Guide to Control Systems for Electric Linear Actuators

Control systems are integral components in the operation of electric linear actuators, designed to manage the operation and direct the behavior of these devices’ motion. Popular solutions such as control boxes are a type of control system for linear actuators that has all the electronic components secured in an enclosure case, often the shape of a box. Essentially, a control system interprets input commands, whether manual or automated and translates these into signals that adjust the actuator's movement.

The primary purpose of these systems is to ensure that actuators perform accurately, efficiently, and reliably according to predefined parameters. The significance of control systems in actuator operation cannot be overstated, particularly when it comes to achieving precise and efficient motion control. These systems are crucial for several reasons:
1. Precision: Control systems allow for the fine-tuning of actuator movements to achieve high levels of repeatability and accuracy. This is essential in applications where exact positioning is critical, such as in robotic surgery or aerospace engineering.
2. Efficiency: By optimizing the way actuators respond to commands, control systems reduce energy consumption and minimize wear and tear. This not only extends the lifespan of the actuator but also enhances the overall efficiency of the system it operates within.
3. Adaptability: Feedback mechanisms can adjust the behavior of compatible actuators in real-time by analyzing the positional feedback from compatible actuators. This adaptability is vital in dynamic environments where conditions change rapidly, such as in automated manufacturing processes or when multiple actuators are experiencing unequal weight distribution.

4. Integration: Control systems often enable actuators to work in conjunction with other pre-existing systems, facilitating complex operations from simple inputs that are being sent to the control system. This integration is supported by advancements in connectivity and programming. In some control systems, their built-in transformers can also serve as seamless integration by doubling as a voltage converter when for example a 120 VAC input source is needed to power a 12 VDC actuator.

5. Safety features: Programmed safety features such as overload protection help in preventing damage to an actuator or the application by stopping operation after the control box has detected an excessively high electric current draw. Another safety feature found in control boxes includes overheat protection to stop operation after a certain amount of cycling time to ensure operation stays within the duty cycle ratings of an actuator, thus avoiding motor burnouts. Control systems are fundamental to the functionality of actuators, providing the necessary intelligence and adaptability to ensure precision, efficiency, safety, and effective motion control. Their role is pivotal in the expanding realm of automation technology, where movement precision is often the cornerstone of operational success.

Control systems for electric linear actuators consist of several key components that facilitate precise and efficient operation. Understanding these components and the principles behind them is crucial for the performance optimization of linear actuators.

Key Components of a Basic Control Box

In a basic control box designed for electric linear actuators, each component plays a crucial role in ensuring efficient operation. Here’s a breakdown of these major components, their functions, and the purposes they serve:

1. Relays: Relays act as switches that control the high-power electrical circuit using a low-power signal. For control boxes designed to manage 2-wire actuators, two relays are essential for reversing the polarity of the voltage applied across the actuator’s two wires, which in turn changes the direction of the movement. This allows for bidirectional control in a simple setup to extend and retract the actuator.

2. Input Channels: Input channels are interfaces through which the control system receives electrical signals from external sources such as power supplies or signals from wired remotes. Control boxes that operate with positional feedback may also receive input from the sensors of an actuator. These channels process the inputs from the user and/or sensors to determine how the actuator should operate, making them fundamental for initiating and controlling actuator movements based on specific requirements.

3. Output Channels: Output channels deliver control signals from the controller to the actuator or other components like relays. Control boxes that operate with positional feedback may also output electric current so that the sensors of an actuator have the power to operate. These channels are crucial for executing the commands determined by the control system, directly influencing the actuator’s behavior.

4. Remote Sync Button: This button is used to synchronize the control system with a remote control device. It ensures that the remote inputs are recognized and processed by the control system, facilitating convenient and flexible operation from a distance.

5. Light Indicator: Light indicators provide visual feedback about the system’s status. They can be an indicator for power on/off, operation modes, error states, or signal reception, which helps in monitoring and troubleshooting the system without needing complex diagnostic tools.

6. Mode Select: This feature allows the user to switch between different operating modes of the control box, such as momentary or non-momentary controls. In momentary mode, a remote’s button must be continuously held in the active position for the device to operate. Once you release the switch, the device stops functioning. Non-momentary mode works like a switch that remains in its last set position until it is changed again, regardless of whether it is being pressed. This means that once activated, the device continues to operate until the switch is manually turned off.

7. Antenna: The antenna is part of control boxes that have a wireless communication setup. Antennas are used to enhance the signal range and quality between the control system and remote control devices or between interconnected systems. It is crucial for maintaining robust communication in environments where direct wiring is impractical or undesirable.

