function of the difference (Θ) and can be entered into the time counting device (15) for setting the waiting time (T _s ), the value to be counted down below Determination of a shorter waiting time (T _s ) is calculated the smaller the larger the difference ...

Description

The present invention relates referring to a display device with a pointer pointing from a Stepper motor is driven.

When using a stepper motor for driving the pointer of one installed in a vehicle Measuring instrument must have the frequency of one placed on the stepper motor Pulse signal corresponding to changes in time of an input signal in appropriately changed become. Such frequency changes so that the pointer shows a steady display, so gentle as possible take place, but at the same time sufficiently quickly go that the pointer changes of the input signal to be displayed follows as closely as possible.

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 pointer change and the rapid change in the frequency of a driving pulse train are two opposite requirements, and it is quite difficult to meet both requirements at the same time. 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. This means that a central processor unit (CPU) calculates, for example, the vehicle speed from a pulse signal that is received from a sensor as a characteristic value for 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 as a function of frequency, as described, for example, in 10 is shown. 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 TA (= 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: 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 / Θ 0 (2) where Θ _{0 is} the angle through which the stepper motor rotates per pulse.

In this way, a sequence of N pulses is output to the stepper motor, for example - as in 8A shown - a pulse after each time T _A within the time interval T. However, in 8A N pulses are output at the beginning of the time interval T, and no pulse is output at the end of the time interval T. This means that in the end 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.

The Japanese utility model with the publication number 64-6556 suggests that the stepping motor drive impulses in the 8B as shown. According to 8B each of the N pulses is output to the stepper motor within a respective time period T / N. 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 distributed more evenly 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 fulfilled 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 start of the time interval T, one obtains from 8B and equation (3) have the following relationship: T ≥ 2T A (4)

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

• (a) Die Differenz Θ wird für jedes T berechnet, deshalb verzögert sich die Reaktion an allen Stellen der in 9 gezeigten Kurve.
• (b) Die Impulsfrequenz ändert sich von einem Zeitintervall T zum anderen. Daher geht die sanfte Bewegung des Zeigers verloren, wenn sich das Signal abrupt ändert, wie in 9 an den Stellen A dargestellt.
• (c) Eine Verlängerung der Zeit T verschlimmert die vorstehenden Mängel (a) und (b).
• (d) Die Zeit T kann nicht kürzer als 2T_A sein, wie aus Beziehung (4) hervorgeht.

The above-mentioned device according to the prior art offers a constant pointer movement, but has the following shortcomings.

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

The input signal to the stepper motor can manifold courses of time , so it is quite difficult to unite for the time interval T. To determine the value for all kinds of changes of the input signal in the best possible way is applicable. So you can a quick reaction and a gentle movement of a pointer is not be compatible with each other. The smoothness of the pointer movement is at the prior art method in which a difference Θ is calculated in each case after a predetermined time T and then at time intervals that correspond to the calculated difference Θ, Drive impulses are output.

The DE 31 51 627 A1 discloses a switching arrangement for a motor vehicle instrument (speedometer) with an electro-optical display unit (continuous line display), the maximum difference between two successive display values being limited on the one hand and the time period between the display of two successive ones to avoid a troubled optical impression (flickering or flickering) different display values can be selected large enough.

The DE 27 30 699 C2 discloses a device for a motor vehicle for displaying a mechanical measured variable (vehicle speed), with a measuring mechanism serving to adjust a pointer, which is connected via a converter to a pulse-generating transmitter, the pulses being proportional to the measured variable and being a measuring mechanism. and reverse stepping motor is provided.

The DE 32 27 986 A1 discloses a device for a motor vehicle for converting a frequency of an electrical measuring pulse proportional to a measured variable into a quasi-analog representable variable, wherein variables such as speed or engine speed can be displayed as precisely as possible according to the measuring principle of the device.

The DE 34 35 539 C2 discloses a pulse counting device with which a pulse signal can be counted, which is generated when a variable to be measured, such as vehicle speed or engine speed, is changed, with a reaction to a change in the measured variables as quickly as possible.

The GB 2 164 152 A discloses an analog meter for displaying a physical quantity, such as the depth of a water sportsman, the meter comprising a stepper motor for driving a pointer and a control device with low power consumption, the meter being provided in a small device such as a wristwatch to be accommodated.

The DE 29 46 328 A1 discloses an analog display device for almost all physical quantities, with a stepper motor to which a number of drive pulses is applied, which is directly proportional to the number of pulses supplied by a counter.

An object of the present invention is in the indication of a display device with one of a stepper motor driven pointer, in which the movement of the pointer runs smoothly and the Response is quick.

An input signal supplied to the display device is converted into an angular position of the pointer. If the size of the input signal changes, a target position Θ _{M is} calculated and the current position Θ _{P is} recorded. 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 0. The greater 0, the shorter the time T _s . The smaller 0 is, the longer the time Ts. In this way, the time interval T _s between adjacent drive pulses that are supplied to the stepper motor is changed in close connection 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 specified small value, no drive pulse is output. If the difference is very small, a fixed predetermined time T ₁ can be used instead of the time T _s .

