Development of Add-On Active Vibration Control (AVC)

Innovate Malaysia Design Competition 2015

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Development of Add-On Active Vibration Control (AVC) for Power Tools D. S. Yiauw, H. S. Wee, A. Z. A. Mazlan and Z. M. Ripin

Index Terms—Active Vibration Control, impact drill, Proportional-Integral-Derivative control technique, Voice Coil Actuator, automatic phase adjustment

I. INTRODUCTION The vibration induced by the electrical tools can be enough to cause physical discomfort, reduced performance or even cause illness related to HAVS, including the decrease of grip strength [1]. To reduce the probability of induced HAVS on workers exposed to power tools, methods or devices have been developed. Reducing the vibration of power tools exerted on the hand of users can reduce the prevalence of HAVS among users. Occurrence of HAVS cases have been reported in Malaysia. An epidemiological study has been conducted on a construction site in Kuala Lumpur, Malaysia [12]. 243 workers were categorised into high vibration exposure group and low-moderate exposure group. Number of cases of finger tingling, finger numbness, musculoskeletal problems on the neck, finger coldness, abnormal Phalen’s test and abnormal light touch sensation were significantly higher in the high vibration exposure group. Symptoms and effects of HAVS vary from tingling and numbness in the fingers, loss of strength in the hands, to the fingers going white and becoming red and painful on recovery known as blanching. For Carpal Tunnel Syndrome (CTS), tingling, numbness, pain and weakness in the hand may occur.

For both HAVS and CTS, symptoms may come and go, but Number of vibration-caused disease cases reported to SOCSO 200 Number of cases

Abstract - Prolonged exposure to high-level vibration induced by power tools can cause vascular, neurological and musculoskeletal disorders, collectively known as hand-arm vibration syndrome (HAVS). To reduce vibration-induced HAVS risk to users, a small add-on with Active Vibration Control (AVC) features is proposed. In this study an impact drill is used as an example of application. The force and acceleration characteristics of the impact drill are measured and these are used in the development of the proportional-integral-derivative (PID) control algorithm implemented on the NI myRIO-1900 platform. Two accelerometers (GY-291) based on ADXL345 chip are used as the control sensor and output sensor for the feedback system. The algorithm then automatically search for the correct phase to achieve the lowest root-mean-square (RMS) vibration magnitude value. Next, the countering signal is sent to the VCA to attenuate the vibration of the system. The actual output signal is then measured by the output accelerometer and evaluated. The effect of frequency change is dealt by automatic adjustment of the phase and amplitude of the output signal to achieve the lowest RMS acceleration. An experimental test rig is developed to test the prototype AVC system, and the results show 52 - 82% of vibration attenuation for frequency range of 20 - 50 Hz. In this case the true power of MyRIO-1900 platform is harnessed where the system is used to as a signal generator to drive the shaker and also as a controller to drive the AVC system. The system is cost effective and prototyping of system can be developed rapidly.

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Year Fig. 1. Trend of increase for the number of vibration-related cases reported to SOCSO [13 – 16]

with continuous exposure to vibration they may become permanent and cause pain, distress and sleep disturbance [29]. Blanching, or also known as Raynaud’s phenomenon and Vibration White Finger (VWF) is the most common pathology associated with the vascular disorder of HAVS [7]. Patients with blanching may experience difficulties in manipulating small objects resulting from the reduced sensitivity in the fingers [30]. Social Safety Organisation (SOCSO) has reported exponential increase in vibration-related disease reported from year 2009 to 2013 [13 - 16]. Fig. 1 gives a graphical representation of the number of cases reported to SOCSO from 2009 to 2013. The severity of vibration-related diseases have caught the attention of the European Union (EU). Owing to the increased risks of HAVS, the EU has adopted a directive in 2009, which provides guidance for making health risk assessments. The directive lays down daily exposure limit value (ELV) of 5 m/s2 and daily exposure action value (EAV) of 2.5 m/s2 for standardised eight-hour reference period for hand-arm vibration. Department of Occupational Safety and Health (DoSH) Malaysia has released Guidelines on Occupational Vibration in 2003, which included the threshold limit values (TLV) for vibrations transmitted to hand-arm [17]. The details of the TLV are shown in Table 2. The TLV specifies the exposure limit for vibrating tools based on their vibration intensities. As specified by the International Organization for Standardization (ISO) [11], the vibration produced by the tool or the vibration transmitted to the hand should be measured in three orthogonal basicentric or biodynamic. The equivalent indication of basicentric directions of the hand on a power tool