JP3294757B2 - Printer head gap measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer head gap measuring apparatus for measuring a head gap for positioning a printer head at an optimum position with respect to a recording medium.

[0002]

2. Description of the Related Art In a dot printer, for example, a wire dot printer or a thermal printer, the distance between a print head and a printing surface of a sheet or a contact (pressing) state (here, referred to as a head gap) greatly increases print quality. Affect. On the other hand, the thickness of paper varies depending on the material and type, and it is necessary to adjust the head gap according to the thickness of the paper used for printing. Therefore, a conventional dot printer is known which automatically measures the thickness of the sheet before printing and automatically adjusts the head gap. There are various methods for measuring the thickness of paper.For example, when a mechanism that moves the print head away from or close to (contact with) the platen is driven by a motor, the excitation coil of the motor (stepping motor) is used. In some cases, the thickness of a sheet is measured by using a generated back electromotive voltage.

[0003] This is because, when the print head is moved so as to be in contact with the surface of the platen or the surface of the paper by driving the motor, and the back electromotive voltage is monitored during the movement, the print head is moved to the surface of the platen or the paper. When the motor comes out of contact with the surface of the platen, the waveform of the back electromotive voltage changes at the moment when the print head comes into contact with the surface of the platen or the surface of the paper. Therefore, based on the detection timing of the change in the waveform of the back electromotive voltage, the surface position of the platen and the surface position of the sheet are measured, and if the difference is calculated, the thickness of the sheet is obtained. If the optimum head gap is calculated from the thickness of the paper and the height of the print head is adjusted so as to be the head gap, high quality print quality can be obtained.

A circuit for detecting a back electromotive voltage of a motor for adjusting the height of a print head of a conventional dot printer is configured as shown in FIG. The motor is an A-phase coil 10
1, a B-phase coil 102 having an opposite phase (180 ° out of phase) with respect to the A-phase coil 101, and an A-phase coil 10
A C-phase coil 103 90 ° out of phase with respect to
A D-phase coil 104 having a phase opposite to that of the phase coil 103 (a phase shift of 270 ° with respect to the A-phase coil 101), and a driving circuit described below is provided for each of the coils 101 to 104 .

[0005] One end of each of the coils 104 to 105 is connected to the drive power supply Vm, and the other end is connected to ground (0 [V]) via NPN transistors 105 to 108, respectively. Driving transistors 105 to 10
8, NPN transistors 109 to 112 for control are connected between the base terminal and the collector terminal of each transistor.
Resistors 113 to 116 are connected between the emitter terminals. On the other hand, resistors 117 to 120 are connected between the base terminal and the emitter terminal of each of the transistors 109 to 112. An excitation control signal A supplied from a control unit (not shown) is supplied to a base terminal of each of the transistors 109 to 112.
f, Ar, Cf, and Cr are supplied, and the on-timing of each of the transistors 105 to 108 is controlled so that the above-described phase shift occurs, and the coils 101 to 104 are excited.

The connection point between the A-phase coil 101 and the collector terminal of the transistor 105 is connected to a diode 1 for preventing backflow.
21 is connected to the anode terminal of the diode 122 for backflow prevention, and the cathode terminal of the diode 121 and the cathode terminal of the diode 122 are connected to each other. It is connected to output a back electromotive voltage Ae. Similarly, the connection point between the C-phase coil 103 and the collector terminal of the transistor 107 is connected to the anode terminal of the diode 123 for backflow prevention, and the connection point between the D-phase coil 104 and the collector terminal of the transistor 108 is used for backflow prevention. Is connected to the anode terminal of the diode 124, and the cathode terminal of the diode 123 and the cathode terminal of the diode 124 are connected to each other to output the back electromotive force Ce.

