1. Field of the Invention
The present invention relates to a method of registering two sheets, for example wood veneer sheets, at one ends thereof by aligning the ends against a registration stop surface, and also to an apparatus for practicing the method.
2. Description of the Related Art
Manufacturing of plywood which is made by gluing and pressing together, three or more veneer sheets, includes a process of cold pressing. In this cold pressing, a number of dried veneer sheets, including those veneer sheets which have both surfaces thereof coated with adhesive, is prepared. Veneer sheets having no adhesive and veneer sheets with adhesive coating are assembled by laying one sheet on another in a predetermined order to form a stack of such veneer sheets which is to be cold pressed. As is apparent to those skilled in the art, the assembling order varies according to the number of veneer layers in the plywood to be made. In making plywood of the simplest three-ply configuration, for example, two veneer sheets with no adhesive and one veneer sheet having adhesive coating on both surfaces are laid up in an alternate manner into a stack form for cold pressing. Informing the stack, veneer sheets should be arranged preferably with two adjoining sides thereof aligned properly so as to improve the yield rate of the resulting plywood.
Though the present invention is applicable to various kinds of sheet material, it can be used advantageously specifically in preparing sets of two registered veneer sheets at least one ends of which are aligned properly.
For better understanding of the underlying background of the present invention, reference is made firstly to FIG. 1 which shows a prior art veneer sheets registration apparatus. The apparatus includes a pair of first and second belt conveyers 1 and 5 which are disposed one above the other in a convergent relation to each other as shown in the drawing for moving first and second veneer sheets W1 and W2 forward in the respective arrow directions at the same speed so that the veneer sheets W1 and W2 meet at a position adjacent to the downstream ends of the conveyers 1 and 5. A third conveyer 9 is arranged which runs at the same speed as the first conveyer 1 and form a continuous conveying path with the first conveyer 1.
First and second sensors 3 and 7 are located in vertical alignment with each other as indicated by a phantom line adjacent to the respective downstream ends of the first and second belt conveyers 1 and 5 for detecting the arrival of the leading ends of the first and second veneer sheets W1 and W2 at positions defined by the sensors 3 and 7. The first sensor 3 is operable in response to the arrival of the leading ends of the first veneer sheet W1 to generate a signal to stop the first belt conveyer 1 and hence the movement of first veneer sheet W1. Likewise, the second sensor 7 generates a signal to stop the second belt conveyer 5 when the leading end of second veneer sheet W2 is detected by the second sensor 7. The first and second veneer sheets W1 and W2 indicated by solid lines in FIG. 1 shows a state where both sheets are stopped with the leading ends thereof positioned at the respective sensors 3 and 7.
After both veneer sheets W1 and W2 have been thus positioned, the belt conveyers 1 and 5 are restarted simultaneously thereby to move forward the veneer sheets W1 and W2 again. On their way of the movement, the veneer sheets W1 and W2 meet each other at their forward edges thereof as shown by phantom lines in FIG. 1 and then transferred to the third belt conveyer 9 in an assembled state wherein the second veneer sheet W2 is laid on top of the first veneer sheet W1 with their leading ends aligned with each other. The aligned two veneer sheets W1 and W2 are then transferred to a subsequent station (not shown) where they are laid on the top of a stack in progress as described before with reference to cold pressing of veneer sheets.
In the above-described apparatus, however, each of the belt conveyers 1 and 5 may move a slight variable distance before it is completely stopped after brake application to its belt driving motors, and also simultaneous restarting of the conveyers 1 and 5 does not necessarily occur with such an accuracy that the second veneer sheet W2 is laid on the first veneer sheet W1 with the desired alignment. Additionally, veneer sheets are usually bent or warped in various ways due to the inherent characteristics of veneer and hence they receives air resistance varying depending on the manner or extend of such bending or warping while moving on the conveyer, so that some veneer sheets may not move exactly in accordance with the movement of the belt conveyer. As a result, alignment of two veneer sheets at their leading ends may not be achieved as intended. Thus, it has been difficult to achieve the desired alignment of two veneer sheets merely by controlling the operation of the first and second belt conveyers 1 and 5 in the above prior art apparatus.
Therefore, it is an object of the present invention to provide sheets registration method and apparatus which can solve the above problems.
In order to achieve the above objects, the invention provides a method of registering two sheets each having opposite ends. According to the method, firstly the two sheets are assembled by laying one sheet on top of the other sheet in an overlapped relation to each other wherein one end of the upper sheet is positioned outward of one end of the lower sheet. Then, the two sheets thus assembled are moved along a conveying path by a conveyer in the above overlapped relation in such an orientation that the above ends are moved as the leading ends.
For registration of the sheets, there is provided registration stop means which has a stop surface extending on the way of the conveying path in perpendicular relation thereto. On the way of movement along the conveying path, firstly the upper sheet is stopped by the registration stop means with its leading end aligned against the stop surface of the registration stop means, and subsequently the lower sheet is stopped by the registration stop means, having its leading end aligned against the stop surface. Thus, both sheets are registered with the leading ends thereof aligned properly against the stop surface of the registration stop means.
