Actuator Arm Drooping Under Load

[Rehan Khan]

TL;DR

A linear Actuator lifts a door upwards against gravity with hinge axis horizontal. Actuator arm is fully extended when the door is fully opened and is horizontal. At this stage, the arm is seen a bit drooping due to weight of the door. How this drooping can be eliminated? Need practically implemented examples addressing this issue.

A linear Actuator lifts a door upwards against gravity with hinge axis horizontal. Actuator arm is fully extended when the door is fully opened and is horizontal. At this stage, the arm is seen a bit drooping due to weight of the door. How this drooping can be eliminated?

Note that Actuator body itself is grounded and fixed. Only its arm has axial DOF to extend or retract. Upon full deployment, only actuator arm gets tilted ( but not curved).

 

[Ivan Nikiforov]

Good afternoon! It seems to me that first of all it makes sense to understand why the drive lever is lowered. Perhaps the reason is mechanical backlash. If these reasons cannot be eliminated, alternatively, you can try to extend the lever more (or move it closer to the axis of rotation of the door) in order to compensate in advance for lowering the lever. Alternatively, you can use a suitable spring between the lever and the door so that it opens and compensates for the lowering of the lever.

 

[Averagesupernova]

TL;DR Summary: A linear Actuator lifts a door upwards against gravity with hinge axis horizontal. Actuator arm is fully extended when the door is fully opened and is horizontal. At this stage, the arm is seen a bit drooping due to weight of the door. How this drooping can be eliminated? Need practically implemented examples addressing this issue.

A linear Actuator lifts a door upwards against gravity with hinge axis horizontal. Actuator arm is fully extended when the door is fully opened and is horizontal. At this stage, the arm is seen a bit drooping due to weight of the door. How this drooping can be eliminated?

Note that Actuator body itself is grounded and fixed. Only its arm has axial DOF to extend or retract. Upon full deployment, only actuator arm gets tilted ( but not curved).

Without more details this is difficult to answer other than a generic reply that is something like: Build it stronger.
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Is this a commercially built door? As I understand it, the linear actuator's ram (part that retracts and extends) is drooping or bowing?

 

[Baluncore]

A linear Actuator lifts a door upwards against gravity with hinge axis horizontal. Actuator arm is fully extended when the door is fully opened and is horizontal.

It would be good if you could insert or attach a diagram, showing the geometry of the situation, showing the sag.

 

[Rehan Khan]

 

[Averagesupernova]

I don't see how that can work at all as it is drawn.

 

[Rehan Khan]

View attachment 358119

 

[Ivan Nikiforov]

As far as I know, the actuator stem is not designed for lateral loads. It is intended only for loads whose force is applied along the axis of the rod. This is a linear actuator. In such a situation, you can try installing a roller support (in red). Or change the kinematic scheme of the mechanism, that is, eliminate the lateral load. This can be done if the intermediate lever is eliminated, and the actuator itself is mounted on a hinge.

 

[Rehan Khan]

I don't see how that can work at all as it is drawn.

Arm (yellow) extends horizontally towards left until fully opened and then it gets tilted (slightly). That's the issue.

 

[Rehan Khan]

As far as I know, the actuator stem is not designed for lateral loads. It is intended only for loads whose force is applied along the axis of the rod. This is a linear actuator. In such a situation, you can try installing a roller support (in red). Or change the kinematic scheme of the mechanism, that is, eliminate the lateral load. This can be done if the intermediate lever is eliminated, and the actuator itself is mounted on a hinge.

View attachment 358125

Yes. Exactly what I was thinking

 

[Ivan Nikiforov]

It may be necessary to move the actuator to the point indicated by the circle and install it on the hinge. When the actuator stem is fully extended, it can be easily deflected to the side. I sometimes design such drives. They only work when loaded along the axis.

 

[Ivan Nikiforov]

Probably need to do something like this.

 

[Rehan Khan]

Yes. Good idea but unfortunately we have space limitation so the Actuator can assume only the shown position in my first image

 

[Baluncore]

If the actuator cannot be mounted on a pin, so it can rotate slightly, then there must be a roller placed under the extended arm, to oppose the down force, from the door, on the arm.

If the link attached to the door was rigidly attached and braced to the door, then very little rotation of the actuator about a pin would be needed to resolve the situation. That is an obvious solution to that door opening requirement.

 

[Averagesupernova]

Arm (yellow) extends horizontally towards left until fully opened and then it gets tilted (slightly). That's the issue.

It is the issue because you have two pinned joints and a rigidly mounted body of the linear actuator. It cannot be expected to do anything except do what you describe is happening. The ram coming out of the linear actuator as well as the actuator itself is being severely strained with that setup.

 

[jrmichler]

Here's a way to do it. The actuator has no side forces, is mounted on a pin, and is up near the top. The forces work out slightly better if the arm is at about 60 degrees to the door instead of the 45 degrees shown. Linear actuators do not last long if they are side loaded.

 

[Tom.G]

referring to post #16, above. https://www.physicsforums.com/posts/7247000/

Just a thought for the 'limited space' aspect of the problem.

@jrmichler, could the actuator mount be solid if the short link attached to the door was variable length, i.e. telescoping, perhaps spring-loaded?

 

[Averagesupernova]

For the actuator to be solid what needs to happen is what @Baluncore described in post #14. If the end of the ram coming out of the actuator had a roller with the pinned joint supported by a track running parallel to the motion of the actuator then the first diagram that the OP posted would work. I personally like what @jrmichler proposed.
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This is good too:

The forces work out slightly better if the arm is at about 60 degrees to the door instead of the 45 degrees shown.

The door pushes easily when first moving off of closed position. If the angle is increased, more leverage exists when it is most needed after the door is a fair way up.

 

[Baluncore]

The real pity with that actuator solution, is that the door is not counterbalanced.

 

[DaveC426913]

If the link attached to the door was rigidly attached and braced to the door, then very little rotation of the actuator about a pin would be needed to resolve the situation. That is an obvious solution to that door opening requirement.

@Baluncore is right!
Just replace that third hinge with a rigid bar.

Now you don't need to add anything such as a roller to eliminate the drooping; it takes care of itself. You remove an element. The build is simpler: less parts means less work, and fewer failure points. Elegant.

 

[Baluncore]

Just replace that third hinge with a rigid bar.

And mount the actuator so it can rotate slightly as it operates.

 

[DaveC426913]

And mount the actuator so it can rotate slightly as it operates.

Yes, although, if that's not possible for whatever reason, there's ways around that too.

 

[Ivan Nikiforov]

I'm sorry, but it seems to me that in such a design there will be a vertical component of the force that works to bend the rod. As I understand it, it is not by chance that a support element is used in such structures, which is located diagonally. The force of his reaction is directed towards the resultant force.
Shock absorbers of rear doors of cars, shock absorbers of furniture shelves, crossbars of bridge beams, hydraulic cylinders of a crane boom - everywhere the diagonal arrangement is applied.

 

[jack action]

There you go, problem corrected:

 

[DaveC426913]

I'm sorry, but it seems to me that in such a design there will be a vertical component of the force that works to bend the rod.

That depends on the forces involved. The OP did not specify how heavy the door is or anything else.

Shock absorbers of rear doors of cars, shock absorbers of furniture shelves, crossbars of bridge beams, hydraulic cylinders of a crane boom - everywhere the diagonal arrangement is applied.

Except a diagonal solution is expressly ruled out by the OP. The location of the actuator is not optional.