Once or twice a month, we like to share IAI Actuator News with the automation community.
Here is a new Easy Automation Application Improvement video Vol.7-2.

This processing machine grinds the inner faces of parts. Its loader/unloader uses air cylinders.

 

Problems when Air Cylinders are used

As the rotary unit turns to the horizontal position, the part being transferred may shift or drop due to a shock upon stopping.
Accordingly, the moving speed must be set lower, which prevents further cycle time reduction from the current level.

The current cycle time is 5.6 seconds, the production volume is 9,000 pieces a day, and the line operates for 14 hours.

The thrust force of the rotary air cylinder used for the rotary unit becomes unstable due to deterioration of gaskets, etc. If the thrust force drops below the drag(*1) of the shock absorber, the rotary unit can no longer reach the set stop position and thus contacts the part removal unit, causing a failure.

To prevent this contact failure, the air pressure was adjusted, and the stop position was confirmed once every two days (11 times a month). These operations take two maintenance people about 30 minutes.

Once a contact failure occurs, recovery operations, including replacement of the rotary air cylinder, straightening of the bracket, position adjustment, and test operation, are required. These operations take three maintenance people eight hours.

During the 18 months from the start of production, five contact failures occurred.

(*1) Drag: Force applied by an object as a counteraction to the force that was applied to the object by another object upon contact.

 

Improvements Achieved by the ROBO Cylinder®

1. Shorter cycle time through optimal operation settings
The ROBO Cylinder lets you set the position, speed, acceleration and deceleration separately. By setting gradual deceleration, high speed and high acceleration, high-speed operation with shock-less stopping became possible.

After the air cylinder was replaced with the ROBO Cylinder, the cycle time was reduced by 0.8 seconds to 4.8 seconds, and the system operating hours per day became shorter.

Cycle time:

Air cylinder: 5.6 seconds

ROBO Cylinder®: 4.8 seconds

System operating hours:

Air cylinder: 14.0 hours

ROBO Cylinder®: 12 hours

 
2. The system always operates consistently, and there are no more contact failures.

 

At least three years has passed since the ROBO Cylinder was implemented, but the system still operates normally based on the same initial settings. There hasn't been any contact failure.

Contact failure:

Air cylinder: 5 times (18 months)

ROBO Cylinder®: 0 times (36 months)

Periodic maintenance (22 days of operation a month)

Air cylinder: 11 times/month

ROBO Cylinder®: 0 times

 
3. Reliable positioning operation

With an air cylinder, completion of positioning operation is generally detected using an auto switch. When the auto switch turns ON, however, the operation is not yet completed. So, a timer is set, and the system waits until the positioning operation is completed.

However, if the speed or thrust force drops due to air pressure fluctuation or deterioration of gaskets, etc., the positioning operation may not complete within the timer period.

Still, the control sequence may determine that the positioning operation has completed and perform the next operation, and a problem may occur as a result.

The ROBO Cylinder comes with a motor unit with encoder(*2).
Feedback control(*3) is performed based on the position data from the encoder to ensure reliable positioning operation.

(*2) Encoder: A sensor that detects the number of revolutions and rotational speed and direction of a motor.
(*3) Feedback control: A type of automatic control method to control the output to be the same as the command by comparing the two.

 

Cost Cutting Effect

(1) Conditions

Required production quantity	9,000 pieces/day
Labor cost	$18*/hour
Annual operating days	264 days (22 days x 12 months)
Number of operators	Production line: 2 operators
	Line inspections: 2 operators
	Line recovery: 3 operators

 
(2) Comparison of air cylinder and ROBO Cylinder®

Item		System using air cylinder	System using ROBO Cylinder
Modification cost		-	$15,000*
Cycle time		5.6 seconds	4.8 seconds
Operating hours (day)		14 hours/day 9,000 pieces x 5.6 seconds = 50,4000 seconds = 14 hours	12 hours/day 9,000 pieces x 4.8 seconds = 43,200 seconds = 12 hours
Labor cost		$133,056* 14 hours/day x $18*/hours x 2 operators x 264 days/year = $133,056*	$114,048* 12 hours/day x $18*/hour x 2 operators x 264 days/year = $114,048*
Loss due to failures that occured before the modification	Time	596 hours [1] Periodic inspection 0.5 hour/time x 11/month x 18 months x 4 operators = 396 hours (2 inspection operators, 2 standby production line operators) [2] System recovery 5 failures x 8 hours/failure x 5 operators = 200 hours (3 recovery operators, 2 standby production line operators) Total [1] + [2] = 596 hours	0 hours
	Labor cost	$10,728* 596 hours x $18*/hour = $10,728*	$0
	Cost of repair parts and materials	$1,500* [1] Cost of replacement air cylinder $200*/unit x 5 replacements = $1,000* [2] Bracket correction cost $100*/unit x 5 corrections = $500* Total [1] + [2] = $1,500*	$0

 
(3) Cost Cutting Effect

	Air cylinder	ROBO Cylinder
Labor Cost (annual)	$133,056* -	$114,048* =	$19,008*
		Total =	$19,008*

•Loss due to the failures that had occurred before the modification (over 18 months)   Labor cost	$10,728* -	$0 =	$10,728*
Cost of repair parts and materials	$1,500* -	$0 =	$1,500*
		Total loss =	$12,228*

 

* Exchange Rate: 1(USD) = 100(Japanese Yen)