Liquid jet recording head

A liquid jet recording device is provided with a head unit having a liquid pathway having an outlet for forming flying droplets by discharging liquid at the tip portion thereof and an energy generating member provided along the liquid pathway. The device comprises a temperature detecting means provided in a part of the head unit and a heating means, which is controlled by the detection signal from the temperature detecting means and has a larger effective heating area than the bottom area of the head unit, provided on the bottom portion of the head unit. The head unit may be provided with an air chamber in a part of said head unit, a temperature sensor provided in said air chamber and a heater. The head unit may be fixed at the heating means side to a carriage, which comprises an air layer provided between said heating means and the carriage. The head unit may comprise a head cover provided in at least a part of said liquid jet recording head and has an air layer between said head cover and said head.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a liquid jet recording head and device, and more 
particularly to a liquid jet recording head and device having a liquid 
heating means in a recording head. 
2. Description of the Prior Art 
FIG. 1 shows a schematic illustration of a liquid jet recording device of 
the prior art. 
In this Figure, the member denoted by the numeral 101 is a head unit having 
a built-in liquid jet recording head, which performs recording on the 
paper 104 by discharging flying droplets of a liquid such as ink fed 
through a tube 103 from a main tank 102. 
The member shown by the numeral 105 is a discharge restoration pump which 
is used when droplet discharging becomes incomplete or interrupted, and 
the pump 105 performs restoration of discharging actuation by sucking 
liquid from an orifice not shown within the head unit through a tube 106. 
During this sucking operation, the liquid within the head unit 101 is also 
sucked through a tube 107. 
The sucked liquid is led to a waste liquor reservoir 108 to be stored 
therein. 
The cap shown by the numeral 109 is provided for preventing the liquid 
within the head unit 101 from drying or from contamination by impurities 
such as dust when liquid jet recording is not performed over a long term 
or during transportation of the device, and it is fitted to the tip 
portion of the head unit 101. 
The member designated by the numeral 110 is a carriage on which the head 
unit 101 is mounted, the numeral 111 showing a platen. 
A liquid jet recording device having such a structure is finding wide use, 
since it generates less noise as compared with an impact device such as a 
wire dot recording device, and yet requires no post-recording treatment 
such as fixing. 
The liquid jet recording devices of this kind may be classified into two 
kinds of an on-demand type and a continuous type. 
The on-demand type device is a system, in which droplets are discharged 
only when a recording command is received, while the continuous type 
device is a system in which droplets are discharged continuously at a 
constant frequency and an electrical field applied on the space through 
which the droplets are flying is changed in response to the recording 
command, thereby changing the route of the droplets to effect recording, 
while recovering and circulating the droplets not concerned with 
recording. 
The on-demand type device has the advantage of being, simpler in structure 
than the continuous type. 
On the other hand, the liquid to be used for recording undergoes changes in 
physical properties such as viscosity or surface tension depending on the 
temperature, and the sizes of droplets discharged change depending on 
temperature changes, even when the same energy is generaed by an energy 
generating member such as piezoelectric element of the droplet forming 
means. As a result, the recorded dots on the recording paper are changed 
in size to give unstable recording quality or image quality depending on 
the conditions of use of the device. This is a great obstacle in obtaining 
recording of high quality. 
For overcoming such drawback, attempts have been made to provide a means 
for detecting the temperature of the environment under which the device is 
placed or of the droplet forming means so as to compensate temperature 
changes by heating a part or whole of the droplet forming means through 
the signals sent from such a detecting means, thereby keeping constant the 
temperature of the droplet forming means. 
FIG. 2 shows an example of the prior art having such a structure. 
In the example shown in FIG. 2, the head unit 101 is constructed of a 
multi-orifice type having a plurality of outlets 112. 
The outlets 112 are formed at the tip ends of the liquid pathways 113, each 
liquid pathway 113 being housed at the bottom within the liquid reservoirs 
114 partitioned independently of each other. 
The respective liquid reservoirs 114 are fed with liquids such as ink with 
the same color or different colors. 
At the bottoms of the respective liquid reservoirs 114, heating means 115 
in the form of a flat plate are fixed. 
In the vicinity of the outlets 112 in the liquid pathways 113, energy 
generating members such as piezoelectric elements are mounted along the 
liquid pathways. 
A temperature detecting means is mounted at either one of the liquid 
reservoirs selected to perform temperature compensation by heating with 
the heating means 115 to keep the liquid at a constant temperature. 
In such a construction, in order that all of the plural number of droplet 
forming sections may be heated with uniform watt density, the portions to 
be heated of the respective droplet forming sections, namely the areas at 
the back face of the respective liquid reservoirs are made equal and the 
effective area on the heating surface of the heating means 115 is also 
made equal to the total sum of the areas of the portions to be heated of 
the respective droplet forming sections. 