8. RF Receiver Module: This module receives radio frequency signals sent by wireless remote controls. It decodes these signals into actionable commands that the control system can understand and act upon. The RF receiver module is essential for wireless control setups, allowing for remote operation of the actuator without physical contact.

Together, these components form a comprehensive control system for 2-wire actuators, each serving a specific function that contributes to the overall effectiveness and efficiency of the actuator’s operation. This system not only allows for precise control over the actuator’s movements but also enhances the user interface and interaction, making it adaptable to a wide range of applications.

Positional feedback is essential for enhancing the precision and accuracy of actuator control. Three common types of feedback mechanisms include hall effect sensors, potentiometers, and limit switch feedback.

Hall effect sensors

The Hall Effect theory, Edwin Hall (who discovered the Hall Effect), stated that whenever a magnetic field is applied in a direction perpendicular to the flow of electric current in a conductor, a voltage difference is induced. This voltage can be used to detect whether a hall effect sensor is in the proximity of a magnet.

By attaching a magnet to the rotating shaft of a motor, hall effect sensors can detect when the shaft is parallel to them. Using a small circuit board, this information can be output as a square wave similar to optical encoders. It is common for hall effect circuit boards to have 2 sensors, resulting in a quadrature output where two signals will rise and fall as the electric motor rotates with a 90° phase difference between them. By counting these pulses and seeing which comes first, control systems can determine the direction which the motor is spinning.

Potentiometers

A potentiometer provides a variable resistance that is proportional to the position of the actuator. Gears are often linked between the potentiometer’s knob and the actuator’s rotating motor. As the actuator moves, the resistance value changes, which can be measured and converted into position data. This information is then used by a control system to make fine adjustments to the actuator's position, enhancing accuracy.

Limit Switch Feedback

The purpose of limit switch feedback signals is to allow a system to determine whether the actuator has physically tripped the internal limit switches. This kind of feedback is simple and useful for applications that mainly just require information on whether the actuator has reached the fully extended or fully retracted positions.

Control systems for actuators can be broadly categorized into two types:

Open-Loop Control Systems: In these systems, the actuator is controlled solely based on the input commands without any feedback on the actual position. While simpler and less expensive, open-loop systems lack the ability to correct errors in positioning, making them less accurate than their counterparts.
One example of a simple open-loop system includes a momentary rocker switch wired to a linear actuator. This requires an operator to physically press and hold the switch for the actuator to continue cycling and letting go of the switch before the actuator has reached the end of travel will result in the actuator stopping motion mid-way.

Closed-Loop Control Systems: These systems incorporate feedback mechanisms, such as Hall effect sensors or potentiometers, to continually adjust the control signals based on the actuator’s actual position. This feedback loop allows for precise control and error correction, making closed-loop systems ideal for applications where accuracy is critical. Closed-loop control systems are commonly found in applications that utilize microcontrollers, control boxes, and PLCs programmed for actuators to perform specific functions.
The choice of control system and its components significantly impacts actuators' functionality and performance optimization. By integrating effective feedback mechanisms and selecting the appropriate control system type, actuators can be optimized for a wide range of applications, ensuring both precision and reliability in their operation.

In an ideal setting, linear actuators would always behave predictably, however, disturbances can come in the form of heavy winds, unequal weight distributions, physical obstructions, and mechanical wear and tear. Some of these disturbances can be accounted for using control systems that have been programmed to work with linear actuators that have compatible feedback to read errors and then execute error correction strategies to reach the desired results.

Variables That Control Systems Correct For

1. Position: Control systems help ensure that an actuator reaches and maintains the desired position accurately by comparing the user’s position to the actual position reading from the positional feedback sensors. Examples include when standing desk users press a controller’s button to have actuators travel to a specific preset memory position to adjust their workspace from the seated to standing height.

2. Speed: Reading positional feedback and dividing the distance traveled by how much time had passed will result in travel speed. Some control systems allow for adjustable speed settings through PWM (Pulse Width Modulation), enabling the actuator to move at different speeds based on the application's requirements. This is useful in applications where varying speeds are necessary such as for actuators driving the motion of flight simulators.

3. Force: Certain control systems can regulate the amount of force exerted by actuators, ensuring that it operates within safe limits and prevents damage to the system or surrounding components. By measuring the electric current draw, control systems can gauge approximately how much force is being exerted by linear actuators. This feature is useful for linear actuators that open and close windows to shut off power and stop applying force in case a person's hand or obstacle is blocking the path of travel.