Characteristics and other tasks of the Invention emerge from the description of the preferred embodiments with reference to the accompanying drawings; in this demonstrate:

1A and 1B Basic principles of in the 2 and 5 illustrated embodiments;

2 the arrangement of a first preferred embodiment;

3 and 4 Flow charts illustrating the operation of the first preferred embodiment;

5 the arrangement of a second preferred embodiment;

6 and 7 Flow charts illustrating the operation of the second preferred embodiment;

8A to 8B the operation of conventional facilities, and 8C the operation of an arrangement according 2 or 5;

9 illustrates the operating characteristics of a pointer according to the prior art on the one hand and a pointer as it according to 2 respectively. 5 driven, on the other hand; and

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

First embodiment

2 Fig. 12 is a block diagram showing a general construction of a first preferred embodiment. The 3 and 4 are flowcharts illustrating the operation of the first embodiment.

A pointer 12 is on the axis of rotation of a stepper motor 10 attached and pointing to markings on the divided scale 11 when the stepper motor 10 rotates. The stepper motor 10 turns every time it passes through an input / output circle 19 a drive pulse is applied to the angle Θ ₀ . A debit position computing unit 14 calculates - for example, based on a vehicle's speed pulse signal - an angular position Θ _M to which the pointer points 12 should move. The angular position calculation is carried out every time a time counter 15 counts down to zero from a given value. The time counter 15 hereinafter as a time counter 15 is designed as a down counter. An actual position detection organ 13 detects the current angular position Θ _P (actual position) to which the pointer is pointing 12 currently shows and sends the determined instantaneous angular position Θ _P to an input / output circuit 20. The actual position detection element 13 can take any shape as long as it is the angular position of the axis of the stepper motor 10 detected. The actual position detection device 13 can by an actual position counter 23 be replaced as he is in 5 is shown. A pulse generator 17 delivers to the stepper motor 10 Pulses that are required to drive the stepper motor 10 to drive so that it turns from the current position Θ _P into a target position Θ _M. An interval arithmetic unit 16 calculates a time interval T _S , which is the time counter 15 is specified based on the difference between the current position Θ _P and the target position Θ _{M of} the stepper motor 10 , A microprocessor or a CPU 21 receives and transmits signals and data between the circuit parts 13 to 20 to perform the necessary calculation and control operations.

In the first embodiment, a sensor (not shown) outputs a pulse every time a vehicle has traveled a distance unit, so that the pointer 12 displays the vehicle speed based on the speed impulses. The speed pulses become an input / output circuit 18 fed. The stepper motor 10 turns every time it passes over the I / O circle 19 a drive pulse is supplied by a minimum angle Θ ₀ .

The mode of operation of the target position computing unit 14 is described below with reference to 4 explained. The target position computing unit 14 Every time a speed pulse is applied to it from the sensor through the input / output circuit 18, an interrupt subroutine begins, as shown in FIG 4 is shown. 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 is via the input / output circuit 18 were supplied to a target position Θ _{M of} the pointer corresponding to the calculated vehicle speed 12 derive. The CPU 21 then saves the calculated value Θ _M in step S13 and thus concludes the interrupt subroutine.

In the first exemplary embodiment, a target position Θ _M is calculated based on a time interval t between successive pulses, but a value of the target position Θ _{M determined} 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 described.

In step S1, it is checked whether the time counter 15 counting 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 the current position Θ _{P of} the pointer from the actual position detection element 13 via the input / output circuit 20 receives. Then the interval arithmetic unit calculates 16 a difference Θ due to 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 Θ ₀ . In step S3 it is checked whether Θ is equal to zero, ie: | Θ | = 0 (7)

Equation (7) indicates that there is no change in the input signal supplied to the display device. Thus, the program proceeds to step S4, in which the CPU counts the time 15 specifies a fixed short time T ₁ , and after a time T ₁ the CPU checks the value Θ 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 during the time T = T ₁ a difference Θ occurs.

The interval computing unit calculates in step S5 16 a new value T _s for time T as follows: T s = | K A / Θ | (8th) where K _{A is} a constant.

The larger the value 0, the smaller the value T _s . In other words, when the input signal (ie the vehicle speed) changes abruptly, the drive pulses are output at shorter intervals. This enables the pointer 12 to closely follow the changes in the input signal.

Very large values of 0 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 if a difference Θ occurs during the time counter 15 a long period of time T = T _s counts down. To solve this problem, the time counter 15 in step S6 to achieve a better response to a finite predetermined value T ₀ if T _{s is} much larger than T ₀ . Then the program proceeds to step S6, in which the time counter 15 a new value for T _{s is} given, after which the time counter 15 starts counting down.

