A novel strategy for controlling forklift’s mast vibration

Abstract

Material handling lift trucks, most commonly known as forklift trucks, have enhanced significantly both in the safety and comfort aspects in the past three decades. However, there are still some rooms for improvement in terms of control, efficiency, user experience, productivity, and the safety of the forklifts. Besides, the efficiency of the equipment is important for the industry; as this can assist in increasing the productivity and business profits. Forklifts are designed to be compact; however, while loading, carrying and offloading heavy loads, they can be unstable at times, causing safety matters. The tilting of the mast can consequently cause the forklift to tip over; therefore, forklifts should not be maneuvered when parts are moving or with the mast raised. Currently, the operator must wait until the vibration of the mast is damped before moving. Therefore, the mast vibration must be dampened with the new strategy that works efficiently and economically. Previous studies carried out in this area were mainly concerned with vibrations in driver cabins, and their main idea was mostly to reduce these vibrations through implementing active damping systems which was not economical for manufacturers. There are a few types of research that are specifically trying to reduce the vibration of mast unit with an active control system or passive control system to base or mast, however manufacturers did not welcome the ideas because of complications of the systems and costs involved. Also it has been found that these mass-dampers are always adjusted to operate in certain frequency and when natural frequency of structure is changed the mass-damper becomes less effective and can even increase the vibration of mast. In the current research, it has been strived to control the vibrations of the forklift’s mast unit with a novel strategy that dampens the vibration of the mast with the semi-active control system and without adding any extra mechanical component to the system. In order to achieve this aim, a numerical model based on a simplified system and the degree of freedom associated with the mast unit oscillations is presented. This research introduced and implemented two methods of second-order linear control (i.e. LQR and SMC) to control the cylinders of the forklift. Then, in order to achieve the maximum force for the cylinders, a PID control method is presented based on flow control of servo-hydraulic valves of the forklift. By comparison with real results, the newly designed controllers have been successful to achieve between 13.6% to 36 % reduction in vibration of forklift’s mast with different loads on the mast unit.