A rotating carrier carries a bent spring past a stronger spring attached to the frame. Their contact presses the bent spring into a ratchet tooth, briefly advancing the ratchet before release. The fixed spring then stops the ratchet until the next carrier revolution.
Bent-spring Driver with Strong-spring Catch Interactive Calculator
Compare linear spring rates, driver preload and catch seating deflection while watching the rotating-carrier engagement sequence. The calculator supplies spring comparisons, not a reliability prediction.
Equation Used
- Both entered rates describe linear spring behavior at their respective tips.
- Preload and seating inputs are deflections at those same tip locations.
- The rate comparison does not establish holding torque or reliable indexing.
- The 12-tooth animation is a prescribed contact sequence, independent of the comparison stroke; it is not an elastic-contact solver.
Construction reference: Brown movement73 and Hiscox movement1015. No fatigue life, safe ratio, guaranteed count accuracy or manufacturing tolerance is inferred from these inputs.
Carrier, bent driver and fixed catch
Brown’s movement 73 shows ratchet A on the same centre as rotating carrier D. Bent spring B is fastened to the carrier. Spring C is attached to the frame. As B passes under C, C presses B inward to engage a tooth of A. The carrier then advances the ratchet briefly. When B escapes C, it springs clear and the fixed spring stops A.
The diagram distinguishes the continuously moving carrier from the intermittently moving ratchet. Blue identifies the bent driver and grey identifies the fixed catch. The animation uses twelve illustrative teeth and one tooth of advance per turn, with approach, engagement, release and dwell shown as separate stages. Spring shapes and transition timing explain the contact sequence; they are not a calculated elastic solution.
Intermittent indexing
This arrangement illustrates how continuous rotary input can produce separated increments of output rotation using elastic engagement. It belongs to the broader family of intermittent ratchet mechanisms. The input here is a rotating carrier, not a reciprocating hand lever.
Adapting this arrangement to a counter or indexing device requires the tooth profile, spring geometry, speed, load and contact behaviour. The staged motion illustrates the engagement sequence without sizing those parts.
What the spring calculator evaluates
For a linear spring with rate k and tip deflection δ, force is kδ. Driver preload force is kdδp. Catch seating force is kc e, where e is explicitly an assumed catch-tip deflection. The rate ratio is kc/kd, while preload percentage is 100δp/s using the entered reference work stroke s.
These scalar comparisons do not include moment arms, friction, tooth pressure angle, contact timing or inertia. Forces at different deflections cannot be turned into a reliable engagement verdict using a stiffness ratio alone. A practical engagement assessment also needs those geometric and dynamic quantities.
Spring comparison example
For kd = 1 N/mm, kc = 7.5 N/mm, δp = 0.4 mm, s = 1 mm and e = 0.1 mm, the rate ratio is 7.5, preload is 40 percent of the reference stroke, driver preload force is 0.4 N and catch seating force is 0.75 N.
Those numbers describe the entered linear-spring assumptions. They do not establish how many teeth a real assembly advances, whether it back-drives, or how long its springs will last.
Geometry controls the contact sequence
Changing spring stiffness changes force for a specified deflection. It does not, by itself, specify the spring shape, the instant a tip engages, or the amount of ratchet travel. Those require the carrier geometry and tooth contacts. The drawing uses a fixed twelve-tooth wheel and prescribed engagement timing to explain the sequence. The spring-force comparisons do not determine tooth count or timing.
Spring-driver questions
Why does the large carrier keep turning when the ratchet stops?
The bent driver is clear of the ratchet during dwell. The fixed catch stops the ratchet while the carrier brings the driver around for another engagement.
Does a higher catch-rate ratio guarantee reliable indexing?
No. Rate ratio omits deflection, geometry, friction, speed and load. The calculator gives comparisons without assigning a reliability score.
What does seating mean here?
It is the assumed catch-tip deflection used in kc e. It is not a recommended tooth clearance or a manufacturing tolerance.
Does work stroke set the tooth pitch?
No. It is the reference displacement in the preload percentage. The animation has a clearly identified illustrative twelve-tooth wheel.
Historical construction references
Henry T. Brown, movement73, describes the rotating carrier, bent driver, strong fixed spring and ratchet dwell.
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, movement1015 on printed page257, shows the same spring-and-ratchet principle and the transfer of stopping action.
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