🔹 What is SCurve Motion?

S-Curve Motion initiates a point-to-point motion using an “S” shaped velocity profile similar to that shown below.

This move type generates a motion that takes the same time as a trapezoidal move but allows the acceleration to have smoother transitions.

This comes at the expense of requiring larger peak accelerations and decelerations. The total move time is always the same as the equivalent trapezoidal move.

Note: You can change the velocity, acceleration, and deceleration of a moveSCurve that is executing on the fly simply by calling the function again with different parameters.

🔹 SCurve Motion Overview

Jerk %

Notes

Acceleration

Velocity

0%

Acceleration is always constant. This is the same as a Trapezoidal move profile.

Peak Acceleration is specified by the user.

50%

Acceleration is ramping 50% of the time and constant for 50% of the time.

Peak Acceleration is 133% of the value specified by the user.

100%

Acceleration is ramping 100% of the time and is never constant.

Peak Acceleration is 200% of the value specified by the user.

Jerk Percent

The Jerk percent is a parameter (from 0 to 100.0) which provides an easy way to change the acceleration profile without changing the move time. In most systems, there is a practical limit to acceleration, as it is proportional to the current in most motor types. Be sure to know the acceleration limitations to your system before trying a move SCurve profile.

Maximum Acceleration

Changing the Jerk Percent will change the max acceleration given by this formula:

Where,

max_accel: the maximum acceleration (or decel) for a point-to-point profile.

accel: the specified acceleration (or decel) from the application code.

jerk_percent: the specified jerk percentage (0 to 100.0) from the application code.

🔹 Multi-Axis SCurve Motion Overview

All Point to Point methods can be used for coordinated motion on multiaxis objects. It is important that you set up your arrays appropriately for a multiaxis object. See the examples below on how to structure your arrays for Multi-Axis SCurve Motion.

EXAMPLE 1 - Three Axis Multi-Axis XYZ with MoveSCurve()

The position data for all three axes are combined into the array. The time array is shared for all axes. This is why you need 3x as many position points than you need time points. See the example below:

Axis1 → relativePosition[0] = 10; velocity[0] = 10; acceleration[0] = 100; deceleration[0] = 100; jerkPCT[0] = 50;\ Axis2 → relativePosition[1] = 10; velocity[1] = 10; acceleration[1] = 100; deceleration[1] = 100; jerkPCT[0] = 50;\ Axis3 → relativePosition[2] = 10; velocity[2] = 10; acceleration[2] = 100; deceleration[2] = 100; jerkPCT[0] = 50;

multiAxis.MoveSCurve(relativePosition, velocity, acceleration, deceleration, jerkPCT);

Note: The jerkPCT in the example above is a double-precision percent value and NOT a double-precision decimal value.; The values passed to the function MoveSCurve() will be multiplied internally by the specified user units (AKA: counts per unit). The reason for this is to avoid creating an extra input array. We simply just use the same array you have passed to the function. Therefore, the values passed to the function might not be the same ones once the function has been triggered.

📜 Sample Code

Basic SCurve Motion

C#
public const double POSITION = 2; // Specify the position to travel to.

public const double VELOCITY = 200; // Specify your velocity. - units: UserUnits/Sec

public const double ACCELERATION = 100; // Specify your acceleration. - units: UserUnits/Sec^2

public const double DECELERATION = 100; // Specify your deceleration. - units: UserUnits/Sec^2

public const double JERK_PERCENT = 50; // Specify your jerk percent (0.0 to 100.0)

axis.MoveSCurve(Constants.POSITION); // Command SCurve Motion. This overload willuse default velocity, acceleration, deceleration, jerk values for the axis. See axis config to learn how to set those values.

axis.MotionDoneWait(); // Wait for motion to finish

C++
// Motion Parameters

const double POSITION_0 = 0;

const double POSITION_1 = 0.5;

const double VELOCITY = 1;

const double ACCELERATION = 10;

const double DECELERATION = 10;

const double JERK_PERCENT = 50;

const double FINAL_VELOCITY = 0.5;

std::cout << "SCurve Motion:" << std::endl;

std::cout << "Moving to position: " << POSITION_1 << std::endl;

axis->MoveSCurve(POSITION_1);

axis->MotionDoneWait(TIMEOUT);

std::cout << "Motion Complete" << std::endl;

std::cout << "Moving back to position: " << POSITION_0 << std::endl;

axis->MoveSCurve(POSITION_0);

axis->MotionDoneWait(TIMEOUT);

std::cout << "Motion Complete\n" << std::endl;

Multi-Axis SCurve Motion

C#
// Constants

const int NUM_OF_AXES = 2; // Specify the number of axes (Make sure your axis count in RapidSetup is 2!)

