JPS628121B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brush position detection method for an endless potentiometer used in a serial printer or the like.

For example, a serial printer includes a type wheel with type and a carriage for moving the type wheel along the print line, the carriage being moved by a direct current motor. Position control and speed control of such a carriage, ie, a DC motor, is performed by synchronizing a potentiometer with the DC motor.

Generally, a potentiometer for controlling a DC motor as described above includes an annular resistor having a notch;
It consists of a brush that slides on this resistor, and in this case, the brush is directly connected to the rotor of the DC motor. In this potentiometer, two brushes are provided in order to avoid discontinuity in the output voltage obtained by the brushes at the notch portion of the resistor, and one brush is selected depending on the brush position.
An endless potentiometer has recently been proposed as a potentiometer that eliminates these drawbacks.

An endless potentiometer includes a resistor formed in an endless shape, at least three taps provided at predetermined intervals along the resistor, one brush that slides on the resistor, and two of the taps. and a tap selection circuit that selects the tap and supplies power. In this endless potentiometer, the position of the tap to which power is supplied is changed depending on the brush position.

On the other hand, in serial printers, it is necessary to return the carriage to the initial position (home position) when the power is turned on. Therefore, when an endless potentiometer is applied to control the DC motor for driving the carriage, Traditionally, the tap selection behavior was confusing because the brush position was unknown.
Therefore, when the carriage returns to its initial position,
There is a problem in that the speed signal is detected at a phase opposite to the actual speed of the carriage, resulting in uneven speed.

An object of the present invention is to detect the brush position based on the concept of performing a tap selection operation multiple times when the power is turned on and comparing the resulting brush voltage with a predetermined voltage. When the endless potentiometer is applied to control the DC motor for driving the carriage, the carriage returns to the initial position at a constant speed when the power is turned on, which solves the problems with the conventional type described above. There is a particular thing.

Embodiments of the present invention will be described below with reference to the drawings.

The attached figure is a block circuit diagram of an apparatus for carrying out the method for detecting the brush position of an endless potentiometer according to the present invention. In the figure, there are four taps 2-1, 2-2, 2-3,
2-4 are provided, each tap 2-1, 2-
2, 2-3, 2-4 are analog switches S ₁ , S ₂ ,
Connect _{the ground} terminal or positive potential terminal (+
V _R ). The brush 3 is slidably provided on the resistor 1, and therefore the voltage of the brush 3 changes depending on the position of the brush 3. The rotating shaft of the brush 3 is linked to a rotor (not shown) of a DC motor for driving a carriage of a serial printer, for example.

The voltage of the brush 3 is applied to the +input of the differential amplifier 6 via a buffer amplifier 4 with high input impedance. In this case, the output voltage of buffer amplifier 4 is _V1 . On the other hand, the analog voltage V ₂ of the D/A converter 5 determined by the position designation signals D ₀ , D ₁ , _. . . Do is applied to the other input of the differential amplifier 6 . The output voltage V ₃ of the differential amplifier 6 is compared with the zero level V ₀ by a comparator 7, and the result of this comparison is determined by a discriminator 8 to detect the position of the brush 3. Note that the output voltage of the D/A converter 9 determined by the speed designation signals V ₀ , V _{1 .} . . , V _o is applied to the + input of the comparator 7;
When detecting the position of , it is set to zero voltage V ₀ .

In addition, when detecting the position of the brush 3, the position designation signals D ₀ , D ₁ , ..., Do _are set so that the voltage V ₂ of the D/A converter 5 is approximately equal to the voltage of the tap 2-2. I'll keep it. As shown in the figure, when there are four taps, two tap selection operations are performed. The first time is carried out by tilting the analog switch S ₁ to the +V _R side and the analog switch S ₃ to the ground side, as shown in the figure, and holding the analog switches S ₂ and S ₄ at the neutral point. In this case, since the brush 3 is located in the fourth quadrant, the output voltage V ₁ of the buffer amplifier 4 is greater than V ₂ (=V _R /2). Therefore, the output voltage V ₃ of the differential amplifier 6 is a positive voltage, and the output voltage V ₄ of the comparator 7 is low. The second tap action is an analog switch.
This is done by tilting S ₄ to the +V _R side, tilting the analog switch S ₂ to the ground side, and holding the analog switches S ₁ and S ₃ at the neutral point. In this case, brush 3
is located in the fourth quadrant, so the output voltage V ₁ of the buffer amplifier 4 is smaller than V ₂ (=V _R /2). Therefore, the output voltage V ₃ of the differential amplifier 6 becomes a negative voltage, and the output voltage V ₄ of the comparator 7 becomes high.

