P R O G R A M M I N G E X A M P L E S
ROTATING KNIFE
Programming Examples
117
A rotating knife system, illustrated at the right, is used to cut
webs of paper or plastics at a given length. The web moves
independently and the knife is synchronized so that the
blade moves at the same linear speed as the web during the
cutting interval. When the cutting is completed, the knife is
advanced or retarded in a manner that produces a required
cut length.
The method illustrated here applies with slight modifica-
tions to applications of printing on moving webs or applying
labels.
Requirements
Web speed: Zero to 120 inches per second, independent
motion (master)
Knife circumference: (
×
diameter) = 20 inch
Required cut length: 16 to 40 inches, programmable
Resolution of web encoder: 1000 counts/inch
Resolution of knife: 10000 counts/rev or 500 counts/inch
Required accuracy: 0.005 inch noncumulative error
The knife is driven by a motor and an external amplifier.
An additional encoder senses the position of the moving
web.
Operation
Suppose that the required cut length is 16 inches. This
implies that the knife must perform one revolution for every
16-inch move of the web. In addition, while the knife is in
contact with the web, its blade must move at the same linear
velocity as the web. Suppose, for example, that the knife
and the web must move in synchronization over 4 inches of
travel. This implies that over the remainder of the cycle the
web moves 12 inches and the blade moves 16 inches. This
indicates that the speed ratio varies over each cycle as shown
in the top graph of the motion figure. The corresponding
position of the knife is as described by the bottom figure.
Such relationship between master position (web) and slave
postion (knife) is known as electronic cam.
To construct the table, note that the motion consists of
four intervals:
Web Knife
Interval Motion Motion Ratio
1
4000
2000 Constant
2
4000
2500 Varies
3
4000
3000 Constant
4
4000
2500 Varies
The above intervals are applied Galil's ECAM program
which generates the table. To reduce the program length, the
table size has been reduced to 16 points only.
To operate the system, the knife is driven to the starting
point of the cutting interval and the program is executed.
Instruction
Interpretation
#CAM
Label
EAX
Define X axis as master
EM 16000, 10000
Table cycles
ET[0]=0,0; ET [1]=1000,500
ET[2]=2000,1000; ET [3]=3000,1500
ET[4]=4000,2000; ET [5]=5000,2531
ET[6]=6000,3125; ET [7]=7000,3781
ET[8]=8000,4500; ET [9]=9000,5250
ET[10]=10000,6000; ET [11]=11000,6750
ET[12]=12000,7500; ET [13]=13000,8219
ET[14]=14000,8875; ET [15]=15000,9469
ET[16]=16000,10000
DP 0,0
Define starting points
EB 1
Activate CAM
EG 1
Engage CAM
Rotating Knife
WEB
KNIFE
0
4000
8000
12000
16000
WEB POSITION
KNIFE
VELOCITY
KNIFE
POSITION
2000
2000
4500
7500
10000
2500
3000
2500
Rotating Knife System
Required Motion Profile
