Control system for blank presser

A control system for a blank presser used to touch down blanks fed from a conveyor controls the blank presser so as to hold down each of the blanks at the proper time, so as to thereby prevent them from scattering or jamming up. The control system can control the blank presser automatically even if the speed or length of the blanks changes.

The present invention relates to a control system for a blank presser used 
to timely and lightly touch down blanks fed from a conveyor, thereby 
preventing them from scattering or jamming up. The control system is 
adapted to adjust the movement of the blank presser automatically in 
response to any change in the blank feed speed and the blank length. 
In the production line of corrugated fiberboard, a web of corrugated 
fiberboard is cut into blanks of a predetermined length by a rotary 
cutter, said blanks being fed by a first conveyor running at a slightly 
higher speed than the web speed and then further fed shingled on a second 
conveyor running at a slightly lower speed than the first conveyor. At the 
supply end of the second conveyor, a blank presser is usually provided. 
The first conveyor serves to prevent the jamming between the rear end of 
the last blank just cut and the front end of the web and/or the cutting 
blade of the rotary cutter. The second conveyor serves to bring the blanks 
fed one after another into a shingled state. Also, the blank presser 
serves to press or hold down the blanks fed at a high speed, thereby 
preventing them from scattering or jamming up. 
The best timing for the blank presser to hold the blank is at the instant 
the blank leaves the first conveyor or just before or just after that. If 
the timing were too late, the blanks would scatter and jam up, causing 
trouble. If the timing were too early so that the blank is held by the 
presser before it leaves the first conveyor, the blank would be rubbed by 
the first conveyor, interfere with the next blank or be bent between the 
first conveyor and the second one. 
Also, the period at which the blank presser touches the blanks has to be 
changed each time the blank length or the blank feed speed is changed. 
Further, the length of the first conveyor has to be taken into 
consideration for optimum timing. Conventionally, the movement of the 
blank presser had to be watched and adjusted by hand each time the blank 
length or the blank speed changes. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a control system for a 
blank presser which eliminates the need of watching and manual adjustment 
of the blank presser even in the presence of any change in the blank 
length or blank speed. 
In accordance with the present invention, a control system for controlling 
a blank presser used to touch or hold down each of blanks fed one after 
another from a conveyor, sets a value (L) proportional to the length of 
the blanks fed from said conveyor and a value (l) proportional to the 
distance by which said blank presser moves in one cycle of its operation, 
and then generates a signal (.phi..sub.A) proportional to the speed at 
which said blanks are fed and a signal (.phi..sub.B) proportional to the 
speed of said blank presser, and then performs a computation expressed by 
l/L.times..phi..sub.A -.phi..sub.B ; the system then combines an error 
voltage proportional to the result of the computation with a reference 
voltage proportional to said signal (.phi..sub.A) multiplied by l/L, and 
then controls a drive for said blank presser by use of the combined 
voltage so that the blanks will be held down by said blank presser at a 
correct timing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 2 showing a blank presser used in the present 
invention, a web 1 of corrugated fiberboard is fed by a pair of feed rolls 
2 to a rotary cutter 3 where it is cut into blanks B of a predetermined 
length. The blanks are fed on a sandwich belt conveyor 4 to a belt 
conveyor 5 which feeds the blanks to the next station. The sandwich belt 
conveyor 4 has at least one pair of belts between which each blank is 
clamped to be fed. The speed of the sandwich belt conveyor 4 is set to be 
equal to or slightly higher than the speed of the web 1 to prevent trouble 
due to interference between the tip of the web 1 and the rear end of the 
last blank B. Also, the speed of the belt conveyor 5 is set to be lower 
than both that of the conveyor 4 and the web speed and the supply end of 
the belt conveyor 5 is below the discharge end of the conveyor 4 so that 
the blanks will be shingled on the belt of the conveyor 5 for feeding to 
the next station. In order to prevent the blanks (fed at a considerably 
high speed) from jamming up, a blank presser brush 6 is provided at the 
supply end of the conveyor 5 so as to touch or hold down each of the 
blanks just about when the blank has left the sandwich belt conveyor 4. 
With the conventional blank presser, the brush 6 was mounted so as to be 
movable back and forth as shown in FIG. 1 by arrow. Conventionally, the 
position of the blank presser had to be manually adjusted back and forth 
according to the length of the blanks and the blank feed speed. 
