# Vibration from Electric Hand-Held Harvesters for Olives
## 4 Discussion  
Vibration exposure is the major physical risk resulting from the use of electrical portable harvesters. Noise risk has been greatly reduced due to the use of electric motors [10] in substitution of pneumatic drives [40] or internal combustion engines [41]. Measured acceleration values may vary significantly depending on harvester head kinematics, rod features, load conditions, and user ability. Unfortunately, in many situations, these are very high acceleration values and expose operators to HAVS risk. In this study, considering the most exposed hand under load conditions (measurement in front position), mean acceleration total value in the worst case (rod R1, lowest diameter, aluminum made) ranged from 41.79 (harvester head H1) to 56.97 m/s\({}^{2}\) (harvester head H3, flat-type model). Better results with harvester heads H1-H3 were obtained with the use of the carbon fiber rod (R2). In this case the acceleration total value ranged from 22.80 (H2) to 24.73 m/s\({}^{2}\) (H1). Similar results are quite common in the literature, with acceleration values in the front position being higher than in the rear position. [PERSON] et al. [32], testing two electric beaters for olives, measured acceleration values under load conditions ranging from 19.9 to 29.8 m/s\({}^{2}\). [PERSON] et al. [18], testing three electric beaters used by five operators, measured values ranging from about 10 to 35 m/s\({}^{2}\). [PERSON] et al. [10], testing five models of electric portable harvesters, measured for a flat-type model, similar to the harvester head H3 analyzed in this study, acceleration values over 40 m/s\({}^{2}\) under full-load conditions. Other research by [PERSON] et al. [42] on five beaters reported acceleration values in the front position under full-load conditions ranging from 10.38 to 24.81 m/s\({}^{2}\). Much higher values (around 60 m/s\({}^{2}\)) may be measured using hook-type harvesters driven by an internal combustion engine [43]. The acceleration values measured with the harvester heads H1-H3 led to daily vibration exposure values, \(A(8)\), computed with an assumption of an exposure time of 4 h per day, ranging from 16.12 to 17.49 m/s\({}^{2}\) (best case) or from 29.55 to 40.28 m/s\({}^{2}\) (worst case). In any case, these values are much higher than the daily exposure action value of 2.5 m/s\({}^{2}\) or the daily exposure limit value of 5 m/s\({}^{2}\) stated by the European Directive 2002/44/EC [44]. To respect the limit of 5 m/s\({}^{2}\), these machines should be used in the best scenario for less than half an hour a day, much lower than the expected time. Vibration can be reduced through properly designing the machine or by an optimal choice of the operating parameters. As an example, [PERSON] et al. [45] proposed some modifications to the harvester head aimed isolating the rotary members, to reduce the transmission of the vibration to the operator's hands. Modifications of the kinematics of the harvester head are probably the best way to reduce vibration. The harvester heads H4-H6 considered in this study have kinematics quite different from the heads H1-H3. The opposing oscillations of the two arms carrying the sticks lead to a partial compensation of the accelerations transversal to the rod axis (\(x\)- and \(z\)-axis), resulting in a modification of the weight of the components and a general lowering of the total vibration. In fact, even if applied to an aluminium rod with a diameter of 35 mm, acceleration values in the front position under load conditions ranged from 16.00 (H4) to 17.70 m/s\({}^{2}\) (H6) (averagebetween the two rods), achieving a reduction of 60-70% with respect to the harvester heads H1-H3 applied to the 35 mm aluminum rod. The different kinematics of the harvester heads modify the harmonic content of the acceleration signals, the relative weight of the acceleration components, and also the behavior with respect to the load conditions.