Patent Application
20140354729
Inkjet printheads are commonly used for printing. It is important to keep inkjet printheads at a predetermined temperature to obtain high print quality. Inkjet printheads typically use thermal sense resistors to regulate the heating of inkjet printheads.
Non-limiting examples of the present disclosure are described in the following description, read with reference to the figures attached hereto and do not limit the scope of the claims. In the figures, identical and similar structures, elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features illustrated in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. Referring to the attached figures:
In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is depicted by way of illustration specific examples in which the present disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.
Inkjet printheads are commonly used for printing. The temperature of inkjet printheads are regulated to obtain high print quality. Thermal sense resistors are commonly used to regulate the heating of inkjet printheads. Due to cost constraints, typically, only one thermal sense resistor is placed on the printhead. For example, the one thermal sense resistor may regulate the temperature of the printhead by averaging the temperature across the entire printhead. The problem with using one thermal sense resistor is that the temperature across the printhead can vary to a large enough level that the temperature rises above or falls below temperatures that produce high print quality. A variation in temperature, such as a variation of three degrees Celsius outside the predetermined temperature range, may cause thermal gradients to have a visible impact on the print quality.
For example, the thermal inkjets in the center of the printhead may achieve a temperature above the temperature needed for high print quality during heavy printing due to the thermal inkjets firing more drops in the center area than the outer portions of the printhead. Conversely, the thermal inkjets on the center of the printhead may achieve a temperature below the temperature needed for high print quality during resting periods. Another factor in uneven temperature across the printhead is the ratio of inkjets to area on the printhead. At the ends of the printhead, there is larger area per inkjet nozzle, occupied with additional circuitry, electrical pads and other features, compared to the area in the center of a rib, where there is minimal area per inkjet nozzle. As such, the ends of the printhead may to be at a lower temperature than the center, especially in high density, high speed printing. Accordingly, the averaged temperature may not account for the portions of the printhead that are above or below the predetermined temperature range needed for high print quality and may cause thermal gradients across the printhead.
Regulating the temperature of the printhead across the entire printhead uniformly using a low cost method is provided herein. In examples, an apparatus, printhead, and method of regulating a temperature of an inkjet printhead is provided. In examples, the apparatus includes an analog memory, a temperature sensor, a comparator, and a pulse circuit. The analog memory is charged to a reference voltage corresponding to a predetermined temperature of a printhead. The temperature sensor measures a thermal voltage of at least one of the plurality of local areas of the printhead. The comparator obtains a comparison result by comparing the reference voltage to the thermal voltage. The pulse circuit selectively transmits a series of warming pulses to the at least one of the plurality of local areas of the printhead based on the comparison result.
The printhead 200 is illustrated divided into a plurality of local areas 20. Each local area 20 may represent a smaller portion of the printhead 200, such as a primitive. For example, the local area 20 may be a primitive that includes a group of inkjet nozzles, such as, a group of eight thermal inkjet nozzle openings 24. The printhead 200 is divided into local areas 20 to regulate the temperature of smaller portions of the printhead 200 using the apparatus 100, such as a temperature regulating circuitry unit. By regulating the temperature of the local areas 20 of the printhead 200, the temperature of the entire printhead may be uniformly regulated without relying on, for example averages. Thus, the temperature regulation allows the local areas 20 to be heated to the predetermined temperature only when necessary and may reduce portions of the printhead having temperatures above and/or below the predetermined temperature.
In a second state, the circuit between the DAC and analog memory 12 is open. The analog memory 12 transmits the reference voltage to the comparator 16 and the temperature sensor 14 transmits the thermal voltage of a local area 20 to the comparator 16. Timing signals may also be used to connect the output of the analog memory 12 to a negative input terminal of the comparator 16 and to connect the thermal voltage of the local area 20 on the printhead 200 to a positive input terminal of the comparator 16. The temperature sensor 14 measures the thermal voltage of at least one of the plurality of local areas 20 of the printhead 200. A local current source 29 provides biasing current to the silicon diodes. The thermal voltage is measured across a set of forward biased silicon diodes 32 in the at least one of the plurality of local areas 20. The forward biased silicon diodes 32 may be biased with a global current that obtains the temperature of the forward biased silicon diodes 32 in the form of a voltage. The forward biased silicon diodes 32 are used as the temperature sensor 14 for a local area 20 of the printhead 200 since the silicon diodes 32 have a strong thermal coefficient, for example approximately −2.2 mV/degree C. Additionally, the silicon diodes 32 may drive a two transistor current source and mirror the two transistor current into the comparator 16 to bias it. This alleviates the need for an extra bias circuit.