FIG. 6 is a circuit diagram showing a circuit that monitors the back electromotive voltages Ae and Ce to determine step-out of the motor.
The A-phase (B-phase) back electromotive force Ae is input to the connection point between the cathode terminals of the constant voltage diodes 131 and 132 whose cathode terminals are connected to each other. The anode terminal of one of the constant voltage diodes 131 is connected to the drive power supply Vm,
The anode terminal of the other constant voltage diode 132 is connected to ground (0 [V]) via a series voltage dividing circuit composed of two resistors 133 and 134. One constant voltage diode 131 clamps the head waveform of the back electromotive voltage Ae at a predetermined voltage by the Zener voltage. When the back electromotive voltage Ae becomes lower than the Zener voltage, the other constant voltage diode 132 cuts off current supply to the resistors 133 and 134. That is, no voltage is applied to the series voltage dividing circuit.

Similarly, the back electromotive voltage Ce of the C phase (D phase) is
Constant-voltage diodes 13 whose cathode terminals are connected to each other
5,136 is input to the connection point of its cathode terminal.
The anode terminal of one constant voltage diode 135 is connected to the driving power supply Vm, and the anode terminal of the other constant voltage diode 136 is connected to ground (0 [V]) via a series voltage dividing circuit composed of two resistors 137 and 138. )It is connected to the.

The voltage dividing output point of the series voltage dividing circuit composed of the resistors 133 and 134 is connected to the inverting input terminal of the comparator 139 via the resistor 140. Comparator 13
The non-inverting input terminal of No. 9 has a voltage dividing output of a series voltage dividing circuit composed of two resistors 142 and 143 for generating a reference voltage connected between the control power supply Vp and the ground via a resistor 141. Points are connected. A positive feedback resistor 144 is connected between the non-inverting input terminal and the output terminal of the comparator 139, and its output terminal is connected to the pull-up resistor 1
The control signal is pulled up by 45 to the control power supply Vp, and the output signal is output to a control unit (not shown) as a determination signal Oa for detecting out-of-step of the motor. Similarly, resistors 137 and 1
The voltage dividing output point of the series voltage dividing circuit 38 is connected to the inverting input terminal of the comparator 146 via the resistor 147. The non-inverting input terminal of the comparator 139 has
Two resistors 149 and 1 for generating a reference voltage connected between the control power supply Vp and the ground via the resistor 148
The divided voltage output point of the series voltage dividing circuit composed of 50 is connected. A resistor 151 for positive feedback is connected between the non-inverting input terminal and the output terminal of the comparator 146, and its output terminal is pulled up to a control power supply Vp by a pull-up resistor 152 to output an output signal of the motor. This is output to a control unit (not shown) as a determination signal Oc that has detected step-out.

FIG. 7 is a diagram showing a flow of a head gap measurement process performed by a control unit (not shown) based on the determination signals Oa and Oc from the above-described circuit for determining out-of-step of the motor. First, a process for discharging the paper remaining on the paper transport path is performed, and when the paper discharge process is completed, a process for retracting (moving) the print head to a position where the print head does not contact the platen (non-step-out area) is performed. . Here, the motor is driven for several pulses in the rotation direction in which the print head approaches the platen, and the high-level pulse width (time) of the judgment signal Oa or Oc at that time is measured and stored as measurement data. Since the measurement data of the high-level pulse width is the same as the number of pulses, the average value is calculated and set as the normal pulse width.

Next, the motor is started to be driven in the direction in which the print head approaches (contacts) the platen, and the high-level pulse width of the determination signal Oa or Oc is measured. The drive of the motor is continued until a pulse narrower (shorter) than the pulse width is detected, that is, until the step-out of the motor is detected. Judgment signal Oa or O
c, when the step-out of the motor is detected, the position of the print head at that time (the rotational position of the motor) is set as the home position, and the motor is moved in the direction in which the print head separates from the platen (the reverse direction). Driving is performed by the number of pulses set in advance so that a sufficient space between the plate and the platen can be ensured so as not to hinder the sheet supply. When the drive of this motor is completed and a sufficient space is secured between the print head and the platen so as not to hinder the paper supply, the paper is fed and conveyed, and the space between the print head and the platen is The conveyance of the paper is stopped by inserting the paper.