// Parameters

double[] positions1 = new double[NUM_OF_AXES] { 5, 10 }; // The first set of positions to be moved to

double[] positions2 = new double[NUM_OF_AXES] { 15, 15 }; // The second set of positions to be moved to

double[] velocities1 = new double[NUM_OF_AXES] { 1000, 1000 }; // The velocity for the two axes for the first move- Units: units/sec (driver will execute 10 rotations per second)

double[] velocities2 = new double[NUM_OF_AXES] { 1000, 1000 }; // The velocity for the two axes for the second move

double[] accelerations = new double[NUM_OF_AXES] { 500, 500 }; // The acceleration for the two axes

double[] decelerations = new double[NUM_OF_AXES] { 500, 500 }; // The deceleration for the two axes

double[] jerkPercent = new double[NUM_OF_AXES] { 50, 50 }; // The jerk percent for the two axes

controller.AxisCountSet(NUM_OF_AXES);

controller.MotionCountSet(NUM_OF_AXES + 1);

Axis axis0 = controller.AxisGet(Constants.X_AXIS_NUMBER); // Initialize axis0

Axis axis1 = controller.AxisGet(Constants.Y_AXIS_NUMBER); // Initialize axis1

HelperFunctions.CheckErrors(axis0); // [Helper Function] Check that 'axis0' has been initialized correctly

HelperFunctions.CheckErrors(axis1); // [Helper Function] Check that 'axis1' has been initialized correctly

// In this application, we have two Axis objects and one MultiAxis object, so three motion supervisors are required

MultiAxis multi = controller.MultiAxisGet(NUM_OF_AXES); // Initialize a new MultiAxis object. MultiAxisGet takes a motion supervisor number as its argument.

// This number is equal to the number of axes since motion supervisors are zero indexed (i.e., motion supervisors

// 0 and 1 are used for axis0 and axis1, so motion supervisor 2 is available for our MultiAxis object).

HelperFunctions.CheckErrors(multi); // [Helper Function] Check that 'multi' has been initialized correctly

controller.AxisCountSet(NUM_OF_AXES); // Set the number of axis being used. A phantom axis will be created if for any axis not on the network. You may need to refresh rapid setup to see the phantom axis.

multi.AxisRemoveAll(); // Remove all current axis if any. So we can add new ones

multi.AxisAdd(axis0); // Add axis0 to the MultiAxis object

multi.AxisAdd(axis1); // Add axis1 to the MultiAxis object

multi.Abort(); // If there is any motion happening, abort it

multi.ClearFaults(); // Clear any faults

multi.AmpEnableSet(true); // Enable the motor

axis0.ErrorLimitActionSet(RSIAction.RSIActionNONE); // Disable poistion error for Phantom Axes.

axis1.ErrorLimitActionSet(RSIAction.RSIActionNONE); // Disable poistion error for Phantom Axes.

multi.MoveSCurve(positions1, velocities1, accelerations, decelerations, jerkPercent); // Move to the positions specified in positions1 using a trapezoidal motion profile

multi.MotionDoneWait(); // Wait for motion to finish

Assert.That(axis0.CommandPositionGet(), Is.EqualTo(positions1[0]), "The first axis in the multi axis object should be commanded to move to the firt element of the array");

Assert.That(axis1.CommandPositionGet(), Is.EqualTo(positions1[1]), "The second axis in the multi axis object should be commanded to move to the second element of the array");

multi.MoveTrapezoidal(positions2, velocities2, accelerations, decelerations); // Move to the positions specified in positions2 using a SCurve motion profile

multi.MotionDoneWait(); // Wait for the motion to finish

Assert.That(axis0.CommandPositionGet(), Is.EqualTo(positions2[0]), "The first axis in the multi axis object should be commanded to move to the firt element of the array");

Assert.That(axis1.CommandPositionGet(), Is.EqualTo(positions2[1]), "The second axis in the multi axis object should be commanded to move to the second element of the array");

multi.AmpEnableSet(false); // Disable the axes
C++
/* CONSTANTS */

// *NOTICE* The following constants must be configured before attempting to run with hardware.