Referring to
In a third state, the warming pulse circuit 39 selectively transmits a series of warming pulses to the at least one local area 20 of the printhead 200 based on the comparison result. For example, when the comparison result indicates that the thermal voltage is greater than the reference voltage. The warming pulse circuit 39 may be connected to the printhead 200, such that when the comparison result indicates warming is needed, a series of warming pulses will be transmitted to a particular nozzle of the local area of the printhead 200. The warming pulses are narrow, sub firing pulses that do not provide enough energy to the thermal inkjet resistors to fire drops. The warming pulses are created globally on the printhead 200 (e.g., one pulse circuit per printhead) and are gated locally onto local areas or primitive groups of thermal inkjet resistors to heat one or more nozzles in a small section of the printhead 200 (i.e., the local area or primitive level). The narrow, sub firing pulses or warming pulses are intended to warm, but not boil ink in a printhead 200. For example, the warming pulse circuit 39 may be connected to at least one firing resistor 33 on the printhead 200 using a metal oxide semiconductor transistor 38, such as a laterally diffused metal oxide semiconductor (LDMOS) transistor, as a switch. At least one firing resistor 33 may warm that local area 20 of the printhead 200. Alternatively, a separate heater, such as a separate inkjet firing resistor 33 connected as above, may be used.
In particular, when the warming pulse circuit 39 is set as enabled, the AND gate 34 output will depend on the output of the comparator 16 (e.g., the comparison result). The output of the comparator 16 determines whether warming pulses are transmitted to the printhead 200 via an OR gate 36, if the comparator output is a logic 1, then warming pulses are passed through from the warming pulse circuit 39 to the OR gate 36. The OR gate 36 is connected to the output of the AND gate 34 and is also be connected to a firing pulse circuitry 35 on the printhead 200. When the printhead 200 is in a printing mode, the firing pulse circuitry 35 will produce firing pulses to go through the OR gate 34 to the printhead 200 to fire drops as desired. The firing pulses are longer than the warming pulses and have enough heat to cause firing of the inkjet, which fire drops of ink. The firing pulses are connected to an OR gate 34 so that the firing pulses may not be blocked.
The temperature regulating circuitry unit 300 may further include a global control unit 37 that is used for one or more printheads to receive the proportional to the temperature voltage from the temperature sensor 14 and to determine an actual temperature of the at least one of the plurality of local areas 20 of the printhead 200 using the temperature voltage, v2, and a reference voltage, v1. The actual temperature may then be obtained, for example, from a voltage sensed from the forward biased silicon diodes 32 on the printhead 200, referred to as a sensing voltage or proportional to temperature voltage. The sensing voltage from the forward biased silicon diodes 32 may be transmitted to the control unit 37. The control unit 37 may include ore or more pass gates and one control signal. The sensing voltage may be transmitted through the pass gate(s) and transmitted to an amplifier and comparator system to convert the sensing voltage from an analog signal to a digital temperature that may be obtained external to the printhead 200.
The temperature regulating circuitry unit 300 has a low cost, as each of the plurality of local areas 20 have sensing and decision making circuitry that may include twelve transistors, one to two diodes, and one capacitor. The size of the circuit is minimal due to the small number of transistors. The temperature regulating circuitry is also cost effective since the same firing resistors and LDMOS transistors may be used to send both the firing pulses and the warming pulses. Furthermore, the temperature regulating circuitry unit 300 may be easily calibrated by using a method to measure the voltage required to trip the comparator 16, such as a wafer test using a known wafer temperature. The voltage value may then be written in the non-volatile (NV) memory on each printhead 200. Additionally, the temperature regulating circuitry unit 300 may be tested using a scan method that observes the output of the comparator 16 in a testing mode.
The method may also obtain the actual temperature of the at least one local areas from the thermal voltage using a temperature sensor to make the actual temperature visible outside of the temperature regulating circuitry unit. The actual temperature may then be utilized by a printing device and/or related systems, such as providing actual temperature readings to a user.
The present disclosure has been described using non-limiting detailed descriptions of examples thereof and is not intended to limit the scope of the present disclosure. It should be understood that features and/or operations described with respect to one example may be used with other examples and that not all examples of the present disclosure have all of the features and/or operations illustrated in a particular figure or described with respect to one of the examples. Variations of examples described will occur to persons of the art. Furthermore, the terms “comprise,” “include,” “have” and their conjugates, shall mean, when used in the present disclosure and/or claims, “including but not necessarily limited to.”
It is noted that some of the above described examples may include structure, acts or details of structures and acts that may not be essential to the present disclosure and are intended to be exemplary. Structure and acts described herein are replaceable by equivalents, which perform the same function, even if the structure or acts are different, as known in the art. Therefore, the scope of the present disclosure is limited only by the elements and limitations as used in the claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2011/042727 | 7/1/2011 | WO | 00 | 6/6/2014 |
