﻿ Symmetrical Coupler Curves

# Symmetrical Coupler Curves

## Symmetrical Coupler Curves

 Symmetrical Coupler Curves are frequently useful. For example, you can find a coupler curve to give two straight lines. These are often useful for Dwell Mechanisms. Mechanisms with symmetrical coupler curves are easy to design with MechDesigner. Design Parameters of a Four-Bar Mechanism to give a Symmetrical Coupler-Curve. The four-bar mechanism to the left is defined by the Points: AoA (Crank), BoB (Output Rocker), AB (Coupler), Point K (Symmetrical Coupler Point on Part AB). Symmetrical Coupler Curves A Coupler Curve becomes symmetrical when: AB = B0B = BK Axis-of-Symmetry Symmetrical Coupler Curves must have an Axis-of-Symmetry. The 'axis-of-symmetry' is the ray: B0.J The angle direction of the axis-of-symmetry, relative to the frame, from B0 is given by: ∠A0B0J  (Θ)= ∠ ABK / 2  (External Angle ∠ABK ) Coupler Point on the Axis-of-Symmetry The Coupler Point is on the Axis-of-Symmetry when the Input Crank angle, α, is 0 or 180

#### Video of Symmetrical Coupler Curve and Axis-of-Symmetry

Video: It is worth watching this video two or three times to understand the mechanism design.

The mechanism is a standard four-bar mechanism. The length of the Coupler and the Rocker are equal. The distance from joint B to the Coupler Point, K, is equal to the length of the Rocker and Coupler. Thus, the Coupler Curve will be symmetrical.

The videos shows,

 • shows a stationary 4-bar
 • the coupler curve for the full cycle of the mechanism [but we are not moving the mechanism]
 • the Crank-Angle, α [BoAoA] is fixed at 180º .
 • the angle ABK changes from 0 to 360

Thus, everything is fixed, but we move the coupler point, K, by rotating it about joint B

Because AB, BoB, and BK have equal lengths, the coupler curve is be symmetrical.

 • the axis-of-symmetry changes and rotates about Bo as we change the angle ABK[2Θ]

Video of Symmetrical Coupler Curve.

#### Application of Symmetrical Coupler Curve with two straight lines: Geneva Indexer

 A Symmetrical Coupler can be applied to index a Geneva Wheel. See videos below. Video of a Geneva Indexer controlled with a Symmetrical Coupler Curve.

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