A heddle cam controls movement of a loom’s heald or heddle frame through a follower and transmission. Moving the frames separates warp threads to form a shed for weft insertion. This calculator converts an assumed cam dwell angle into time and multiplies cam lift by an entered travel ratio; it does not determine a loom’s permissible speed or complete shedding sequence.
Heddle Cam Interactive Calculator
Compare assumed upper-dwell time and frame travel. The model has one rise, one dwell and one fall per cam revolution.
Equation Used
The selected dwell occupies a fraction of one cam revolution. Camshaft speed converts it to time, and cam lift times the entered ratio estimates frame travel. Actual shed clearance and weft timing are not calculated.
- One cam revolution defines one heddle motion cycle.
- Remaining cam angle is split equally between rise and fall.
- Lever motion is treated as rigid with no lost motion or compliance.
- Cam lift is converted to shaft travel by the treadle lever ratio.
Cam motion and frame travel
A cam profile moves its follower through a rise, a period of unchanged position called dwell, and a return. Linkages transmit this movement to a heddle frame. Multiple frame motions must be coordinated with the weave and the rest of the loom.
The calculator represents one rise, one upper dwell and one fall per cam revolution. It divides all angle outside the dwell equally between rise and fall and has no separate lower dwell. That simplified cycle is not a complete cam specification for a particular weave.
Lever ratio in the calculator is a constant multiplier from cam lift to frame travel. The animation uses a grooved cam, roller, rigid treadle and separate connecting link to a vertically guided frame. The short treadle arm and connecting link each have an illustrative length equivalent to 123.1 mm; the long arm follows the entered ratio. Link-angle changes slightly increase the drawn frame travel beyond the calculator’s LR estimate. Contact forces and a particular loom’s dimensions are not calculated.
The companion illustration shows the default 120 degree dwell. The animation follows the selected lift, ratio and dwell, with cycloidal rise and fall and no lower dwell. Playback runs at one hundred and twentieth of entered camshaft rpm. A roller follows the rotating groove; the treadle and connecting link retain their lengths. Yarn tension, shuttle passage and collision clearance are not simulated.
Cam shedding in weaving
Stäubli describes cam motions as shedding equipment for plain and other basic weaves on rapier and air-jet weaving machines. Its frame-weaving systems include transmissions that carry movement to the heald frames.
Cam shedding, dobbies and Jacquard systems provide different ways of controlling the warp. Selection depends on the pattern, machine and production needs. The arithmetic here does not establish a universal speed ranking, number of shafts, replacement interval or cost comparison.
Dwell time and travel
t = Tθ/360 milliseconds
shaft travel = LR
dwell fraction = 100θ/360 percent
rise angle = fall angle = (360 − θ)/2 degrees
N is camshaft rpm, θ is the selected dwell angle, L is cam lift in millimetres and R is the entered travel multiplier. The time output belongs to one cam revolution, not automatically one pick.
The connection between camshaft rpm and picks per minute depends on the actual drive and weave repeat. No pick count, shaft phasing, shuttle or rapier crossing time, or lower-dwell duration is entered.
Comparing dwell time with an insertion time alone would not prove clearance. Actual frame motion, thread geometry, synchronization and settling behavior also matter. The tool computes none of those quantities.
Example using the displayed inputs
At θ = 120°, N = 400 rpm, L = 30 mm and R = 3.3, a revolution takes 150 ms. The selected dwell occupies one third of it, or 50 ms. The assumed shaft travel is 30 × 3.3 = 99 mm, dwell fraction is 33.3%, and rise and fall each occupy 120°.
Reducing camshaft speed to 200 rpm doubles dwell time to 100 ms without changing travel or the angular fractions. Increasing dwell angle at fixed rpm increases dwell time while reducing the equal rise and fall angles.
These input values are illustrative. Neither 50 ms nor 100 ms establishes that a particular shuttle or rapier can clear a shed.
Timing choices require the full motion
Allocating more cam angle to dwell leaves less angle for movement in this model. To understand the resulting acceleration and loads, the rise-and-fall displacement law and moving components must also be known.
Likewise, increasing the entered lever ratio increases the calculated travel but does not assess leverage, required force or linkage reach. No follower upgrade, cam regrinding or speed increase can be justified from these four results.
Frequently asked questions
Does camshaft rpm equal picks per minute?
Not necessarily. The relationship depends on the drive and weave repeat. This calculator has no picks-per-revolution input.
Why does lift not change dwell time?
Dwell time depends only on dwell angle and camshaft rpm. Lift is used with the entered ratio to estimate travel.
Does a larger dwell guarantee shuttle clearance?
No. The tool does not model the shuttle, rapier, warp geometry or synchronization with other loom motions.
What does lever ratio mean here?
For the numerical travel result it is the assumed multiplier from cam lift to frame travel. In the drawing it sets the long-to-short treadle-arm ratio; the separate connecting link adds a small angle-dependent difference to frame travel.
Why does the rise/fall result decrease when dwell increases?
All remaining angle is divided equally between rise and fall. There is no additional lower dwell in this simplified cycle.
Can I use the output to uprate a loom?
No. It contains no dynamic loads, component ratings, contact analysis or equipment-specific limits.
Does the separate schematic respond to the sliders?
No. The companion diagram shows the default 120 degree dwell. Use the animation and calculator readouts to explore your selected inputs.
References
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