JPS6255282B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an endless potentiometer used in serial printers and 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 cutout portion of the resistor, and the brush must be selected depending on the brush position. An endless potentiometer has recently been proposed as a potentiometer that eliminates these drawbacks.

An endless potentiometer consists of a resistor formed in an endless manner, at least three power supply taps spaced equally apart along the resistor, a brush that slides over the resistor, and a power source. The apparatus is equipped with tap selection means for selecting two of the supply taps to supply power. Conventionally,
In order to position the brush, the output voltage of the D/A converter to which a digital position designation signal is supplied is compared with the output voltage obtained from the brush, and the brush position is controlled according to this voltage difference. Ta.

However, in the conventional type described above, the voltage obtained at the brush is affected by the contact resistance between the resistor and the power supply tap, and the potential difference due to the on-resistance of the analog switch included in the tap selection means. Therefore, even if the position specifying voltage of the D/A converter is highly accurate, there is a problem that the accuracy of brush positioning is low.

An object of the present invention is to add a voltage detection tap on a resistor to generate first and second voltages, and use the difference between the first and second voltages as a reference for a position specifying D/A converter. Based on the concept of compensating the difference between the position specifying voltage of the D/A converter and the output voltage of the brush using the first or second voltage, the above-mentioned contact resistance and analog switch are calculated from the position control voltage of the brush. The object of the present invention is to eliminate the influence of the on-resistance of the brush, thereby improving the accuracy of brush positioning, and solving the problems of the conventional type described above.

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

FIG. 1 is a block circuit diagram of a conventional endless potentiometer. In FIG. 1, an endless, unnotched, annular resistor 1 has four power supply taps 2-1, 2-
2, 2-3, 2-4 are provided, and a brush 3
is slidably provided on the resistor 1. Taps 2-1, 2-2, 2-3, and 2-4 are connected to the analog switch 4 of the power supply analog switch circuit 4.
The reference voltage V _R1 or the ground voltage is selectively applied by -1, 4-2, 4-3, and 4-4. In this case, the CPU (not shown) sends analog switch control signals A ₀ and A ₁ to the circuit 4 according to the position of the brush 3, so that each analog switch 4-
1, 4-2, 4-3, 4-4 work. For example, when A ₀ A ₁ = “00”, the first terminal is selected. Hereinafter, when A ₀ A ₁ = "10", the second terminal is selected, and when A ₀ A ₁ = "01", the third terminal is selected, and A ₀ A ₁ ="11", the fourth terminal is selected. In FIG. 1, the case where A ₀ A ₁ =“00” is shown.
That is, the reference voltage V _R1 is applied to the first tap 2-1, and the ground voltage is applied to the third tap 2-3. Therefore, the current flows through analog switch 4-1, tap 2-1, resistor 1, and tap 2-3.
and flows through analog switch 4-3.

The position of the brush 3 is stopped by supplying the D/A converter 5 with digital position designating signals D ₀ , D ₁ , . . . , _Do. That is, the output analog voltage V ₁ of the D/A converter 5 and the brush 3 obtained through the buffer amplifier 6 with high input impedance.
The difference between the voltage V ₂ and the voltage V 2 is amplified by the differential amplifier 7, and the DC motor 9 is driven until the output voltage V ₃ of the amplifier 8 becomes zero volts. In this case, since the DC motor 9 is interlocked with the brush 3, the brush 3
When reaches the predetermined position, the output voltage of brush 3
V ₂ corresponds to the position specifying voltage V ₁ and as a result, the output voltage V ₃ of the amplifier 8 becomes zero volts and the DC motor 9, ie, the brush 3, stops. Note that in FIG. 1, V _R2 is a reference voltage applied to the D/A converter 5 and is constant. Further, 10 is a differentiator which generates a speed signal.

In the endless potentiometer shown in FIG. 1, the reference voltage V _R1 and the ground voltage are not directly applied to the taps. In other words, taps 2-1, 2-2, 2-3, 2-4 and resistor 1
There are contact resistances R ₁ , R ₂ , R ₃ , and R ₄ between
In addition, analog switches 41, 42, 43, 44
This is because there are on-resistances R ₄₁ , R ₄₂ , and R ₄₄ , so there is a voltage drop due to these resistances. However, considering these voltage drops, D/
Digital position designation signal D ₀ of A converter 5,
Since it is difficult to determine D ₁ ,...,D _o ,
The brush control voltage _V3 is affected by the above-mentioned contact resistance and on-resistance, and as a result, the actual stopping position of the brush 3 deviates from the designated position, resulting in a problem of low positioning accuracy.

FIG. 2 is a block circuit diagram of an endless potentiometer as an embodiment of the present invention. Second
In the figure, the same reference numerals are given to the same elements as those in FIG. 1. That is,
On resistor 1, tap 2 for power supply.
Between 1, 2-2, 2-3, 2-4, voltage detection taps 11-1, 11-2, 11-3, 11-
4 is provided. These taps 11-1,
Two taps from 11-2, 11-3, and 11-4 are selected by the voltage detection analog switch circuit 12, and as a result, two voltages V ₁₁ and V ₁₂ are applied to the buffer amplifiers 13-1 and 13-2. obtained for each output.