Referring again to FIG. 2, a blank presser generally designated by numeral 
9 comprises a presser brush 6 fixedly mounted on an arm 10 through a 
mounting bar 11, said arm being coupled through a rod 12 to a crank disc 
13. By this arrangement, the rotation of the crank disc is converted to a 
rocking motion of the presser brush 6. The blank presser 9 is disposed at 
such a position that the brush 6 can hold down all the blanks at a fixed 
position some distance away from their rear end even if the length of the 
blanks is minimum. The brush is adapted to touch each of the blanks at its 
fixed position while rocking in a vertical plane. 
The sandwich belt conveyor 4 is driven by a first driving motor 7 to which 
is connected a first pulse generator 8 for generating pulses, the number 
of which is proportional to the revolutions of the motor 7. The crank disc 
13 is driven by a second driving motor 14 to which are connected a 
tachometer generator 15 giving a signal proportional to the speed of the 
motor 14 and a second pulse generator 16 for generating pulses, the number 
of which is proportional to the revolutions of the motor 14. 
In order to detect that each rocking motion of the brush 6 has been 
completed, a marker 17 is fixedly mounted on the crank disc 13 and a 
detector 18 is provided near the crank disc to detect the marker, giving a 
detection signal S. The detector 18 is adapted to give the detection 
signal when the presser brush 6 starts holding down the blank B. 
Next, a control circuit for the blank presser embodying the present 
invention will be described with reference to FIG. 3. 
Firstly, two values L and are set in a first setter 30. The values L and l 
are proportional to the length of the blanks B and the circumference of 
the crank disc 13, respectively. These values L and l are given to a 
divider 31 which divides the value l by L to obtain a coefficient K 
(=l/L). 
A multiplier 32 multiplies the coefficient K by a pulse signal .phi..sub.A 
from the first pulse generator 8 which is proportional to the length for 
which the blank has been fed. The signal K.phi..sub.A from the multiplier 
32 is put into a first frequency/voltage (F/V) converter 33 which converts 
the frequency of the signal K.phi..sub.A to a voltage, which is used as a 
reference voltage V.sub.A for the second motor 14. 
A first counter 34 starts the counting of the pulse signal .phi..sub.A in 
response to an external signal A and gives a timing signal T when the 
count has reached a value X proportional to the distance between the web 
cutting point and the discharge end of the sandwich belt conveyor 4. The 
external signal A is a signal indicating that the blank has been supplied 
to the sandwich belt conveyor 4, e.g. a cutting complete signal given at 
the instant when the rotary cutter 3 has completed the cutting. The first 
counter 34 and the divider 31 will be described later in more detail. 
A position compensation circuit 35 receives a pulse signal .phi..sub.B from 
the second pulse generator 16, the timing signal T and the detection 
signal S; the circuit then checks the position of the marker 17 each time 
the timing signal T is given, and gives a compensation value E 
proportional to the amount of deviation from the correct position of the 
crank disc 13. (It should be at such a position that the brush comes to 
the operative position just when the timing signal T is given.) The 
compensation value is set to be negative when the marker 17 is leading 
against the correct position and be positive when it is lagging. 
In the position compensation circuit 35, a second counter 36 for counting 
the pulse signal .phi..sub.B from the second pulse generator 16 is reset 
and restarts the counting each time the detector 18 senses the marker 17 
and gives a detection signal S. The count N in the second counter 36 is 
stored in the memory circuit 37 in response to the timing signal T. The 
value l, which is the same as the one set in the first setter 30, is set 
in a second setter 38 and given to a comparator 39, which compares the 
count N from the memory circuit 37 with the value l/2 and gives a value E 
(E=-N when N&lt;/2 and E=-N when N.gtoreq.l/2.) The comparison of N with l/2 
is done to check whether the marker 17 is at the correct position or is 
lagging or leading when the timing signal T is given. The count N may be 
compared with a value l/3 or any other suitable value. Because the control 
does not have to be so accurate, the position compensation circuit 35 may 
be adapted so that its output will be zero if the absolute value of the 
compensation value E is below a predetermined value. 
A third counter 40 counts up the signal K.phi..sub.A, from the multiplier 
32 and counts down the pulse signal .phi..sub.B from the second pulse 
generator 16. It also reads the compensation value E from the position 
compensation circuit 35 in response to the timing signal T from the first 
counter 34 and gives the result of the computation M=K.phi..sub.A 
-.phi..sub.B +E, to a digital/analog converter 41 which converts the value 
M to an analog error voltage Vc. The error voltage Vc and the reference 
voltage V.sub.A are given to an operational amplifier 42 which combines 
them and gives a speed reference voltage Vo (=V.sub.A +Vc) for the second 
motor 14. 