Here, the motor is started to be driven in the direction in which the print head approaches (contacts) the platen, and the high-level pulse width of the determination signal Oa or Oc is measured. The drive of the motor is continued until a pulse shorter than the pulse width is detected, that is, until the step-out of the motor is detected. When the step-out of the motor is detected from the determination signal Oa or Oc, the position of the print head (distance from the home position) at that time becomes the thickness of the sheet, and the optimum print head and sheet ( A gap (head gap) with the platen) is calculated, the calculated head gap is set, and the head gap measurement processing ends. The height of the print head is adjusted based on the head gap set as described above, and after the adjustment, printing is performed on the paper.

FIGS. 8 and 9 show a current waveform or a voltage waveform at each point of the circuit shown in FIGS. 5 and 6 for the A-phase coil 101. FIG. The waveforms of the other excitation phases (driving circuits and detection circuits of the coils 102 to 104) are basically the same except for the timing shift, so that the drawings and description are omitted here. FIG. 8A illustrates a voltage waveform of a drive control signal supplied to the transistor 109. The following waveform shows a waveform generated in response to the drive control signal. FIG. 8B shows the state during normal driving (
7 shows a current waveform of a drive current (which is affected by a back electromotive current) flowing through the A-phase coil 101 during normal operation. FIG. 8 (c)
Shows a voltage waveform due to the back electromotive force generated at the cathode terminal of the constant voltage diode 131 during normal driving (normal operation). FIG. 8 (d) shows the resistance 13 during normal driving (normal operation).
3 shows a voltage waveform of a divided output of a series voltage dividing circuit composed of 3,134. FIG. 9A shows a voltage waveform of the determination signal Oa output from the comparator 139 during normal driving (normal operation).

FIG. 8E shows an A-phase coil 101 at the time of step-out.
Shows the current waveform of the drive current (which is affected by the back-EMF) flowing through the IGBT. FIG. 8F shows a voltage waveform due to the back electromotive force generated at the cathode terminal of the constant voltage diode 131 at the time of step-out. FIG. 8 (g) shows the resistances 133, 13
4 shows a voltage waveform of a divided output of a series voltage dividing circuit composed of No. 4;

FIG. 9B shows the state of the comparator 13 at the time of step-out.
9 shows a voltage waveform of a determination signal Ob output from FIG.

That is, when the drive control signal changes from on to off, back electromotive force is generated. At this time, the voltage waveform that is equal to or higher than the voltage value set by the zener voltage is clamped by the constant voltage diode 131 at the set voltage (it does not become a sharp peak waveform like a surge). Further, since the voltage waveform below the voltage value set by the Zener voltage is cut off by the constant voltage diode 132, the cut-off voltage waveform is applied to the divided voltage output of the series voltage dividing circuit composed of the resistors 133 and 134. No corresponding waveform is generated and 0
[V]. Therefore, the comparator 139 compares the divided output of the series voltage divider composed of the resistors 133 and 134 with the reference voltage Vr of the series voltage divider composed of the resistors 142 and 143, and the determination signal Oa is a constant voltage. The signal has a pulse width substantially equal to the time clamped by the diode 131.

At the time of step-out, the back electromotive force is reduced because the rotation of the motor is hindered, and the waveform of the back electromotive voltage is also reduced. Therefore, the time (pulse width) clamped by the above-described constant voltage diode 131 is shorter (narrower) during step-out than in normal operation. For example, an intermediate time between the normal pulse width and the step-out pulse width is set, and if the pulse width of the determination signal is shorter than the set time, the step-out is determined.

[0018]

SUMMARY OF THE INVENTION Each of the coils 101 to 10
And the constant voltage diodes 131, 132, 135, and 13;
6, the voltage waveform input to the comparators 139 and 146 is changed by the reference voltage of the series voltage dividing circuit composed of the resistors 142 and 143 and the series voltage divided by the resistors 149 and 150 due to the variation of the Zener voltage of FIG. Since the waveform is not always suitable for the determination based on the reference voltage of the voltage circuit, there is a problem that the out-of-step determination accuracy is reduced if the waveform is inappropriate.

For example, constant voltage diodes 131 to 134
When the difference between the voltage to be clamped by the Zener voltage and the reference voltage increases, the waveform of the step-out determination signal gradually drops after clamping by the constant voltage diode, so that the accuracy of the step-out determination decreases. . That is, the step-out is not determined until the motor finally stops (the pulse width of the determination signal becomes 0).

