Almost every mechanical application we encounter involves moving parts that require some degree of precision and accuracy to function properly. This is especially true when it comes to equipment and machinery involving electric linear actuators. Factors such as backlash, build tolerances, mounting alignment, and application dynamics can greatly affect the precision and accuracy of linear motion systems using electric linear actuators. In this article, we describe the key aspects of precision and accuracy that need to be considered when integrating electric linear actuators in any application.
What Is Actuator Precision and Accuracy?
For electric linear actuators, the ability to get as close as possible to a target position is considered accuracy, while precision represents the ability to reproduce the same result relative to each other every time. Accuracy measures the error between the target position and the achieved position. Accuracy measures the margin of error of all previously achieved positions relative to each other.
An archery target can be used as an analogy to describe the difference between the precision and accuracy of an actuator, where the target position of the actuator is represented by the center of the target (the bull's eye). High and low precision can be seen when the actuator can get very close to the target position, however, it may not land on the same point every time.
Low precision and high precision can be seen when the actuator does not reach the target position but is able to consistently move to the same position it was before.
Ideally, the combination of high precision and accuracy will allow the actuator to travel to the target position and be able to consistently reach the same position over and over again.
Establish Tolerances in Part Manufacturing and Actuators
Actuator build tolerances are a factor in post-installation precision and accuracy. During the manufacture of any product, most mass-produced products will have some physical limitation on how closely the manufacturer can reproduce the listed specifications.
It is also important to note that the precision and accuracy of a linear actuator when fully installed may be affected by a variety of conditions other than the device itself. Other components used in the system may also have certain build tolerances, which may introduce another source of errors when installed with the actuator, for example:
- Mounting bracket
- Frame material
- Backlash in use with linear actuators
Backlash, also known as backlash or ramp, is lost motion or backlash in a mechanism due to the play between each part (as seen, for example, from the distance between mating gear teeth). When we try to reverse the direction of rotation of a rotating gear, we see that the lost motion or slack is eliminated before the gear starts to reverse. This phenomenon of internal gears is one of the reasons why actuator backlash is very common, and depending on the model of the actuator, the extent of backlash may vary.
Frames, mounting brackets, and other attachable accessories can also be designed with some play to allow for pivot points and correct intended operation. A slight backlash will add to the already existing actuator backlash and may further reduce overall precision and accuracy.
Position errors can also occur due to non-mechanical error sources such as potentiometer feedback, Hall sensors, and motor drivers used to programmatically control and read the position of the actuator. For applications requiring high precision and accuracy, dead time and other timing delays that may occur in the control system should also be considered.
Taking into account general wear and tear, regular inspections as part of overall system maintenance, and making necessary tuning adjustments can help improve long-term precision and accuracy. Even when all tolerances are at their maximum, the worst-case scenario rarely occurs, but considering all potential tolerances is critical to gaining a complete understanding of the system and evaluating potential failures.
How Important Are Precision and Accuracy?
The importance of precision and accuracy can vary depending on the use of the electric linear actuator. Some applications may find precision and accuracy to be equally important, while other applications may find one to be of relative importance over the other. While it is possible to use components with high precision and accuracy, doing so when it is not necessary increases the overall cost and system complexity without much benefit. Here are a few examples that reflect how the importance of precision and accuracy has changed:
Automated Furniture - Locking and unlocking the doors of large wooden cabinets by sliding a latch with an actuator does not require much precision or accuracy as the latch mechanism has a lot of room to move.
Home Automation - Automated glazing with actuators may not require much precision as the user can adjust its initial position during installation, but requires precision so that it reaches the same position every time.
Food Industry - Actuators used in pizza topping dispensers don't need to move to the exact same position every time, but accuracy is needed to successfully land the toppings on the pizza's intended area.
Medical Applications - Robot-assisted surgery and fluid dispensers used in the manufacture of drugs use models such as precision actuators because a high level of precision and accuracy is critical.
Actuators used for basic tasks often do not require high levels of precision and accuracy to function within their requirements, and it may be better to use standard model actuators for overall simplicity and cost-effectiveness. Most general applications may require precision over accuracy, or vice versa, depending on the specific use case. In more specialized applications, precision and accuracy are both critical to proper operation. Therefore, it is critical to fully understand your application requirements and any potential effects that mounting, orientation and tolerances may have on system precision and accuracy.
Electric linear actuators can have varying levels of precision and accuracy; however, it is also important to consider other sources of error that are part of the overall system. By thoroughly validating the precision and accuracy requirements of your application, you can select the appropriate components and integration techniques and then design around their constraints.
We hope the contents of this article are helpful to you. If you have any questions or would like to discuss our products further, please feel free to contact us!
UG is a professional custom valve actuator manufacturer. We use our engineering expertise and industry experience to continuously improve our products, striving to provide efficient solutions and competitive prices. UG is also a global supplier of highly engineered actuators and accessories to the Oil & Gas, Mining, Chemical, Pharmaceutical, Water & Power, Food & Beverage, and general industrial markets.