Development of a small 6-axis force/moment sensor for robot's fingers

Abstract

This paper describes the development of a small 6-axis force/moment sensor for robot's fingers (grippers), which detects forces Fx, Fy and Fz, and moments Mx, My and Mz, simultaneously. In order to safely grasp an unknown object using the robot's fingers, and accurately perceive its position in the fingers, it should measure the force in the gripping direction, the force in the gravity direction and moments in each direction, and perform the force control using the measured forces and moments. Also, it should detect moments Mx (x-direction moment), My and Mz to accurately perceive the position of the object in the fingers. Thus, the robot's fingers should be composed of 6-axis force/moment sensors that can measure forces Fx, Fy and Fz, and moments Mx, My and Mz, simultaneously. It is very important for the 6-axis force/moment sensor for an intelligent robot's fingers to be of small size in its body and in its interference errors. Therefore, the new modelling of a small 6-axis force/moment sensor is needed. In this paper, the small 6-axis force/moment sensor for measuring forces Fx, Fy and Fz, and moments Mx, My and Mz simultaneously was newly modelled using several parallel-plate beams (PPBs), designed and fabricated. A characteristic test of the made sensor was performed, and the result shows that the interference errors of the developed sensor are less than 3.93%. Thus, the developed small 6-axis force/moment sensor can be used for robot's fingers.

Development of 6-axis force/moment sensor for a humanoid robot's intelligent foot

“…Wheastone bridges are made for each sensor in 6-axis force/moment sensor [5][6][7][8][9][10]. The rated strain of each sensor under each rated force or moment is determined from the strain values of the attached strain-gages to each sensor.…”

“…The rated strain of each sensor under each rated force or moment is determined from the strain values of the attached strain-gages to each sensor. Total strain of Wheastone bridge can be calculated as following equation [5][6][7][8][9][10]:…”

“…The other is the same rated forces F x , F y , F z , and the same rated moments M x , M y , M z . The rated output of the variables for designing 6-axis force/moment sensor is determined by about 0.5 mV/V [5][6][7][8][9][10][11][12], the size of the sensor is 80 mm × 80 mm × 19 mm in consideration of robot's ankle, the size of force/moment transmitting block is 30 mm, the attaching locations of strain-gages in length-direction are 1 mm from the end of the plate-beams, the attaching locations of strain-gages in width-direction are on the center line of the plate-beams in consideration of the grid size of strain-gage (1.2 mm × 1.6 mm), and the rated strain at the attaching location of strain-gage is about 250 m/m. The rated forces and moments of 6-axis force/moment sensor…”

“…That is, the rated forces and moments of the sensor in 6-axis force/moment sensor for direction of robot's weight are larger than except it in the same or similar rated output. But, the developed 6-axis force/moment sensors [5][6][7][8][9][10][11][12] have been had no consideration for robot's weight in its design. So, they are not proper for a humanoid robot's foot.…”

“…So, they are not proper for a humanoid robot's foot. The sensor [5,6] has the small capacities that the rated force of F z sensor is 100 N, those of M x sensor and M y sensor are 1 N m, the sensor [7] has only F x sensor, F y sensor and M z sensor, the sensor [8,9] has larger size of 170 mm × 1700 mm × 150 mm for robot's foot, the sensor [10] is smaller size of 40 mm × 40 mm × 80 mm and the small capacities F x , F y , F z sensor is all 10 N and M x = M y = M z is 1 N m for robot's foot, the sensor [11,12] has smaller or larger size, and larger capacities.…”