JPH08156245A - Drive power supply circuit of ink jet head - Google Patents

Abstract

PURPOSE: To prevent the overvoltage output of the output voltage of a drive power supply circuit. CONSTITUTION: When a voltage setting circuit 2 is not normally connected and a resistor 1 is disconnected, output voltage Vout rises to reach the voltage turning a Zener diode 15 ON. When the Zener diode 15 is turned ON, the output voltage Vout does not become the voltage at the point of time when the Zener diode is turned ON or more. The output voltage at that time becomes Vout= Vref (reference power source voltage) + Vz (Zener voltage). That is, the output voltage of a drive power supply circuit reaches the highest voltage of the formula. If the sum of the Zener voltage Vz and the reference power supply voltage Vref is matched with the max. rated voltage of a head driving circuit or the head or less, the drive power supply circuit does not output overvoltage exceeding the max. rated voltage of the head driving circuit or the head to prevent the destruction of the head driving circuit or the head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power source for an ink jet head drive power source circuit having a replaceable print head unit.

[0002]

2. Description of the Related Art An ink jet recording apparatus is provided with a print head having a plurality of ink ejection ports and an energy generator for generating energy for ejecting the ink from the ejection ports. Recording is performed by driving the energy generator based on the signal to cause ink droplets to fly from the corresponding ink ejection ports and adhere to the paper.

Conventionally, as such an ink jet recording apparatus, there has been proposed one in which a print head portion including an ink supply system such as a print head and an ink tank is unitized and each unit is replaceable.

In such an ink jet recording apparatus,
Variations in the processing accuracy of the ink ejection diameter and shape of the print head among the units, or the characteristics of the energy generator, that is, the electric-thermal energy converter such as a heating element and the electric-mechanical energy converter such as a piezoelectric element. There are variations and the like. Due to this variation, the optimum drive voltage of the head, that is, the head drive voltage for obtaining the optimum ink ejection state may be different for each print head unit. For example, when the standard head drive voltage is 24V, some print head units have an optimum ejection state at 23V, and other print head units have a variation such that 25V shows an optimal ejection state. .

Therefore, in order to eliminate the variation in the optimum drive voltage of the head, when the print head unit is replaced, the drive voltage of the print head is set so that the optimum ejection state is obtained each time. It was necessary to adjust to an appropriate voltage corresponding to. However, it is very time-consuming and difficult to make an accurate adjustment by measuring whether or not the print head unit is optimally ejected every time it is replaced and adjusting the optimal drive voltage based on that. It was

In order to solve such a problem, an ink jet recording apparatus having a driving power supply circuit as shown in FIG. 4 has been proposed. The circuit shown in FIG. 4 is generally called a step-up chopper regulator,
The output voltage Vout is higher than the input voltage Vin.

The schematic configuration and operation of FIG. 4 will be described. The print head unit is provided with a voltage setting circuit 41 composed of a resistor 40 having a resistance value Rb for setting an optimum driving voltage, and is connected to the driving power supply circuit through an interface circuit (not shown). When the transistor 42 is turned on, a current 45 flows from the input 43 connected to the power source (not shown) of the voltage Vin through the coil 44. At this time, the collector-emitter voltage V of the transistor 42
cesat is Vout> Vcesa as compared with the voltage Vout appearing at the output 46 because the transistor 42 is in a saturated state.
t. Therefore, no current flows to the output through the diode 47.

The coil 44 stores energy during the ON period Ton of the transistor 42, and when the transistor 42 is turned off, a counter electromotive force is generated in the coil 44, and a current 49 flows while charging the capacitor 48 through the diode 47. .

The output voltage Vout can be controlled by adjusting the length of the ON period Ton, which is performed by the control circuit 50. The voltage Vref generated by the reference voltage source 51 is input to one input terminal of the control circuit 50, and the resistors 52, 40,
The voltage divided by the output voltage dividing circuit composed of 53 is input to the other input terminal. This control circuit 5
0 changes the output so that the both input voltages become equal, and adjusts the time of the current flowing into the base of the transistor 42, so that the ON period T of the transistor is 0.
Adjust on. In this way, the output voltage Vout higher than the input voltage Vin can be obtained at the output 46.

The voltage Vout generated at the output 46 can be expressed by the following equation.

[0011]

[Equation 1]

In the above equation, if the resistance value Rb is properly selected, the voltage Vout can be set to the optimum head drive voltage. Therefore, it was possible to automatically control the head drive voltage for each print head unit to a unique optimum value without any special adjustment work.