However, with such a structure as mentioned above, when the difference 
between the temperature controlled by temperature compensation and the 
environmental temperature is great, dissipation of heat from the portions 
other than the portions to be heated of the droplet forming sections, 
namely the portions at the upper faces or four side faces of the liquid 
reservoirs 114 which contact the air, becomes great, and the temperature 
of the droplet forming sections at both ends with greater areas contacting 
the air becomes lower than the temperature of the droplet forming 
selections located inside of the device. 
Thus, temperature compensation cannot effectively performed which can cause 
marked lowering in recording quality or image quality such as different 
sizes of recorded dots for respective orifices. 
On the other hand, in a structure as shown in FIG. 2, the tip end of the 
temperature sensor 117 is inserted into the liquid, and at least a part of 
the temperature sensor is formed of a metal, and in most cases an 
appropriate voltage is applied for detection of the temperature. 
Also, since a dye which is an electrolyte is employed in the liquid such as 
ink for the purpose of coloration, there was involved the drawback that 
electrolytic dissolution occurs at the metal portion of the temperature 
sensor on prolonged usage, whereby the device can no longer be used. 
Accordingly, an attempt has been made to coat the surface of the 
temperature sensor with a fluorine resin or the like to prevent the 
dissolution, but this method leads a corresponding increase in cost. 
A structure as shown in FIG. 3 has been proposed for alleviating these 
drawbacks. 
In the example shown in FIG. 3, in order to avoid electrolytic dissolution 
of the temperature sensor 117, an detection piece 118 is provided at the 
side of the head unit 101 and the temperature sensor 117 is provided on 
the detection piece. 
The temperature sensor 117 detects the environmental temperature under 
which the device is set on initial actuation of the device, and gives heat 
quantity corresponding to this temperature to the liquid through the 
heater 115. 
However, when such a structure is employed, since the liquid temperature is 
not detected directly, there is involved the drawback that accurate 
temperature compensation in real time is not possible. 
As another drawback, the head unit 101 with a structure as shown in FIG. 2 
has a projection 101a as shown in FIG. 4 and fixed by screwing onto the 
carriage 110 through the projection 101a. 
Whereas, by employment of such a mounting structure, the heat of the 
heating means will escape toward the carriage 110, whereby the heat unit 
101 and the carriage 110 are regarded as one body, with the 
disadvantageous result that it will take a long time before reaching the 
target control temperature even if the device may be actuated to actuate 
the temperature compensating circuit, thereby making the waiting time of 
the device longer. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished to eliminate the drawbacks of 
the prior art as described above, and a primary object of the invention is 
to provide a liquid jet recording head and device capable of performing 
recording of high image quality and high quality without being influenced 
by the environmental temperature under which the device is placed. 
Another object of the present invention is to provide a liquid jet 
recording head and device which are constructed so as to be capable of 
recording of high quality by giving good temperature compensation to the 
liquid with good precision at real time, thereby maintaining constantly 
the temperature of the liquid. 
Still another object of the present invention is to provide a liquid jet 
recording head which is constructed so as to give a short waiting time by 
temperature compensation and involve no superfluous generation of heat by 
heat generating means. 
A further object of the present invention is to provide a liquid jet 
recording head comprising a multi-nozzle head provided with a plurality of 
flying droplet forming means, which enables controlling uniformly the 
temperature distribution between the respective flying droplet forming 
means heated, thereby giving good quality of printed letters. 
According to one aspect of the present invention, there is provided a 
liquid jet recording device, provided with a head unit having a liquid 
pathway having an outlet for forming flying droplets by discharging liquid 
at the tip portion thereof and an energy generating member provided along 
the liquid pathway, which comprises a temperature detecting means provided 
in a part of the head unit and a heating means, which is controlled by the 
detection signal from the temperature detecting means and has a larger 
effective heating area than the bottom area of the head unit, provided on 
the bottom portion of the head unit. 
According to another aspect of the present invention, there is provided a 
liquid jet recording head, provided with a head unit having a liquid 
pathway located in a liquid reservoir having an outlet for forming flying 
droplets by discharging liquid at the tip portion thereof and an energy 
generating member provided along the liquid pathway, which comprises an 
air chamber provided in a part of said head unit, a temperature sensor 
provided in said air chamber and a heater, which is provided on the bottom 
face of the head unit, and generates heat by the signal from the 
temperature sensor. 
