Method for orientating print material for correct printing in a printing position externally of a printing position

A method for correctly orienting print material in a silk screen printer includes determining the position of the print material relative to a reference position, storing that position, moving the print material to a printing position, printing a pattern on the print material, returning the print material to the previously determined position, and determining if a discrepancy exists between the desired position of the pattern and the actual position of the pattern on the print material. If a discrepancy exists between the desired and the actual position, one of a stencil frame, the print material, a printing table, and a first registered position is displaced for successive pieces of print material to minimize the discrepancy in successive actual pattern positions.

TECHNICAL FIELD 
The present invention relates to a method for orientating a second pattern 
deriving from a first pattern formed on a stencil in relation to print 
material intended to receive said second pattern, so that the second 
pattern will have a pre-determined position or location in relation to 
said print material. 
When the present invention is applied in a silk screen printer, the second 
pattern is formed by causing, in a printing location, coating substance or 
ink paste to pass through perforations in a cloth forming the first 
pattern and onto the print material, e.g. with the aid of a squeegee 
arrangement in a silk screen printer. 
The present invention is also based on the assumption that the co-ordinates 
which define the position of the second pattern in relation to the print 
material are stored in a memory, so that co-ordinates applicable to a 
selected position can be compared with the co-ordinates applicable to the 
determined position of the pattern in relation to the print material. 
BACKGROUND PRIOR ART 
The U.S. Pat. No. 4,516,495 teaches a method of positioning in a printing 
location a second pattern, deriving from a first pattern formed on a 
stencil, in relation to print material intended to receive the second 
pattern, and in which method the second pattern is formed by causing a 
coating substance or an ink paste to pass through perforations or open 
meshes in the cloth forming the first pattern and onto the print material, 
e.g. with the aid of a squeegee arrangement in a silk screen printer. 
According to this known method the two-dimensional position of the second 
pattern in relation to a reference point, normally a frame part of the 
printer, is stored in a memory, and when the material to which the second 
pattern is transferred has been moved to a printing position, the 
prevailing position of the material or the prevailing position of a 
pattern applied to the material is evaluated together with any discrepancy 
which would occur if the second pattern were to be applied to the print 
material while the material occupied its present position. 
It is also proposed that a frame carrying a stencil exhibiting the first 
pattern and/or a printing table and/or the actual printing material is 
displaced in response to the magnitude and directional sense of the 
discrepancy to an extent such that when the second pattern is applied to 
the print material in this printing position, the pattern will have a 
position on the material in which the previously identified discrepancy is 
fully compensated for or satisfactorily compensated for. 
The proposed method requires one or more material-positioning detecting and 
establishing devices to be introduced between stencil and print material 
when the material occupies a printing position, so as to enable the 
magnitude and directional sense of the discrepancy to be evaluated, and 
further requires the print material or the pattern to be displaced in 
order to compensate for the evaluated discrepancy prior to commencing the 
printing operation. 
The disclosures made in U.S. Pat. No. 4,221,165 also form part of the prior 
art, this specification teaching a silk screen printer which includes a 
plurality of gripping beams which, in a first position--a material feed 
position, grip the material on which print is to be applied in a second 
position, a printing position, while registering the gripping beams. 
This enables the print material to be moved along a precise transport path 
from the material feed position to the printing position. This precise 
transport path is afforded by the fact that each of the gripping beams can 
be registered relative to the printer chassis, or a part thereof, both of 
said positions. 
For the purpose of registering the print material in the first position, it 
is proposed that in addition to a first registering means co-acting with 
the gripping beams a separate means is provided for co-action with the 
print material, so as to obtain precise registration of the print material 
in the first position, such that a registered gripping beam is able to 
collect a pre-registered print material and transport said material 
through an exact distance to the printing position. 
SUMMARY OF THE INVENTION 
Technical Problems 
When considering the state of the prior art, as expressed in the aforegoing 
it will be seen that a technical problem resides in orientating print 
material externally of a printing position with the aid of simple means, 
so that when the print material is moved to the printing position the 
material will take a position such that a second pattern deriving from a 
first pattern carried by the stencil is applied to the material with a 
minimised discrepancy, by allowing a previous print on a print material to 
first serve as a standard, by storing in a computer system, via an optical 
detecting means, prevailing two-dimensional position values applicable to 
the earlier print in relation to the printer chassis or some other 
reference point, so that the position of the print material can be changed 
in the material feed position by stepping motors to a position in which 
the subsequent displacement to the printing position and subsequent 
printing affords correct orientation of the second pattern on the print 
material. 
