Master Document
Automating the Bedroom Window
Concepts:
- Gilles' working concept as of 2-13-21 (follow link)
- Using a linear actuator - see below
- hybrid concept
Using a linear actuator:
This is an attempt to use a linear actuator (self-contained unit) to solve the problem. While these can be expensive, the tradeoff will potentially be in time spent engineering, proving, and troubleshooting a custom solution. Therefore, this can also be thought of as an "easy-button" to solve the problem, which is not inherently an easy problem.
Considerations:
Drive type:
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- Ball-screws vs. lead screws
- Ball screws ~90% efficient - > can backdrive
- lead screws ~ 40% efficient - > usually can't backdrive do to inefficiencies
- Ball screws are more precise and expensive
- lead screws sometimes use a plastic carriage rather than a steel
- Belt drive seems more oriented towards horizontal applications, whereas ours is vertical
- Ball screw is most likely the most appropriate for our application
- Ball-screws vs. lead screws
Lubrication:
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- Screw drives and linear bearings usually require periodic lubrication
- Lubricate using grease rather than oil for vertical applications
- Some ball screws will advertise that they are maintenance and lubrication free (internally lubricated)
- These products have a finite lifespan. Once the internal lubrication runs out, the product may fail.
- Depending on our intended # of cycles and lifetime, such a product may still be appropriate.
- Some lead screws advertise lubrication free
- plastic on metal
- Likely not suitable for our heavy-lift application
Linear guides:
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- will help align the window pane and resist the overhanging moment loads
- therefore, these must be robust due to the high pitch and yaw moments (366 Nm)
- a counterweighted system would be unable to counterbalance these moments, so we need robust guide rails to do so.
Travel life:
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- Travel life seems to be an important factor:
- Assumptions for travel life. Raised/lowered once per day, everyday for 100 years
- 605 mm of travel (1300 mm per open/close)
- 48 KM traveled in 100 years worst case - on the very low side for these sorts of applications
Electronic Brake:
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- Some systems allow electronic emergency brakes. These are electric open (24 V) - spring close
- In other words, these are energized during actuation of the window, and normally stay closed
- This can alleviate the need for a counterweight and/or other safety systems
Selecting a linear actuator: