Most all of us have suffered the embarrassing consequences of inadvertently sitting on a broken, height-adjustable chair, where the chair despite being set repeatedly at the height you would like to sit at sinks to its lowest height.
This is because the pneumatic linear actuator in the chair that allows you to adjust the height has no brakes or stopping mechanism.
Electrical linear actuators have become popular recently in applications like a standing desk, not only due to its light and sleek design and small footprint but also because of the ease in its ability of the operator to accurately to start and stop. In addition, an electric actuator usually includes a brake of a self-stopping mechanism that ensures that it remains in the position where it was last set.
The purpose of a brake, in a linear actuator, is to ensure that the actuator stubbornly maintains its position where it was stopped. This should hold true even when the power has been turned off.
This can usually be accomplished in an electrical linear actuator in one of two ways:
- Designing a self-locking actuator
- Including a mechanical mechanism to induce self-locking, or
- Including an electrical mechanism to induce self-locking.
Self-Locking Electrical Linear Actuators:
Self-locking mechanisms are designed to enable an actuator to resist back-tracking. This inherently prevents the linear actuator from moving in any particular direction (forward or backward) when not actuated. This is particularly effective in a screw-type electrical actuator where a ball shaft screw converts the rotational mechanical motion of a motor into the linear movement of a linear actuator block.
Linear Actuators with a Locking Mechanism:
In some instances when an actuator is highly efficient and utilizes a high spindle pitch and gear ratio, a braking or locking mechanism is mandatory.
Dual Self-Locking Actuator Brakes:
A dual acting actuator brake is usually what is used for high-efficiency linear actuators that work in either direction and in instances where the actuator is being manually pushed or pulled to move in either direction.
Dual self-locking brakes often have a minimum self-locking ability that defines how quickly such a self-locking mechanism should prohibit movement beyond such a limit. A high-duty linear actuator is usually allowed a 1-spindle of movement before the self-locking mechanism is activated.
So, if the movement originates from the motor a linear actuator can freely move in both directions accurately as desired by the user. If however, if the movement originates from the spindle the self-locking mechanism stops such movement within 1-spindle of the movement of the ball-shaft screw.
Where to Add a Brake in a Linear Actuator?
The location of the brake is directly related to the size and the power needed to apply the brake. In other words, the location of the brake, whether it is located on the spindle itself, in the gear-box or directly attached to the motor would determine how much power would be needed to apply it and how responsive the braking will be.
When you are designing a linear actuator it is a good rule of thumb to remember that the distance of the braking mechanism from the spindly shaft the lower the force needed to apply or actuate the braking. However, the endplay in affective braking will increase as the distance between the spindle and the brake increases.
In other words, installing a brake at the motor will require the least force, while installing a brake at the spindle will require the most force, but the brake situated at the spindle will have the least endplay and will stop the movement of the linear actuator immediately and the brake at the motor will have the most endplay.
In the ideal world, the brake is located in the gearbox where both the force needed to apply it and the endplay are acceptable.
In conclusion, these are the technical details of how electric linear actuators make the use of breaks and locking. Well designed and compact linear actuators and lifting columns ensure both safety and performance and make LoctekMotion the global leader in linear actuators, and lifting columns for applications in standing desks, conference tables, storage racks or kitchen cabinets.