Advanced PLC Functions For Electrical Drives

Cutting-edge Technology Functions for High-Performance Motion Control

DriveXpress: Precision Motor Speed Control for Any PLC Platform

Introducing DriveXpress – the ultimate solution for precise motor speed control without the need for specialized technology CPUs. Whether you’re managing conveyors, pumps, fans, or other motion-driven applications, DriveXpress ensures smooth, safe, and accurate motor speed transitions, protecting both your motor and mechanical components from excessive stress.

Why Choose DriveXpress?

Universal PLC Compatibility: Forget about specialized technology CPUs! DriveXpress runs seamlessly on real-time PLC platforms including Siemens S7, Siemens TIA Portal, Rockwell Studio AIO, Rockwell RSLogix 5000, Rexroth IndraWorks, B&R Automation Studio, and Beckhoff TwinCAT, all while delivering the same high performance across the board.
Seamless Integration with Existing PLC Programs: The DriveXpress PLC function can be easily purchased and directly integrated into your existing PLC programs. This allows for effortless scaling and enhancement of your current automation systems without the need for extensive reprogramming or system overhauls.
Simplified Commissioning and Parameterization: With comprehensive input/output documentation and practical examples, DriveXpress makes commissioning and parameterization incredibly straightforward. This reduces setup time and ensures a smooth transition from installation to operation, empowering your team to get up and running quickly with minimal effort.
Advanced Trajectory Generator: At its core, DriveXperss features a powerful trajectory generator that plans the ideal motor speed profile using a trapezoidal acceleration profile. This approach delivers smooth and precise motor speed transitions.
Immediate Stop Functionality: With a built-in Stop input, DriveXpress allows you to halt your motor safely and instantly, applying a controlled deceleration to prevent jolts or system damage.
Versatile Applications: Whether you’re controlling the speed of a conveyor belt, pump, or fan, DriveXpress offers the flexibility to meet your specific speed requirements while ensuring smooth, reliable operation.

Description

The DriveXpress PLC function block is designed specifically for precise control of a motor’s rotational speed. This function generates a speed setpoint for the motor, ensuring that the acceleration and jerk (rate of change of acceleration) remain within predefined limits. This is essential for applications where smooth, controlled speed transitions are required to protect both the motor and mechanical components from excessive stress.

One of the key features of this function is the inclusion of a Stop input. This allows for an immediate stop of the motor at any time, applying a controlled deceleration based on the configured deceleration value. This en sures that the motor can be safely halted without causing sudden jolts or damaging the system.

This function is crucial for maintaining precise speed control in applications such as conveyors, pumps, and fans, where smooth operation and quick, controlled stopping are necessary. It ensures the motor operates within safe parameters, minimizing wear and tear while providing the flexibility to handle a wide range of speed requirements.

It is important to note that this function only generates the motor speed setpoint. The actual speed control and regulation must be managed by a motor frequency drive, which will adjust the motor speed according to the set point. Additionally, the motor control word and status word for communication with the frequency drive must be handled outside of this function, by the user. This separation ensures flexibility in integrating the function with various motor drive systems while maintaining precise control over speed setpoints.

The following diagram illustrates how the DriveXpress function block integrates into the overall control system, highlighting its role in achieving precise and reliable speed control of the electrical motor.

Compatible with various PLC platforms like Siemens S7, Siemens TIA Portal, Rockwell Studio AIO, Rockwell RSLogix 5000, Rexroth IndraWorks, B&R Automation Studio, and Beckhoff TwinCAT, DriveXpress provides the same high performance on any platform.

Block Diagram

Inputs Description

GenPar
	SampleTime
	Digits

GenPar → SampleTime - Calling frequency of the controller -REAL-

The sample time, in second, of the cyclic interrupt task of the plc at which the function is running. A higher sampling frequency allows for more precise control.

GenPar → Digits - Resolution of the calculated movement trajectory, -INT-

The Digits input is an integer value that determines the resolution of the decimal places for the calculated motor speed trajectories. This setting controls the precision of the trajectory calculations, ensuring accurate speed transitions. A value of 4 is recommended, which provides a good balance between precision and computational efficiency, allowing the function to generate smooth and accurate speed profiles.

ParSpdCtrl
	TgtSpd
	MaxAccSetPnt
	JerkSetPnt

ParSpdCtrl → TgtSpd - Target for the motor speed, -REAL-

The TgtSpd input defines the desired motor speed. This input specifies the rotational speed the motor should achieve, and it is typically expressed in units such as RPM (revolutions per minute), rad/s, or as a percentage of the motor’s nominal speed, depending on system configuration. This input works in conjunction with the predefined acceleration and jerk limits to ensure smooth and controlled transitions to the target speed. The function will gradually adjust the motor’s speed towards the setpoint, adhering to the specified dynamics. According to figure 1, when the function is enabled (as seen from the Enb signal at the top), it immediately responds to any changes in the TgtSpd input. The speed trajectory (SpdTrj ) closely follows the target speed setpoint with smooth transitions, respecting the configured acceleration (AccTrj ) and jerk limits. Each adjustment in the target speed is reflected in the output SpdTrj. The graph also shows how the acceleration profile (AccTrj ) adapts according to the changes in the target speed, indicating that the function continuously calculates the necessary acceleration to reach the setpoint.

