Application
Physical Measurement Technologies' IMD-1 Step/Skirt Index Measurement Device is the standard for evaluating entrapment potential on escalator systems.The IMD-1, in combination with the EVA-625 (or MMC-1) system, and EVA Elevator & Escalator Analysis tools software, allows the complete evaluation of the newly defined step/skirt performance index (A17.1-2000). The index is meant to provide a quantitative measure of entrapment potential based on both the loaded gap and coefficent of friction.
- Step/Skirt Index
- Loaded Step/Skirt Gap
- Coefficient of Friction
- Real Time Evaluation
- Recording/Documentation
Operation
The Step/Skirt Performance Index was defined under a multi-year study with the purpose of establishing measurable parameters that affect the potential for entrapments on escalators. Entrapments in this case include finger/hand, calf, and shoes trapped between the escalator step and skirt. Based on empirical data, it was determined that the gap between the step and skirt, and the coefficient of friction (skirt panel and skin/shoes) were quantities that had a significant affect.
Step/Skirt Performance Index
The step/skirt performance index is calculated from the measurement of two quantities and is defined only for the inclined section of the escalator. The first quantity is the loaded gap(Lg). This is the distance between the edge of the step and skirt, while the step is 'pushed away' from the skirt using a force of approximately 110 N (25 lbs). The second quantity measured is the coefficient of sliding friction (µ) between the skirt panel and a standard polycarbonate test sample (PMT supplied). The Index is defined as:
Step/Skirt Performance Index = ey/(ey + 1)
Where: y = -3.77 + 2.37(µ) + 0.37 (Lg)
e = 2.7183
(Lg in mm)
This is an example of an Index Measurement Time History (EVA Software). The values of loaded gap (upper graph) and coefficient of friction (middle graph) are used, at each point in time, to calculate the Step/Skirt Performance Index (lower graph) using the formula above. Measurements are made on each side of two representative steps (a total of 4 measurements).