According to still another aspect of the present invention, there is 
provided a liquid jet recording device, provided with a head unit having a 
liquid reservoir for housing a liquid for recording a liquid pathway of 
which one end side is inserted into said liquid reservoir and the other 
end side has an outlet formed for discharging the liquid to form flying 
droplets, an energy generating member provided along the liquid pathway, a 
temperature detecting means provided in a part of said liquid reservoir 
and a heating means which is controlled in temperature by the detected 
signal from the temperature detecting means, said head unit being fixed at 
the heating means side to a carriage, which comprises an air layer 
provided between said heating means and the carriage. 
According to further aspect of the present invention, there is provided a 
liquid jet recording head, having an orifice provided for formation of 
flying droplets, a liquid pathway for supplying to said orifices, an 
energy generating member provided along said liquid pathway and utilized 
for formation of said droplets, and a liquid reservoir provided upstream 
of said liquid pathway, a means for heating the liquid and a means for 
detecting the temperature of the liquid, which comprises a head cover 
provided in at least a part of said liquid jet recording head and has an 
air layer between said head cover and said head.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention is described in detail below by referring to the 
embodiments as shown in the drawings. 
FIG. 5 shows a first embodiment which can accomplish the objects of the 
present invention. 
In this embodiment, the heating means 115 is made to have a greater heating 
area than the bottom area of the head unit 101, and there is a portion of 
the heating means which contacts the outside air around the head unit 101. 
Since this embodiment is constructed as described above, even if the 
difference between the controlled temperature for compensation and the 
environmental temperature in which the device is placed becomes greater 
and connection of the outside air may occur at the contact surface of the 
head unit 101 with the outside air, the air heated by the heating means 
115 covers the side surface of the head unit 101 so that the heat will not 
be dissipated from this portion. 
Thus, the plural liquid reservoirs 114 can be controlled substantially 
uniformly in temperature, and high quality recording is achievable 
independently of the environmental temperature. 
As the heating means 115, there may be employed a heater in which a heat 
generating meaterial is patternized by means of etching, etc., sealed with 
a heat-resistant material such as silicon rubber, etc. and an 
electroconductive wire is laminated with a heat-resistant film, etc. 
As the temperature detecting means, there may be employed a thermocouple, 
for example, a heat-sensitive resistant element such as Posister (trade 
name: produced by Murata Seisakusho). 
Although the temperature detecting means is shown in the illustration as 
being inserted into the liquid reservoir 114, it can also be provided 
outside the liquid reservoir. 
According to the embodiment as shown in FIG. 5, since the heating means for 
temperature compensation is formed to have greater effective area than the 
bottom area of the head unit 101, the whole of the head unit 101 can be 
heated uniformly, whereby the temperature compensation of the liquid can 
be conducted accurately irrespectively of the change in environmental 
temperature to enable recording of high quality. 
FIG. 6 through FIG. 8 illustrate a second embodiment which can accomplish 
the objects of the invention, and the same numerals are given to the same 
or corresponding portions as in FIG. 1 through FIG. 4, and explanations 
thereabout are omitted. 
In this embodiment, an air chamber 119 containing no liquid is provided 
between the plural number of liquid reservoirs, and a temperature sensor 
117 is inserted into the air chamber 119. 
By employment of such a structure, the temperature sensor is kept away from 
direct contact with the liquid and therefore electrolytic dissolution can 
be avoided and the treatment with a fluorine type resin, etc. is not 
required on its surface. 
On the operation of the recording device with the construction described 
above, the temperature of the recording head is detected by the 
temperature sensor 117, and the heater 115 is actuated in response to its 
signal to heat the whole head unit. 
On the other hand, the whole of the head unit 101 inclusive of the air 
chamber 119 may be considered as one heat capacitor and therefore the 
temperature in the air chamber will be shifted similarly as the 
temperature of the liquid for forming droplets. 
Accordingly, it is possible to control temperature compensation with good 
precision at real time. 
The temperature sensor 117 may be mounted other than at the central portion 
of the head unit. 
As is apparent from the above description, in the embodiment as shown in 
FIG. 6 through FIG. 8, due to a structure having a temperature sensor 
provided in the air chamber formed in a part of the head unit, it is 
possible to perform temperature compensation with good precision at real 
time for the liquid to given high recording quality. 
FIG. 9 and FIG. 10 illustrate a third embodiment which can accomplish the 
objects of the invention, and the same numerals are given to the same or 
corresponding portions in FIG. 1 through FIG. 4 without explanations 
thereabout. 
In this embodiment, a recess portion 110a having substantially the same 
area as the heating means 115 is formed on the upper surface of the 
carriage and at the portion where the head unit 101 is to be fixed. 
The head unit 101 is mounted through the projected piece 101a so that the 
heating means 115 may be located above the recess portion 110a, as shown 
in FIG. 10. 
