Indicating instrument

An indicating instrument includes an indicating needle provided in an instrument board, a stopper device to define a turning start position and a returning position of the indicating needle, a stepping motor for driving the indicating needle, and a control device to control the stepping motor; the control device outputs a zero reset signal for returning the indicating needle to the stopper device and a signal for moving the indicating needle away from the stopper device to the stepping motor when the stepping motor is turned on or turned off to carry out a missed step reset processing.

CROSS-REFERENCE TO THE RELATED APPLICATION

This application claims the priority benefit of Japanese Patent Application No. 2004-53830, filed on Feb. 27, 2004, the entire descriptions of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an indicating instrument for driving an indicating needle by a stepping motor.

2. Related Art Statement

Conventionally, by way of an example, a stepping motor has been used as a source of power for turning an indicating needle of an instrument board and so on of an automobile and the like. The stepping motor is configured such that the rotation of the stepping motor is transferred to the indicating needle by using a reduction gear, and then the indicating needle indicates vehicle speed, engine revolution, and so on.

However, such a stepping motor may produces missed steps by various reasons. As a device for carrying out a missed step reset, a stopper projection is provided in the indication board on which the stepping motor is mounted. The stopper projection is provided in a position where the indicating needle of the indicating board starts the turning. When the stepping motor produces the missed steps, the indicating needle is returned to the stopper projection side by outputting a zero reset signal to the stepping motor, and when the indicating needle comes into contact with the stopper projection, it is determined that the missed step reset is completed, then the zero reset signal is stopped (reference to Japanese Patent Laid Open Nos. 2001-314099, 2002-250641).

However, regarding conventional stepping motor control for an indicating instrument, when the indicating needle comes into contact with the stopper projection, the processing of missed step reset is completed by stopping the output of the zero reset signal with a state that the indicating needle is pressed onto the stopper projection. Therefore, when the reduction gear includes the allowance in a stopped position, there may be a case that an appropriate position which should be originally stopped is deviated by the allowance of the gear with the backlash of the reduction gear; even after the missed step is eliminated, there was a case that the indicating needle did not indicate an appropriate position.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem. It is, therefore, an object of the present invention to provide an indicating instrument capable of performing a missed step reset by returning the indicating needle to an appropriate initial position even though there are factors such as backlash and deformation of a gear when returning the indicating needle to the initial position by a zero reset signal in case of missed steps of a stepping motor.

According to the indicating instrument of the present invention, it comprises an indicating needle provided in an instrument board, a stopper device to define a turning start position and a returning position of the indicating needle, a stepping motor for driving the indicating needle, and a control device to control the stepping motor, and the control device outputs a zero reset signal for returning the indicating needle to the stopper device and a signal for moving the indicating needle away from the stopper device to the stepping motor when the stepping motor is turned on or turned off to carry out a missed step reset processing.

According to the indicating instrument of the present invention, the missed step reset processing alternately outputs the zero reset signal and the signal for moving the indicating needle away from the stopper device to the stepping motor one or more times to set an initial angle position in which the indicating needle is moved away from the stopper device by a predetermined angle in a direction moving away from zero.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, an embodiment for carrying out the invention will be described.

FIG. 1is a view illustrating a schematic structure and a block structure of an indicating instrument according to an embodiment of the present invention.

In this embodiment, a speed meter for a vehicle will be explained as an indicating instrument. The indicating instrument1comprises a 2 phase type stepping motor2, an indicating needle3to be turned through a reduction gear mechanism (not shown), a stopper mechanism4(stopper device) to stop the turning of the indicating needle3, a CPU portion5, and a zero-position detecting portion7.

The indicating instrument1operates by receiving power supply from a battery (not shown). The CPU portion5comprises a power supply circuit, etc., to be connected to a battery. When an automobile key is in a running state and a running standby state from the start of traveling to the end of traveling, the CPU portion5drives the stepping motor2based on the outputs detected from a vehicle speed sensor (not shown), and then turns the indicating needle3to a scale position indicating a vehicle speed of a not shown dial plate (instrument plate).