// Axis configuration parameters

const int AXIS_COUNT = 2;

const int AXIS_X = 0;

const int AXIS_Y = 1;

const int MOTION_COUNT = 1;

const double USER_UNITS = 1048576;

// Motion parameters

const double START_POSITION[AXIS_COUNT] = { 0, 0 };

const double END_POSITION[AXIS_COUNT] = { 1, 2 };

const double VELOCITY[AXIS_COUNT] = { 1, 2 };

const double ACCELERATION[AXIS_COUNT] = { 10, 20 };

const double DECELERATION[AXIS_COUNT] = { 10, 20 };

const double JERK_PERCENTAGE[AXIS_COUNT] = { 0, 0 };

// To run with hardware, set the USE_HARDWARE flag to true AFTER you have configured the parameters above and taken proper safety precautions.

USE_HARDWARE = false;

/* SAMPLE APP BODY */

// Create and initialize RsiController class

MotionController* controller = MotionController::CreateFromSoftware();

SampleAppsHelper::CheckErrors(controller);

// Setup the controller for the appropriate hardware configuration.

if (USE_HARDWARE)

{

SampleAppsHelper::SetupControllerForHardware(controller);

}

else

{

SampleAppsHelper::SetupControllerForPhantoms(controller, AXIS_COUNT, { AXIS_X, AXIS_Y });

}

try

{

// enable one MotionSupervisor for the MultiAxis

controller->MotionCountSet(controller->AxisCountGet() + 1);

// Get Axis X and Y respectively.

Axis* axisX = controller->AxisGet(AXIS_X);

SampleAppsHelper::CheckErrors(axisX);

axisX->UserUnitsSet(USER_UNITS);

axisX->PositionSet(0);

axisX->ErrorLimitActionSet(RSIAction::RSIActionNONE);

Axis* axisY = controller->AxisGet(AXIS_Y);

SampleAppsHelper::CheckErrors(axisY);

axisY->UserUnitsSet(USER_UNITS);

axisY->PositionSet(0);

axisY->ErrorLimitActionSet(RSIAction::RSIActionNONE);

// Initialize a MultiAxis, using the last MotionSupervisor.

MultiAxis* multiAxisXY = controller->MultiAxisGet(controller->MotionCountGet() - 1);

SampleAppsHelper::CheckErrors(multiAxisXY);

multiAxisXY->AxisAdd(axisX);

multiAxisXY->AxisAdd(axisY);

// make sure all axes are enabled and ready

multiAxisXY->Abort();

multiAxisXY->ClearFaults();

multiAxisXY->AmpEnableSet(true);

// Set SYNC_START motion attribute mask.

multiAxisXY->MotionAttributeMaskOnSet(RSIMotionAttrMask::RSIMotionAttrMaskSYNC_START);

printf("\nMotionStart...");

// Commanding motion using Syncpptart to start motion for both the axis at the same time.

multiAxisXY->MoveSCurve(END_POSITION, VELOCITY, ACCELERATION, DECELERATION, JERK_PERCENTAGE);

multiAxisXY->MotionDoneWait();

// Calling function created on top.

PrintResult(axisX, axisY);

// Set SYNC_END motion attribute mask

multiAxisXY->MotionAttributeMaskOnSet(RSIMotionAttrMask::RSIMotionAttrMaskSYNC_END);

printf("\nMotionStart...");

// Commanding motion using SyncEnd to end motion for both the axis at the same time.

multiAxisXY->MoveSCurve(START_POSITION, VELOCITY, ACCELERATION, DECELERATION, JERK_PERCENTAGE);

multiAxisXY->MotionDoneWait();

// Calling function created on top

PrintResult(axisX, axisY);

printf("\nTrapezoidal Motion Done\n");

// Disable the all the axes

multiAxisXY->AmpEnableSet(false);

}

catch (RsiError const& err)

{

printf("\n%s\n", err.text);

return -1;

}

controller->Delete();

return 0;

Motion: Modify

This sample application demonstrates how to use change the velocity parameter of a motion that is partially complete.

C#
axis.MoveSCurve(20, Constants.VELOCITY, Constants.ACCELERATION, Constants.DECELERATION, Constants.JERK_PERCENT);

if (axis.CommandPositionGet() > 2)

{

// Go 10X faster

axis.MoveSCurve(20, Constants.VELOCITY * 10, Constants.ACCELERATION, Constants.DECELERATION, Constants.JERK_PERCENT);

}

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