S-Curve Trajectory Profiles Menu
This menu allows you to create custom acceleration profiles to control motion. After a profile is defined, you can specify its use with a number of V+ instructions and commands, including ACCEL, SPEED, and SCALE.ACCEL. If no profiles are defined, the default square-wave acceleration profile is used. For additional information on s-curve and other motion profiles, see Details below.
When you select a menu option, the following information is provided on screen:
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Instructions for the selected option
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Current value
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Value range for the parameter if applicable
For details on a menu option, click the desired link in the following list to view the description:
Enable and edit a profile
Disable a profile
Menu Options
Enable and edit a profile
Allows you to select a profile and edit the acceleration and deceleration values for that profile.
For each robot, there can be as many as nine different profiles. Profile 0 is always defined to be a square-wave acceleration curve with all four ramp times set to zero. Profiles 1 through 8 are defined by the robot manufacturer and are a function of the mechanical design of the manipulator and the applications for which the robot was designed. For instance, the manufacturer might define a general purpose profile that has all of the ramp times set equal to a nominal value for the mechanism. This profile could be used whenever smooth performance throughout the motion was more important than minimum cycle time.
In instances where cycle time is more important, a profile with high jerk values during the acceleration and low jerk values during the deceleration might be more appropriate. If you are using SPEC to set up a mechanism that you have built, then you are the "robot manufacturer" and should choose ramp times to suit the capabilities of your mechanism.
Disable a profile
If you don't want to use a profile, choose this option to disable it. If all the profiles are disabled, the default is used: Profile 0 is always defined to be a square-wave acceleration curve with all four ramp times set to zero.
Details
While there are many different motion profiles that can be characterized as "S-curves", in V+ an S-curve is a trajectory that has a trapezoidal acceleration profile, giving an S-shaped velocity profile. V+ also supports a square-wave acceleration profile, which gives a trapezoidal velocity profile.
The benefit of a trapezoidal acceleration profile is that the rate of change of acceleration (the "jerk") can be controlled. (By comparison, the magnitude of the jerk for a square-wave acceleration profile is always infinite.) For many mechanisms, controlling the jerk is significant because high jerk values can cause the mechanical structure of the robot to vibrate. Minimizing structural vibrations is especially important at the end of a motion since such oscillations can adversely affect the settling time of the robot. This can affect the cycle. However, for stiff, strong mechanisms, a square-wave profile may result in shorter cycle times.
For a general trapezoidal profile, there are four acceleration values that can be specified, as shown in S-Curve (Trapezoidal Acceleration) Profile: the ramp up to maximum acceleration, the ramp down from maximum acceleration, the ramp up to maximum deceleration, and the ramp down to zero acceleration. In V+ each of these four acceleration values can be individually specified, and a set of the four values defines a specific acceleration "profile".
For a given motion, the duration of the motion and the characteristics of the acceleration profile depend on several parameters. These parameters are controlled by a number of V+ instructions and commands, including ACCEL, SPEED, and SCALE.ACCEL (see the V+ Language Reference Guide).
