First, an impact wrench was suspended by a balancer
so that the handle does not need to be held while working (from 1987 to 1988). A mold was introduced that does not require screwing in or unscrewing of bolts (1990). An apparatus was set up seven times to automatically screw in or unscrew bolts (from 1990 to 1999). However, technical improvements in the motors of vibrating tools and introduction of a
vibration-proof vibrating tool were not done during the study period.