A discriminator 8 monitors the output voltage V ₄ of the comparator 7 as described above and discriminates the position of the brush 3 . That is, when the output voltage _V4 of the comparator 7 is low during the first tap selection operation, it is determined that the brush 3 is located in either the 1st or 1st quadrant; When the output voltage V ₄ is high, it is determined that the brush 3 is located in either the 1st or 1st quadrant. Similarly, during the second tap selection operation, if the output voltage _V4 of the comparator 7 is low, it is determined that the brush 3 is located in either the second or fourth quadrant; If the output voltage is high, it is determined that the brush 3 is located in either the 1st or 3rd quadrant. In this way, when the tap selection operation is performed twice, the brush 3 is
The discriminator 8 determines whether it is located in the 1st, 3rd, or 3rd quadrant.

In the figure, the number of taps is 4, so the number of tap selection operations is 2, but of course,
If the number of taps increases, the number of tap selection operations for detecting the position of the brush 3 must be increased. Note that 10 is a differential circuit that obtains a speed signal when controlling the movement of the carrier by rotating the DC motor.

In addition, the above-mentioned position designation signals D ₀ , D ₁ , ..., D _o
and speed designation signals V ₀ , V ₁ , . . . , V _o are both generated by a digital controller (not shown) that controls the movement of the printer's carriage. In this case, the position designation signals D ₀ , D ₁ , . . . , D _o are generated based on type selection information from the central CPU. However, one revolution of the endless potentiometer brush 3 does not necessarily correspond to one carriage stroke, for example, 136 characters; for example, seven and a half revolutions of the endless potentiometer brush 3 correspond to one carriage stroke. Therefore, when the number of type selection pitches corresponds to more than half a revolution of the brush of the endless potentiometer, the digital controller performs multiple tap selection operations and multiple position designation signals.
D ₀ , D ₁ , ..., D _o will be generated. Also, the speed designation signals V ₀ , V _{1 ,} . That is,
When the number of type selection pitches is large, a high speed is specified, and conversely, when the number of type selection pitches is small, a small speed is specified. Such calculations and control are performed by a digital controller.

As explained above, according to the present invention, since the brush position can be detected, the tap selection operation can be performed appropriately when the power is turned on, so that it is possible to obtain a speed signal with a phase that matches the actual operation of the carriage. It becomes possible. Therefore, when an endless potentiometer is applied to control a DC motor for driving a carriage, the carriage can be returned to its initial position at a constant speed when the power is turned on, which helps solve the problems with the conventional type described above. It is something.

[Brief explanation of the drawing]

The attached figure is a block circuit diagram of an apparatus for carrying out the method for detecting the brush position of an endless potentiometer according to the present invention. 1: Endless resistor, 2-1, 2-2,
2-3, 2-4: tap, 3: brush, 4: buffer amplifier, 5: D/A converter, 6: differential amplifier, 7: comparator, 8: discriminator.

Claims (1)

[Claims] 1. A resistor formed in an endless shape, at least three taps provided at predetermined intervals along the resistor, one brush that slides on the resistor, and two of the taps. In an endless potentiometer equipped with a tap selection circuit that selects and supplies power, the selection operation by the tap selection circuit is performed a plurality of times with the brush not sliding, and the voltage of the brush is adjusted for each selection operation. A method for detecting a brush position of an endless potentiometer, characterized in that the position of the brush is detected by comparing it with a predetermined voltage.