Curve Tool: Units of Measurement

Four quantities are conveyed in the Curve Tool: time (or master position), position, velocity, and acceleration. These terms can be somewhat confusing since the curves created by the curve tool can be followed with respect to time or with respect to another axis. Therefore, this topic is devoted to helping clarify the use of these terms and define the units used by each:

Time (Master Units)

By default this quantity is labeled Time (sms) and refers to actual time in short milliseconds (sms). A short millisecond is 1/1024th of a second. This term is used because, when the RMC follows a curve based on time, it processes one time unit every 976 microseconds, or 1024 time units per second. However, in many applications this quantity actually refers to a master position. Therefore, this label can be changed. For example, a general label that fits most geared curve applications would be Master Pos (pu). For details on changing this label, see Curve Axis Labels.

Position (Slave Units)

By default this quantity is labeled Position (pu) and refers to position units of the axis following the spline. In applications in which the curve is being followed with respect to another axis, it may be useful to change the label to help differentiate it from the axis it is geared to. Therefore, this label can be changed. For example, a general label that fits most geared curve applications would be Slave Pos (pu). For details on changing this label, see Curve Axis Labels.

The units for this field will always be position units, as defined for the axis from the main RMCWin screen and used throughout the RMC product.

Velocity

This quantity appears on the velocity scale bar, in the Detail window, in the data tips, in the Point Properties dialog box, and in the Options dialog box under the General tab for setting the speed limit. The label for this quantity cannot be changed.

The speed units are position units per 1024 time units. Therefore, if a curve is followed with respect to time, each time unit is 1/1024th of a second, so the speed units are position units per second.

If the curve is followed with respect to another axis, then the speed units are less clear: the speed will be slave position units per 1024 master position units. For example, a 1:1 gear ratio would have a speed of 1024.

Acceleration

This quantity appears on the acceleration scale bar, in the Detail window, in the data tips, in the Point Properties dialog box, and in the Options dialog box under the General tab for setting the acceleration limit. The label for this quantity cannot be changed.

The acceleration units are position units per 1024 time units per 1024 time units. Therefore, if a curve is followed with respect to time, each time unit is 1/1024th of a second, so the acceleration units are position units per second per second.

If the curve is followed with respect to another axis, then the acceleration units are less clear: the acceleration will be slave position units per 1024 master position units per 1024 master position units.