On the other hand, in the ink in the unit, the physical properties such as the viscosity and the surface tension have a high temperature dependency, and the change of the physical properties has a great influence on the ejected state of the ink. In general, the ink has a high viscosity at low temperatures and is difficult to eject normally. Therefore, the optimum driving voltage of the head varies depending on the environmental temperature of the place of use. For example, a print head unit having an optimum head drive voltage of 24 V at 25 ° C. shows an optimum discharge state at 30 V at 10 ° C. and an optimum discharge state at 18 V at 35 ° C. Was there. Therefore, following the temperature change of the optimum drive voltage of this head,
It has been necessary to detect the temperature of the print head or the vicinity thereof and change the drive voltage of the print head to an appropriate voltage corresponding to the detected temperature so that the ink is always in the optimum ejection state.

Therefore, conventionally, in the drive power supply circuit as shown in FIG. 4, the resistor 40 in the voltage setting circuit 41 is provided with a temperature sensitive element having a temperature characteristic, for example, a negative characteristic temperature coefficient thermistor or a positive characteristic temperature coefficient. It has been proposed to replace the thermistor with a temperature-sensitive resistor. This makes it possible to supply a drive voltage suitable for the physical properties of the ink in response to changes in the head temperature.

[0015]

However, in the drive power supply circuit for the ink jet head of the conventional example as described above, the print head unit is not mounted on the apparatus main body or is incompletely mounted on the apparatus main body. The power of the main body was sometimes turned on. That is, the drive power supply circuit may operate while the resistor 40 of the voltage indicator 41 is not connected to the drive power supply circuit. In such a state, the above formula 1
Since the resistance value Rb therein is equivalent to infinity, the output voltage of the drive power supply circuit exhibits the output upper limit voltage value of the drive power supply circuit, and the head drive circuit or the head drive circuit is caused by an overvoltage exceeding the maximum rated voltage of the head itself. There is a problem that the head is destroyed.

Therefore, the voltage setting circuit 41 is provided in the driving power supply circuit.
By installing a resistor in parallel with the resistor 40 of
Even if not connected, it is possible to limit it so that it does not reach the output upper limit voltage of the drive power supply circuit by making it equal to or lower than the maximum rated voltage of the head drive circuit or head. However, if the head drive circuit or the head is used in the vicinity of the maximum rated voltage, the resistance value Rb of the resistor 40 must be set to a high resistance value, which causes a problem that the circuit configuration becomes very difficult.

Even if the ink jet recording apparatus is provided with a mechanism for detecting whether or not the print head unit is attached to the apparatus main body, the interface circuit of the voltage setting circuit 41 is defective, that is, the resistor 40 is not connected. In addition, avoid the problem that the output voltage of the drive power supply circuit becomes the output upper limit voltage value of the drive power supply circuit and exceeds the maximum rated voltage of the head drive circuit or the head itself and destroys the head drive circuit or the head due to overvoltage. I couldn't.

As a further big problem, when a negative characteristic temperature coefficient thermistor is used in place of the resistor 40, if the power of the apparatus is turned on within the temperature range assumed for the ink jet recording apparatus, the negative characteristic temperature coefficient thermistor The resistance value is extremely large. At that time, the drive power supply circuit outputs an overvoltage that exceeds the maximum rated voltage of the head drive circuit and the head, and there is a problem that the head drive circuit and the head are destroyed.

When a positive temperature coefficient coefficient thermistor is used instead of the resistor 40, the resistance value of the positive temperature coefficient coefficient thermistor is changed when the power of the apparatus is turned on at a temperature above the expected temperature range of the ink jet recording apparatus. , Which is an extremely large value. At that time, the drive power supply circuit outputs an overvoltage that exceeds the maximum rated voltage of the head drive circuit and the head, and there is a problem that the head drive circuit and the head are destroyed.

The present invention has been made in order to solve the above-mentioned problems of the conventional method. The object of the present invention is to prevent the output voltage of the drive power supply circuit from changing in any state of the print head unit. An object of the present invention is to provide an inkjet head drive power supply circuit that does not exceed the maximum rated voltage of the head drive circuit or head.

[0021]

In order to achieve this object, an ink jet head drive power supply circuit according to the present invention is provided in an ink jet recording apparatus in which a replaceable print head unit can be mounted, and the print head unit is provided in the print head unit. A voltage setting unit for supplying a driving voltage, the voltage setting unit having a circuit element having a predetermined circuit constant for setting the driving voltage of the print head unit, the voltage setting unit being provided in the interface unit of the print head unit; A driving power supply unit that forms a voltage generation circuit together with the voltage setting unit by being electrically connected to the printing unit, and that generates a head driving voltage of the print head unit based on a circuit constant set in the voltage setting unit. And a voltage limiting unit that limits the upper limit of the head drive voltage output by the voltage generating circuit.