The stepping motor2comprises a stator (not shown) having S-phase coil (field coil)21and C-phase coil (field coil)22, and a magnetic rotor23. A lot of north poles and south poles are alternately magnetized on the outer circumference surface of the magnetic rotor23. The rotation of the magnetic rotor23is transmitted to a reduction gear mechanism (not shown), and then the indicating needle3turns along the rotation of the reduction gear mechanism.

The stopper mechanism4is constructed to prevent the indicating needle3from turning in the zero-returning direction by the contact of the indicating needle3to a projection provided on the dial plate. With the state that the turning of the indicating needle3in the zero-returning direction is prevented by the stopper mechanism4, the rotation of the reduction gear mechanism and the magnetic rotor23is also prevented.

The CPU portion5is constructed by using a micro-computer and a peripheral circuit. The CPU portion5comprises a driving control portion6, a missed step reset controlling portion8, and a zero reset determining device73constituting a part of the zero-position detecting portion7. A vehicle speed indicating control device61and a PWM signal generating device62of the driving control portion6, the missed step reset controlling portion8, and the zero reset determining device73constituting a part of the zero position detecting portion7are constructed by programs.

The driving control portion6is connected with ports P1, P2connected to the both end portions of S-phase coil21of the stepping motor2, and ports P3, P4connected to the both end portions of C-phase coil22of the stepping motor2. One end portion of the C-phase coil22is connected with an induced voltage detecting circuit70constituting the zero-position detecting portion7.

FIG. 2shows the constructions of the driving control portion6, the zero-position detecting portion7, and the missed step reset controlling portion8.

The driving control portion6comprises the vehicle speed indicating control device61to which an electric signal indicating a vehicle speed is input from a vehicle speed sensor (not shown) provided in a vehicle body, the PWM signal generating device62for generating a PWM signal by a vehicle speed data signal from the vehicle speed indicating control device61, and an output circuit63for supplying induced current to the S-phase coil21or the C-phase coil22by the output of the PWM signal generating device62.

With on-state of an ignition switch, the vehicle speed indicating control device61calculates a turning direction and a turning angle of the indicating needle3based on a vehicle speed signal supplied from the vehicle speed sensor, and then outputs the vehicle speed data signal to the PWM signal generating device62. The PWM signal generating device62generates a PWM signal based on the output signal from the vehicle speed indicating control device61, and then outputs the PWM signal to the output circuit63. The output circuit63drives the stepping motor2based on the PWM signal, and turns the indicating needle3to a dial position corresponding to a vehicle speed of the above dial plate.

The PWM signal generating device62generates respective PWM signals, which supply current from one end of the S-phase coil21to the other end of the S-phase coil21(positive direction) or from the other end of the S-phase coil21to one end of the S-phase coil21(opposite direction), and respective PWM signals, which supply current from one end of the C-phase coil22to the other end of the C-phase coil22(positive direction) or from the other end of the C-phase coil22to one end of the C-phase coil22(opposite direction). The 4 systems of the PWM signals generated by the PWM signal generating device62are supplied to the respective output ports P1to P4through the output circuit63.

The output circuit63comprises a known protection circuit such as a switching element and diode of a transistor, etc., which outputs current for driving the S-phase coil21and the C-phase coil22in a predetermined order from a emitter or a collector by the PWM signal supplied from the PWM signal generating device62to a base.

When the indicating needle3turns in the direction moving away from the stopper mechanism4, respective PWM signals are generated and output in a direction in which an electric angle of the stepping motor increases. When the indicating needle3turns in the zero-returning direction, respective PWM signals are generated and output in a direction in which the electric angle decreases.

When supplying the positive direction current to the S-phase coil21, pulse current flows from the output port P1to the output port P2through the S-phase coil21. When supplying the opposite direction current to the S-phase coil, the pulse current flows from the output port P2to the output port P1through the S-phase coil.

