1. Field of the Invention
The present invention relates to a technology for testing whether or not ink droplets are expelled in printers, and more particularly to an adjustment technology for testing devices that perform such testing.
2. Description of the Related Art
Inkjet printers print images by expelling ink droplets from a plurality of nozzles. The print head of an inkjet printer has many nozzles, but due to such causes as increased viscosity of the ink or inclusion of air bubbles, some of the nozzles may become clogged up and no longer able to expel ink droplets. If the nozzles are clogged, the image includes missing dots, which results in a deterioration in image quality.
As a device that tests whether or not ink droplets are being expelled, a testing device using light has been proposed. FIG. 11 shows a concept drawing showing one example of a conventional ink droplet expulsion testing device using light. This testing device has a photo-emitter unit 302 and a photo-receptor unit 304. The photo-emitter unit 302 emits light L such that the light crosses the locus of the ink droplets Ip expelled intermittently from the print head 300 of the printer.
The photo-receptor unit 304 has a photo sensor 306. A so-called gain resistor Rg is connected between a gain adjustment terminal Pa of the photo sensor 306 and a power source voltage Vcc. An output signal Vout is output from an output signal terminal Pb of the photo sensor 306.
The sensitivity of the photo sensor 306 is adjusted by setting the value of the gain resistor Rg to an appropriate level in advance. In other words, where an appropriate adjustment is achieved, the output signals Vout from the photo sensor 306 alternate between the ON level and the OFF level depending on whether or not the ink droplet Ip blocks the light L.
However, in conventional devices of this type, there are situations in which, even if the value of the gain resistor Rg is set to an appropriate level in advance, the photo sensor 306 does not function well when the environment conditions are changed.
Accordingly, an object of the present invention is to provide a technology by which an ink droplet expulsion testing device using light may be appropriately adjusted even when the environment conditions are changed.
In order to attain at least part of the above and other related objects of the present invention, there is provided a testing device to test whether or not ink droplets are expelled from a print head in a printer. The testing device comprises: a photo-emitter unit configured to emit light such that the light crosses a locus of the ink droplets; a photo-receptor unit configured to receive the light that has crossed the locus of the ink droplets, and a controller configured to control the photo-emitter unit and the photo-receptor unit. The photo-receptor unit includes: (i) a photo sensor having a gain adjustment terminal and an output signal terminal; and (ii) a variable voltage supply unit configured to supply a variable voltage signal to the gain adjustment terminal. The controller detects an output signal from the output signal terminal of the photo sensor while changing a voltage level of the variable voltage signal output from the variable voltage supply unit, and sets the variable voltage signal to an appropriate level for the ink droplet expulsion test before the test is carried out, in accordance with the relationship between the voltage level of the variable voltage signal and the output signal of the photo sensor.
In the above arrangement, the voltage level of the variable voltage signals can be adjusted to an appropriate level for the expulsion test, and the testing device can accordingly be appropriately adjusted even when the environment conditions are changed.
The variable voltage supply unit may includes a D-A converter, which has an input terminal for receiving a digital input signal and an output terminal for outputting the variable voltage signal. In this case, the controller may adjust the voltage level of the variable voltage signal output from the D-A converter by adjusting the digital input signal supplied to the D-A converter.
Using a D-A converter, the voltage level of the variable voltage signal can be adjusted by means of a minute adjustment range, and therefore the voltage level may be set to an appropriate level in response to the environment conditions. In addition, since a digital signal is transmitted between the controller and the D-A converter even if they are some distance apart, noise impact can be easily avoided.
The variable voltage supply unit may further include a voltage controlled current source having a voltage input terminal and a current output terminal, where the voltage input terminal is connected to the output terminal of the D-A converter, and the current output terminal is connected to a node between the output terminal of the D-A converter and the gain adjustment terminal of the photo-receptor unit.
In this structure, a more stable adjustment may be carried out.
The controller may execute: (i) determining a threshold value at which a level of the output signal of the photo sensor changes from a prescribed first level to a prescribed second level while monotonically changing the digital input signal supplied to the D-A converter; (ii) determining a calibrated value for the digital input signal by adding a prescribed difference to the threshold value; and (iii) inputting the digital input signal having the calibrated value to the D-A converter in order to set the variable voltage signal to an appropriate level.
In this way, the variable voltage signals can easily be set to an appropriate level.
The present invention may be realized in various forms, such as an ink droplet expulsion testing device, an adjustment method therefor, a printer having the above testing device, a computer program to realize these methods or device functions in computers, a recording medium in which the computer program is recorded, and data signals embodied in a carrier wave including the computer program.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.