The voltage limiting section may be composed of a voltage generating element, and may be provided at least in parallel with the voltage setting section in the voltage generating circuit.

The voltage setting section may set the head drive voltage by a circuit including at least one resistance element.

The voltage setting section may use a resistance element having a positive or negative temperature coefficient as the circuit element and set the drive voltage in accordance with the temperature change.

[0025]

In the ink jet head drive power supply circuit according to claim 1 of the present invention having the above structure, the interface section and the drive power supply section are electrically connected by mounting the print head unit in the ink jet recording apparatus. It Then, a voltage generation circuit is formed by the voltage setting unit provided in the interface unit and the drive power supply unit, and based on the circuit constant set in the voltage setting unit,
An appropriate head drive voltage is generated in the print head unit. Further, the voltage limiting unit prevents the voltage generating circuit from generating an overvoltage.

In the ink jet recording apparatus according to the second aspect, the voltage generating element is provided in parallel with the voltage setting section, and the upper limit of the voltage value applied to the voltage setting section is set.

In the ink jet recording apparatus according to the third aspect, the head drive voltage is set by the resistance value of the circuit incorporated in the voltage setting section.

In the ink jet recording apparatus according to the fourth aspect, the appropriate head drive voltage is generated in response to the change in the ink characteristic due to the environmental temperature by the resistance element having the positive or negative temperature characteristic provided in the voltage setting section. Is set.

[0029]

EXAMPLE As an example of the present invention, an example applied to a dot-on-demand type ink jet recording apparatus using a piezoelectric element will be given.

In the present embodiment, a print head in which a plurality of ink ejection ports and a piezoelectric element, which is an energy generator, are arranged corresponding to the ejection ports, and a voltage setting circuit 2 described later.
A print head unit is configured by uniting an interface circuit including a connector and an ink supply system including an ink tank. Then, the print head unit can be detachably attached to the ink jet recording apparatus.

When the print head unit is mounted on the main body of the ink jet recording apparatus, the interface circuit is electrically connected to the main power source provided on the apparatus side by the connector to form a drive power source circuit which will be described later, and at the same time, is provided on the apparatus side. The output of the driver circuit is also electrically connected. The driver circuit side has the same number of terminals as the ink ejection ports, and the terminals are connected to the piezoelectric elements in a one-to-one correspondence. Then, the driver circuit uses the head optimum drive voltage supplied from the drive power supply circuit to drive the head based on the recording data sent to the inkjet recording apparatus, and the ink is ejected from the ink ejection port onto the paper to perform printing. Let

An embodiment of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows an embodiment of an ink jet head drive power supply circuit according to the present invention. The circuit shown in FIG. 1 is generally called a step-up chopper regulator,
The output voltage is higher than the input voltage.

First, the schematic configuration of the circuit shown in FIG. 1 will be described.

The print head unit (not shown) has a structure shown in FIG.
A voltage setting circuit 2 as a voltage setting unit as shown in FIG. 3 is provided, and the voltage setting circuit 2 provided in each print head unit has a unique circuit constant depending on the characteristic values of the elements in the circuit. Is set. The circuit constant determines the drive voltage value (= optimum drive voltage) with which the print head unit can optimally print. The print head unit is
Connected through an interface circuit (not shown),
A drive power supply circuit as shown in FIG. 1 is configured.

The drive power supply circuit includes a coil 5, a transistor 3 whose emitter is grounded, a rectifying diode 8, and
A control circuit 11, a capacitor 9, an output voltage dividing circuit including resistors 13, 14 and a voltage setting circuit 2, and a resistor 13
And a Zener diode 15 provided in parallel with the voltage setting circuit 2 and a reference voltage source 12. Control circuit 11
Has two input terminals and one output terminal, one input terminal receives the voltage divided by the output voltage dividing circuit, and the other input terminal outputs from the reference voltage source 12. The input voltage Vref is input. The base of the transistor 3 is connected to the output terminal. The drive power supply circuit is supplied with a predetermined voltage Vin from a main power supply (not shown) to the input 4, converts the voltage based on the circuit constant of the voltage setting circuit 2, and outputs the optimum drive voltage Vout from the output 7.

Next, the operation of this circuit will be described. The voltage setting circuit 2 is assumed to consist of the single resistor 1 shown in FIG.