Figure 1: General behavior of the function.

ParSpdCtrl → MaxAccSetPnt - Maximum Motor Acceleration/Deceleration, -REAL-

The MaxAccSetPnt input defines the maximum allowable acceleration for the motor when the function is controlling the motor speed. This parameter sets a limit on how quickly the motor can accelerate or decelerate when moving toward the target speed. The value of MaxAccSetPnt is typically expressed in units such as rpm/s or rad/s² or as a percentage of the motor’s nominal speed per second, depending on the system configuration. It ensures that the motor’s acceleration stays within safe or desired limits, preventing excessive wear on mechanical components and ensuring smooth transitions during speed changes. According to figure 2, changes to the MaxAccSetPnt input are not possible during a speed transition. As shown, once the speed trajectory is in progress, the function does not respond to adjustments in the maximum acceleration setpoint until the transition has completed.

Figure2: Behavior of the function with different acceleration limit values

ParSpdCtrl → JerkSetPnt - Maximum MotorJerk, -REAL-

This input defines the jerk of the motor during speed changes. Jerk is the rate of change of acceleration or deceleration and is measured in units such as rpm/s², rad/s³ or as a percentage of the motor’s nominal speed per second cubed.

ParStop
	DecSetPnt

ParStop → DecSetPnt - deceleration of the motor stop, -REAL-

The function block includes a stop feature that allows the motor to be halted immediately. As soon as a rising edge is detected on the Stop input, the function triggers a stop ramp to bring the motor to zero speed. The deceleration during this stop is defined by the DecSetPnt input, which can be configured in units such as [rpm/s], [rad/s²], or as a percentage of the nominal speed per second. After the stop input is activated, normal operation of the function can only resume once the acknowledge (Ack ) input is activated. This ensures that the system is properly reset and ready for continued use after an emergency or controlled stop. See figure 3.

Figure 3: Maximum deceleration of the stop trajectory

Enb - Turn controller on or off, -BOOL-

The Enb input is a boolean signal used to enable or disable the function. When the Enb input is set to True, the function block becomes active, allowing it to process inputs and generate outputs . If the Enb input is set to False , the function block is deactivated, and it will no longer respond to changes in the input setpoints. Additionally, when the function is disabled, the outputs are reset to zero.

When the Enb input transitions from False to True , the function generates a motor speed profile starting from the initial speed defined by InitSpd and with an initial acceleration defined by InitAcc . See table 1 and figure 4.

Figure 4: Behavior of the function when enabling and disabling

	SpdTrj	AccTrj
Enb = True	calculated by speed trajectory generator	calculated by acceleration trajectory generator
Enb = False	0.0	0.0

Table 1: Behavior of the output signals depending on the Enb input

InitSpd - Initial speed when enabling the function, -REAL-

See description of input Enb.

InitAcc - Initial acceleration when enabling the function, -REAL-

See description of input Enb.

Stop - Safety stop, -BOOL-

The Stop input is a critical safety and control feature. Regardless of the current value of the output SpdTrj the function block is in, when a rising edge is detected on the Stop input, the function immediately sends a zerospeed setpoint to the motor. This command is executed with a configurable deceleration rate DecSetPnt, ensuring the motor comes to a controlled and safe stop. This input is essential for emergency stops or situations where an immediate halt of the motor is required, providing a reliable way to quickly bring the system to a stop. See figure 3.

Ack - Acknowledge , -BOOL-

The Ack input is used to reset the function block after a stop command has been executed via the Stop input. Once the motor has been stopped, the function block is locked, preventing any further operations until a rising edge is detected on the Ack input. This input serves as a safety feature, ensuring that the system cannot resume normal operation until the stop event has been acknowledged by the user. It allows the user to verify and confirm that the system is ready to continue, ensuring controlled and safe operation after a stop condition. See figure 3.

Output Description

SpdTrj - Speed trajectory, -REAL-

The SpdTrj output is the main output of the function block, responsible for providing the motor speed profile. This output ensures that the motor achieves the target motor speed, or safely stops the motor. The unit of this output—whether rpm, rad/s, or a percentage of the motor’s nominal speed—depends on the unit of the input parameters TgtSpd .

The SpdTrj signal must be connected to a motor speed controller, such as a frequency drive, which translates the setpoint into the actual motor speed.

AccTrj - Acceleration trajectory,-REAL-

The AccTrj output represents the acceleration profile of the motor as it’s speed transit toward the target speed. See figures 1 to 4.

Error - Error conditions of the function block, -Boolean Array of 2 Elements-

The Error output is a boolean array with 2 elements, each indicating a specific error condition that prevents the function block from executing certain operations. Understanding these elements is crucial for diagnosing issues and ensuring the function block operates correctly.

Element 1, (Invalid Acceleration or Jerk setpoint): If True , no new speed trajectory SpdTrj can be calculated. This indicates that one or more of the inputs MaxAccSetPnt or JerkSetPnt of the struct ParSpdCtrl are zero or negative. •
Element 2 (Stop Condition Error): If True , no new speed setpoint can be issued. This element remains True if the stop function has been activated and will only reset when the function’s main output SpdTrj is zero and the Ack input has been activated.

	Firs Element=True	Second element=True
Error	Invalid parameters ParSpdCtrl	Not Acknowledged after Stop