Innovative Systems Design and Engineering www.iiste.org ISSN 2222-1727 (Paper) ISSN 2222-2871 (Online) Vol.4, No.1, 2013 30 Static and Dynamic Calibration for FlexiForce Sensor Using a Special Purpose Apparatus Somer. M. Nacy 1* , Mauwafak. A.Tawfik 2 and Ihsan. A. Baqer 3 1. Al-Khwarizmi College of Engineering, University of Baghdad, Baghdad, Iraq 2. Mechanical Engineering Department, University of Technology, Baghdad, Iraq 3. Mechanical Engineering Department, University of Technology, Baghdad, Iraq * Email of the corresponding author: [email protected]Abstract: This paper introduces an experimental apparatus to be implemented for calibrating the FlexiForce sensor both statically and dynamically. This sensor uses a resistive – based technology and it has force range of (0-111N). The static calibration is done with static weights under static conditions, also these sensors are calibrated dynamically with the use of an inertial force of a mass as the known dynamic force; the acceleration of the mass is measured by an accelerometer board attached to the oscillating mass. These sensors are calibrated with the same conditions under which force sensors are supposed to be used, as to measure the force on the fingertip of a robotic manipulator. Results of both calibration methods are presented and discussed herewith. Keywords: Force sensors, dynamic calibration, special apparatus 1. Introduction In a wide variety of applications (Sheplak et al.2001) (Kalamdani et al.2006) ( Abu-Faraj et al.1997), force measurement has five basic mechanisms, namely, (a) Balancing the unknown force with a standard mass through levers mechanism. (b) Measuring the acceleration of a known mass. (c) Converting the force to electrical signal by different methods (magnetic field, optical cells, variable resistance or capacitance). (d) Using the force to generate pressure on a specific area and then measuring the pressure. (e) Converting the applied force into deformation in an elastic element. But all of these mechanisms need to be calibrated both statically and dynamically. Statically, by using static weights under static conditions, and dynamically by using known reference varying forces, such as, impact force, oscillating force or step force. The state of dynamic force calibration must cover all conditions under which force sensors are supposed to be used for proving the validity of the calibration procedure under different types of dynamical load. In this field, Jensen et al.(1991) used a thin force sensor to measure the grasping force for the human hand injury rehabilitation; this sensor was calibrated with a strain gage dynamometer and the results of this calibration were similar to those when using static method. Kumme et al. (2000)(2001) used an oscillating force as reference force for dynamic calibration, since the force transducer to be calibrated was mounted on a shaker and a load mass is screwed to the head of transducer. This procedure shows that in many cases the force indicated by the force transducer can noticeably differ from the force which must be determined in dynamic application and this is due to the effect of resonance behavior of the force transducer and resonance behavior of the surrounding mechanical structure of the calibration devices. Fujii (2006)(2009) has proposed the Levitation Mass Method (LMM); in this method the inertial force of a mass levitated by using a pneumatic linear bearing was used as a reference force for dynamic calibration and its results showed that the differences between the static and the dynamic calibration results are derived mainly from the difference between the static and dynamic characteristics of the sensor. Sun et al.(2006) has proposed and developed a new design of two-axis MEMS (microelectromechanical system), this sensor was calibrated by mounting the sensor in different situations (vertically and horizontally), since the weight of the movable parts of the sensor acts as a constant-magnitude load to the sensor in x and y directions. Link et al.(2009) described a linear least-squares fit method for system identification to estimate the transfer function from sinusoidal
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Innovative Systems Design and Engineering www.iiste.org
ISSN 2222-1727 (Paper) ISSN 2222-2871 (Online)
Vol.4, No.1, 2013
30
Static and Dynamic Calibration for FlexiForce Sensor
Using a Special Purpose Apparatus Somer. M. Nacy
1*, Mauwafak. A.Tawfik
2 and Ihsan. A. Baqer
3
1. Al-Khwarizmi College of Engineering, University of Baghdad, Baghdad, Iraq
2. Mechanical Engineering Department, University of Technology, Baghdad, Iraq
3. Mechanical Engineering Department, University of Technology, Baghdad, Iraq *