This paper presents the design optimization of a mechanically decoupled six-axis force/torque (F/T) sensor by minimization of cross coupling error. The new term ‘principal coupling’ is proposed to define the largest cross coupling error. In the first design step of the F/T sensor, the locations of twenty-four strain gages in a sensor structure are predetermined, and four structural design variables are selected to be optimized. In the second step, an optimization framework that reduces principal coupling is developed. Multiple constraints on good isotropic measurement and safety are considered and formulated using the output strain of each strain gauge circuit. The optimal design utilizes FEM software and MATLAB interactively to perform effective shape optimization. As a result of shape optimization, principal coupling of a six-axis F/T sensor was reduced from 35% to 2.5% with good isotropy. The final design of the F/T sensor was fabricated for experimental verification and there was only 0.7% difference in principal coupling and 5.2% difference in the overall strain output between the numerical and experimental results. The optimal design results in this paper are expected to provide a design guideline for multi-axis F/T sensors with significantly reduced cross coupling error, one of the biggest technical obstacles in developing F/T sensors.

Shape optimization of a mechanically decoupled six-axis force/torque sensor

Design and optimization of a novel six-axis force/torque sensor for space robot

This paper presents a novel multi-component strain-gauge external balance to measure lift and drag forces as well as pitching moment in wind tunnel experiments. First, an innovative structure is proposed and its geometry is determined through a tedious trial and error scheme using finite element (FE) simulation. The sensor dimensions are thus chosen so as to acquire acceptable sensitivity and negligible interference error among the components considering maximum loading capacities. Appropriate locations of the strain gauges on the structure are determined via simulation. Then, sensitivities of the balance components are found using the FE analysis. Finally, the designed external balance is constructed and calibrated. It is found that the interference error among the balance components is less than 2.01%. Furthermore, the measured sensitivities of the sensor components are in a good agreement with the simulation results through which the design procedure is validated.

A novel multi-component strain-gauge external balance for wind tunnel tests: Simulation and experiment

The objectives of this study were to develop a real-time tillage depth measurement system for agricultural tractor performance analysis and then to validate these configured systems through soil non-penetration tests and field experiment during plow tillage. The real-time tillage depth measurement system was developed by using a sensor fusion method, consisting of a linear potentiometer, inclinometer, and optical distance sensor to measure the vertical penetration depth of the attached implement. In addition, a draft force measurement system was developed using six-component load cells, and an accuracy of 98.9% was verified through a static load test. As a result of the soil non-penetration tests, it was confirmed that sensor fusion type A, consisting of a linear potentiometer and inclinometer, was 6.34-11.76% more accurate than sensor fusion type B, consisting of an optical distance sensor and inclinometer. Therefore, sensor fusion type A was used during field testing as it was found to be more suitable for use in severe working environments. To verify the accuracy of the real-time tillage depth measurement system, a linear regression analysis was performed between the measured draft and the predicted values calculated using the American Society of Agricultural and Biological Engineers (ASABE) standards-based equation. Experimental data such as traveling speed and draft force showed that it was significantly affected by tillage depth, and the coefficient of determination value at M3-Low was 0.847, which is relatively higher than M3-High. In addition, the regression analysis of the integrated data showed an R-square value of 0.715, which is an improvement compared to the accuracy of the ASABE standard prediction formula. In conclusion, the effect of tillage depth on draft force of agricultural tractors during plow tillage was analyzed by the simultaneous operation of the proposed real-time tillage depth measurement system and draft force measurement system. In addition, system accuracy is higher than the predicted accuracy of ±40% based on the ASABE standard equation, which is considered to be useful for various agricultural machinery research fields. In future studies, real-time tillage depth measurement systems can be used in tractor power train design and to ensure component reliability, in accordance with agricultural working conditions, by predicting draft force and axle loads depending on the tillage depth during tillage operations.

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Development of a Real-Time Tillage Depth Measurement System for Agricultural Tractors: Application to the Effect Analysis of Tillage Depth on Draft Force during Plow Tillage.

In this study, a novel strain gauge arrangement and error reduction techniques were proposed to minimize crosstalk reading and simultaneously increase sensitivity on a decoupled six-axis force–moment (F/M) sensor. The calibration process that comprises the least squares method and error reduction techniques was implemented to obtain a robust decoupling matrix. A decoupling matrix is very crucial for minimizing error and crosstalk. A novel strain gauge arrangement that comprised double parallel strain gauges in the decoupled six-axis force–moment sensor was implemented to obtain high sensitivity. The experimental results revealed that the maximum calibration error, F/M sensor measurement error, and crosstalk readings were reduced to 3.91%, 1.78%, and 4.78%, respectively.

K.S Na

Papers

Design and evaluation of a six-component load cell