Further, when a plate-shaped platen is used, for example, as shown in FIG. 10, the signal is input to a comparator due to a load fluctuation of a mechanical mechanism such as a deflection of the platen or a variation of a motor rod. However, there is a problem in that the voltage waveform of the divided voltage output is deformed and it is determined that there is no step-out even though the step-out actually occurs, and the accuracy of the determination of step-out is reduced.

A waveform as shown in FIG. 10 may also be generated when the print head comes into contact with the surface of the platen or the surface of the paper. It does not coincide with the contact of the print head with the platen surface or the paper surface, but with the state in which the print head is pressed into the platen or paper with a predetermined pressing force.

That is, the conventional head gap measuring apparatus has a problem that the thickness of the paper cannot be accurately measured in a strict sense. Furthermore, as described above, when measuring the head gap, the print head is moved until the paper is pressed with a predetermined pressing force.Therefore, in a printer using an ink ribbon, the print head also applies a predetermined pressing force to the paper with the ink ribbon. There is a problem that the paper is pushed in and soils the paper.

Therefore, the present invention provides an output voltage of a driving power supply,
The platen surface position and the paper surface position can be measured accurately without being affected by the zener voltage of the constant voltage diode, the variation of the motor rod, and the load fluctuation. It is an object of the present invention to provide a head gap measuring device for a printer without any problem.

[0024]

The invention corresponding to claim 1 is:
A motor that generates and drives a plurality of excitation phases by energizing a plurality of excitation coils by turning on and off an excitation transistor, and a contact that comes into contact with the platen from a position distant from the platen by driving the motor. A back electromotive voltage detection circuit that clamps the head of the back electromotive voltage waveform generated in the exciting coil to a predetermined voltage value, and a back electromotive voltage waveform whose head waveform is clamped by the back electromotive voltage detection circuit. A voltage drop detecting means for monitoring a change and detecting a voltage drop from a constant voltage value; and a position of a contact member when a voltage drop is detected by the voltage drop detecting means when the storage medium is not supplied or stored in advance. A head gap calculating means for calculating a head gap from the surface position of the platen and the position of the contact member when the voltage drop is detected by the voltage drop detecting means when the recording medium is supplied. In which the provided.

According to a second aspect of the present invention, in the first aspect of the present invention, the back electromotive voltage detecting means includes, as a power supply terminal, a series circuit of a pair of a constant voltage diode having a cathode terminal connected to each other and a resistance voltage dividing circuit. The backflow prevention diode has its anode terminal connected to the connection point between the excitation coil and the excitation transistor, and its cathode terminal connected between the cathode terminals of each constant voltage diode of the back electromotive voltage detection circuit. The voltage drop detecting means connects the voltage dividing output point of the resistance voltage dividing circuit to the inverting input terminal of the comparing circuit, and at the same time through a series circuit of a capacitor and a parallel circuit in which two diodes are bidirectionally connected. And a connection point between the parallel circuit and the capacitor is connected to the non-inverting input terminal of the comparison circuit via a resistor.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a head gap measuring device of a printer to which the present invention is applied. 1 is a print head. The print head 1 as a contact member is fixed to a linear drive plate 3 meshed with the teeth of the gear 2. The motor 4 rotates the gear 2 by a rotation transmission mechanism (not shown). Accordingly, the rotation of the motor 4 controls the movement of the print head 1 in the vertical direction via the gear 2 and the linear drive plate 3.

A flat platen 5 is disposed to face the printing surface (lower end surface) of the printing head 1, and an ink ribbon 6 is inserted between the printing surface of the printing head 1 and the platen 5. I have. Further, the ink ribbon 6 and the platen 5 inserted in front of the print surface of the print head 1 are provided.
The sheet 7 as a recording medium is conveyed between the steps.