When mounted in such a manner, an air layer is formed by the recess portion 
110a beneath the heating means 115, the air layer insulating heat transfer 
to the carriage 110, and the heat generated by the heating means 115 being 
used only for elevation of temperature of the head unit 101. Consequently, 
the target control temperature for temperature compensation can rapidly be 
achieved to make waiting time shorter without loss time. 
In the above embodiment, the recess portion is provided on the carriage 
side, but it is also possible to provide a recess portion at the bottom of 
the head unit 101 and a heating means may be provided in said recess 
portion. 
As is apparent from the above description, according to the embodiment 
shown in FIG. 9 and FIG. 10, by employment of a structure wherein an air 
layer is provided between the heating means provided at the lower surface 
of the head unit and the carriage at which the head unit is to be 
provided, the heat generated by the heating means is used for heating the 
head unit without heat loss toward the carriage side, whereby the target 
temperature for temperature compensation can rapidly be reached to make 
waiting time shorter. 
FIG. 11 through FIG. 13 illustrate a fourth embodiment which can accomplish 
the objects of the invention. 
FIG. 11 is a schematic plan view, FIG. 12 a schematic front view as viewed 
from the outlet side, and FIG. 13 a schematic side view for illustration 
thereof. 
In FIG. 11, FIG. 12 and FIG. 13, 201a, 201b, 201c, 201d and 201e are each 
on outlet provided for forming flying droplets, 203 is a liquid pathway 
for supplying liquid to said orifices, 202 is an energy generating member 
provided for generating energy for formation of discharged droplets, 204 
is a liquid reservoir provided upstream of said liquid pathway 203 for 
storing the liquid discharged. In the embodiment shown in FIG. 11 through 
FIG. 13, the principal portion of the flying droplet forming means is 
substantially constituted of the above outlets 201a-201e, the liquid 
pathway 203, the energy generating member 202 and the liquid reservoir 
204. As shown in FIG. 11, a plurality of said flying droplet forming means 
are provided. As shown in FIG. 11, a heater 205 is provided as a means for 
heating the liquid for forming flying droplets below the abovementioned 
flying droplet forming means. As shown in FIG. 11 thorugh FIG. 13, a 
temperature sensor 206 is provided as the means for detecting the 
temperature of liquid upstream of the liquid pathway. On at least a part 
of the surface other than the part having the above outlets 201a-201e 
provided thereon and the surface having the above heater 205 provided 
thereon, an air layer 208 formed by said surface and the head cover 207 is 
provided, said air layer 208 being located so as to be heated by the 
heater 205 at the same heat density as the flying droplet forming means. 
That is, during temperature control, the head body which is the aforesaid 
droplet forming means is constructed so as to be surrounded by the air 
layer 208 of substantially the same temperature as the head body. The head 
cover 207 is made of a material of low thermal conductivity such as a 
plastic, etc. and the thickness of the air layer 208 formed between the 
head cover 207 and the head body is made thin, generally desirably 10 mm 
or less. Table 1 shows the temperatures of the ink in the respective 
droplet forming means in the prior art example having no air layer 208 and 
the liquid jet recording head of the present invention, when the control 
temperature is made 50.degree. C. at an environmental temperature of 
5.degree. C. 
TABLE 1 
______________________________________ 
Ink temperature at various positions of 
droplet forming means in the respective heads 
when temperature control is conducted (control 
temperature: 50.degree. C.) 
Position of droplet 
forming means a b c d e 
______________________________________ 
Head of the prior art: 
49 55 58 55 49 
Head of the invention: 
49 50 50 50 49 
______________________________________ 
As can be seen in Table 1, according to the liquid jet recording head as 
shown in FIG. 11 through FIG. 13, there is no occurrence of heat loss by 
the air convection with cold outer air on the surface of the head body, 
which has been the case for nonuniform temperature distribution in the 
liquid jet recording head of the prior art provided with a plurality of 
flying droplet forming means, and heat exchange of the head body is 
effected only with the air layer 208 heated to the temperature 
substantially equal to the main body, whereby the nonuniform temperature 
between the respective flying droplet forming means can be substantially 
avoided. Further, the recorded dots formed recording medium by the outlet 
201c located at the central portion of the head and by the outlets 201a 
and 201e have substantially equal sizes and accordingly good printed 
letter quality can be given to provide a good recorded product. 
According to the liquid jet recording head of the fourth embodiment of the 
present invention, by forming an air layer surrounding the head body which 
is the above-mentioned flying droplet forming means and locating the 
above-mentioned heating means so as to heat uniformly not only the head 
body but also the air layer, the temperatures of the respective outlets 
can be controlled uniformly to perform good recording.