Abstract
The purpose of this paper is to show the feasibility of grasping force control by feeding back signals of the developed micro-laser Doppler velocimeter (μ-LDV) and by discriminating whether a grasped object is slipping or not. LDV is well known as a high response surface velocity sensor which can measure various surfaces—such as metal, paper, film, and so on—thus suggesting the potential application of LDV as a slip sensor for grasping various objects. However, the use of LDV as a slip sensor has not yet been reported because the size of LDVs is too large to be installed on a robotic fingertip. We have solved the size problem and enabled the performance of a feasibility test with a few-millimeter-scale LDV referred to as micro-LDV (μ-LDV) by modifying the design which was adopted from MEMS (microelectromechanical systems) fabrication process. In this paper, by applying our developed μ-LDV as a slip sensor, we have successfully demonstrated grasping force control with three target objects—aluminum block, wood block, and white acrylic block—considering that various objects made of these materials can be found in homes and factories, without grasping force feedback. We provide proofs that LDV is a new promising candidate slip sensor for grasping force control to execute target grasping.
Highlights
Robotic hands are desired in a variety of environments—such as industrial factories, hospitals, homes, etc.—for grasping and manipulation of various objects by hands as humans do
We have developed a micro laser Doppler velocimeter (μ-LDV) by the size of an LDV is large for a robotic finger, due to its constituent elements and requirement of modifying the design adopted from MEMS fabrication process assembling accuracy as described later in the Section 2.2
We provide proofs that laser Doppler velocimetry block, wood block, and white acrylicfor block—as material samples target existing in homes and could be a new candidate slip sensor graspingvarious force control of unknown objects
Summary
Robotic hands are desired in a variety of environments—such as industrial factories, hospitals, homes, etc.—for grasping and manipulation of various objects by hands as humans do. There are various object, weight, and surface friction conditions which are unknown, but robots need to manipulate without any trouble including slippage or break of contact, damage, and destruction. Two fingers grasping a target with the grasping force FG, the gravitational force Fmg, and the lifting force FL resulting from friction are on the target object. Lifting force which is described as FL = μFG , 2FL = 2μFG = Fmg must be satisfied considering the balance of forces, Sensors 2018, 18, 326; doi:10.3390/s18020326 www.mdpi.com/journal/sensors
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