In practice, a guide plate (not shown) for guiding an ink ribbon inserted in front of the print surface of the print head 1 is integrated with the print head 1 and furthermore, The guide plate comes in contact with the platen 5 or the paper 7 as a contact member when measuring the head gap, and the print surface of the print head 1 is Or, it does not contact the paper 7. Further, an optical transmission type home position sensor 8 is disposed above the linear drive plate 3, and when a sufficient space is secured between the print head 1 and the platen 5 (the paper 7). In addition, the upper end of the linear drive plate 3 just blocks the optical path of the home position sensor 8.

FIG. 2 is a block diagram showing the main circuit configuration of the head gap measuring device.

Reference numeral 11 denotes a CPU (cen) constituting the control unit main body.
tral processing unit). A ROM (read onl) storing program data of the processing performed by the CPU 11
y memory) 12, RAM (random accumulator) in which various memory areas used when the CPU 1 performs processing are formed.
ss memory 13, an I / O (input / output) port 15 for inputting an output signal from the home position sensor 8 and a back electromotive voltage determination circuit 14 described later, and a motor drive circuit 16 for controlling the drive of the motor 4, Each is connected to the CPU 11 via a system bus 17. Although not shown, the system bus 17 is connected to a circuit for driving and controlling an internal memory, an external memory, a print head, a display, a keyboard, a transport mechanism, and the like as a printer. That is, this head gap measuring device is not a single device,
Built into the printer configuration.

FIG. 3 is a circuit diagram showing the back electromotive voltage determination circuit 14. Since the configuration of the motor is the same as the circuit configuration described in FIG. 5 of the related art, the description is omitted here, and the reference numerals in FIG. 5 are used. A
The back electromotive voltage Ae of the phase (B phase) is input to the connection point between the cathode terminals of the constant voltage diodes 21 and 22 having their cathode terminals connected to each other. The anode terminal of one of the constant voltage diodes 21 is connected to the driving power supply Vm, and the anode terminal of the other constant voltage diode 22 is connected to ground (0 [0] via a series voltage dividing circuit composed of two resistors 23 and 24. V]). One of the constant voltage diodes 21 has a back electromotive voltage Ae due to its Zener voltage.
Is clamped at a predetermined voltage. When the back electromotive voltage Ae becomes lower than the Zener voltage, the other constant voltage diode 22 cuts off current supply to the resistors 23 and 24. That is, no voltage is applied to the series voltage dividing circuit. Similarly, the back electromotive voltage Ce of the C phase (D phase)
Is a constant voltage diode 2 having cathode terminals connected to each other.
5 and 26 are input to the connection points of their cathode terminals. The anode terminal of one of the constant voltage diodes 25 is connected to the drive power supply Vm, and the anode terminal of the other constant voltage diode 26 is connected to the ground (0 [0] via a series voltage dividing circuit composed of two resistors 27 and 28. V]).

The voltage dividing output point of the series voltage dividing circuit composed of the resistors 23 and 24 is connected to the inverting input terminal of the comparator 29. The divided output point is connected to one end of a diode parallel circuit in which two diodes 30 and 31 are connected bidirectionally (in opposite directions), and the other end of the diode parallel circuit is connected via a capacitor 32. And to the non-inverting input terminal of the comparator 29 via a resistor 33. Between the non-inverting input terminal and the output terminal of the comparator 29,
A resistor 34 for positive feedback is connected, and its output terminal is pulled up to a control power supply Vp by a pull-up resistor 35, and the output signal is output at the moment when the print head 1 contacts the surface of the platen or the surface of the paper (completely). Is output to the I / O port 15 as a determination signal Oa indicating the moment when the step-out occurs before the step-out occurs.

Similarly, the voltage dividing output point of the series voltage dividing circuit composed of the resistors 27 and 28 is connected to the inverting input terminal of the comparator 36. The partial pressure output point is
Two diodes 37 and 38 are bidirectional (opposite to each other)
) Is connected to one end of a diode parallel circuit. The other end of the diode parallel circuit is connected to ground via a capacitor 39 and to the non-inverting input terminal of the comparator 36 via a resistor 40. ing. A positive feedback resistor 41 is connected between the non-inverting input terminal and the output terminal of the comparator 36, and its output terminal is pulled up to a control power supply Vp by a pull-up resistor 42, and its output signal is A determination signal O indicating the moment when the print head 1 contacts the surface of the platen or the surface of the paper.
The signal is output to the I / O port 15 as c.

