Elevator safety gear can use wedge elements to bring braking surfaces into contact with a guide rail. This calculator illustrates the take-up geometry of an ideal pair of sliding wedges. It calculates travel to first contact and an ideal force ratio, not elevator braking performance or a component rating.
Elevator Safety Gear Interactive Calculator
Explore how ramp angle and per-side gap determine wedge travel to first contact. The animation stops there; the calculator does not predict braking or rated capacity.
Equation Used
- Symmetric ideal sliding wedges.
- Per-side gap and straight guides.
- Motion ends at first contact.
- Force ratio assumes frictionless virtual work.
Angle is measured from vertical. Geometry demonstration only, not a safety-gear rating or adjustment specification.
Wedges approaching a rail
The section view is fixed to the housing. Each blue wedge follows an inclined guide and moves upward and inward, closing its initial clearance to the central rail. The illustration stops at first contact; no uncalculated clamp deflection or stopping event is shown.
The two inputs are ramp angle and per-side gap. Changing angle changes the drawn wedge slope and take-up travel. Changing gap changes the starting clearance and distance to first contact.
Real safety gears differ in their gripping elements, springs, guides and actuation. The image is an educational symmetric wedge arrangement, not a replica of a certified product. The governor and synchronized actuating linkage are omitted.
What this geometry comparison establishes
Use the controls to explore why a shallow guide needs more vertical motion to close a given lateral clearance. The animation keeps the wedges connected to their guides and does not let them pass through the rail.
Actual stopping behavior additionally depends on the complete gear construction, loads, speed, rail condition, friction and its specified configuration. None of those is entered here. The slider limits are demonstration ranges rather than approved installation values.
Take-up travel and ideal force ratio
Let α be the guide angle measured from vertical. For vertical wedge travel y, inward movement is x=y tan α. If the initial gap on each side is g, first contact occurs at y=g/tan α.
Under ideal frictionless virtual work, vertical input force Fy and horizontal output force Fx obey Fy·y=Fx·x, giving Fx/Fy=1/tan α. This ratio is not an actual braking force: friction, spring compliance and self-energizing behavior are not included.
The last result is 100g/(3 mm). The 3 mm denominator is a numerical reference; it is not a required clearance or a penalty threshold.
Default geometry
At an 18° guide angle and 2.5 mm per-side gap, tan α is approximately 0.32492. Each wedge moves vertically about 7.694 mm before first contact. The ideal frictionless force ratio is approximately 3.078:1.
Doubling the gap doubles take-up travel but does not change the ideal ratio. Increasing the angle shortens take-up travel and lowers that ratio. These relationships do not determine stopping distance.
Separate illustration from safety-gear selection
This page does not set tripping speed, rail clearance, material hardness, maintenance interval or permitted load. A two-input wedge model cannot establish these equipment-specific values.
Manufacturer documentation is specific to a gear variant, guide rail and operating configuration. The moving sketch is not installation, adjustment, testing or reset instructions.
The repeated return motion only resets the visualization. It does not represent how a loaded elevator is released after a safety-gear trip.
Wedge geometry questions
Does the force ratio tell me the clamp force?
No. There is no input force, friction or spring model, and the ratio is an ideal work balance only.
Why stop at first contact?
Before contact, geometry determines clearance take-up. After contact, forces and compliance are needed to predict further motion.
Is the gap the total clearance across both sides?
No. It is the initial gap between each wedge and its rail face. The drawing is symmetric.
Is 3 mm the recommended gap?
No. It is only a numerical comparison reference.
References
- US5159995A: Safety gear for an elevator — wedge, housing and guide-rail interaction.
- Wittur: Safety Components — manufacturer examples of distinct safety-gear constructions.
- Dynatech: Mechanical progressive safety gears — product-specific configurations rather than a universal gap.
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