Proceedings of the 4th International Product Design & Development
Yogyakarta, 9-10 November 2011
Development of Active Vibration Control Cancellation Pad for Orbital Sander Ahmad Zhafran Ahmad Mazlan and Zaidi Mohd Ripin School of Mechanical Engineering, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia. Fax: 6.04.5941024, Tel: 6.04.5941025. Corresponding author :
[email protected].
Abstract: Orbital sander is widely used in the automotive repair, composite manufacturing and in fabrication of metallic panels product. However, the use of orbital sander will lead the user to health hazard associated with Hand Arm Vibration Syndrome (HAVs). Development of aftermarket active vibration cancellation (AVC) pad is explored in this paper where the conceptual design of AVC pad is applied to the orbital sander using coupled sander-hand-arm model and the effectiveness was calculated. The design parameters are addresses which include sensor and actuator location and selection and also the modeling approach. Various control scheme were applied in the AVC system including PD and active force control (AFC) technique. The result shows that control scheme with AFC input can provide a very robustness result compared to classical PD controller in the AVC pad system and the AVC pad is an effective way of achieving low vibration orbital sander. Keywords: Orbital sander, active vibration cancellation, active force control, hand-arm model.
1 INTRODUCTION Orbital sander is widely used in the preparation of surface for further coating, to achieve the required surface roughness and to remove rust. It is widely used in the automotive repair, composite manufacturing and in fabrication of metallic panels product. Since the application of orbital sander are highly irregular and unplanned such as in the application of correction of pressed panels, its use is mainly manual since automation is not cost effective. However, the use of orbital sander will expose the user to hand arm vibration and if uncontrolled can lead to health hazard associated with Hand Arm Vibration Syndrome (HAVs). There are several ways of reducing the vibration level transmitted to the hand. The best method is to remove all the unbalanced force in the system. For example, in the commercial world the hand tool manufacturer, Makita has managed to dynamically balanced the motor of the electric jigsaw which resulted in 40% reduction of vibration [1]. Some manufacturer has resorted to create counter rotating head of the sander to balance the orbital motion and has claimed that the design was able to reduce the vibration level of the sander. For some reason, most major orbital sander did not have two counter rotating head due to the more complex design of the housing and the increased number of components which increases the overall costs of the sander. As such for the aftermarket demand, the remaining solution is to go for passive or active vibration attenuation technology. For the passive way, this can be achieved by inserting
isolators between the hand and the sander. The isolator can be in the form of anti-vibration glove or simple insertion of elastomeric pad. However antivibration gloves limit the dexterity of the fingers and elastomeric pad lack the positive feeling of control when the palm is grasping the orbital sander. Another possibility is the use of dynamic vibration absorber (DVA) which can be tuned to match the operating frequency however this has problem when the sander is loaded since the speed of the sander will be reduced and the tuning effectiveness diminished. Wideband DVA is still under research and the technology has not matured. The aftermarket for vibration protection is not well documented. There are anti-vibration gloves which are priced from USD 8 for a simple padded glove lined with with Viscolas™ VEP Padding to the more expensive gloves of USD 30 for glove with AntiVibration Mechanic's Air Glove®, Full Finger Synthetic Leather, Patented Air Technology, and Meets ANSI / ISO 10819 [2]. Figure 1 shows a typical application of anti vibration glove when using the orbital sander [3]. The use of gloves in general provide protection but these are not effective at low frequency and also it restricts the dexterity of the fingers and also heat dissipation from the hand. For angle grinders, Bosch has developed anti vibration handle which is priced at USD 15. The anti-vibration handle worked on the isolation effect when damping element is inserted between the handle and the motor housing with the damping element frequency characteristics tuned to match the characteristics of the motor. The magnitude of isolation has achieved however was not mentioned [4]. An almost similar 1