Various methods may be contemplated for assembling the two sheets in the above overlapped relation. According to one preferred embodiment of the invention, one sheet may be laid on the other sheet while moving the two sheets at substantially the same speed along separate feed paths one disposed below the other and extending in a convergent relation to each other toward the conveying path of the conveyer. In such a case, movement of the first and second sheets is controlled such that the sheet coming out from the upper feed path is laid on the sheet coming out from the lower feed path in the desired overlapped relation.
In another method of assembling the sheets, two feed paths are provided one above the other and substantially in parallel to each other, and one sheet placed in the upper feed path is dropped onto another sheet placed in the lower feed path, as will be described more in detail in later part hereof.
The present invention also provides an apparatus of registering two sheets. The apparatus comprises a first conveyer for moving a first sheet along a first path and a second conveyer disposed above the first conveyer for moving a second sheet along a second path at substantially the same speed as the first sheet moved by the first conveyer. In association with the first conveyer, there is provided first sensor means disposed at a first predetermined position adjacent to the downstream end of the first conveyer as seen in the moving direction of the first sheet for detecting the arrival of the leading end of the first sheet moved by the first conveyer at the first predetermined position and generating a detection signal in response to detection of such arrival. Similarly, second sensor means is disposed at a second predetermined position adjacent to the downstream end of the second conveyer as seen in the moving direction of the second sheet for detecting the arrival of the leading end of the second sheet moved by the second conveyer at said second predetermined position and generating a detection signal in response to detection of such arrival. The apparatus further includes a third conveyer disposed so as to form a conveying path continuing from the first path. The first and second paths of the first and second conveyers are directed in a convergent relation to each other toward the third conveyer so that the second sheet coming out from the second conveyer is laid on the first sheet coming out from the first conveyer and the two sheets thus assembled are transferred onto the third conveyer. The third conveyer is operable to move the sheets at substantially the same speed as the first sheet moved by the first conveyer. Operation of the first and second conveyers is controlled according to the detection signals from the first and second sensor means such that the first and second conveyers are stopped when the arrival of the leading ends of the first and second sheets at the respective first and second predetermined positions are detected by the first and second sensor means, respectively. It is also controlled such that, after both sheets have been stopped, the first and second conveyers are restarted in such controlled timing that the second sheet is laid on the first sheet in an overlapped relation wherein the leading end of the second sheet is positioned forward of the leading end of the first sheet. The apparatus further includes registration stop means having a stop surface extending perpendicularly to the conveying path of the third conveyer and movable between the operative position thereof where the stop surface is placed so as to stop the sheets moved by the third conveyer at their leading ends, and the inoperative position thereof where the stop surface is retracted away from the conveying path of the third conveyer. While being moved by the third conveyer, firstly the upper second sheet is stopped at its leading end thereof by the stop surface and subsequently the first lower sheet is stopped at its leading end by the stop surface, whereby both sheets are registered with the leading ends thereof properly aligned against the stop surface of the registration stop means.
The third conveyer has at least one conveying belt which is made of such a material that the coefficient of friction between the conveying belt and sheet is greater than that between two sheets. By so providing the third belt conveyer, after the leading end of the second sheet has been stopped by the registration stop means, the first sheet is continued to be moved forward by the third conveyer in frictional contact with the moving belts thereof while sliding relative to the lower surface of the second sheet until its leading end is stopped by the registration stop means.
The apparatus may include third sensor means which is disposed adjacent to the stop surface of the registration stop means for detecting the arrival of the leading end of the second sheet at the stop surface and generating a detection signal in response to detection of such arrival. In such a case, operation of the third conveyer is so controlled that movement of the conveyer is stopped with a predetermined length of time delay after generation of the detection signal from the third sensor means and then to retract the registration stop means to its inoperative position, which is followed by restarting of the third conveyer. The time delay is set long enough for the leading ends of both sheets to be aligned completely against the stop surface of the registration stop means.
The apparatus of the invention should preferably include regulating means for preventing the sheets from being buckled when they are stopped by the registration stop means.
According to the present invention, it may be so arranged that the first and third conveyers are combined together to form a single conveyer for feeding the first sheet and moving the assembled two sheets toward the registration stop means.
Additionally, the second conveyer may be disposed above and substantially in parallel to the first conveyer and constructed so that it allows the second sheet thereon to be dropped off therefrom toward the first conveyer so that the second sheet is laid on the first sheet in an overlapped relation wherein the leading end of the second sheet is positioned forward of the leading end of the first sheet.
Features and advantages of the present invention will become more apparent to those skilled in the art from the following description of preferred embodiments of the the invention, which description is made with reference to the accompanying drawings, wherein: