Modified-Trapezoidal Motion-Law

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Modified-Trapezoidal Motion-Law

Modified-Trapezoid Cam-Law, Motion-Law

Motion Description

A Traditional Motion-Law. Its name is often reduced to Mod-Trap.

A motion with continuous Velocity and Acceleration, from start to end. The Jerk is finite at its start and end. Its peak acceleration is moderate.

It is commonly used in high-speed mechanisms. It was often used in Dwell-Rise-Dwell-Return cam-mechanisms. It has a low peak acceleration and velocity.

The Drive Torque is high and reverses rapidly, when compared to the Modified-Sinusoid motion-law.


You CAN specify the:

Start Position

The Start-Position usually flows from the End-Position of the Previous-Segment.

End Position

You CANNOT specify the:

Start Velocity & End Velocity

Start Acceleration & End Acceleration

Start Jerk & End Jerk

Segment Parameters




End- Range

0 ≤ Start-Range < End-Range ≤ 1

See also : MD-Globe-www-24 Tutorial 5: Edit the Start of a Traditional Motion-Law.

See also : MD-Globe-www-24 Tutorial 9: Asymmetrical Motions.

Modified Trapezoid Cam-Law / Motion-Law

Modified Trapezoid Cam-Law / Motion-Law

Motion-Law Coefficients

Velocity Coefficient :

Acceleration Coefficient :

Jerk Coefficient :

Jerk at Cross-over :

Application Notes

Dynamic Performance

This Motion-Law is a good general purpose type particularly in applications where the period ratio is above about 5. It is not good in applications where the input drive has backlash or is relatively flexible. As long as the drive satisfies these conditions, then this segment exhibits low residual vibrations.

Pressure Angle Considerations

This one of the Traditional Motion-Laws that produce a relatively large pressure angle - and so might need a large cam for a given lift and pre-prescribed maximum pressure angle.

Drive Torques

This Motion-Law exhibits a rapid reversal of acceleration at the cross-over (mid) point. Only the Constant-Acceleration Motion-Law is more rapid, of the Traditional Segments. It is unsuitable to drive heavy masses at high speeds. The rapid reversal of torque may give rise to severe vibrations and shock loading especially if the period ratio is less than 10.

More information:

The acceleration function of the Modified-Trapezoidal is:

0.125 of Segment-Width - 1/4 Sine function

0.250 of Segment-Width - Constant-Acceleration

0.250 of Segment-Width - 1/2 Cosine function

0.250 of Segment-Width - Constant-Acceleration

0.125 of Segment-Width - 1/4 Sine function