Analog switches 121, 122 of analog switch circuit 12 have the same configuration as analog switches 41, 42, 43, 44 of analog switch circuit 4, and analog switch control signals
Controlled by A ₀ and A ₁ . That is, when taps 2-1 (V _R1 voltage) and 2-3 (zero voltage) are selected, taps 11-1 and 11-2 are selected,
When taps 2-2 (V _R1 voltage) and 2-4 (zero voltage) are selected, taps 11-2 and 11-3 are selected, and taps 2-3 (V _R1 voltage) and 2-1 (zero voltage) are selected. voltage) is selected, taps 11-3, 11-4
is selected, tap 2-4 (V _R1 voltage), 2-2
(0 voltage) is selected, tap 11-4,1
1-1 is selected.

The difference V ₁₃ between the two voltages V ₁₁ and V ₁₂ mentioned above is obtained by the differential amplifier 14 with a gain of 1, and
is applied as a reference voltage. Here, since the buffer amplifiers 13-1 and 13-2 have high input impedance, almost no current flows through the analog switch circuit 12. Therefore, tap 11-
Contact resistance R ₁ ′, R ₂ ′, R ₃ ′, R ₄ ′ between 1, 11-2, 11-3, 11-4 and resistor 1, and on-resistance R ₁₂₁ of analog switch 121, 122, _R122
has almost no effect on voltages V ₁₁ , V ₁₂ , and V ₁₃ . As a result, the D/A converter 5 equally divides the voltage between the taps for voltage detection, for example, between the taps 11-1 and 11-2, using digital signals D ₀ , D ₁ , _... , Do to specify the position. can do.

When positioning the brush 3, it is sufficient to detect the difference between the voltage V ₁₆ of the brush 3 and the position specifying voltage V ₁₄ , but in this case, the voltage of the brush 3 is
In addition to the voltage drop from the tap 2 to the brush 3 position, the voltage drop includes the voltage drop due to the on-resistance R ₄₃ and the contact resistance R ₃ , and the voltage drop from the tap 2-3 to the tap 11-2. Therefore, the latter two voltage drops (this is the output voltage of buffer amplifier 13-2)
V ₁₂ ) to the position designation voltage of the D/A converter 5 V ₁₄
The adder 15 adds this to compensate. As a result, the contact resistance R ₃ and the on-resistance R ₄₃ have almost no influence on the differential voltage V ₁₇ . In this way, the brush 3 can be positioned with high precision between the voltage detection taps.

Further, the speed signal from the differentiator 10 is required in actual control. In this case, since it would be inconvenient if the electric field distribution at the sliding position of the brush 3 fluctuates, the voltage V _R1 ' is adjusted by the operational amplifier 16 so that the voltage V ₁₃ is constant. That is, if the voltage _V13 is constant, the voltage difference between the voltage detection taps will also be constant, and the operation will be stable.

In FIGS. 1 and 2, the total number of taps is eight, but it goes without saying that other numbers may be used. However, the number of taps for power supply is three or more, and the number of taps for voltage detection is also the same.

As explained above, according to the present invention, the influence of the contact resistance of the tap and the on-resistance of the analog switch can be eliminated from the brush control voltage _V17 , and therefore the brush positioning can be made highly accurate. , which is useful for solving the problems in the conventional type mentioned above.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a conventional endless potentiometer, and FIG. 2 is a block circuit diagram of an endless potentiometer as an embodiment of the present invention. 1...Resistor, 2-1, 2-2, 2-3, 2-4
…Power supply tap, 3…Brush, 4…Power supply analog switch circuit, 5…D/A converter, 9
...DC motor, 11-1, 11-2, 11-3,
11-4... Tap for voltage detection, 12... Analog switch circuit for voltage detection, V ₁₁ ... First voltage, V ₁₂ ...
Second voltage, A ₀ , A _{1 .} . . analog switch control signals, D ₀ , D ₁ , . . . , D _{o .} . . position designation signals.

Claims (1)

[Claims] 1. A resistor formed in an endless shape, at least three power supply taps provided at predetermined intervals along the resistor, one brush that slides on the resistor, and a brush at the position of the brush. a first tap selection means for selecting two power supply taps from among the power supply taps according to the power supply taps and supplying power;
In the endless potentiometer comprising a D/A converter for specifying the stop position of the brush, a voltage detection tap provided between each of the power supply taps and selection of the first tap selection means. second tap selection means for selecting two of the voltage detection taps to generate the first and second voltages in synchronization with the voltage detection tap;
The difference between the first and second voltages is used as the reference voltage of the D/A converter, and the difference between the designated voltage of the D/A converter and the output voltage of the brush is used as the first or second voltage.
An endless potentiometer, characterized in that the position of the brush is controlled by compensating with the voltage of the endless potentiometer.