Linear Bearing Free Body Diagram (FBD) Problem
Reading: Free Body Diagrams Guidelines
Overview:
Linear slides can be subject to jamming (like screen doors). This is the reason many designers prefer rotary pivots whenever possible. However, if one would like to build a linear slide that does not jam, one needs to understand the reasons behind jamming.
In this assignment each student will analyze a Linear Slider, which is similar to the one shown in lecture. The overall objective of the assignment is to identify how to build good Linear Sliders that do not jam, and to develop skills in applying Free Body Diagrams (FBD). But do NOT forget, it is often better to replace a linear bearing with a rotary bearing when possible.
Analysis Problem:
Consider the linear slide shown in the sketch below in blue. The slider is held in place by two bearings shown in red, and a horizontal force, F, is exerted at a distance h from the bearings. Determine under what conditions the slider will move to the right.
Assumptions:
where m is a given coefficient of friction, and N is the normal force. For this analysis the static and dynamic coefficients of friction can be considered the same.
Steps In Analysis
The assignment will be graded on clarity, neatness, as well as the final result. Each solution should include:
Students are encouraged to pickup the Linear Slides in the Design Studio and feel the jamming effect themselves. Look carefully to see where the contact points which are indication of the load path in the mechanism. |