Introduction

Flat indexers are cam mechanisms designed to convert the uniform rotating motion of the input shaft (input) to intermittent motion of the output shaft (output). These mechanisms are characterised by having parallel input and output shafts.

Motion is transmitted by a pair of conjungated-contour cams keyed to the input shaft and coupled with a roller detector on the output shaft. Cam profiles are designed to have always two opposite rollers in contact (one for each cam) in order to take up the slack: with consequent improvement in precision and repeatability of positioning, in decreasing noise and vibrations and in reducing wear. Intermittent - oscillating drives are contained in airtight - cast iron boxes. All surfaces present machined planes and threaded mounting holes. The mechanism doesn’t need scheduled maintenance because it is used a long life lubricating grease.

Project parameters

Parallel axis intermittent drives are classified on the basis of three main parameters:

• wheelbase: distance between input and output shaft (I)
• number of stops (S)
• displacement angle (B)

The series of standard ITC drives produced by ITALCAMME includes a wide range of combinations of these parameters, suitable for covering most of applications of these devices. We also build special types in order to satisfy customer specifications.

The WHEELBASE (I) determines the size of the unit and its mechanical characteristics. It must be chosen on the basis of the static and dynamic characteristics of the applied load.

The NUMBER OF STOPS (S) is the number of stops of the output shaft while completing a single rotation. The amplitude of output shaft rotation between one station and the next is called "ANGULAR STROKE" and is calculated by the simple equation: H = 360 / S (degrees).

The DISPLACEMENT ANGLE (B) is the rotation angle of the input shaft corresponding to the movement of the output shaft from one station to the next one. The cycle is completed by a rest phase corresponding to one input shaft rotation, called PAUSE ANGLE, which normally is not reported in the catalogue, since it is easily determined by the difference between the cycle angle and the displacement angle. One cycle corresponds, for the input shaft, to a rotation of 360 degrees for indexers having 1 to 4 stations, whereas for indexers having 6 and 8 stations, the rotation is 180 degrees.

Standard laws of motion

Long term experience in the field of cams has led ITALCAMME to the development of LAWS OF MOTION for the produced mechanisms, which represent the best kinematic and dynamic properties.

The standardised LAWS OF MOTION are characterised by continuous acceleration curves, without sharp variations at any point during the movement, those are symmetrical, with the axis of symmetry coinciding with the mid-point of the movement; initial and final speed and acceleration values are zero.

Each law is distinguished by its own speed (Cv) and acceleration (Ca) coefficients, which respectively represent the maximum speed and acceleration for a unit displacement implemented in the unit of time. The laws of motion normally used are the following:

Cycloidal (Cv=2, Ca=6.28)

This curve is also known as a sinusoidal curve. Among the standardised curves, this one has the highest maximum acceleration value, but it also has the smoothest passage from zero acceleration to full acceleration.

Modified cycloidal (Cv=1.76, Ca=5.53)

This curve is obtained by the combination of the sinusoidal acceleration curve and cosinusoidal acceleration curve. Its main characteristic is that it features, among the standardised curves, the smoothest passage between maximum acceleration and maximum deceleration values. It’s also known as Modified Sinusoidal.

Modified trapezoidal (Cv=2, Ca=4.89)

This curve is obtained from the combination of the sinusoidal acceleration curve and constant acceleration curve. Its main characteristic is that, among the standardised curves, it has the lowest maximum acceleration.

Modified sinusoidal with section at constant speed (Cv=1.4, Ca=6.62)

This curve is obtained from the modified cycloidal curve. The introduction of a section with constant speed and zero acceleration at the middle point of the acceleration curve reduces maximum speed and makes this curve especially suitable for applications with long strokes. This curve is the prototype of a family of derived curves, differentiated by their slightly different acceleration and speed coefficient values, which are applied in specific cases, where they are more advantageous than standard normalised curves.