A rocking wiper bears against an inclined toe on a vertically guided rod. As the rockshaft turns back and forth, the contact moves and the rod rises and falls through its guides. Explore that contact motion in the animation, with a separate calculator relating a small offset to a reference length.
Angular Wipers Interactive Calculator
Compare a positive offset with a reference arm length using arctan(offset/length). The animation illustrates a rocking wiper and guided rod; the calculated angle is not a cam-profile or valve-travel solution.
Equation Used
The geometric angle is arctan(δ/L), where δ is a positive offset and L is the reference length. This right-triangle comparison does not generally predict the sweep error caused by a manufacturing change in an actual cam mechanism.
- Geometry error is small compared with the arm length.
- The arm is treated as rigid with no bushing slop or compliance.
- Offset is entered as a positive magnitude.
The arctan(error/length) calculation is a tolerance comparison, not a synthesized wiper profile or predicted valve stroke. The historical mechanism shown is a rockshaft wiper contacting an angled toe on a guided rod.
A rocking wiper and an inclined toe
The rockshaft carries a shaped wiper. Its surface bears against an inclined toe on the rod. When the wiper rocks, the height of that supporting contact changes and the guided rod moves vertically.
The guides constrain the rod’s lateral movement. The illustration keeps the toe in contact with the wiper throughout the cycle. It does not calculate the forces needed to maintain contact, follower bounce or friction at the sliding surfaces.
Parts to follow
- Rockshaft: supplies the back-and-forth angular input.
- Wiper: presents the changing contact surface.
- Inclined toe: receives the wiper’s motion.
- Guided rod: carries the vertical output.
The contour and proportions are illustrative. A working valve or other driven device would require its own contact geometry, return arrangement, loading and timing analysis.
Studying rocking contact motion
This arrangement demonstrates how a rocking shaft can lift a guided member through direct surface contact. It is useful for comparing angular input with a translating output and seeing why the guide and contact face have different roles.
The word wiper is also used for other devices, including automotive and packaging-machine linkages. Their geometry, drive motion and timing are not established by this illustration. No named production machine, duty rating or service life is specified here.
A separate geometric angle comparison
The calculator uses θ = arctan(δ/L), converted from radians to degrees. L is a positive reference length and δ is a positive offset, both expressed in millimetres. The angle is also displayed in milliradians, and the offset ratio is 100δ/L percent.
The sensitivity card divides the calculated angle in degrees by the entered offset in millimetres. At zero offset it uses the limiting value 180/(πL) degrees per millimetre. For small δ/L, θ in radians is approximately δ/L.
This expression describes a right-triangle comparison. It does not determine wiper lift, dwell, pressure angle, contact force or a finished cam contour. The drawing’s rocking motion is illustrative rather than a motion law derived from these two inputs.
Worked angle comparison
For L = 100 mm and δ = 0.5 mm, the offset ratio is 0.5%. The geometric angle is arctan(0.005) = 0.28648°, or about 5.000 milliradians. Dividing by 0.5 mm gives an average angle-to-offset ratio of about 0.57295°/mm.
With the same 0.5 mm offset and L = 200 mm, the angle is about 0.14324°. Increasing the reference length reduces this comparison angle. These values are not a prediction of valve travel or the angular error of a particular manufactured wiper.
Contact geometry and actual operation
A rocking wiper transfers motion through contact with its follower. A pin-jointed linkage transfers motion through connected links; a shaped cam can define a specified follower-motion law. Selecting among them requires the desired motion, loads, available space and control requirements.
The two calculator inputs do not establish a universal operating speed, bearing type, spring preload, material hardness or rebuild interval. Those depend on the actual mechanism and its service conditions.
Angular-wiper questions
What does the animation show?
A rockshaft wiper bears against an inclined toe on a vertically guided rod. The rod follows the changing contact height while remaining in its guides.
Does the angle result equal the rod’s stroke?
No. The angle is arctan(offset/reference length). Rod stroke depends on the wiper surface, pivot position, toe angle and contact geometry.
Does changing length specify a new cam profile?
No. It changes the comparison angle and illustrative wiper reach. The calculator does not synthesize a manufacturable cam or valve-timing profile.
What does the sensitivity card mean?
For a nonzero offset it is the calculated angle in degrees divided by that offset in millimetres. At zero offset it displays the small-offset limiting ratio.
Does the animation predict follower bounce or wear?
No. Contact is maintained geometrically in the drawing. Dynamic contact force, return force, friction, wear and material deformation are not calculated.
Is this the same mechanism as a windshield wiper?
No. The related video shows automotive wiper linkages. The interactive drawing here shows a rocking surface lifting a guided rod through an inclined toe.
References & Further Reading
- Wikipedia contributors. Cam (mechanism). Wikipedia
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