Design Checklist with the Cam-Data FB

Cam Data FB icon

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
Radius-of-Curvature

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.

Force Analysis:

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.

See: Configure the Power Source for Payload Analysis

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: is the superposition (addition) of the different payloads that act on the Cam-Follower - the total load.

Payload Signature: is how the payload varies over one machine cycle.

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.

Payload Signatures vs Motion-Derivative

Payload Signatures

Motion-derivative and Payload Type

Examples

CamForce-constant

Not a function of the motion

Constant Load

Gravity, 'Friction', Spring Pre-load

CamForce-ProportionalPosition

First Motion-Derivative

Load Proportional to Displacement

Spring Displacement

CamForce-ProportionalVelocity

Second Motion-Derivative

Load Proportional to Velocity

Viscosity, Air-Cylinder

CamForce-ProportionalAcceleration

Third Motion Derivative

Load Proportional to Acceleration

Inertia Forces

CamForce-ProportionalSpecial

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'.

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 output1s (cam output displacement)
The acceleration force is low.

High-Speed:

Maximum payload is on the cam flank2s 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 3s 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 loads at 'High Speed'.

Cam loads at 'High Speed'.

Cam-Follower: Payload 'Signature'

Typical Load Signature of a Cam-Follower

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.

Cam: Payload 'Signature'

Cam: Payload Signature of Body-Closed Cam

Cam: Payload Signature of Body-Closed Cam

Mean-Stress = (Max+Min)/2;

Stress Amplitude = (Max-Min)/2;

Max Stress = 2*Mean;

Minimum Stress = 0 MPa

Each point along the cam surface (and just below) becomes stressed at one 'machine angle'* in the machine-cycle

The stress that the point experiences is zero at all other machine angles.

For each point along the cam, the stress is said to be 'pulsatile' (like heart-beat pulses) with a 'period' of 2.π* or 360º*.


The image shows the Payload 'pulse' at a single point on the cam.

This Point on the Cam experiences this stress one time per rotation.


* Assumes the cam rotates one time per machine cycle.

Help Files for MechDesigner and MotionDesigner 11.1 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd