Emergency Brake in Elevator (dumb waiter)

Hi Ron @zander,

  Mechanical systems are certainly not my area, but for something like this, I would have expected a system to 'fail-safe'.

I realise you can use motors as generators, and short the load, but I doubted if it would provide sufficient breaking. At best, it might slow a fast moving load, but couldn't stop a slow moving load, as it wouldn't generate enough power.

I was tempted to think of the brakes they put on rotary mowers and even my modest battery Bosch drill, that (more or less) locks the shaft when the power is removed. I haven't looked at the mechanism, but it is clearly a mechanical brake, which I assume is 'applied' by a spring, and 'released' when the power is applied, by a solenoid or similar. It sounds like you are describing something similar, albeit on a larger scale, and obviously a lift needs the addition of a cabling system. I can also see the importance of making the braking at least moderately progressive and smooth, but the system is also 'failing' to the brakes on situation, with no requirement of electrical power, let alone electronics and software.

One difference between lifts for humans, and dumb waiters, is the risks to life. Lifts for humans are most likely to damage humans riding in the lift, assuming the access arrangements are secure, whilst a dumb waiter is only likely to be hazardous if it strikes someone accessing the lift shaft area. Hence, the braking on a dumb waiter could be 'harsher', providing it does put such a high loading on the cables, etc. to cause a secondary failure.

So, generally, this task doesn't sound like something an Arduino would be well-matched for, albeit there may be a side issue it could address.

Sorry, if it sounds defeatist, but a safety system has different requirements from a normal control system.

Best wishes and stay safe, Dave

PS Ron, I just saw the post you added whilst I was writing this one, and that motor looks close to what I was imagining, albeit I have never seen a lift motor, etc. As for the motor itself, if it is fairly 'recent', then I would guess it might be a distant(?) relation of a stepper motor and a BLDC (Brushless DC). In all of these cases, there are two or three (or more?) field windings, and the current is progressively controlled to force the armature to follow changing magnetic field. And as you say, PWM will be used to vary the currents. 

@davee I am not sure what your point was. It seemed to me you missed the description of the 'fail safe' on passenger lifts. Power goes out, brakes are applied by strong springs.

Dumbwaiters in the OP's case in in may similar cases do to require any safety mechanism other than normal door interlocks. Only if in an area where children could get inside to ride would it be required. The OP has stated this is not the case.

The building I live in was built in the 70's and I do not notice the brakes being applied. They basically are applied after the motor stops turning and before the door opens. The slow to stop uses a technique very similar to PWM that we are familiar with.

@will Thanks Will much appreciated😊😎

Hi Ron @zander,

Our posts have crossed in the ether again...

You say

It seemed to me you missed the description of the 'fail safe' on passenger lifts. Power goes out, brakes are applied by strong springs.

My first message asked "Have you considered what happens if the power fails, a connection breaks, the Arduino crashes, etc.. Does that automatically enable the brakes? (The algorithm outline suggests that 0V means no braking.)"

" 'Emergency' system would be rather more 'basic', and possibly largely mechanical, "

My second message included "but it is clearly a mechanical brake, which I assume is 'applied' by a spring, and 'released' when the power is applied, by a solenoid or similar."

Remember, my second message was posted after your hoist motor picture, but I was writing my reply whilst you posted yours, and didn't see yours, until after I had posted mine.

In short ... I imagined the approach, using my personal experience of drills and mowers, before I saw your hoist motor picture ... we actually 'agree' for once!

---------------------

The OP is not looking at safety mechanisms, in terms of access doors, etc. but in terms of an Emergency brake for the lifting mechanism, even though it is a dumb waiter.

So surely, the approach should be similar to that of a passenger lift, albeit some simplification etc. is appropriate because the lift 'occupants' are not alive, the size/weight (I assume) to carry will be less, and the number of levels (again, I assume) will be less.  

And hence, I am trying to point that the appropriate primary safety mechanisms are probably not sophisticated computer controls, but rather crude, simple, fail-safe, brakes and springs.

Best wishes, Dave

Sam additional information to put members at ease:

1. Main Drive is a totally separate system with it’s own brake.

2. A totally separate mechanical brake will be incorporated.

3. If I design this redundant system correctly it will engage with any loss of power from Arduino electrical systems (just like a breakaway coupling system)

4. As stated “not for people or public use.

With all respect, can we focus on my questions at hand. Happy for you request further “relevant” information to gain a full understanding of my questions 🙏🙏😉😊👌

PS I am well aware of liability issues too 😊
PPS I’m all good with the structural aspects of the build as well 😊

PPPS (if that’s a thing 🤔) for the majority of members, I think you appreciate where I’m coming from, don’t want to offend the masses 😉

@dbwfred So #1 main drive is a done thing, no changes needed?

You want to add a second mechanical brake?

The Arduino losing power and engaging brake is trivial, is that all you need?

@zander mechanical brake all sorted 👌

main drive sorted 👌

loss of power should be sorted without too much effort 👌

just leaves the original couple of questions 😉

@will agree with the RPM, m/s might be more appropriate 👌

@will Hey Will very impressed with what you have drafted, not saying I fully understand it yet 😳 but, WOW. Been reading it over several times to get my head around it. 

Looking forward to putting it into action. 

 Thanks again 🙏🙏

@dbwfred 

You shouldn't be impressed with it as it's just an example of the structure you'll eventually need.

The overall flow will be more or less as indicated but the eventual sketch may extend over several pages, depending on how complex interaction will be with your included devices and what safety measures will need to be integrated.

All I was trying to do was give you a sort of overview of what the sketch would have to do with none of the details (which are as yet unknown). You said that you were new to electronics and programming but had sorted out the equipment you intended to use without actually knowing exactly how you'll cobble them all together into a working system. I offered this as the same kind of overview of what your sketch will need to do AT A MINIMUM to give you some scope on your future programming work. I was hoping that it would help you understand the organization of the code required before delving into exactly what's required to make it work.

There's still a LONG way to go. If you have specific questions about the sketch, just ask them here and I'll try to explain.