Once bench testing of the linear actuator has been completed, it is time to test it under load. The load should match what will be expected when in the desired application. The bench test methods are all applicable to the lab tests, with a few additions. The lab tests also include:
- True load speed test
- System current draw test
- Environmental compatibility test
- Duty cycle test
- Accelerated lifecycle test
- Feedback compatibility
By conducting these lab tests, it will provide you with even deeper accuracy on the compatibility of the chosen actuator with your application.
True Load Speed Test
The speed results from the bench test will be the maximum speed that is possible for your linear actuator. When your actuator is under load, it will slow down the speed to a rate that is proportional to the load (see above graph for reference). Measuring the speed of the linear actuator under load will help determine whether it still falls within a specific range to work within your application.
To measure the speed of the linear actuator, ensure it is loaded with a weight that resembles how it will operate in your application. Then redo the step-by-step process used with the speed bench test using a stopwatch. This method is for applications where speed is not a crucial factor.
For applications where precision speed measurements are needed for the linear actuator under load, use an automated time measurement system. This system will involve using a microcontroller such as an Arduino with code that will start/stop a timer when either of the two end stroke limit switches of the linear actuator is reached. Please reach out to us if this is the case, as we can help with setting up a jig to achieve this.
Lastly, depending on your application, you may also want to test the limits of your linear actuator by applying a load close to its rated maximum load to see how the speed changes and how the linear actuator responds (e.g., does the motor get hot? Is the movement of the stroke still smooth and controlled?).
System Current Draw
Since the linear actuator is now under load, the speed will decrease, and the actuator will draw more current. Knowing the current draw of the linear actuator under load will help select an appropriate power supply. It is important to take into consideration other electrical components that are being attached to the linear actuator such as a control box, active sensors, etc. These additional components can draw current from the power supply and result in the linear actuator not receiving enough current to reach its full-load capacity.
To measure the current draw of the linear actuator under load, use a multimeter, as in the bench test. Alternatively, much like for the lab speed test, use a microcontroller with a current sensor module connected in series. Please reach out to us if you need help with setting up a jig to achieve this.
Once you know the current draw of your whole system, you can size your power supply accordingly to ensure the linear actuator can receive enough current when under full load.
Environmental Compatibility
Progressive Automations’ linear actuators come with an International Protection Marking (IP) rating. It is a rating of a product’s ability to withstand liquid and dust intrusion. The IP rating system uses a 2-digit system to define its protection rating for all products. The first digit represents protection against solids and the second against liquids.
Once a product has completed testing at an approved facility, it will achieve a specific numeric rating, which can be deciphered using the IP rating chart below:
Based on your application, testing the IP rating of a linear actuator might be helpful. For example, if you know that your linear actuator is going to be exposed to a lot of water, the PA-10 model has the highest IP rating with IP68M and IP69K. It can operate underwater and can withstand high-pressure water jets when it is not in motion. The best way to test this kind of linear actuator is to simply submerge it in water and let it run.
However, units rated for IP66, like the PA-04 Linear Actuatorand PA-09 MiniIndustrial Actuator, can also withstand both dust and moderate liquid ingress. These linear actuators are best suited to tests within the environment of the intended application. If you know that the linear actuator will not get exposed to dust or water, you can opt for a lower IP rating for your application.
An IP rating does not test for outdoor/weather resistance during seasonal changes and long periods (e.g., years outside during multiple seasons). Therefore, consider the environment you are going to use the linear actuator in to make sure it is suited for that environment. Progressive Automations offers various certifications besides the IP rating. These certifications could be requirements that may apply to your application. Speak to us if you require specific certifications for your actuator and/or application.
It is generally best practice to mount the actuator with the stroke end pointing downwards if there is any risk of water exposure. This way, gravity will pull liquid away from the motor housing and help prevent premature failure.
Duty Cycle
The duty cycle of a linear actuator is the ratio of on-time and off-time and is expressed as a percentage. If your application requires the linear actuator to run continuously, the duty cycle is incredibly important to ensure you do not burn out the motor. For applications like this, the duty cycle would need to be 100%.
To achieve a 100% duty cycle, a brushless DC motor will need to be used, as opposed to a standard brushed DC motor. For linear actuators with a brushed DC motor, Progressive Automations offers a 20% duty cycle, which limits how long it can run. The duty cycle for Progressive Automations linear actuators is based on a 20-minute period, which means that at a 20% duty cycle, the linear actuator can run continuously for 4 minutes, and then needs to rest for 16 minutes.
The same principle applies to anything under 20 minutes. For example, using 10 minutes at a 20% duty cycle, the linear actuator can run for 2 minutes and then needs to rest for 8 minutes. Anything over 20 minutes at a 20% duty cycle will damage the motor due to overheating.
The best way to test the duty cycle of your linear actuator is to set it up using a microcontroller, as before. However, the code will need to be adjusted to allow the actuator to turn on and off at set times (e.g., run for 2 minutes, rest for 8 minutes, and repeat). Ensure the actuator is loaded accordingly and check up on the system at set time intervals to ensure it is still running as intended. Repeat the test until you are satisfied that the linear actuator will work in your application.
Accelerated Lifecycle Test
After all the specs have been verified, it is also important to make sure the life rating of the actuator is enough. We offer actuators rated for 20,000 cycles and we also offer actuators rated for 300,000 cycles. Some applications require the actuator to be operated only once a day, and some require it to be operated a couple of hundred times a day. In scenarios where the actuator will be used quite often, it is very crucial to make sure the actuator will live up to the required life of the application. Some applications do not allow for easy removal of parts so making sure that the actuator is rated for enough life is important.
This can be achieved by using a simple jig setup (if you are familiar with creating such setups). If you would like to do some accelerated testing yourself but you are unsure as to how to do it, please feel free to reach out to us and we can provide you with the right equipment to do so.
Feedback Compatibility
Certain applications and pre-existing systems may require actuators with a specific type of feedback to work correctly. Determining an actuator’s position is useful for applications which require multiple actuators to travel at the same speed, store preset positions and/or to collect positional information for user analysis. When selecting an actuator, ensuring that it has the suitable feedback is important for compatibility with your system. In electric linear actuators, there 3 major types of positional feedback:
- Potentiometer feedback
- Hall effect sensor feedback
- Limit switch feedback
Built-in potentiometer feedback
Potentiometer Feedback
Potentiometers make mechanical contact with the gears that rotate inside the actuators. As a result, the potentiometer can retain its positional information without the need to “home” if the system loses power. Because potentiometers are just voltage dividers with a large resistor, they are also good at dealing with electromagnetic interference (EMI). The biggest advantage of this type of feedback is its simplicity for applications that need quick drop-in solutions, while not requiring as much accuracy or high precision.
Built-in Hall effect sensor feedback
Hall Effect Sensor Feedback
Hall effect sensors provide electrical pulses when the magnet is aligned with sensing electronics. For this reason, they are suitable for high-speed applications and allow to pre-program certain motor shaft angles. With no need to make any contact, they are useful in harsh environments, highly resistant to wear and tear, and reliable in high shock environments. This is the feedback option for you if your application requires reliability, precision, and long life.
Limit switch feedback example
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.
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