Different control strategies are used in the industry to achieve a reasonable level of precision in motion control. Each of these control strategies offers different benefits and is suitable for various applications, depending on the level of control and precision required by the system. Some of the widely used control strategies for electric linear actuators include:

1. On/Off Control: This is the simplest form of control used with electric linear actuators commonly found in open-loop control systems. It involves turning the electric current supplied to the actuator on or off with no in-between state. This method is straightforward and is used in applications where precise control over the position is not necessary. The actuator operates at full power until it reaches a set limit switch or completes its task, at which point it turns off.

2. P (Proportional Control): Proportional control adjusts the actuator's power input based on the error, which is the difference between the actual position/force measured and the user’s desired value. The control signal is proportional to this error, meaning the larger the error, the stronger the actuator's response. This method allows for smoother operation than on/off control but can still result in a steady-state error if not combined with other types of control.

3. PI (Proportional-Integral Control): This strategy enhances proportional control by adding an integral term, which addresses the issue of steady-state error. The integral component sums the past errors over time, providing a cumulative corrective action that drives the error to zero. This allows the actuator to not only reach but also maintain the user’s desired position/force more accurately.

4. PID Control (Proportional-Integral-Derivative): PID control is a more advanced method that combines three types of control strategies—proportional, integral, and derivative—to provide precise and stable control of the actuator. The proportional component depends on the current error, the integral component sums up past errors, and the derivative component predicts future errors based on the rate of change. This comprehensive approach allows for highly accurate control over the actuator’s position, force, and speed, making it ideal for complex and dynamic systems where precision is critical.

When selecting control systems for your electric linear actuators, it is important to consider the following factors:

• Ingress Protection
• Compatibility
• Budget

1. Ingress Protection: Assess the specific environmental requirements of your application to determine the type of control systems needed. The PA-33 control box for example has an ingress protection rating of IP65 for dust and water resistance. An ingress protection rating of IP65 or higher is recommended for control systems exposed to outdoor elements such as rainwater, dust, and debris.

2. Compatibility: Ensure that the control system is compatible with the electric linear actuators you have chosen or are currently using to ensure seamless integration. Check if your actuator has the matching communication protocols/positional feedback to the controllers you were considering. For example, the PA-12-T (TTL/PWM) and PA-12-R (RS-485) Micro Precision Servo Actuator provide precise position control with positional accuracy up to 100 um and require advanced communication protocols for such performance. Another thing to consider is whether the type of motor your actuator has will be compatible with a control system. Continuously operating brushless motors such as those found in our custom ordered PA-14 actuators would require control boxes compatible with their operation such as the LC-241 control box.

To see which of our control boxes and actuators are compatible with each other, check out our control box comparison and compatibility charts linked below:

https://7717445.fs1.hubspotusercontent-na1.net/hubfs/7717445/PDF%20Manuals/Desk%20Accessories/Control%20Boxes%20Compatibility%20Chart%202023.pdf

https://7717445.fs1.hubspotusercontent-na1.net/hubfs/7717445/PDF%20Manuals/Desk%20Accessories/Control%20Boxes%20Comparison%20Chart-1.pdf

3. Budget: Consider if there were any budget constraints for the project and choose a control system that offers the best value for your investment while meeting your performance requirements. For example, simple indoor projects that do not require high precision would work without any issues by wiring a basic rocker switch without high ingress protection to control a 2-wire mini linear actuator at an affordable price.

Control boxes such as our FLTCON series allow for the ability to have programmed functions, safety features, and other user settings that can be accessed through the connected remote control. When multiple hall effect type actuators are connected to an FLTCON control box, the control box ensures the synchronization of the motors so they move together at the same speed.
Read our blog on applications for the FLTCON control boxes for more information.

When choosing a configuration with 2x hall effect actuators, our FLTCON-2 accepts 110 VAC input voltage, however, we also offer the FLTCON-2-24VDC which accepts 24 VDC input voltage. When paired with our PA-BT1-24-2200 Portable FLT Battery Pack (outputs 24 VDC), the FLTCON-2-24VDC and PA-BT1-24-2200 combination allows for full portability. We offer a wide range of remote control options to choose from so you can enjoy all the unique features of our different programmable wired remotes – they can also be used together with our RT-14 wireless remotes for extra convenience.

The PA-39 control boxes are designed for 2x Progressive Automations actuators with potentiometer feedback to ensure that both actuators are synchronized throughout their motion. Even if one of the actuators experiences a different load, wiring the PA-39 control box ensures both actuators are synchronized with each other. Additionally, the PA-39 has features such as preset memory position programming, actuator sequencing, and preset recall with the hand-held remote or preset position wires.