Tech Tips - Selecting Pneumatic Linear Slides for Automation Projects

sponsored by: 4 Load Capacity A slide must support a workload over the length of the linear motion within the limits of precision required by the application. A linear slide carrying a paddle that knocks boxes off of a conveyor does not need the same degree of precision as a parts placer on an Assembly Machine. Because of these wide variances in application requirements, the engineering data pertaining to the slide’s load capacity will indicate safe loading in pounds and predict the amount of toolbar deflection, or bending, in thousandths of an inch. The largest category of linear slides common today employ two or more shafts as the guiding mechanism. Most workloads are attached to the reciprocating toolbar, producing an overhung load. The load capacity is ultimately determined by two factors - the strength of the guide shaft to resist deflection, and the ability of the linear bearing to support that load. Although overhung workloads produce undesirable loading to the leading edge of the linear bearing, most bearings have a much higher load rating than the strength of the guide shafts (to resist deflection). Note that a slide with linear ball bearings may be rated for 20 pounds with .005” deflection in an overhung load situation, and yet the four bearings may have a combined load rating of several hundred pounds. This bearing “over- capacity” assures precision and long life even in overhung loading situations. slide selection - continued Linear bearings, whether ball bearings or sleeve type bearings, will support the highest loads when that load is applied over the entire length of the bearing(s). This is commonly known as a carriage load. Slide Motion Load Two styles of carriage loads are shown here. Figure 2A shows a load attached to a mounting plate on the reciprocating slide. Figure 2B shows a stationary slide with a load plate attached to reciprocating guide shafts. Stationary Cylinder Load Motion Load Figure 2A Figure 2B