When supplying the positive direction current to the C-phase coil22, pulse current flows from the output port P3to the output port P4through the C-phase coil22. When supplying the negative direction current to the C-phase coil22, the pulse current flows from the output port P4to the output port P3through the C-phase coil22. The exciting current flowing the S-phase coil21and the pulse current flowing the C-phase coil22are expressed as pseudo Sin−curve and Cos−curve for a direction and acceleration and slow down processing of the current flowing the coils.

The output circuit63enables the output ports P1to P4to be open (high impedance) states by turning off the respective switching elements.

The zero-position detecting portion7comprises an induced voltage detecting circuit70and the zero reset determining device73of the CPU portion5.

The induced voltage detecting circuit70is adopted to detect that the indicating needle3has returned to the zero reset position (zero-position). The induced voltage detecting circuit70comprises a filter circuit71having a low-pass characteristic for reducing and eliminating high-frequency noise element superimposed on the induced voltage induced in the C-phase coil22, and a voltage comparator72to generate binary output by comparing the induced voltage and previously set threshold voltage. The binary output of the voltage comparator72is input to the zero reset determining device73in the CPU portion5through an input port.

The zero reset determining device73shown inFIG. 2detects that the rotation of the magnetic rotor23has been stopped based on the output of the voltage comparator72, thus, the zero reset determining device73determines that the indicating needle3has returned to the zero (reference) position.

The missed step reset controlling portion8comprises the zero reset processing device64shown inFIG. 2. When the ignition switch is turned off, the zero reset processing device64carries out a zero reset processing enabling the indicating needle3to return to the zero (reference) position and a missed step reset processing. Moreover, when the ignition switch is turned on, the zero reset processing device64performs the zero reset processing enabling the indicating needle3to return to the zero (reference) position once and the missed step reset processing, and then allows the indicating needle3to be drivable in the direction moving away from the zero position.

The zero reset processing device64comprises an output port opening control device65for controlling one end of the C-phase coil22to be the open state. In case of performing the missed step reset processing, the output port opening control device65waits for the output of the zero reset determining device73.

The zero reset determining device73is adopted to determine the zero reset of the indicting needle3to the zero position, where the indicating needle3stops by the contact to the stopper mechanism4, in corporation with the output port opening control device65of the missed step reset control portion8. When starting the zero reset processing, the zero reset determining device73loads the output of the voltage comparator72in time just before stopping the opening of the output port P3by the instruction from the zero reset processing device64. If the output of the comparator72is H level, the zero reset determining device73determines that the indicating needle3has not returned to the zero reset position yet. If the output of the comparator72is L level, the zero reset determining device73determines that the indicating needle3has returned to the zero reset position. With the zero reset processing, the turning of the indicating needle3is stopped by the stopper mechanism4. With the state that the turning of the magnetic rotor23is stopped, the induced voltage does not generate in the C-phase coil22, so that the output of the voltage comparator72becomes L level.

In other words, as illustrated inFIG. 6, when the electric angle of the pseudo Sin+curve flowing the S-phase coil21is from 45° to 90° and from 225° to 270°, the pulse current dose not flow in the C-phase coil22; however, the induced current generates in the C-phase coil22by the rotation of the magnetic rotor23. Here, the voltage comparator72compares the induced voltage induced to the C-phase coil22at this point and the threshold. When the induced voltage is higher than the threshold voltage, it is determined that the magnetic rotor23rotates and the indicating needle3is turning, and then the zero reset processing is continued.

In the zero reset processing, the zero reset processing device64drives the stepping motor2in the direction that the indicating needle3is returned to the stopper mechanism4side as the first step, and enables the output port P3of Cos+side to be the open (high impedance) state at the right time outputting the PWM signal of Sin+side as the second step. As the third step, the zero reset determining device73loads the detected output of induced voltage (the output of the voltage comparator72) from the voltage comparator72. As the fourth step, if the logical level is the H level, the zero reset determining device73determines that the indicating needle3is turning, and sets back the output port P3of Cos+side to be the output state of the PWM signal, and then continues the driving of the indicating needle to the zero reset direction. In the fourth step, if the detected output of induced voltage (the output of the voltage comparator72) is L level lower than the threshold, the zero reset determining device73determines that the indicating needle is returned to the zero position, and sets back the output port P3of Cos+side to be the output state of the PWM signal, and then stops the driving of the stepping motor.

