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PTU-D300 User's Manual (v2.19)
PP500 *
TP400 *
XS0 *
PP600 *
TP800 *
XG0
4.4 Speed Control Commands & Queries
4.4.1 Speed Control & Relevant Terms
The Pan-Tilt Unit provides for precise control of axis speed and acceleration. This subsection
briefly describes how speed control is performed and it introduces relevant terms.
As shown in Figure 5, upper and lower speed limits determine the bounds on nonstationary
pan-tilt velocities. The base (start-up) speed specifies the velocity at which the pan-tilt axis can be
started from a full stop without losing synchrony (as described in Section 3.8), and it is more a
function of the motors rather than load characteristics. Due to base speed requirements and the
property that motors lose torque as speed increases, acceleration is required to achieve axis speeds
above the base rate. The pan-tilt controller uses trapezoidal acceleration and deceleration for
speeds above the base rate and less than the maximum allowed speed. Figure 5 shows two
acceleration cases. In the first, an axis accelerates up to a desired constant speed (slew rate), then
decelerates. The second case shows the case when the unit does not have sufficient time to
accelerate up to the desired slew speed before the need to decelerate to the desired position.
The pan-tilt controller provides for on-the-fly position and speed changes. If the direction is
changed on-the-fly, the controller manages all deceleration, direction reversal, and acceleration to
achieve the most recently specified target pan-tilt speed and acceleration rates.
Because speed, acceleration, and position are precisely controlled, you can accurately and
simply predict the position attained by the pan-tilt unit in time.
UPPER SPEED LIMIT
BASE (start-up) SPEED
LOWER SPEED LIMIT
Figure 5: Axis Speed, Instantaneous Speeds, Trapezoidal Acceleration,
4.4.2 Speed (absolute)
Description
Specify or query desired axis speed. Desired speed is specified in positions/
second and it can be changed on-the-fly. The speed specifies the rate at which
the pan-tilt moves to achieve position movement commands.
are not executed.
and On-The-Fly Speed and Position Changes
Desired speed commands outside the speed bounds return an error and
COMMAND REFERENCE
speeds
requiring
acceleration
instantaneous
speed
changes
time
page 17
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