FIG. 4 is a diagram showing the flow of the head gap measuring process performed by the CPU 11. First, a process for discharging the paper remaining on the paper transport path is performed, and when the paper discharging process is completed, a process for returning to the home position is performed. In this home position return processing, first, after confirming that the detection signal from the home position sensor 8 is a signal indicating that the optical path is not interrupted, the motor 4
Is rotated in the rotation direction in which the print head 1 is separated from the platen 5 (moves upward), and the home position sensor 8 is rotated.
This is a process of stopping the motor 4 at the moment when the detection signal from the CPU changes to a signal indicating that the optical path is blocked. If the first detection signal from the home position sensor 8 is a signal indicating that the optical path is interrupted, the print head 1 controls the motor 4 until the signal indicating that the optical path is not interrupted. Approaching (moving downwards)
After the rotation is performed in the rotation direction, the above processing is performed again. When the home position return processing is completed, the motor 4 is driven for several pulses in the rotation direction in which the print head 1 approaches the platen 5, and the low level pulse of the determination signal Oa or Oc from the back electromotive voltage determination circuit 14 at that time. Width (time
) Is measured, measured data is stored. Since the low-level pulse width measurement data has the same number of pulses, the average value is calculated and set as the normal pulse width.

Next, the motor 4 is started to be driven in the rotational direction in which the print head 1 approaches (contacts) the platen 5, and the low-level pulse width of the determination signal Oa or Oc from the back electromotive voltage determination circuit 14 is reduced. The pulse width is measured until a pulse width that is narrower (shorter) by a predetermined amount or more than the set normal pulse width is detected, that is, until the moment when the print head 1 contacts the surface of the platen 5 is detected. , And continue driving the motor. When a signal that is narrower (shorter) by a predetermined amount or more than the normal pulse width set from the determination signal Oa or Oc is detected, the position of the print head 1 (the rotational position of the motor 4) at that time is changed from the home position to the platen. 5
Set as the distance to the surface of.

Next, the home position return processing is performed again. When the home position return processing is completed,
The sheet is supplied and conveyed, the sheet is inserted between the print head 1 and the platen 5, and the conveyance of the sheet is stopped. At this point, the print head 1 moves the motor 4 close to the platen 5 (contact
), The driving is started in the rotating direction
The pulse width of the low level of the determination signal Oa or Oc is measured, and a pulse width that is narrower (shorter) by a predetermined amount or more than the set normal pulse width is detected, that is, the print head The motor continues to be driven until the moment 1 contacts the surface of the platen 5. When a signal that is narrower (shorter) by a predetermined amount or more than the normal pulse width set from the determination signal Oa or Oc is detected, the position of the print head 1 (the rotation position of the motor 4) at that time is changed from the home position to the paper. 7, the thickness of the paper 7 is calculated from the already set home position and the distance from the surface of the platen 5, and the optimum head gap is calculated and set based on this thickness. I do.

When the process of calculating and setting the head gap is completed, the process of returning to the home position is performed again.
Is driven in the rotation direction in which the print head 1 approaches the platen 5 by the number of pulses (gap setting pulse number) positioned at the calculated head gap position, and the print head 1 is optimally mounted on the platen 5 or the paper 7. Then, the head gap measurement process is terminated after positioning at a suitable head gap position. When the head gap measurement processing is completed, normal printing processing is performed.

In this embodiment having such a configuration, the back electromotive force generated in each of the coils 101 and 102 (103 and 104) is connected to diodes 121 and 122 (123 and 124) for preventing backflow. The voltage is output to the back electromotive voltage determination circuit 14 via the control circuit.

In the back electromotive voltage determination circuit 14, the head of the back electromotive voltage waveform is clamped by the constant voltage diode 21 (25) at a predetermined voltage determined by its zener voltage.

