Development and Design of a MechanicalLocking Device for a Hydraulic Lifting Mechanism

Sammanfattning

This thesis aims to design a fail-safe locking device for a hydraulic lifting mechanism that moves a pivoting structure between a lowered and raised position. Hydraulic systems are common in many industries due to their ability to generate large forces while maintaining a compact design. The systems are generally reliable, but there are cases in which the hydraulics fail, which often lead to pressure loss in the system. This type of failure causes the piston rod to retract unintentionally, which in turn may cause equipment damage and system failure. The project originates from a request for a safety measure from the market even though the current system is yet to fail, forwarding the question of perceived reliability. This is investigated in relevant literature along with design parameters for mechanical reliability, specifically focusing on geometric design, loads, failure modes and the effects of weather and wear. The impact of these parameters were explored in the development of this project's locking mechanism. The product development process started with multiple idea generation methods to create a broad base of ideas, which are then evaluated, with the most promising ones selected for continued development and refinement through calculations and simulations. A risk assessment is made for the final concept, identifying potential risks with the concept as well as recommended actions for future development of the product. The project results in a final concept that consists of three parts; automatic locking and unlocking, manual unlocking and safe lowering. The locking mechanism engages automatically if pressure in the hydraulic system is lost, and is capable of holding both the weight of the structure and applied external forces. Three concepts for manual unlocking are presented, as well as one for secure lowering of the structure. In the end, conclusions are drawn as to which design parameters are most important when designing a fail-safe system for a hydraulic product, as well as for perceived reliability.