Musculoskeletal and Performance Effects of Monocular Display Augmented, Articulated Arm Based Laser Digitizing

Littell, N., Babski-Reeves, K., McFadyen, G., & McGinley, J. (2007). Musculoskeletal and Performance Effects of Monocular Display Augmented, Articulated Arm Based Laser Digitizing. Human Computer Interaction International 2007. Bejing, China: LNCS Digital Library (LNCS, http://www.springer.com/lncs).

Abstract

To remain competitive within the global economy, manufacturers strive to produce goods with advanced features and of better quality. Though various quality measures exist, feature geometry inspection for quality requires specific equipment for measurement. Processes of capturing solid geometry features as three-dimensional data for analysis, simulation, or reverse engineering requires the use of laser based reverse engineering hardware, known as a digitizer. The most common digitizers used in manufacturing contexts are articulated arm-based coordinate measuring machines augmented with a laser-head probe. While the equipment performs satisfactorily, this emerging technology forces operators into non-neutral postures for prolonged periods of time, specifically for the upper extremities, back, and cervical spine. Additionally, operators monitor feedback from the system via a traditional computer monitor to ensure that certain conditions are being met and sufficient data are collected to construct the virtual part. Thus, the existing visual feedback system introduces additional rotation loads on the neck musculature for prolonged periods of time. Typical usage times for the digitizing equipment can range into the hours, thereby placing operators at risk for the development of musculoskeletal disorders (MSDs), though exact load magnitudes of exposure to risk factors for MSDs during object digitization are unknown. Further, other technologies exist (such as monocular/heads-up displays) that may be combined with laser digitizers that may reduce load magnitudes. Therefore, the objectives of the study are to: (1) quantify musculoskeletal loads associated with articulated arm usage for the neck, shoulder, and back, and (2) quantify the impact of incorporating heads up (monocular) displays during object digitization on musculoskeletal loads and digitizing efficiency. Twelve participants (6 males and 6 females), free of existing arm, neck, and back injuries or history of motion sickness participated in the study. A familiarization session in which participants practiced using a Faro brand articulated digitizer to digitize a small object. Two experimental test sessions were completed by each participant. In both sessions, participants digitized a small teapot, once using the standard laser digitizing setup and once using an occluded monocular heads up display for data visularization. Muscle activity using surface electromyography (EMG) was collected using a Noraxon 8 channel telemetered system. Muscles evaluated included the splenius capitis and sternocleidomastoid muscles of the neck; the trapezius, levator scapule, and rhomboid major muscles of the shoulder blade region; and the multifidi-erector spinea complex muscles of the lower back of the dominate side of participants Maximum voluntary exertion (MVE) procedures were used for normalization of obtained muscle activity profiles. Body postures were captured using an optical based motion capture camera system. Participants wore a suit that allows for the attachment of tracking balls (Figure 1). For this study, 8 cameras were used to capture the posture of the entire body. At the completion of the test session, participants completed a body discomfort map and usability questionnaire. The body discomfort map includes a picture of the human body divided into regions (eg, head/neck, upper back, lower back, shoulder, upper arm, lower arm, hand/wrist, etc.) with associated visual analog scales (VAS) 10cm in length with the anchors of “No discomfort” to “Extreme discomfort”. Participants were asked to place a vertical mark on each VAS scale. A custom usability questionnaire was developed and completed by the subjects to assess participant perceptions of the traditional digitizing set up and the monocular display set up. Data analysis is currently ongoing, though results of this study suggest that the posture of the user can be improved through the incorporation of an occluded monocular display used to replace the conventional computer monitor. An outline of this experiment will be presented and the final results of this experiment will be presented at this conference, followed by a brief question and answer period.