JP2003226012A - Inkjet printer head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce costs by lessening the number of pads related to temperature detection and reducing a chip size and to highly accurately detect temperatures by using a wiring line in common in an HB having many colors and many nozzles formed in one chip. <P>SOLUTION: In the recording head having a plurality of temperature detection elements set on the same semiconductor substrate is provided with a selecting circuit for selectively outputting respective detecting terminals of the temperature detection elements to a common terminal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting circuit for a printer head in an inkjet printer.

[0002]

2. Description of the Related Art In a printer using an ink jet recording head for ejecting ink to record an image, if the ejected ink droplets are not uniform in size, the quality of the recorded image is deteriorated, and uneven density occurs. Since the image quality may be deteriorated due to this, it is desirable to always keep the size of the ink droplet constant in order to perform high-quality printing.

Among ink jet recording heads, in a recording head which employs a method of heating ink to foam and ejecting ink by the pressure, the size of the ink droplet is affected by the viscosity of the ink and the pressure at the time of foaming. Since the viscosity of the ink and the pressure at the time of bubbling depend on the temperature of the ink, the size of the ink droplet changes when the temperature of the ink changes. The change in ink temperature deteriorates the quality of the recorded image.

Therefore, conventionally, the temperature of the ink droplet is detected, and the pulse width applied to the heater is changed according to the ink temperature to control the bubbling energy to keep the size of the ink droplet constant. It was Further, control is also performed in which the recording operation is stopped by detecting an abnormal temperature rise such that the recording head is destroyed during the ink shortage or the high-speed recording operation.

Japanese Unexamined Patent Publication No. 6-336071 proposes a temperature detecting means for performing such control. In this publication, the temperature is detected by a diode built in a semiconductor substrate in which a heater for a recording head is built. Since the forward voltage (VF) of the diode has a voltage change of about −2 mV / ° C., the head temperature is detected by detecting this voltage change. FIG. 3 shows a circuit for detecting the temperature of the recording head in the conventional inkjet printer. A current circuit and an amplifier circuit provided outside the print head apply a current to a diode provided in the print head to amplify and correct the forward voltage at the diode. This output voltage is input to the A / D conversion circuit of the CPU of the printer body, and the temperature of the recording head is detected from the change in voltage.

[0006]

Due to the higher definition of color printers in recent years, a plurality of colors on the same semiconductor chip are mounted on the same semiconductor chip in order to improve the alignment accuracy of each color in the conventional head in which semiconductor chips for each color are mounted side by side. It has been formed to improve the definition. As a result, the area of one semiconductor chip becomes larger than before and the printing frequency for each color is different.Therefore, temperature distribution occurs within the same semiconductor chip and the temperature difference within the chip becomes larger than before. ing. Conventionally, even if the temperature is measured at 2 to 1 point in the semiconductor chip, the temperature difference in the temperature distribution in the chip is small, so even if the temperature is detected at the average value of 2 points or at 1 point in the chip, Although there was little error from the temperature of each part, in a recording head in which a plurality of colors are formed on the same semiconductor chip, the temperature distribution in the chip is large, so that it is necessary to measure the temperature at a plurality of points.
The circuit of the temperature detecting element on the head substrate in this case is shown in FIGS.

If pads for electrically connecting to the outside of the chip are provided corresponding to each terminal of the temperature detecting element, the number of pads electrically connected to the chip and the outside of the chip increases as the number of points for temperature detection increases. Since the pads are usually arranged in a line on the outer periphery of the chip, there is a problem that the chip size increases due to an increase in the area required for the pad region as the number of pads increases.

When the number of signal lines to the outside of the printer head increases, the number of contacts connecting the printer head and the printer head also increases. As a result, it becomes difficult to contact the contact pads uniformly, and the contact resistance increases, which causes malfunction. When detecting temperature with multiple temperature sensing elements, if the connection resistance value at the contact of each temperature sensing element is non-uniform, the sensing voltage at each element will vary, and as a result, the sensing temperature at each sensing point There is a problem that an error occurs and accurate print control cannot be performed.

An object of the present invention is to detect temperature at a plurality of points without increasing the number of pads in a printer head which detects a temperature using a plurality of temperature detecting elements.

[0010]

In order to achieve the above object, the present invention has a circuit for driving a recording element and a plurality of temperature sensing elements on the same semiconductor substrate, and each of the plurality of temperature sensing elements is provided. There is provided a recording head including a selection circuit that selectively outputs a detection terminal to a common terminal.

With the above structure, the detection terminals of the plurality of temperature detection elements are drawn out to the common pad by the selection circuit, so that the number of pads can be reduced as compared with the case where the detection terminals of the respective detection elements are drawn out. As a result, the chip area of the semiconductor chip can be reduced, so that the number of chips taken per wafer increases and the cost per chip decreases.

