﻿ Design Checks with the Cam-Data FB

# Design Checks with the Cam-Data FB

## Design Checklist with the Cam-Data FB

 Add a Cam-Data Function-Block (FB)... ...edit the FB to link it to a 2D-Cam... ...use the data available at its output-connectors to check various 2D-Cam design parameters. See Add Cam-Data FB and Edit Cam-Data FB

In MechDesigner, it is very easy to add cams that are 'good' and 'bad'.

What we mean by 'good' or 'bad' is whether the cam has the capacity to perform its duty for a specified life.

For convenience, we have classified our analysis as:

 • Geometric Analysis : We might refer to this as a Kinematic Analysis.
 • Force/Stress Analysis : We might refer to this as a Kinetostatic Analysis.

### Geometric Analysis:

The Geometric Analysis reviews the:

 • Cam Size
 • Pressure Angle / Overturning Moment

The cam's size, pressure-angle and radius-of-curvature are related to each other. They are a function of the dimensional layout of the cam mechanism, given a fixed motion. It is critical that you review these parameters early in your cam design.

## Before looking at Contact-Force and Contact-Stress... the model must represent the power flow in the machine correctly.

You may need to 'Configure the Power Source' to make sure that the force between the cam and cam-follower is correct.

The Force Analysis reviews the:

 • Contact-Force

Contact-Force is mostly used to find the Life of the Cam-Follower.

 • Contact-Stress (Hertzian Stress)

Contact-Stress is mostly used to find the Life of the Cam.

### Generic Payload Types and 'Signatures'

Payload Type: are payloads types that are a function of the motion-derivative, and thus, they are a function of machine-angle and machine-speed.

Examples

Not a function of the motion

First Motion-Derivative

Spring Displacement

Second Motion-Derivative

Viscosity, Air-Cylinder

Third Motion Derivative

Inertia Forces

A different function of Machine Angle, for example an engine's piston load.

'Power' stroke of an Engine

### Importance of Machine Speed

In the case of the example below, the payload is a superposition of three load types:

 • Constant Force (Green), for example: Gravity, Air-Cylinder.
 • Displacement Force (Blue), for example: Spring Force.
 • Acceleration Force (Magenta), for example: Inertia Force.

Cam forces at 'Low Speed'.

In the case when the machine is operating at:

Low-Speed:

 • Maximum payload is at the maximum value of the cam output (cam output displacement)
 • The acceleration force is low.

High-Speed:

 • Maximum payload is on the cam flank at the large positive acceleration (and also when the Pressure Angle will be greater)
 • Minimum payload is a negative force that is less than 0N at the large, negative acceleration.

Note: The X-axis of the graph is Machine-Angle. The time duration of the X-axis is shorter for the high-speed graph.

Cam-Follower: Payload Signature of 'Force-Closed Cam'.

In this example, the Cam-Follower Roller is contact is 'active' for all of the machine cycle.

First: review whether the contact-force is active against the cam for the complete machine cycle or only part of the machine cycle.

The Contact-Force Signature maybe different for a Force-Close Cam when compared to a Body-Closed Cam.

Body Closed Cam - Type 1: Conjugate-Cam

 • Cam-follower '1' is active during the acceleration phase of the 'Rise', and the deceleration phase of the 'Return'.
 • Cam-follower '2' is active for the other phases.

Body Closed Cam - Type 2: Groove-Cam

 • One roller is active for almost the complete machine cycle.
 • The roller is in contact with one cam-flank as the cam-follower accelerates and the other cam-flank as it decelerates. The roller must reverse its rolling direction when it chances cam-flanks.
 • As it changes rolling direction, it must must scuff when the linear speed of the roller-surface and speed of the cam-flank are not equal.
 • The contact force is zero [0] while the roller moves between flanks within the backlash zone.

Force-Closed Cam

 • The roller is 'active' for the complete machine cycle, assuming the Contact-Force does not become ≤ 0N.