It is reported that the efficiency of a teleoperation in stereoscopic images of the working site is lower than that in the direct viewing of the site. It is assumed that one of the causes of lower efficiency of the teleoperation in the stereoscopic images would be the difficulty ofthe fusion of images, which would be caused by the imperfect overlapping ofimages on each eye. Through most of a teleoperation the convergence of the stereoscopic cameras is fixed at a certain point, usually in the middle of the working area. When the plane of the operator's eye-fixation-point is apart from the plane of the convergence point of the stereoscopic cameras, the two images do not overlap perfectly. It requires a great deal of effort for the images to be fused when the difference ofthe depth oftwo planes is over a certain value. We hypothesized that imperfect overlapping ofthe images on the left and right eyes would cause a decrease in efficiency for a teleoperation. We examined the efficiency of a teleoperation in two kinds of camera convergence conditions in a virtual reality (VR) environment. (Condition 1): The convergence point of two cameras was set on the target object which subjects moved and inserted in a hole. When the convergence point of the cameras follows the point on the target object on which subjects fixate with their both eyes, the ratio of the overlapped area of two images is always nearly at maximum. (Condition 2): The convergence point of both cameras is not set on the target object, but at the center of the hole-base. The larger the difference between the plane of the camera's convergence point and the plane ofthe subject's fixation point becomes, the more the rate ofthe overlapped area of the two images decreases. We prepared four cylinders and a hole-base with four holes in which the cylinders were inserted. The subject was asked to insert a cylinder in a hole using a three-dimensional mouse which allows free movement in the VR space. We measured the completion times of the operation and the number of errors in each condition to evaluate the efficiency of the operation. As a result of the experiment, the completion times of the operation and the number of errors under nearly-perfectly overlapped conditions were significantly smaller than the ones under the conditions in which the overlapping is less than maximum value. The experiment revealed work performance decreased when the ratio of overlapping of two images, which were projected on each eye, is less than maximum value. These results led to the conclusion that in order to achieve good performance in a teleoperation, the convergence point ofthe cameras should follow the target object on which subjects fixate with their both eyes.

According to the results of the simulated teleoperation experiment, the larger the ratio of the overlapping area of stereoscopic images, the smaller the completion times and the number of errors. For this paper we did an experiment using the actual stereoscopic video system. We examined the performance of the teleoperation of an insert task in two experiments. In experiment 1, we set three fixed overlap rate conditions for the stereoscopic image pairs. (High overlap rate condition): The convergence point of the two cameras was set at the goal point where a cylindrical object was inserted. When subjects fixated their eyes on the goal point, the overlap rate of the images from the cameras was 95%. (Middle overlap rate condition): The convergence point of the cameras was set at the center of the working area. When subjects fixated their eyes on the goal points, it was 76.7%. (Low overlap rate condition): Convergence point of the camera was set at the point in the situation where the ratio of the overlapped area was 49% when subjects fixated to the goal point. Completion times and the numbers of errors of the insert task were measured. As a result, these were smallest at the high overlap rate condition. In experiment 2, we compared the performance between a fixed and a variable overlap rate conditions in a pick-and-insert task. The experimental results suggested that the number of errors of variable overlap rate condition was less than that of the fixed condition although the completion time of the former condition was not shorter than that of the latter condition.

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