Furthermore, since the constant voltage diode 22 (26) is in a non-conducting state in a portion of the waveform of the back electromotive voltage below the zener voltage of the constant voltage diode 22 (26), the two resistors 23, 24 (27, 28) is greater than the Zener voltage of the constant voltage diode 22 (26) having a counter electromotive voltage waveform, and the head of the voltage divider output waveform is output from the constant voltage diode 21 (26). 25) corresponds to a waveform clamped at a predetermined voltage.

This divided voltage output waveform is directly supplied to the comparator 2
9 (36) and a capacitor 32 (39) connected to ground via a diode parallel circuit in which two diodes 30, 31 (37, 38) are bidirectionally connected. It is input to one end, and is input from one end of this capacitor to the non-inverting input terminal of the comparator 29 (36) via the resistor 33 (40). The circuit including the diode parallel circuit, the capacitor 32 (39), and the resistor 33 (40) has a delay function and moderates the change of the divided voltage output waveform.

Therefore, the divided voltage output waveform is input to the inverting input terminal of the comparator 29 (36) in real time, while the divided voltage output waveform is delayed to the non-inverting input terminal of the comparator 29 (36). Input is made with a gradual change. Therefore, when the divided voltage output waveform rises, the voltage input to the inverting input terminal becomes higher than the voltage input to the non-inverting input terminal, so that the output voltage of the output terminal of the comparator 29 (36) becomes low level, Conversely, when the divided voltage output waveform drops, the voltage input to the inverting input terminal becomes lower than the voltage input to the non-inverting input terminal.
The output voltage of the output terminal of the comparator 29 (36) becomes high level.

That is, the comparator 29 (36)
Output is a constant voltage diode 2 with a back electromotive force waveform
1 (25) becomes low level corresponding to the portion clamped by, and becomes high level corresponding to the other portions.

As described above, according to this embodiment, the constant voltage diode 21 (25) for clamping the head of the back electromotive voltage waveform at a predetermined voltage, and the constant voltage diode 21 (25) for cutting the portion of the back electromotive voltage waveform below the zener voltage. A voltage diode 22 (26);
A series voltage dividing circuit composed of resistors 23 and 24 (27, 28) for dividing the waveform processed by these constant voltage diodes, and a diode 30 for applying a delayed action to the divided voltage output from the series voltage dividing circuit. 31 (37, 38) and a capacitor 32 (3)
9), a resistor 33 (40), and a comparator 29 () which directly inputs the divided output from the series voltage dividing circuit to the inverting input terminal, and inputs a signal obtained by delaying the divided output to the non-inverting input terminal. 36), the rising and falling changes of the back electromotive force waveform whose head waveform is clamped at a predetermined voltage by the constant voltage diode 21 (25) can be detected, and the head of the back electromotive force waveform can be detected. Only the clamp portion of the portion can be detected as a low pulse signal.

Therefore, the output voltage of the back electromotive force drive power supply,
The back electromotive voltage is obtained at the moment when the print head 1 contacts the platen 5 or the paper 7, that is, before the motor does not completely step out, without being affected by the variation of the zener voltage of the constant voltage diode, the variation of the rod of the motor, and the load. The deformation appearing in the waveform can be accurately detected as a reduction in the time of the clamp portion by the constant voltage diode 21 (25), and the surface position of the platen 5 and the surface position of the paper 7 can be accurately measured. In addition, the moment when the print head 1 contacts the paper 7 can be accurately detected.
Can be prevented from being pressed against the sheet 7, so that it is possible to prevent the sheet 7 from being stained due to the ink ribbon 6 being pressed against the sheet 7.

In this embodiment, the home position sensor 8 is provided, and the distance from the home position to the surface of the platen 5 and the home position are measured with respect to the home position based on the detection of the home position sensor 8 when measuring the head gap. Since the distance from the position to the surface of the sheet 7 is measured, the surface position of the platen 5 and the surface position of the sheet 7 can be measured more accurately than when a step-out position of a conventional motor is used as a reference.

In this embodiment, since the head gap is measured using the print head,
There is no need to separately provide a detecting member that comes into contact with the surface of the platen or the surface of the sheet and a moving mechanism that moves the detecting member, so that the cost can be reduced and the entire apparatus can be downsized.

