Tri-axial evaluation of the vibration transmitted to the operators of crawler compact loaders

Vibrations transmitted to the operators of earth moving machines may be severe under certain working and/or operating conditions. This is even worse when crawler machines are considered due to the hard contact between the track belt and the ground which is not dampened in any way by the air present in the tires as it happens in wheeled machines. This paper reports a study conducted on different machines in their standard configuration under different operating conditions: two fixed travelling velocities (low and high) on two defined surfaces (a path in asphalt and an artificial normalized track), with and without the presence of a ballast in the bucket and with the same operator driving all the machines. The accelerations were measured either on the seat cushion and on the cab floor in order to detect the amount of vibration transmitted between these two points. The analysis was primarily focused at the assessment of the acceleration values measured on the cab floor to detect whether they are balanced among the different vector components (x, y and z) and whether they show significant differences among the different machines and operating conditions, in terms of surface, velocity and presence of the ballast. Then, a comparison between the acceleration measured on the floor and those measured on the seat was performed in order to evaluate the seat damping characteristics and to detect the amount of vibration that is transmitted to the operator. Finally, the evaluation of the whole body vibration exposure levels was performed to assess the grade of comfort reasonably perceived by the operator. Relevance to industry - This paper highlights the importance to review the standard configurations currently used on this kind of machines (cab and seat suspensions): they turn out to be absolutely ineffective to assure the operators of safe and comfortable working conditions. Compact loader manufacturers should consider the vibration problem at the machine design stage and choose cab suspension systems and seats able to reduce accelerations along the three different axes. Similarly, seat manufacturers should pay attention in reducing rolling and pitching effects using specific seat suspensions effective also along the horizontal and lateral directions. Unfortunately standards currently in force do not require to control horizontal and lateral vibrations. Consequently, the address of this issue at ISO level in order to update the current legislation could be a strong stimulus for seat and machine manufacturers and a progress towards the operator comfort