When considering the state of the prior art, as described in the 
aforegoing, it will also be seen that a technical problem resides in the 
ability to print the second pattern in the printing position precisely on 
the print material with a degree of accuracy similar to the accuracy 
achieved in a silk screen printer of the kind described and illustrated in 
the U.S. Pat. No. 4,516,495, but where the position of the print material 
can be read off without needing to introduce position-detecting devices 
between stencil and print material. 
It will also be seen that a further technical problem, and one that 
requires qualified technical insight, resides in the realisation that the 
position of a table serving as a material feed location and displaceable 
in two directions can be changed with the aid of stepping motors, three 
stepping motors, in a manner such that the position of the table, and 
therewith the position of the print material, can be adapted to the 
position of the subsequent second pattern before the material is gripped 
by grippers or moved in some other way to the printing position through an 
exact known transport distance. 
Another technical problem resides in the ability of increasing the printing 
rate, preferably to a rate higher than that achieved with a printer 
according to U.S. Pat. No. 4,516,495, without departing from the 
requirement of satisfactory accuracy with regard to the position of the 
second pattern on the print material, particularly when manufacturing 
printed circuit cards. 
It will also be seen that a further technical problem is one of creating 
conditions, with the aid of simple means, which will enable the prevailing 
position of print material intended for receiving a second pattern to be 
established in a material feed position and in response to the detected 
position, and when necessary to so change the position of the first 
pattern formed on a stencil relative to the print material when said 
material is displaced to the printing position through an exact transport 
distance that a second pattern applied in the printing position to said 
print material obtains a pre-determined orientation in relation to the 
print material. 
It is advantageous in this case to incorporate measures which will enable 
the print material to be moved along an exact transport path, to within 
narrow tolerances, from a material feed position to a printing position or 
location without altering the orientation of the material there-between. 
With regard to the determining of the position of the print material in a 
material feed location it will also be seen that a further technical 
problem resides in the ability to compensate for the discrepancy which can 
be expected to occur in a printing location or position as a result of 
stretching the first pattern on the stencil when this first pattern is 
transferred with the aid of a squeegee to the print material in the form 
of a second pattern. 
A further technical problem resides in the provision of conditions, in a 
simple manner, which will enable compensations to be made for the 
unambiguous and constant discrepancy which is caused when a new stencil 
frame with a stretched stencil therein is inserted into the frame holder 
of the printer. 
A further technical problem resides in the provision of conditions, with 
the aid of simple means, which will enable print material to be moved in 
an exact manner from a first material feed location to a printing position 
and, subsequent to printing a second pattern on said material, to move the 
thus printed material back to the first material feed position for 
registration so as to be able to establish in said feed position the 
position of the print applied on the print material and to store 
two-dimensional co-ordinate data thus obtained. 
It will also be seen that a further technical problem resides in the 
provision of conditions, with the aid of simple means, whereby with the 
aid of this information printing of the second pattern on subsequent print 
material can be controlled in a manner such that the second pattern would 
be printed in a pre-determined position with a positional deviation 
smaller than 0.5 mm, preferably smaller than 0.03 mm, such accuracy being 
necessary in the manufacture of printed circuit board. 
Another technical problem in this regard is one of realising that the 
accuracy afforded is related strongly to the resolution of the detecting 
means or camera equipment used. 
Finally, it will be seen that a further technical problem resides in 
registering print material upstream of the printing position in a manner 
which affords substantially the degree of accuracy obtained with an 
arrangement according to the U.S. Pat. No. 4,221,165, but where a print 
serving as a reference value consititutes a standard for positioning the 
print material in the material feed position or location. 