Wiring to the outside of the head relating to the temperature detection is common to a plurality of temperature detecting elements, the number of wiring to the outside of the head is reduced, and the cost of flexible wiring related to the wiring can be suppressed. Also, variations in wiring resistance, contact resistance, etc. when individual wiring is taken out for multiple sensing elements can be ignored by using common wiring, and the measurement conditions are the same between each temperature sensing element and accurate temperature It becomes possible to measure.

[0013]

(First Embodiment) First Embodiment of the Present Invention
1 is shown in FIG. FIG. 1 shows a circuit relating to temperature detection in a printer head. 101 is a head substrate,
Reference numeral 102 is a diode which is a temperature detecting element, 103 is a selection circuit, and 104 is a pad for connecting to the outside of the substrate.

The selection circuit 103 comprises one common terminal and a plurality of selection terminals, and one of the arbitrary selection terminals is connected to the common terminal by a switch by a control signal from the outside of the head. The common terminal is connected to the external connection pad 104. Two sets of the selection circuit 103 and the pad 104 are provided, and each selection circuit is provided with one of the temperature sensing elements 102 according to a control signal.
One of them is selected, and the detection terminal of the temperature detection element 102 (the anode terminal of the diode in the figure) is connected to the two external connection pads 104 via the switch of the selection circuit 103. The anode terminals of the plurality of temperature detection elements 102 are connected to the selection terminal sides of the two selection circuits 103, respectively.

FIG. 2 shows an equivalent circuit for measuring the temperature of the head shown in FIG. The method of temperature detection by the diode is as follows. When temperature detection is performed by a diode formed on a silicon semiconductor substrate, when a constant current is applied to this diode, the terminal potential (VF) at both ends of the diode has a temperature coefficient of about -2 mV / ° C. Although the voltage between the terminals of the diode has voltage variations due to variations in manufacturing, the temperature dependence of VF is relatively stable with respect to variations in manufacturing. Therefore, a constant current is applied to a known temperature such as room temperature in advance. The temperature can be accurately detected by measuring the VF at, and measuring the change amount of the VF when the temperature changes.

In FIG. 2, the anode terminal of the diode 102 is connected to the two selection circuits 103, and the selection circuit 10
The three common terminals are connected to the pads 104, respectively. Two
The two selection circuits and the pad 104 are external constant current circuits 2
01 and the voltage measuring circuit 202, respectively.

Selection circuit 103 formed on a semiconductor substrate
Is an analog switch composed of a transistor such as a MOS. In the case of an analog switch composed of a MOS, a voltage drop occurs in the switch due to the ON resistance of the switch when a current is applied. The on-resistance value of the switch changes greatly with temperature. For this reason, if voltage detection is performed on the same pad as the current-applied pad, the change amount of the voltage drop of the switch due to the temperature change is also included, and an accurate change amount of the VF of the diode due to the temperature cannot be measured. Therefore, the selection circuit 103 and the pad 104 have two systems, one for applying a current and the other for measuring a voltage. By selecting a voltage from a selection circuit and a pad different from the selection circuit and the pad to which a constant current is applied, The voltage drop in the selection circuit to which the voltage measurement circuit is connected can be made extremely small, and the amount of change in VF with temperature can be accurately detected.

Although a diode is used as the temperature detecting element in the present embodiment, the same effect as that of the present embodiment can be obtained by using an element whose electrical characteristics change with temperature, such as a resistance element. .

[0019]

As described above, according to the present invention, it is possible to reduce the number of pads involved in temperature detection in a printer head having a plurality of temperature detection elements on the same substrate.

Further, the size of the semiconductor chip can be reduced, and a low-cost printer head can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a temperature detection circuit which is a typical embodiment of the present invention.

FIG. 2 is an equivalent circuit showing temperature measurement by a temperature detection circuit according to the present invention.

FIG. 3 is a circuit diagram of a conventional temperature detection circuit.

FIG. 4 is a circuit diagram of a conventional temperature detection circuit.

FIG. 5 is a circuit diagram of a conventional temperature detection circuit.

[Explanation of symbols]

101 head substrate 102 temperature sensing element 103 selection circuit 104 pad 201 constant current circuit 202 Voltage measurement circuit

Claims (3)

[Claims] 1. A selection circuit having a circuit for driving a recording element and a plurality of temperature detection elements on the same semiconductor substrate, and selectively outputting each detection terminal of the plurality of temperature detection elements to a common terminal. A recording head comprising: 2. The recording head according to claim 1, wherein the temperature detecting element is a diode. 3. A recording head according to claim 1, wherein the temperature detecting element is a resistance element.