Browse Prior Art Database

Force-Sensing Device

IP.com Disclosure Number: IPCOM000043140D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Griffing, BM: AUTHOR

Abstract

A practical, inexpensive force-sensing device specifically applicable to grippers in robots but applicable to force measurement in general is provided. The device could replace quartz load cells and strain gages. The arrangement combines two physical phenomena: magnetostrictive effect and Hall effect. Referring to Fig. 1, there is shown a gripper pad 10 constructed of annealed electrical iron that supplies a gripping force F. Rods 12 made of a magnetostrictive material, such as 45 permalloy, are provided which are surrounded by magnetizing coils and which are physically attached to the gripper pad 10 and to a base 14 which is also constructed of annealed electrical iron. A Hall effect device 13 is placed centrally in the structure between two soft iron pole pieces 15 that form a flux return path from 10 to 14.

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Force-Sensing Device

A practical, inexpensive force-sensing device specifically applicable to grippers in robots but applicable to force measurement in general is provided. The device could replace quartz load cells and strain gages. The arrangement combines two physical phenomena: magnetostrictive effect and Hall effect. Referring to Fig. 1, there is shown a gripper pad 10 constructed of annealed electrical iron that supplies a gripping force F. Rods 12 made of a magnetostrictive material, such as 45 permalloy, are provided which are surrounded by magnetizing coils and which are physically attached to the gripper pad 10 and to a base 14 which is also constructed of annealed electrical iron. A Hall effect device 13 is placed centrally in the structure between two soft iron pole pieces 15 that form a flux return path from 10 to 14. The total force F is supported by the two rods 12. The sum of the forces on the two rods is equal to F, although one of the forces may be negative. Fig. 2 shows qualitatively the magnetostrictive effect of stressing a biased nickel-iron alloy. Over a range of small stress (approximately Å 1000 psi), the change in flux density WB is linear with stress, i.e., positive for positive stress and negative for negative stress. The change is approximately Å 1 Gauss for Å 1 psi. Note that the H field must be held constant and that there must be some initial magnetization, the optimum value depending on the exact material used. In an unstressed ma...