A second F/V converter 43 converts the pulse signal .phi..sub.B from the 
second pulse generator 16 to a voltage V.sub.B proportional to its 
frequency. A speed command unit 44 compares the voltage V.sub.B fed back 
with the speed reference voltage Vo to check to see if the second motor 14 
for the blank presser is operating at a speed corresponding to the 
reference voltage. If there is any difference therebetween, the speed 
command unit 44 will add it to, or subtract it from, the reference voltage 
Vo so that the motor will rotate just at Vo. If the voltage Vo is zero, 
the speed command unit 44 will stop the motor 14. 
The blank presser is controlled so that the crank disc 13 makes one full 
turn each time one blank is fed from the sandwich belt conveyor 4. 
In short, a computing means 45 including the setter 30, divider 31, 
multiplier 32, F/V converter 33, counter 34, counter 40, D/A converter 41 
and operational amplifier 42 multiplies the pulse signal .phi..sub.A from 
the first pulse generator 8 by a coefficient K (equal to the circumference 
l of the crank disc 13 divided by the length L of blanks), counts up the 
product K.phi..sub.A and counts down the pulse signal .phi..sub.B from the 
second pulse generator, and combines the voltage Vc corresponding to the 
result of counting, K.phi..sub.A -.phi..sub.B or K.phi..sub.A -.phi..sub.B 
+E (E is the compensation value from the circuit 35) with the voltage 
V.sub.A corresponding to the product signal K.phi..sub.A, and gives a 
voltage V.sub.A +Vc. 
Although in this embodiment the product signal K.phi..sub.A is first 
obtained and then the reference signal V.sub.A is obtained therefrom, 
V.sub.A may be obtained in any other way, e.g. by converting the pulse 
signal .phi..sub.A to a voltage and multiplying the voltage by the 
coefficient K. 
Referring next to FIG. 4, the first counter 34 comprises a 4-bit ring 
counter 47 for counting the external signal A, four presettable counters 
48a to 48d, and an OR circuit 50. The divider 31 comprises a dividing unit 
51, four memories 49a to 49d, and a data selector 52. The counters and the 
memories with the same suffix make a pair, respectively. The ring counter 
47 gives a signal for selecting one of the counters 48 and its respective 
memory 49 one after another each time it receives the external signal A. 
The selected counter starts the counting in response to the signal from 
the ring counter 47 and gives a signal to the OR circuit 50 when its count 
reaches the preset value X. The OR circuit 50 gives a timing signal T in 
response to the signal from one of the counters 48. The selected memory 49 
registers the output of the dividing unit 51 which reads the values L and 
l from the setter 30 and performs a division l/L. 
The data selector 52 outputs to the multiplier 32 the value stored in the 
memory 49 associated with that counter 48 from which a signal has been 
given, from when one counter has given a signal to when the next counter 
gives a signal. For example, it outputs the value stored in the memory 49a 
from the instant the counter 48a has given a signal to the instant the 
counter 48b gives a signal. 
The number of the counters 48 and the memories 49 must be the same and may 
be predetermined according to the length of the blank and that of the 
sandwich belt conveyor 4 and thus the value X. The data selector 52 may be 
a memory circuit registering the value registered in the associated memory 
49 in response to the signal from one of the counters 48. 
The change in the setter 30 from one blank length L (that is the cutting 
length) to another is done at the same time as the issuance of the 
external signal A, e.g. in the following manner. The rotary cutter 3 gives 
a cutting complete signal, that is, the external signal. In response to 
the signal, a new cutting length is written in a setter on the speed 
controller for the rotary cutter 3. It is simultaneously it is set in the 
setter 30 of the control system according to the present invention. 
Although the divider 31 shown in FIG. 4 includes a plurality of memories 49 
and a data selector 52, if the web cutting length, that is, the blank 
length, does not change but is fixed, the memories and the data selector 
may be omitted. In this case, the divider 31 merely registers the value L 
(blank length) from the setter 30, divides the value l by the value L, and 
gives the result of division to the multiplier 32. 
The divider 31 may be comprised of a plurality of blank length memories 
paired with the counters 48 and a dividing unit. Each time the count of 
the ring counter 47 changes, the associated blank length memory registers 
the blank length L which will be selected at the same time when the 
respective counter gives a signal, the dividing unit determining the 
coefficient K.sub.1 (=l/L) and supplying it to the multiplier 32. Thus, 
the requirement for the divider is that it gives to the multiplier 32 a 
coefficient determined on basis of the length of the blank next to the 
blank that has just left the sandwich belt conveyor 4. 