SOLUTION 
The present invention is based on the fundamental features described and 
illustrated in the U.S. Pat. No. 4,516,495 and relates to a method of 
orientating a second pattern, deriving from a first pattern formed on a 
stencil, in relation to print material intended to receive said second 
pattern, so that the second pattern will have a predetermined position in 
relation to said print material, and in which method the second pattern is 
formed by causing, in a printing position, coating substance intended for 
said print material to pass through the first pattern and onto the print 
material, e.g. with the aid of a squeegee in a silk screen printer, and in 
which the position of the second pattern determined in relation to said 
print material is stored in a memory. 
The present invention proposes in particular; 
(a) That in a first registered position, a material feed position, the 
position of the print material is read-off in relation to a reference 
value, e.g. a printer chassis or part thereof, and the measurement value 
stored; 
(b) That the print material is again passed to a second registered 
position, a printing position for receiving the second pattern. 
(c) That the print material to which the second pattern is applied in 
accordance with "b" above is passed to the first position and registered 
in said position, and the position of the printed second pattern relative 
to said reference value is read-off and the resultant measurement value 
stored; 
(d) That the stencil frame carrying the first pattern and/or the print 
material, and/or the printing table or alternatively the first registered 
position for the material is displaced in response to the established 
discrepancy between the actual position on the pattern, obtained in the 
transfer to "b", and its pre-determined position, to an extent such and in 
a direction such as to minimise the established discrepancy; 
(e) That each subsequent print material, registered in the first and the 
second position in a similar manner is coated in the second position with 
a second pattern applied with minimised discrepancy. 
In the capacity of a further development, the expression "minimised 
discrepancy" used in connection with the present invention implies full 
compensation of an established discrepancy, or compensation which can be 
deemed satisfactory in view of prevailing circumstances. 
In accordance with a further development, the discrepancy which constantly 
occurs with an exchange of a stencil and stencil frame for applying a 
further pattern to print material in relation to the earlier applied 
second pattern is compensated for by applying the further pattern to the 
print material in accordance with "b", by establishing any discrepancy in 
the second pattern in accordance with "c", and compensating an occurrent 
discrepancy by displacing position-detecting means in the first registered 
position into the material feed position to an extent and a direction such 
as to minimise the established discrepancy and to lock these means in a 
thus set new position. 
ADVANTAGES 
Those advantages primarily afforded by a method according to the present 
invention reside in the provision of conditions for registering the print 
material in a material feed position, and there establish the position of 
the material optically upstream of the printing position, so that when the 
material is moved through a constant transport path to the printing 
position, the second pattern can be applied exactly without needing to 
subsequently check the position of the print by introducing 
position-detecting means between stencil and material. 
The primary characteristic features of a method according to the present 
invention are set forth in the characterising clause of the following 
claim 1.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED 
FIG. 1 is a horizontal view of a silk screen printer 1 incorporating a 
squeegee arrangement 2 and a filler 3 arranged for reciprocating movement 
in guides 4,4a extending transversally to the material transport direction 
"P". A stencil 6 which has a first pattern 6a is stretched in a stencil 
frame 5, which is fixed in relation to the printer chassis. The pattern 6a 
is transferred by the squeegee arrangement 2 to print material 7, to form 
a second pattern 7a on said material. The two patterns 6a and 7a are 
slightly different from one another. This difference does not solely 
reside in the fact that one is formed on the stencil and the other is a 
print applied to the material, but also because the first pattern is 
slightly distorted when applied to the print material to form said second 
pattern, due to stretching of the stencil cloth as the squeegee moves 
thereacross. 
For the sake of clarity, the position of the second pattern 7a on the print 
material 7 has been slightly exaggerated in FIG. 1 and is shown on one 
side of the pattern 6a. 
The invention thus relates to a method of orientating the second pattern 
7a, which derives from the pattern 6a carried by the stencil 6, in 
relation to the print material 7 onto which the first pattern is printed 
to provide the second pattern 7a, so that the second pattern 7a will take 
a predetermined position relative to the print material 7, without needing 
to introduce material position-determining devices between stencil and 
printing table in the printing position. 
The second pattern 7a is formed by causing, in a printing position, coating 
substance, printing paste or the like to pass through perforations or 
meshes conforming to the first pattern 6a in the stencil cloth, and onto 
the print material 7 located in the printing position, e.g. with the aid 
of the squeegee 2 in the printer 1. 
