Fluid handling – Processes – Involving pressure control
Reexamination Certificate
2001-10-09
2004-04-06
Krishnamurthy, Ramesh (Department: 3753)
Fluid handling
Processes
Involving pressure control
C137S487500, C222S001000, C222S063000, C222S387000, C222S390000, C141S026000, C141S095000, C118S684000, C118S692000
Reexamination Certificate
active
06715506
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fixed-amount-of-liquid ejecting method and apparatus which are suitably used for ejecting a liquid in fixed amount, the liquid including a viscous fluid, a material having consistency, etc. More particularly, in the field of ejecting or applying a very small amount of liquid, the present invention relates to a technique for controlling the operation of ejecting or applying a very small amount of liquid in a high-speed and precise manner. Further, the present invention relates to a technique for filling a liquid in a liquid reservoir for use in all kinds of processes, e.g., an electronic parts manufacturing process and an electronic parts assembling process, which require a step of ejecting or applying a liquid that includes a viscous fluid and a material having consistency.
BACKGROUND ART
Generally, a fixed-amount-of-liquid ejecting apparatus is employed for the purpose of ejecting a desired amount of liquid, and a method of utilizing both the fixed-amount-of-liquid ejecting apparatus and a robot capable of moving a member to which a liquid is to be applied (referred to also as an applied member hereinafter) or a nozzle is employed for the purpose of applying the liquid in a desired pattern.
As techniques for ejecting a liquid, there are known a pneumatic type method and a plunger type method. In the pneumatic type method, compressed air regulated in pressure is imparted to a liquid for a desired period of time. In the plunger type method, a push member operatively connected to a driving source is disposed in a liquid-tight condition, and it is moved through a desired distance.
The pneumatic type method is a quite simple method utilizing compressed air. Since only compressed air contacts a liquid except for a reservoir, this provides such an advantage that the liquid can be employed while it is kept clean. For this reason, the pneumatic type method is very popularly practiced.
On the other hand, the plunger type method is advantageous in that the volume of liquid ejected can be determined based on a cross-sectional area of the push member contacting the liquid and a distance through which the push member is moved. For this reason, the plunger type method is a method utilized when applying a very small amount of liquid as required in operation of filling or pipetting the liquid.
Conventionally, a liquid has been applied in a desired pattern as follows. A liquid in a reservoir is forced to move using one of the above-described methods, causing the liquid to be ejected through a nozzle end serving as an apparatus ejection orifice. Simultaneously, one or both of the apparatus ejection orifice and a member to which a liquid is to be applied are moved relatively to each other so that the liquid draws the desired pattern. However, because the above-described methods require a time until a flow speed of the liquid reaches a certain constant value, it has been very difficult to draw a uniform line of the applied liquid for a time until the constant flow speed is obtained. Such an adverse effect is significant particularly in the case of employing a highly viscous liquid or applying a liquid at a high speed. Concretely, the adverse effect appears in the form of narrowing or discontinuity in a starting portion of the applied liquid line, and in the form of fatting or pooling in an ending portion of the applied liquid line.
Japanese Unexamined Patent Publication No. 4-49108, for example, discloses one example of a conventional fixed-amount-of-liquid ejecting apparatus for use in regularly or irregularly coating an electronic material on a board in the form of points and lines in semiconductor manufacturing processes. In the disclosed ejecting apparatus, the amount of liquid ejected through an ejection orifice is controlled in accordance with such a parameter as the speed and cycle time of rotation of a screw, etc. With the disclosed apparatus, the rotational speed and the stop timing of the screw are controlled with high accuracy. Therefore, the amount of the ejected liquid is stabilized and the liquid ejection in fixed amount can be achieved even in a continuous ejection mode without being affected by the viscosity and fluidity of the liquid and the amount of liquid present in a reservoir. In the above prior art apparatus, however, the liquid is ejected and stopped respectively upon rotation and stoppage of the screw, and the ejection orifice is left in a physically open state during the time in which the ejection is stopped. This has raised the following problem, particularly in the case of the liquid having a low viscosity or the case of pressurizing the liquid in the reservoir. If there is a relatively large clearance between an outer peripheral surface of the screw and an inner peripheral surface of a screw housing, the liquid is not positively shut off at the time of stopping the liquid ejection, and the liquid tends to leak due to the own weight and a force applied to pressurize the liquid. On the other hand, if the clearance between the outer peripheral surface of the screw and the inner peripheral surface of the screw housing is set to such a small value as able to overcome the above problem, another problem has arisen in that fillers, for example, mixed in the electronic material are broken.
Further, the pneumatic type method employed a highly compressible air, and therefore has a big difficulty in achieving a desired pressure in a short time. Stated otherwise, it has been more difficult to form the applied liquid line having the same shape between start and end points and an intermediate area with the pneumatic type method. Another problem has been encountered in that because the liquid viscosity changes depending on, e.g., variations in an ambient atmosphere and a chemical reaction of the liquid itself, the amount of the ejected liquid is also changed depending on a change of the liquid viscosity when the pneumatic type method is employed in which a regulated constant pneumatic pressure acts upon the liquid. Thus, it has been impossible to apply a liquid tending to change its viscosity in the fine uniform form by using a pneumatic type ejecting apparatus.
The plunger type method has a basic function in ejecting a liquid in predetermined volume, and therefore it has been primarily used in applications for precisely pipetting or filling a desired amount of liquid. Also, the plunger type method has features superior in preciseness and constant amount because the amount of the ejected liquid is determined by a distance through which a piston moves. For that reason, the ejection operation is generally performed in a very cautious and slow manner. Thus, in the technique using the plunger type method, the essential purport resides in precisely ejecting and applying a fixed amount of liquid, and even if a change occurs in flow speed of the liquid during the ejection, there is no problem so long as the resulting amount of the applied liquid is uniform. Further, the plunger type method is avoided from being used for ejecting a highly viscous liquid. The reason is that a highly viscous liquid requires a very great force to be acted on the liquid for producing a flow of the same. Such a great force causes expansion and distortion of the reservoir and the piston, as well as compression of a liquid which hardly develops elastic deformation. These deformations impair the features of the plunger type method, i.e., preciseness and constant amount.
Particularly, when applying a highly viscous liquid at a high speed, or when using a narrow or long nozzle even in the case of applying a low viscous liquid, a very high pressure requires to be acted upon the liquid, and deformations such as expansion, distortion and compression become more remarkable. Further, because of such a specific feature of the plunger type method that only an ejection orifice is opened to the atmosphere, an adverse effect of those deformations is increased as a higher pressure is acted upon the liquid and as the ejection orifice has a smaller diameter. Concretely, the adver
Krishnamurthy Ramesh
Musashi Engineering Inc.
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