Next, it will be described how the blank presser is controlled if the blank 
length has changed. 
Firstly, let us assume that the web is cut by the rotary cutter into blanks 
of a length L.sub.1 and that L.sub.1 is set in the setter 30 and that all 
the memories 49a to 49d register the coefficient K.sub.1 =l/L.sub.1. When 
the last cutting into lengths L.sub.1 is complete, the blank length set in 
the setter 30 changes from L.sub.1 to L.sub.2 (as mentioned above, L.sub.2 
has been preset) in response to the cutting complete signal for the last 
cutting into length L.sub.1. Now, the dividing unit 51 outputs K.sub.2 
=l/L.sub.2. In response to the cutting complete signal, which is the 
external signal A, the ring counter 47 changes in its counts and gives a 
signal to select the pair of counter 48 and memory 49 corresponding to its 
new count. If the counter 48a and the memory 49a are selected, for 
example, the former starts the counting and the latter newly registers the 
coefficient K.sub.2 =l/L.sub.2 from the dividing unit 51. When the count 
reaches the value X, the counter 48a gives a signal. In other words, the 
instant the last blank of length L.sub.1 has left the sandwich belt 
conveyor 4, the counter 48a gives an output signal. The data selector 52 
selects the memory 49a, which gives the coefficient K.sub.2 =l/L.sub.2 to 
the multiplier. The rest is the same as when the blank length is fixed. 
The presser is controlled so that the brush presses the blank with the new 
length L.sub.2 at a correct timing when it has just left the sandwich belt 
conveyor. 
The circuit arrangement is such that the result of computation M 
(=K.phi..sub.A -.phi..sub.B +E) from the counter 40 will be zero. If M is 
less than zero (&lt;0), the error voltage Vc will be negative. Thus, the 
speed reference voltage Vo is V.sub.A +(-.vertline.Vc.vertline.)=V.sub.A 
-.vertline.Vc.vertline.. This means that it is lower than the reference 
voltage V.sub.A by the absolute value of the error voltage Vc. Therefore, 
the second motor 14 for the blank presser is decelerated so that the pulse 
signal .phi..sub.B will decrease. Thus, M(=K.phi..sub.A -.phi..sub.B +E) 
will go back to zero. 
If M becomes above zero (&gt;0), Vc will be positive. Thus, Vo (=V.sub.A +Vc) 
is higher than the reference voltage V.sub.A by the error voltage Vc. The 
second motor 14 is accelerated so that the pulse signal .phi..sub.B will 
increase. Thus, M will go back to zero. In short, control is made so that 
the value M will be zero. This means that the second motor 14 for the 
blank presser is controlled so as to rotate at a predetermined ratio of 
revolutions with respect to the first motor 8 for the conveyor. 
Summing up, what is done in this control system is to multiply the pulse 
signal .phi..sub.A proportional to the blank feed speed by a coefficient K 
(=l/L), use the signal K.phi..sub.A as the reference speed of the second 
motor 14 for the blank presser 9, compare the actual speed of the sandwich 
belt conveyor 4 with the reference speed, and if there is any difference 
therebetween, accelerate or decelerate the second motor 14 to eliminate 
the difference. If there is any time difference between the occurrence of 
the detection signal S and that of the timing signal T (this means that 
the crank disc 13 is turning too quickly or too slowly for satisfactory 
pressing of the blank), too, the second motor 14 is accelerated or 
decelerated according to the amount of time difference. This compensation 
is performed by means of the position compensation circuit 35. 
The sandwich belt conveyor 4 may be replaced with any other type of 
conveyor, e.g. a suction conveyor. 
Although in the preferred embodiment a brush is used for the blank presser, 
it may be replaced with a roller or any other suitable member. 
Although in the preferred embodiment the brush is adapted to rock, it may 
be adapted for an up-and-down or any other movement. 
The control system for a blank presser according to the present invention 
may be used with any other type of conveyor than the conveyor 5 used in 
this invention, e.g. a vertically movable stacker on which the blanks are 
stacked one upon another. 
For the control system for the blank presser in accordance with the present 
invention, a computer such as a microcomputer may be used with the use of 
software (program) for part or all of the control. 
It will be understood from the foregoing that the present invention 
eliminates the need for watching and manual adjustment of position or 
movement of the blank presser because the blank presser is automatically 
controlled according to the change in the blank length and the blank feed 
speed to ensure that the blanks will be timely held down by the brush so 
that they will not jam up.