The established position of the second pattern 7a in relation to the print 
material 7 is stored in a memory of a central control unit 8 which is 
preferably constructed for printer operation and positioning of the second 
pattern. The central unit 8 is connected with a first camera arrangement 
10 via a cable 9 and to a second camera arrangement 12 by a conductor 11. 
The central unit 8 is of a kind known to the art and the principle 
construction of said unit does not therefore form any part of the present 
invention and the following description will only relate to those 
functions of the central unit necessary for evaluating the position of the 
pattern on the print material and for controlling the actions of known 
stepping motors 13, 14 and 15. 
A more comprehensive understanding of the manner in which the aforesaid 
positions are determined, and discrepancies calculated, together with the 
manner in which the stepping motors are activated, can be obtained from 
the U.S. Pat. No. 4,610,200. 
In the case of the exemplifying embodiment illustrated in FIG. 1, the 
position of the print material 7' in a first registered material-feed 
position "A" is established in relation to a reference value by means of 
the camera 10, 12, said reference being the printer chassis 16 for 
example, and the co-ordinates thus obtained are stored in the memory of 
the central unit 8. 
The material is then moved to a second registered position "B", namely a 
printing position where the second pattern 7a is applied to the print 
material by means of the squeegee 2. The distance moved by the print 
material is determined precisely. 
In accordance with the invention, the print material 7 with the second 
pattern 7a thereon is moved back to the first registered material-feed 
position "A" and the position of the second pattern 7a is established in 
said registered position and the co-ordinates read-off and stored, in a 
known manner, in the central unit 8. 
When the co-ordinates defining a desired position of the second pattern 
have previously been determined, it is possible with the aid of the camera 
arrangements 10 and 12 and the control unit computer to establish any 
discrepancy between the intended position of the pattern and its actual 
position and to activate the stepping motors 13, 14 and 15 in a manner 
which will ensure that all subsequent prints will be positioned correctly 
on the respective print materials. 
If the co-ordinates of the desired pattern position have not previously 
been determined, the relevant co-ordinates can be obtained by inserting 
the position of the first print and the displacement required for 
correctly positioning the print on the print material. 
Thus, in response to a discrepancy established between the actual position 
of a pattern obtained when transferring the first pattern to the print 
material to obtain said second pattern and its pre-determined position, 
the stencil frame 5, carrying the stencil 6 which exhibits the first 
pattern 6a, or alternatively the print material 7 and/or the printing 
table 17 is displaced with the aid of the stepping motors 13,14 and 15 to 
an extent and in a direction such as to minimise the discrepancy 
established. The established discrepancy and the extent to which the 
different stepping motors are activated are evaluated in the central unit 
8. 
Each subsequent print material registered in a similar manner in the first 
position "A" and in the second position "B" are printed in said second 
position "B" with the second pattern 7a, which is applied with minimised 
discrepancy. 
By "minimised discrepancy" is meant full compensation for an established 
discrepancy, or a compensation which can be considered satisfactory under 
the circumstances. 
In accordance with the invention, when a stencil and stencil frame are 
changed in order to apply further pattern on the print material, any 
discrepancy, normally a constant discrepancy, in relation to the second 
pattern occurring as a result of this change is compensated for by, in the 
same manner as a further pattern applied to the material and the 
subsequent possible discrepancy in relation to the pattern is compensated 
for, displacing the position-detecting devices 10, 12 to an extent and in 
a direction such as to minimise the established discrepancy, whereafter 
these devices are locked in their respective set positions. 
In the case of the embodiment illustrated in FIG. 2, the material feed 
position "A" has the form of a table 20' which can be moved selectively in 
the direction of two coordinates. The table 20' is moved by means of three 
stepping motors 13', 14' and 15', in a manner similar to the stepping 
motors illustrated in FIG. 1. 
This embodiment enables the position of the table to be changed so that the 
print material 7' is registered in a position such that, subsequent to 
moving along the precisely defined transport path to the printed position, 
the material will be located in the desired printing position, where the 
second pattern is applied to the print material in a predetermined 
position or orientation. 
It will be understood that the described and illustrated embodiments do not 
restrict the invention and that modifications can be made within the scope 
of the following claims.