Knife replacement studies at an automobile carpet manufacturing plant

Donghyun Park, Myung Hwan Yun, Andris Freivalds

Research output: Contribution to journalConference articlepeer-review

2 Scopus citations


This study mainly examined the molding operations of an automobile carpet manufacturer in order to recommend changes in knife shape, usage, or other alternative approaches, so as to reduce the incidence of CTD in the plant. There were five independent factors of interest: 1) type of carpet, 2) type of trim line cut (straight within a trim line, or curved along the edge of the mold with several small indentations and edges on which the knife could get caught), 3) the temperature of the knife (cold or hot), 4) blade angle of the trimming knife (-30, 0, 30 degree), and 5) trim direction (push or pull). The dependent variables included: 1) smooth rectified electromyogram(EMG) from the forearm flexor, 2) EMG from the biceps brachii as an indication of pulling strength, 3) wrist dorsal/volar deviations, 4) wrist radial/ulnar deviations, 5) grip force as measured by a matrix of force sensitive resistors (FSR), 6) Borg's subjective ratings of perceived exertion (RPE). Finally, a supplemental experiment to validate the usage of RPE as dependent variable. was performed. For this experiment, a spring loaded cutting mechanism was prepared and factor effects on RPE were investigated. Four independent factors of interest were: 1) type of carpet, 2) knife angle, 3) spring force, and 4) temperature. Corresponding dependent variable was the length of the cut. The type of carpet, the type of mold trim line, and blade angle were important factors in determining the difficulty of trimming performance and operator stress. Particularly, the type of carpet was a significant factor for Borg's subjective ratings. To a lesser degree, the temperature of the knife blade also affected performance, with a hot knife reducing operator stress. Forces generated by the two major muscles (biceps brachii and forearm FDS) involved in trimming carpet were highly correlated with the type of carpet and the of trim line. Particularly, the curved trim line showed a higher level of stress than the straight line. The angle of the blade had the expected effects on the wrist angle, but showed much less of an effect for the other dependent variables except for grip FSR. A difference in EMGs was also found, favoring pulling as opposed to pushing along the trim line. In the third experiment, carpet type & temperature showed significants effect on cutting length and cutting length correlated significantly with previous RPE.

Original languageEnglish (US)
Pages (from-to)848-852
Number of pages5
JournalProceedings of the Human Factors Society
StatePublished - 1991
EventProceedings of the Human Factors Society 35th Annual Meeting Part 1 (of 2) - San Francisco, CA, USA
Duration: Sep 2 1991Sep 6 1991

All Science Journal Classification (ASJC) codes

  • General Engineering


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