Conveyors and jacks

1. Scissor Jack (Nůžkový zvedák) Conveyors and jacks

2. Nůžkový zvedák před zvednutím Nůžkový zvedák ve zvednuté pozici

3. Scissor jack (also called scissor lift or scissor mechanism) is a type of a screw jack. • Description • The main difference from other screw jacks is that the leadscrew of a scissor jack is in horizontal position (typical screw jack has the leadscrew positioned vertically). The leadscrew operates two metal arms, which are usually of equal length. The term “scissor“ is derived from its shape, because the two arms resemble the letter X. • Operation  • When turning the screw, the arms can move nearer or farther from each other, and thus the crossing pattern is elongated and the load is lifted. The force that is necessary to apply to the leadscrew can be calculated from the following scissor jack equation: • Where: • F is the force provided by the leadscrew • W are combined weights of the load and the load platform • Wa is the combined weight of the two scissor arms • φ is the angle between the scissor arms and the horizontal • If the lift consists of several pairs of scissors combined in a series, then the force (F) has to be multiplied by the number of scissor mechanisms. The equation can be applied only to the scissor jacks with equally long arms.

4. Vocabulary  • Scissor jack, scissor lift, scissor mechanism – nůžkový zvedák • Screw jack – šroubový zvedák • Screw – šroub • Leadscrew – vodící šroub • Metal – kovový • Arm – rameno • Equal – stejný • Shape – tvar • Resemble – podobat se • Pattern – vzor • Elongate – prodloužit • Lift – zvednout; zvedák • Force – síla • Apply – použít • Calculate – vypočítat • Equation – rovnice • Weight – hmotnost • Load – náklad, zatížení • Platform – plošina • Angle – úhel • Horizontal – horizontála • Multiply – násobit