Reducing Operator Burden During Nut Runner Operation
CKD Corporation, Komaki Plant

This case study highlights improvements made to screw tightening processes at the CKD assembly plant.Operators using a 1kg nut runner for screw tightening experienced strain on their shoulders, arms, and wrists due to the repetitive nature of the task.
Issues

Awkward working postures lead to significant physical strain.
Previously, a suspension-type spring balancer was used, and the screw tightening task was performed approximately 40 times per day.
- Accessing the tool from above shoulder height and repeatedly pulling it down put a significant strain on the shoulders.
- While the tool itself was not excessively heavy, the high repetition of the task resulted in noticeable strain on the shoulders, arms, and wrists.
- Strong vibrations during screw tightening caused wrist strain.
These were common complaints from the operators.
With the high frequency of daily repetitions, reducing operator burden and improving work efficiency were major challenges.
Reasons for Adoption

The in-house development of the Compact Arm prompted a review of screw tightening processes.
This internal development project presented an opportunity to address screw tightening challenges that were previously a lower priority.
The Compact Arm was selected for internal implementation based on its potential to address the identified challenges, thanks to the following features:
- As an air balancer, the tool remains stationary when released, allowing horizontal access and eliminating the need to lift the shoulders.
- The low-friction cylinder enables effortless operation with minimal force.
- Compared to suspension systems, the Compact Arm’s design minimizes tool-generated vibration and reaction force.
The simple installation process, enabled by compatibility with a 60 mm aluminum frame, further supported the decision to implement the Compact Arm.
Results after introduction

Significantly reduced physical strain on operators and improved overall workability.
Implementation of the Compact Arm resulted in improved operator posture and reduced fatigue.
Operators have reported positive feedback, including, "The ability to operate the tool without raising my shoulders has significantly reduced shoulder strain," and "The reduced vibration during screw tightening makes the work much easier. I wouldn't want to go back."
The vertical movement of the balancer enables perpendicular screw tightening, further enhancing workability and allowing for precise tightening of even small screws.