“Seashell Effect” Pretouch for Robot Grasping

The term “Pretouch” refers to sensing modalities that are shorter range than vision but longer range than tactile sensing. The hypothesis that pretouch sensing can be useful for manipulation is being explored actively [1][2][3][4][5]. It is viewed as potentially beneficial for manipulation because it provides reliable geometric information in the last centimeter before contact. The disadvantage of using tactile sensing for collecting local geometric information is that contacting the object may displace it— an outcome that is particularly likely when the object’s geometry is initially uncertain. An advantage of pretouch over vision is that pretouch is not subject to the problem of the hand occluding the camera, because the sensor is integrated into the hand; another is that there are no camera-to-hand registration errors since the sensor is in the coordinate frame of the hand. This paper introduces a new form of pretouch that works with a wider variety of materials than our earlier electric-field based pretouch [1][2][3]. The paper illustrates the advantages of pretouch over contact sensing by demonstrating that pretouch can detect objects that are too compliant for the PR2’s tactile sensors to detect.