Printing – Stenciling – Processes
Reexamination Certificate
2000-08-24
2003-10-28
Yan, Ren (Department: 2854)
Printing
Stenciling
Processes
C101S123000, C101S484000
Reexamination Certificate
active
06637326
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a screen printing apparatus for pushing a printing material out of a printing head and printing the printing material on an object through a screen having one or more through-holes, and particularly to a method and an apparatus for controlling a pushing pressure applied to the printing material.
2. Related Art Statement
A conventional screen printing apparatus is disclosed in Japanese Patent Application laid open under Publication No. 8(1996)-48024. The screen printing apparatus includes (a) a printing-material container which accommodates, in a printing-material chamber thereof, a printing material and opens toward a screen and (b) a printing-material pusher which applies a pushing pressure to the printing material accommodated in the chamber and pushes the material out of the chamber. The pusher includes a pushing plate which is slideably fitted in the chamber and pushes the printing material out of the chamber, and a pushing air-cylinder device as a drive source that drives or moves the pushing plate in the chamber. The screen printing apparatus further includes a control device which controls the pressure of air supplied to the air cylinder, such that the pushing plate pushes, with a predetermined pushing pressure, the printing material out of the chamber. The pushing pressure is predetermined depending upon the sort and/or viscosity of the printing material used.
The above-described screen printing apparatus maintains the predetermined pushing pressure throughout one printing operation. However, the through-holes of the screen have different shapes, sizes and/or orientations, and are distributed at different densities. If the predetermined pressure is kept during one full printing operation, an insufficient amount of printing material may be printed on some portions of the object, and an excessive amount of printing material may be printed on other portions of the object. Thus, an uneven printing may occur to the object. For example, in the case where the printing material is squeezed into a through-hole having such a shape that the hole is wide in the direction of extension of the opening outlet of the printing-material chamber, a sufficient amount of printing material can be easily squeezed into the hole with a low pushing pressure. On the other hand, in the case of a through-hole having a shape that the hole is narrow in the above direction, there is such a tendency that a considerably high pushing pressure may be needed to squeeze a sufficient amount of printing material into the hole. Thus, in the case where a screen has a plurality of through-holes which have different shapes, sizes and/or orientations and/or are distributed at different densities (hereinafter, simply referred to as “a complex printing pattern”), an uneven printing is likely to occur. Therefore, when a screen having a complex printing pattern is used, an operator needs to carefully adjust the pushing pressure. However, this adjusting operation takes a lot of time, and the quality of printing depends on the skill of the operator.
SUMMARY OF INVENTION
The present invention provides a pushing-pressure controlling method, a screen printing apparatus, and a recording medium which have one or more of the following technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (21). Any technical feature that includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. In addition, in the case where one technical feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items.
(1) According to a first feature of the present invention, there is provided a method of controlling a pushing pressure which is applied to a printing material, such as a creamed solder, to push the material out of a printing head of a screen printing apparatus and print the material on an object, such as a printed wiring board, through at least one through-hole of a screen of the apparatus while at least one of the head and the screen is moved relative to the other of the head and the screen in a direction parallel to the screen, the method comprising the step of changing the pushing pressure applied to the printing material, while a printing operation is carried out on the object by the screen printing apparatus.
The pushing-pressure controlling method according to the first feature (1) can change the pushing pressure while one printing operation is carried out on one object. Therefore, the printing material can be printed, with an appropriate pushing pressure, on each portion of the object, depending upon, e.g., the shape of each through-hole of the screen. Thus, the quality of printing can be easily improved. However, it is difficult for an operator to change the pushing pressure during one printing operation.
Accordingly, it is preferred to prepare, before one printing operation, a command to change the pushing pressure, and automatically change, during the printing operation, the pushing pressure according to the prepared command. In addition, it is preferred to change the pushing pressure at a time when the printing material is not squeezed into any through-holes of the screen, that is, a pushing portion of the screen printing apparatus that pushes the printing material is moving above the screen but is not facing any through-holes of the screen, or when the material is being squeezed into the least number of through-holes. Moreover, it is preferred to complete changing the pushing pressure in a short time.
(2) According to a second feature of the present invention that includes the first feature (1), the step of changing the pushing pressure comprises changing the pushing pressure according to a predetermined pressure pattern representing a relationship between relative position of the printing head and the screen, and pressure.
The pushing-pressure controlling method according to the second feature (2) employs a predetermined pattern indicating the change of pushing pressure, and changes the pushing pressure according to the pattern. A shorter time is needed for an operator to prepare the pattern than a time needed for the operator to prepare one or more individual commands to change the pushing pressure. Thus, the efficiency of operation of the operator is improved. In addition, the quality of printing is stabilized irrespective of the degree of skill of the operator. It is preferred to prepare the pressure pattern based on, e.g., the shape(s) of the through-hole(s) of the screen, and it is preferred to prepare respective exclusive pressure patterns for individual screens.
(3) According to a third feature of the present invention that includes the second feature (2), the method further comprises the steps of inspecting a condition of the printing material printed on the object; and adjusting, based on a result of the inspection, the pushing pressure changed according to the predetermined pressure pattern.
The pushing-pressure controlling method according to the third feature (3) adjusts, based on the inspected condition of the printing material printed on the object, the pushing pressure for being used in another printing operation for another object. Therefore, even if the quality of printing performed in an initial period according to the predetermined pressure pattern may be not satisfactory, the quality of printing can be eventually improved and satisfied as the total number of objects printed increases. The condition of the
Adachi Jun
Isogai Takeyoshi
Mizuno Manabu
Saito Tatsumi
Fuji Machine Mfg. Co. Ltd.
Oliff & Berridg,e PLC
Yan Ren
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