Design team member: Allison Keens
Supervisor: Professor Amir Khajepour
Background
Timberjack is a Finnish based company that manufactures logging vehicles. This project is concerned with the skidder line of vehicles (seen below). A skidder has a dozer blade on the front and a grapple on the rear of the it. The main purpose of this vehicle is to drag logs with the grapple to a landing where they are prepared for transport. The grapple is attached to the boom via a device called a "snubber," which acts as a two degree of freedom rotational damper. The snubber reduces grapple oscillations in the side to side and for and aft directions of rotation.
Grapple oscillations only occur while the grapple is traveling empty. This is because when it is carrying a load, the weight of the trees deadens any significant swinging. Grapple oscillation is undesirable for many reasons, the most important being the damage a 1000 kg grapple head can do to itself and anything it hits such as the boom, rear frame or tires. Repairs can be very costly, both in replacement components and also in lost working time. An improved, unique snubber design is desired to replace the current design Timberjack and most of their competitors are using.
Problem description
Timberjack currently offers two snubber designs for its skidders. The first is manufactured by a company called Esco. These snubbers were reliable in the past but due to a design change, they have not performed well since. The current Esco design works on the principle of dry friction to dampen the grapple motion. There is a conical wear sleeve that can be adjusted to increase or decrease the damping. This design is unreliable, does not meet the current industry standard of 2000 hour design life, requires frequent adjustment due to component wear and boasts a costly rebuild price tag. Since Timberjack installs these snubbers on their own vehicles, they are being bombarded with warranty claims from customers for rebuild and replacement costs of the units.
Timberjack also sells its own snubber design. This design also operates on the dry friction, but it consists of friction plates sandwiched together on each axis of rotation. It meets the service life standard, but still exhibits some of the same issues the Esco snubber does. It has to be adjusted often to maintain an acceptable level of damping and it requires frequent maintenance to prolong the life of the wear components. In addition, since these snubbers have been designed to last longer then Esco models, they have a higher purchase price.
Clearly a new technology is needed to replace the flawed, but simple friction dampers. The new technology must be able to operate over a wide temperature range, be self-contained, compact, lightweight, easily adjustable in the field and have the potential for active damping control in the future. It must set Timberjack apart from their competitors in the snubber market.
The goals of this eight month project are to a) investigate all possible damping technologies, b) select one of these technologies to benchmark test at the University of Waterloo and c) create a detailed design of the components necessary to prototype the chosen technology.
Design methodology
Alternative damping technologies will be researched through the first four months of the project. Also, during this time simulations will be run to learn more about the maximum torque generated by the grapple during oscillation and about hydraulic damper characteristics. These Matlab simulations will be used to size components for the prototyping phase. After market, industry and competitive analyses are completed, the information will be summarized and the technology that best satisfies pre-determined criteria will move on to prototyping. The technology will be benchmark tested to determine its feasibility in the snubber application. If testing is successful, the data will give Timberjack the building blocks to design their own unique snubber design.