Further, since head gap measurement is performed using a print head, the present invention is not limited to a printer using a flat platen, but is also applicable to a printer using a cylindrical platen. Applicable.

[0049]

As described in detail above, according to the present invention,
It is possible to accurately measure the platen surface position and paper surface position without being affected by the output voltage of the drive power supply, the zener voltage of the constant voltage diode, the variation of the motor rod, and the load fluctuation. It is possible to provide a printer head gap measuring device that does not stain a sheet by measurement.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a head gap measuring device of a printer according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a main circuit configuration of the head gap measuring device according to the embodiment;

FIG. 3 is a circuit diagram showing a back electromotive voltage determination circuit of the head gap measurement device according to the embodiment.

FIG. 4 is a view showing a flow of a head gap measuring process performed by the head gap measuring device of the embodiment.

FIG. 5 is a circuit diagram showing a motor driving circuit and a circuit for detecting a back electromotive voltage.

FIG. 6 is a circuit diagram showing a conventional circuit for determining motor out-of-step from a back electromotive voltage of the motor.

FIG. 7 is a diagram showing a flow of a head gap measuring process performed in a conventional head gap measuring device.

FIG. 8 is a diagram showing a current waveform or a voltage waveform at each point of a conventional circuit for detecting a back electromotive voltage of a motor and a circuit for determining motor out-of-step from the back electromotive voltage of the motor.

FIG. 9 is a diagram showing a divided voltage output waveform and a determination signal waveform during normal motor drive and motor step-out in a conventional circuit for determining motor step-out from a back electromotive voltage of the motor.

FIG. 10 is a diagram showing a conventional divided voltage output waveform and a determination signal which are deformed due to a load fluctuation of a mechanical mechanism such as a deflection of a platen or a variation in a rod of a motor in a circuit for determining motor out-of-step from a back electromotive voltage of the motor. The figure which shows an example of the waveform of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Print head, 3 ... Linear drive plate, 4 ... Motor, 5 ... Platen, 7 ... Paper, 8 ... Home position sensor, 11 ... CPU, 14 ... Back electromotive voltage determination circuit, 21, 22, 25, 26 ... Constant Voltage diodes 23, 24, 27, 28, 33, 40 ... resistors, 29, 36 ... comparators, 30, 31, 37, 38 ... diodes, 32, 39 ... capacitors.

Claims (2)

(57) [Claims] 1. A motor driven by generating and exciting a plurality of excitation phases by energizing a plurality of excitation coils by an on / off operation of an excitation transistor; A back electromotive voltage detection circuit that clamps the head of the waveform of the back electromotive voltage generated in the exciting coil to a predetermined voltage value; and the head waveform is clamped by the back electromotive voltage detection circuit. A voltage drop detecting means for monitoring a change in the waveform of the back electromotive voltage, and detecting a voltage drop from the constant voltage value, and the voltage drop detecting means when the voltage drop is detected by the voltage drop detecting means when the storage medium is not supplied. The position of the contact member or the surface position of the platen stored in advance and the position of the contact member when the voltage drop is detected by the voltage drop detecting means during supply of the recording medium. Head gap measuring device of the printer, characterized in that a head gap calculating means for calculating the Luo head gap. 2. The back electromotive voltage detecting means is configured by connecting a series circuit of a pair of a constant voltage diode having a cathode terminal connected to each other and a resistance voltage dividing circuit to a power supply terminal. The anode terminal is connected to a connection point between the excitation coil and the excitation transistor, the cathode terminal is connected between the cathode terminals of the constant voltage diodes of the back electromotive voltage detection circuit, and the voltage drop detection means includes: A voltage dividing output point of the resistor voltage dividing circuit is connected to an inverting input terminal of a comparing circuit, and two diodes are connected to ground via a series circuit of a bidirectionally connected parallel circuit and a capacitor. 2. The printer according to claim 1, wherein a connection point between the parallel circuit and the capacitor is connected to a non-inverting input terminal of the comparison circuit via a resistor. Head gap measuring device.