5-1 Speed Compensation
Introduction To Speed Compensation
What Is It?
“Speed compensation” refers to the ability of the PS-6244 controller to automatically
advance or retard setpoints in any output channel depending on the speed of the ma-
chine. Speed compensation allows devices with fixed response times, such as glue
guns, to perform their functions with high accuracy over a wide range of machine speeds.
Without speed compensation, a glue bead may tend to “drift” out of position as machine
speed increases. By properly programming speed compensation for the output chan-
nel controlling the glue gun, the glue bead position can be maintained precisely over
the complete range of machine speeds.
Benefits
Proper use of speed compensation can provide substantial benefits:
• Increased Productivity—If a machine incorporates components with fixed response
times, speed compensation can often increase line speeds by as much as 50%.
• Reduced Scrap Rate—Speed compensation maintains the accuracy of critical oper-
ations such as gluing, thereby reducing rejects, rework, and scrap.
• Simplified PLC Systems—Programming speed compensation into standard motion
control equipment such as PLC’s, stepper motors, and stepper motor controls is dif-
ficult. To perform speed compensation at high machine speeds, the PLC hardware
must be extremely fast, and therefore expensive. Integrating a PS-6244 into the con-
trol system eliminates the need to write custom PLC speed compensation program-
ming, and provides excellent high speed control at a fraction of the hardware cost.
Fixed Response Times
Electromechanical components of automated systems often have fixed response times
regardless of the line speed. For example, a glue gun may require ten milliseconds
from the time the gun is actuated to the time that glue begins flowing. At the slowest line
speed, the gun might need to be triggered when the carton is one inch away, so that the
carton arrives under the gun just as glue begins flowing. As the line speed increases
and the product travels faster, the lead distance from the carton to the gun must in-
crease in order for the gun, with its fixed response time, to still hit the correct spot on the
product. By programming speed compensation into the PS-6244, the timing of glue
guns and similar mechanisms can be automatically advanced as speed increases, main-
taining proper operation over a wide range of machine speeds.
Example
Figure 24 on the next page illustrates a simple carton gluing application. A conveyor
moves cartons under a glue gun which releases glue onto the flaps. The conveyor is
connected through a timing chain and sprocket to a transducer which rotates one revo-
lution for each carton that passes under the gun.
As the transducer dial shows, SHAFT POSITION has been programmed so that the
leading edge of the box passes under the gun at 110
°
and the trailing edge at 360
°
.
Glue begins flowing ten msec after the gun is energized, and it stops flowing ten msec
after the gun is de-energized. Once the glue leaves the nozzle, it requires another five
msec to travel to the carton. Combining the glue gun response time with the travel time
results in a system response time of 15 msec, regardless of line speed.
At very slow, or essentially zero speed, the gun would be energized at a transducer
position of 110
°
and de-energized at 360
°
. As the line speed increases, however, the
gun needs to be energized before 110
°
to allow the glue to hit the carton in the correct
spot. The faster the line speed, the earlier in the transducer cycle the gun must be
triggered.
Calculation
To calculate the amount of speed compensation required, use the following relation-
ships between the transducer's RPM (revolutions per minute) and degrees of rotation:
1 RPM = 360
°
/min = 6
°
/sec = 0.006
°
/msec,
RPM x 0.006 = deg/msec,
thus:
@ 100 RPM, the transducer will rotate 0.6
°
/msec
@ 1000 RPM, the transducer will rotate 6.0
°
/msec