Moreover, in the last half of the opening period of the output port P3, the zero reset determining device73can load the output of the voltage comparator72for more than once with a predetermined time interval.

In the missed step reset processing of this embodiment, the missed step reset processing is carried out by performing the zero reset processing more than once to eliminate the triggers for the missed steps such as the backlash and deformation of the reduction gear.

FIGS.3,4indicates the flow of the missed step reset processing of the present invention, andFIG. 5shows the changes in the electric angle at this point. Namely, when the ignition switch is turned on or tuned off, the missed step reset processing flag is started. In step S.1, an initial angle of the magnetic rotor23when the indicating needle3is in the position of the stopper mechanism4is output. In the step S.2, the S-phase coil21and the C-phase coil22are energized by the driving control portion6in order to turn the indicating needle3by substantially 1° (the first predetermined angle) of the mechanical angle in the direction moving away from the zero position (reference toFIG. 4). In the step S3, in order to return the indicating needle3to the stopper mechanism4side again, the S-phase coil21and the C-phase coil22are energized by the driving control portion6to start the zero reset. In the step S4, after the driving control portion6performs a slow down processing in the vicinity where the indicating needle3comes into contact with the stopper mechanism4in this zero reset processing (reference toFIG. 5), the zero reset processing is once completed at the point when the indicating needle3comes into contact with the stopper mechanism4. In the next step S5, the S-phase coil21and the C-phase coil22are energized by the driving control portion6to move the indicating needle3away from the stopper mechanism4by 1.5° (the second predetermined angle) in the direction moving away from the zero. In the step S6, the zero reset processing is carried out such that the indicating needle3is again returned to the stopper mechanism4side by 0.5 degree (the third predetermined angle). Therefore, the missed step reset processing flag is completed.

In this missed step reset processing of this embodiment, at first, the initial angle is detected, secondly, the indicating needle3is turned by 1°, thirdly, the zero reset processing is performed such that the indicating needle3comes close to the stopper mechanism4side, fourthly, the processing for moving the indicating needle3away from the stopper mechanism4is again carried out such that the indicating needle3rises from the stopper mechanism4by 1.5°, and fifthly, the zero reset processing for returning the indicating needle3to the stopper mechanism4side by 0.5°, in other words, the missed step reset processing for setting an initial angle position where the indicating needle3is removed in the direction moving away from the zero by a predetermined angle is performed. Therefore, the triggers for the missed steps such as backlash and deformation of the reduction gear mechanism are eliminated, and the indicating needle3can be adjusted to indicate an appropriate speed. Moreover, the above first to third predetermined angles are the examples, thus, these angles are not limited the above.

In this embodiment, the example is shown that one end of the C-phase coil22is adopted to be the open state, and the C-phase coil22is used as the coil for detecting the induced voltage. However, one end of the S-phase coil21can be used to be the open state, and the induced voltage can be detected by the S-phase coil21side. In this case, one end of the S-phase coil21is set to be the open state at the right time when the S-phase coil21becomes a non-excited state. Accordingly, it is possible to determine whether the indicating needle3is turning or in the stopped state by detecting the induced voltage without having influence on the driving of the stepping motor2.

The indicating instrument according to the present invention can always maintain an appropriate indicating needle by solving the triggers for the missed steps such as backlash and deformation of the reduction gear when conducting the missed step reset of the stepping motor used for the instrument board.

When the missed steps of the stepping motor is reset and when the indicating needle is returned to the initial angle setting position, the indicating instrument according to the present invention conducts the turning of the indicating needle with respect to the stopper device in the zero reset direction and in the direction moving away from the zero respectively one or more times. Accordingly, even though backlash, deformation and so on occur in the reduction gear between the indicating needle and the stepping motor, the indicating instrument of the present invention can eliminate these triggers, and enable the indicating needle to be in an appropriate initial angle.