Ink Jet Recording Apparatus With an Improved Ink Sensor

This invention relates to an ink jet recording apparatus with an improved ink sensor, particularly to an ink sensor which is used for detecting disorder in recording.

In an ink jet recording apparatus, ink under pressure is vibrated with a constant frequency at a nozzle of the apparatus. Therefore, the ink emitted from the nozzle becomes droplets of a constant size with a regular interval. The ink droplets are charged by a charging plate in accordance with electric voltage applied thereto.

In this kind of ink jet recording apparatus a problem may occur often such that the phase between emission of ink droplets out of the nozzle and charging thereof does not accord, which may result in disorder in recording. Accordingly the phase should be corrected.

In order to detect disorder in record, a microphone, which is disposed in a flying path of the ink droplets to be detected and converts impinging energy of the ink particles into an electric signal, has been used. The microphone, however, has the following defects or disadvantages:

1. Since the ink droplets impinge directly with a diaphragm of the microphone, it needs to be completely water-proof, which results in difficulty of manufacture thereof and raising the cost thereof.

2. Since the deflection amount of the ink droplets charged is small, it is necessary to construct the microphone into a small size, which is difficult in manufacture thereof.

3. A vibrating face of a conventional microphone varies in sensibility according to the position at which the ink droplets impinge therewith, and it is necessary to adjust the microphone such that ink droplets impinge with the highest sensibility position of the microphone. Therefore the adjustment becomes difficult.

Further known is an ink sensor comprising an induction rod of which one end is disposed to face a flying path of ink droplets to be detected and a pair of shielding plates between which the end of the induction rod is disposed. The shielding plates each are provided with a hole through which the ink droplets pass. In this sensor, it is difficult to adjust the position of the sensor relating to the ink jet recording apparatus without contacting the flying ink droplets with the shielding plates.

An object of the invention is to provide an ink sensor which is able to detect ink droplets without contacting the sensor with the ink droplets.

Another object of the invention is to provide an ink jet recording apparatus with an ink sensor in which adjustment of the position of the sensor relative to a flying path of the ink droplets is easy.

Further another object of the invention is to provide an ink jet recording apparatus with an ink sensor, which sensor has high sensibility and is simple in construction.

The present invention is characterized by an ink sensor comprising induction means including a pair of faces disposed such that ink droplets to be detected pass through therebetween and shielding means mounted on the induction means through insulating means for shielding electric noise.

FIG. 1 is a schematic view of an ink jet recording apparatus employing a sensor according to the present invention;

FIG. 2 is a diagram showing a relation between ink droplets emitted and electric signals including video signals and phase detecting signals;

FIG. 3 is a front section view of the sensor; and

FIG. 4 is a side view of the ink sensor shown in FIG. 3.

Referring to FIG. 1, an ink jet recording apparatus employing an ink sensor according to the present invention will be described hereinafter in detail.

A nozzle 1 emitting ink is fixed to a casing 3, which casing 3 is fixed to a stationary portion 5 at brackets 301,303. The bracket 301 has an elliptical hole in which a screw 302 is inserted and fixes the casing 3 to the stationary portion 5 so that the nozzle 1 can be adjusted axially of the nozzle 1. The bracket 303 also has an elliptical hole in which a screw 304 is inserted. By the screw 304, the nozzle 1 is fixed to the stationary portion 5 so that angle of the jet portion of the nozzle can be adjusted.

The nozzle 1 is provided with a transducer such as a piezo-electric crystal which vibrates the nozzle receiving electric signals. The electric signal is transmitted from an amplifier 23 after being generated by a clock pulse generator 27, converted into sine curve by a filter 25 and amplified by the amplifier 23.

Ink under pressure from a reservoir 9 is emitted from the nozzle 1 and made into droplets synchronized with vibration frequencies of the electric signals. The droplets are electrically charged by charging plates 17 to which electric signals generated by a signal generating circuit 31, as shown in FIG. 1, are applied through an amplifier 29. The signals comprise synthesized video signal portions A and phase detecting portions B, as shown in FIG. 2. The video signal A of the signal corresponds to alternate droplets from the nozzle 1 and apply voltage (positive) according to the video signal A to the droplet in case of presence of voltage in the video signal. The other alternate droplets correspond to the phase detecting signal B applying negative voltage to the droplets to appear repeatedly as a period of alternate successive 6 droplets. The droplets charged thus are deflected by deflection plates 19. In one 191 of the deflection plates 19 positive voltage is applied and in the other 192 negative voltage is applied. Accordingly, droplets carrying video signals impinge with recording medium such as paper, articles or the like, and droplets carrying phase detecting signals or droplets not charged impinge with a gutter 11. The gutter 11 is fixed to a stationary portion 13 of the ink jet recording apparatus. Ink held here is returned to the ink reservoir 9 through a tube 8. The droplets carrying the phase detecting signals are detected electrically by an ink sensor 15 mounted on the gutter 11. Electric signals thus detected are transmitted to a level comparator 35 after being amplified by an amplifier 39, and removing electric noise by a filter 37. When the level comparator 35 detects whether emission of the droplets and charging of the droplets accord or not, and when not accorded, that is disorder in recording may occur, the level comparator 35 emits electric signals which are transmitted to a video signal generating circuit 31 with the phase of electric signals from the clock pulse generator 27 shifted by a phase shift 33. Electric signals including phase detecting signals from the video signal generating circuit 31 are transmitted the charging plate 17, after being amplified by an amplifier 29 to charge the droplets with corrected phase.

Thus, the sensor 15 detects charges impressed on the droplets emitted from the nozzle 1, that is the droplets to be detected and emits the electric signals.

The sensor 15 is illustrated in FIG. 3 in detail. In FIG. 3, a pair of induction plates 151 are made of conductive material, such as copper, and fixed to a pair of insulators 153 with adhesive material. The pair of insulators 153 carrying the pair of induction plates 151 are secured to an insulator at one end thereof so that the pair of induction plates 151 are in parallel to each other and opposite to each other with a constant separation distance. The induction plates are electrically connected to each other by a wire 156. The pair of induction plates each have conductive plates 152 secured to the insulator 153 at opposite sides from to the induction plates 151. The conductive plates 152 also are electrically connected to each other by a wire 155 which is grounded thereby providing shielding. The sensor 15 is coated on the outside thereof by insulating material as shown by a dotted line.

The sensor 15 is assembled into the ink jet recording apparatus such that the droplets carrying phase detecting signals pass through between the pair of induction plates 151 in non-impinging relation to the induction plates 151. For this, first, ink is emitted so that droplets to be detected fly over the sensor, then the flying path of the droplets to be detected is directed into the space defined by the pair of induction plates from the top of the space. The adjustment of the flying path is made by the screws.

Width l of the sensor 15 is preferably p(n+3) .about. p(n+7), wherein p = a pitch in a series of droplets emitted.

When the droplets are emitted at speed of 20 m/s, frequency of 60 KHZ, the pitch p nearly equals to 0.32 mm.

n = the number of successively charged droplets to be detected, for example 6 as shown in FIG. 4.

The sensor 15 has current induced therein by the charges impressed on the droplets to be detected flying near or between the pair of induction plates 151 of the sensor 15 and provides electric signals due to the induced current.

The sensor 15 may be employed to the other ink jet recording apparatus for example one described in U.S. Pat. No. 3,836,912 than that described above .