In step S7 the pulse generator gives 17 via the input / output circuit 19 a drive pulse to the stepper motor 10 out. The drive pulse is accompanied by a logically high marker bit (flag) if the difference Θ is a positive value and by a logically low marker bit (flag) if the difference Θ is a negative value, so that the stepper motor 10 turns in a direction corresponding to the flag. 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 in 8C shown from. 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.

= 0 are checked if Θ <(Θ _0/2) applies | If the values Θ _M and Θ _P are not rounded, in step S3 instead of checking | Θ.

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 = Θ 0 / T s = | Θ M - Θ P ) Θ 0 / K A | (9)

Equation (9) can be rewritten as follows: Θ = Θ M {1-exp (-Θ 0 / 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 reaction.

Second embodiment

With reference to the 5 to 7 a second preferred embodiment will now be described. 5 shows a general structure of the second embodiment. The 6 and 7 are flowcharts of the second embodiment.

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

The target position computing unit 14 leads that in 4 shown subroutine exactly as in the first embodiment to calculate Θ _M and then update the value for Θ _M in memory.

The following is the mode of operation of the target position computing unit 14 with reference to 7 described. The difference calculator 24 leads that in 7 shown interrupt subroutine every time the time counter A 22 has counted down to zero. Reads in step S21. the CPU has the value of Θ _M and proceeds to step S22, in which the CPU reads a counter reading N _P from the actual position counter 23 reads out to calculate Θ _P as follows: Θ P = N P × Θ 0 (11) where Θ ₀ denotes the angle through which the stepper motor rotates per drive pulse.

In step 523, 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, the difference calculator calculates 24 every time the counter A 22 counts down to zero, a new value of the difference Θ.

The operation of the second embodiment will now be described with reference to FIG 6 described. Steps S1 to S7 after 6 are related to 3 described similarly.

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

The actual position counter counts in step S8 23 upwards if the difference Θ is a positive value and downwards if the difference Θ is a negative value.

Claims (8)

Display device with a stepper motor ( 10 ) driven pointer ( 12 ); at least one time counter ( 15 ), into which a value can be entered, which counts down to zero from this value and thereby generates a corresponding waiting time (T _s ); a target position computing unit ( 14 ), of which after the waiting time (T _s ) the target position (Θ _M ) of the pointer ( 12 ) is predictable; an actual position recording body ( 13 ; 23 ), of which after the waiting time (T _s ) the actual position ( Θ _P ) of the pointer ( 12 ) is detectable; a differential computing unit ( 16 ; 24 ), of which the difference (Θ) between the target position (Θ _M ) and the actual position ( Θ _P ) of the pointer ( 12 ) is predictable; an interval computing unit ( 16 ), from which the value to be counted down to generate the waiting time (T _s ) depending on the difference (Θ) can be calculated and into the time counter ( 15 ) can be entered for setting the waiting time (T _s ), the larger the difference (Θ), the smaller the value to be counted down by determining a shorter waiting time (T _s ), and the value to be counted down by determining a longer waiting time (T _s ) the smaller the difference (Θ), the greater the calculation; and a pulse generator ( 17 ), of which a drive pulse can be generated after the waiting time (T _s ), if the amount of the difference (Θ) is greater than a predetermined amount, and the stepper motor ( 10 ) to turn the pointer ( 12 ) can be fed by a standard angle (in ₀ ) in one direction according to the sign of the difference (Θ). Display device according to claim 1, wherein the pulse generator ( 17 ) the stepper motor ( 10 ) delivers a first signal together with the pulse sequence when the stepper motor ( 10 ) is to be rotated in a first direction, and the stepper motor ( 10 ) supplies a second signal together with the pulse sequence if the stepper motor ( 10 ) is to be rotated in a second direction. Display device according to Claim 2, in which an actual position counter ( 23 ) from the pulse generator ( 17 ) counts output pulses, whereby the actual position counter ( 23 ) counts up when the stepper motor ( 10 ) in the first direction and counts down when the stepper motor ( 10 ) is to be rotated in the second direction, and the actual position (Θ _P ) from a counter reading of the actual position counter ( 23 ) is derived. Display device according to claim 1 or 2, wherein the pulse generator ( 17 ) the output of drive pulses to the stepper motor ( 10 ) Terminated if the difference (Θ) is below a predetermined value (Θ ₀ / is 2). Display device according to Claim 1 or 2, in which the interval computing unit ( 16 ) the time counter ( 15 ) Sets when the difference (Θ) is below a predetermined value (Θ _0/2) is at a predetermined waiting time (T _1). Display device according to claim 1 or 2, wherein the pulse generator ( 17 ) the output of drive pulses to the stepper motor ( 10 ) ends when the difference (Θ) is zero. Display device according to Claim 1 or 2, in which the interval computing unit ( 16 ) the time counter ( 15 ) to a predefined waiting time (T ₁ ) when the difference (Θ) is zero. Display device according to one of Claims 1 to 7, in which the time counting device ( 15 ) a second time counter ( 22 ), which is designed to count down to zero starting from a predetermined fixed time.