When the transistor 3 is turned on, a current 6 flows from the input 4 connected to the power source of the voltage Vin through the coil 5. At this time, the collector-emitter voltage Vcesat of the transistor 3 is Vout> Vc as compared with the voltage Vout appearing at the output 7 because the transistor 3 is in a saturated state.
esat. Therefore, output 7 through diode 8
Current does not flow to. After that, the coil 5 stores energy in the ON period Ton of the transistor 3.

When the transistor 3 is turned off, a counter electromotive force is generated in the coil 5, and a current 10 flows while charging the capacitor 9 through the diode 8.

To control the output voltage Vout, the ON period T
It suffices to adjust the length of on, which is performed by the control circuit 11. The control circuit 11 controls the voltage Vref as described above.
Is connected to an output voltage divider circuit composed of a reference voltage source 12 and resistors 13, 1 and 14, and the outputs of the output terminals are adjusted so that the voltages applied to the two input terminals are equal to each other. Adjust the ON period Ton.

The voltage generated at the output 7 can be expressed by the following equation.

[0042]

[Equation 2]

The above description is for the case where the voltage setting circuit 2 is normally connected.

On the other hand, when the voltage setting circuit 2 is not normally connected or when the resistor 1 is disconnected, the output voltage Vout rises and reaches the voltage at which the Zener diode 15 turns on. Zener diode 15 is ON
Then, the output voltage Vout does not exceed the voltage at the time of turning on. The output voltage at that time is

[0045]

(Equation 3)

It becomes That is, the output voltage of the drive power supply circuit is up to the voltage of Expression 3.

Zener voltage Vz and reference voltage source voltage Vref
If the sum of and is set to the maximum rated voltage of the head drive circuit or head or less, the drive power supply circuit does not output an overvoltage exceeding the maximum rated voltage of the head drive circuit or head, and the head drive circuit or head Will not be destroyed.

The voltage setting circuit 2 shown in FIG. 1 is used when the optimum driving voltage is different due to variations in head characteristics.
It is also possible to instruct the optimum drive voltage by a combination of a plurality of resistors 20, 21, 22 and cut points 23, 24 as shown in FIG. However, even in this method, when the voltage setting circuit 2 is not normally connected or when the selected resistor among the resistors 20, 21, and 22 is disconnected, if the Zener diode 15 is not provided, the drive power supply It becomes the output upper limit voltage of the circuit, and exceeds the maximum rated voltage of the head drive circuit and the head itself, and the head drive circuit and the head are destroyed due to overvoltage. However, since the Zener diode 15 is present, the output voltage Vout is up to the voltage of Expression 3, and the drive power supply circuit does not output an overvoltage exceeding the maximum rated voltage of the head drive circuit or the head.
Does not damage the head drive circuit or head.

Further, in the ink jet recording apparatus, since the physical properties such as the viscosity and surface tension of the ink change depending on the temperature, the optimum driving voltage of the head, that is, the head driving voltage for obtaining the optimum ink ejection state, differs depending on the temperature. For example, 2
When the optimum head driving voltage at 5 ° C. is 24 V, the optimum driving voltage changes at 30 ° C. at 10 ° C. and 18 V at 35 ° C.

In order to follow the temperature change of the optimum drive voltage of the head, it is necessary to detect the temperature of the print head or the vicinity thereof so as to achieve the optimum ejection state and change the appropriate voltage of the print head drive voltage.

Therefore, in the driving power supply circuit as shown in FIG. 1, the resistor 1 of the voltage setting circuit 2 of FIG. 1 has a temperature sensitive element 30 having a temperature characteristic as shown in FIG. A coefficient thermistor, a positive temperature coefficient coefficient thermistor, and a voltage setting circuit 2 configured to be a temperature-sensitive resistance are provided and connected through an interface circuit.

The output voltage of the drive power supply circuit is set by the voltage setting circuit 2, and it is possible to supply the head optimum drive voltage to variations in the characteristics of the head and changes in the head temperature.

However, when the negative characteristic temperature coefficient thermistor is used, the resistance value of the negative characteristic temperature coefficient thermistor becomes extremely large in the temperature range below the assumed operating temperature range. That is, it becomes equivalent to the case where Rb of the equation 2 is extremely large, and the output Vout of the drive power supply circuit exceeds the maximum rated voltage of the head drive circuit and the head, resulting in overvoltage breakdown in the head drive circuit and the head. However, since the Zener diode 15 is present, the output voltage Vout is
The drive power supply circuit does not output an overvoltage exceeding the maximum rated voltage of the head drive circuit or the head and does not damage the head drive circuit or the head.

When a positive temperature coefficient thermistor is used instead of the resistor 1, when the power of the apparatus is turned on at a temperature higher than the assumed operating temperature range of the ink jet recording apparatus,
The resistance value of the positive temperature coefficient thermistor is extremely large. At that time, the drive power supply circuit outputs an overvoltage that exceeds the maximum rated voltage of the head drive circuit and the head, which causes destruction of the head drive circuit and the head. However, since the Zener diode 15 exists, the output voltage Vout
Will not exceed the voltage of Equation 3, and the drive power supply circuit will not output an overvoltage exceeding the maximum rated voltage of the head drive circuit or head, and will not damage the head drive circuit or head.

As described above, in any state of the print head unit, that is, in any state of the voltage setting circuit, the output voltage of the drive power supply circuit is less than the maximum rated voltage of the head drive circuit or the head, By providing a head drive circuit and an inkjet head drive power supply circuit that does not damage the head, it is possible to provide a highly reliable inkjet recording apparatus.

Although the step-up type chopper regulator is used in this embodiment, the step-down type chopper regulator, the polarity reversal type chopper regulator and the series type chopper regulator are used.
The same effect can be obtained for a regulator and a regulator combining these regulators.

The print head unit is not limited to the one in the above-described embodiment, but may be one in which the print head portion and the ink tank portion are configured separately or separably, and each of which can be independently and interchangeably connected. Good. Further, the replacement of the print head unit is not limited to the user of the apparatus.

Further, in the above embodiment, an example in which the invention is applied to a dot-on-demand type ink jet recording apparatus using a piezoelectric element, but a so-called bubble jet type ink jet using a heat generating element as an energy generator. It can be applied to the recording device as well, and can also be applied to the continuous jet type.

In the above embodiment, only the resistor 1 which is the voltage setting portion is provided on the print head unit side, but as a further modification, the resistors Ra and Rc, the capacitor 9 and the Zener diode 15 are also provided on the head unit side. Both may be provided on the print head unit side.

Further, in the above-mentioned embodiment, the voltage limiter is composed of one Zener diode 15. However, as a modified example, other diodes such as LEDs or semiconductor elements are allowed if the conditions of the head drive voltage to be restricted permit. May be used. Further, the voltage limiting unit may be configured by a circuit such as a two-terminal constant voltage generating circuit or a three-terminal constant voltage generating circuit including a plurality of circuit elements or ICs.

[0061]

As is apparent from the above description, according to the ink jet head drive power supply circuit of the present invention, the voltage setting section is the drive voltage of the print head unit provided in the interface section of the print head unit. The voltage generation element is connected to the output voltage error detection unit of the inkjet head drive power supply circuit to limit the upper limit of the output voltage. Therefore, even if the print head unit is arbitrarily replaced, complicated voltage adjustment work is not performed, output of overvoltage that may damage the inkjet recording device is prevented, and printing is always performed at the optimum drive voltage. The head can be driven.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an inkjet head drive power supply circuit of an inkjet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a voltage setting circuit according to the first embodiment.

FIG. 3 is a diagram showing a configuration of a voltage setting circuit according to a second embodiment. You.

FIG. 4 is a block diagram showing a configuration of an inkjet head drive power supply circuit of an inkjet recording apparatus of a conventional example.

[Explanation of symbols]

 1 resistance 2 voltage setting circuit 13,14 resistance 15 Zener diode 20,21,22 resistance 23,24 cut point 30 thermistor

Claims (4)

[Claims] 1. An inkjet head drive power supply circuit, which is provided in an inkjet recording apparatus to which a replaceable print head unit can be attached and which supplies a drive voltage to the print head unit, is provided in an interface section of the print head unit, By a voltage setting unit having a circuit element having a predetermined circuit constant for setting the drive voltage of the print head unit, and electrically connected to the interface unit,
A drive power supply unit that forms a voltage generation circuit together with the voltage setting unit and generates a head drive voltage of the print head unit based on a circuit constant set in the voltage setting unit; and a head drive voltage output by the voltage generation circuit. And a voltage limiting section for limiting the upper limit of the above. 2. The ink jet head drive according to claim 1, wherein the voltage limiting unit is composed of a voltage generating element, and is provided at least in parallel with the voltage setting unit in the voltage generating circuit. Power supply circuit. 3. The inkjet head drive power supply circuit according to claim 1, wherein the voltage setting unit sets the head drive voltage by a circuit including at least one resistance element. 4. The voltage setting unit uses a resistance element having a positive or negative temperature coefficient as the circuit element, and sets a drive voltage in response to a temperature change. The inkjet head drive power supply circuit described.