Emergency Brake in Elevator (dumb waiter)

@dbwfred Sorry if this sounds a bit harsh, but as a former elevator mechanic and designer, I hope this is in your own house and you are okay with injuring the inhabitants. If either of those two statements is false, STOP.

I am hoping this is in your house so I will give you some info. Emergency brakes (in passenger Elevators) don't work that way at all, they use sharp hard steel knives that shoot into the rails to stop the falling car. They are spring loaded. The mechanism to fire the knives is indeed built on a MECHANICAL overspeed pulley. I don't recall how dumb waiters are treated although I bet in a public setting like a restaurant the same rules apply.

99% of the electronic/electrical parts in an elevator are for safety. The annual test involved me being in he car with the government inspector and my partner would manually trip the safety as we were descending. We had to be very sure of our equipment.

You live in a different jurisdiction and it's been a while since I had anything to do with elevators, so maybe something has changed from the above, but I would be surprised.

I may or may not help depending on your answers.

BTW, it is ALWAYS just code, NEVER codes or a code.

Posted by: @zander

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@dbwfred Sorry if this sounds a bit harsh, but as a former elevator mechanic and designer, I hope this is in your own house and you are okay with injuring the inhabitants. If either of those two statements is false, STOP.

Ron, it's a dumb waiter. It isn't going to carry people!  How could it injure the inhabitants?

😎

Bill

@dronebot-workshop If it falls and some debris blows out the door that someone is near it can. I know it's a slim chance, but in the elevator business, you are taught to be super safety-oriented.

Also, workers have been known to bypass the safeties to look up to see if the dumb waiter is coming or not and that is an opportunity for catastrophic injuries.

I want to be sure this is for his own use before I comment much further given the litigious state of society nowadays. I think between my wife and I we received 4 class action lawsuit notices to participate in the last 12 months, and I have received payments 3 times in the last few years so I am perhaps more aware than most.

@dronebot-workshop Also Bill, we don't know if he has kids, or if this dumb-waiter is located in a space that children can access. This is the ultimate 'attractive nuisance', riding in a dumb waiter. Here is a link to the Wiki about that legal doctrine. https://en.wikipedia.org/wiki/Attractive_nuisance_doctrine

@zander not commercial use, no public access

@dbwfred Fantastic. Now I will re-read your opening post to see if I can be of any help.

@zander “code” hey🤔, thanks for that info 😉

@dronebot-workshop Thanks Bill. This is why members don’t like putting too many details about their projects. All the good advice in the world without actually answering the question/s asked. It kills forums. No doubt all have good intentions😊

@dbwfred Most of the time we don't get enough information.

@dbwfred To answer your questions.

Q1. YES

Q2. Depends.

Hi @dbwfred,

  I'll leave Ron (@zander) to provide his specialist elevator experience, but hoped a few quick general thoughts for you to ponder might be helpful... apologies if you have already considered them.

1. 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.)
2. The 'graduated' braking scheme suggests this is more of 'normal use' control system .. but I would assume that would be the responsibility of the main cable, motor, etc. If this is an 'Emergency Brake', then I would have expected it to be as simple as possible, even if that means it is rather 'harsh', so that you can be sure it will work.
3. An 'emergency anything' system should normally be separate from, and not require anything from the 'Normal' system. A complex system could end up 'fighting' with the 'Normal' system, or an 'unexpected' fault in the 'Normal' system might disable the 'Emergency System'. The 'graduated' approach suggested the Emergency system was being invoked on a 'light touch' basis under normal conditions, which can get 'messy'.

Personally, I would have thought the Arduino, etc. would be responsible for the 'Normal' operation, motor control etc. and the 'Emergency' system would be rather more 'basic', and possibly largely mechanical, with perhaps a simple electrical speed sensing part that would be triggered if it starts falling too quickly.

I wish you luck with your project. And whilst I appreciate this is a dumb waiter, please be careful, as falling objects can easily become dangerous.

Best wishes, Dave

@dbwfred 

Q2 - partly

Here's a simple outline of what you'd need as the sketch for this activity. I am not familiar with the braking system nor the measurement device that you want to use, so I have just put in dummy calls.

I'm using the descent rate instead of RPM because you'll measure it and calculating RPM from it just wastes time. The array of boundary speeds may be adjusted as you refine your braking requirements while testing the prototype. You may need to change the return value from int to float if you find that you need to control the voltage values finer than 1 volt apart.

This is intended only as an example of the layout of the final sketch, it will require significant refinement and change as your project progresses.

I have not tested this sketch in any way. I only claim that it compiles clean for an Arduino UNO.

//
//    Array of descent rates used for braking voltage calculations
//    
//
  
float boundary[] = {0.05, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16,
                    0.18, 0.20, 0.22, 0.24, 0.28, 0.30};

long  loopDelay = 2000;                     // 2 second sampling delay
//
//    Initialization and module setup
//
void setup() {
  Serial.begin(9600);                        // Start serial monitor
}
//
//    Method to return rate of descent of cage using HC-020K 
//
float descentRate() {
  float mpsec = 0.0;
  //
  //    Put code to calculate descent rate here
  //    Returns value in metres/second
  //
  Serial.print("Calculated descent rate is ");
  Serial.println(mpsec);
  return mpsec;
}
//
//    This compares the measured rate at which the cage is dropping and
//      compares it to the list of boundary speeds listed above. The
//      rates are arranged so that the index of the first element that is
//      greater than the rate is the voltage to apply to the braking
//     mechanism
//
int brakeVoltage(float rate) {
  for (int i=0;i<12;i++) {
    if (rate<=boundary[i])
    return i;
  }
  //
  return 12;
}

//
//    Apply the braking force to the brake drum
//
void applyBrake(int voltage) {
  Serial.print("Brake voltage is ");
  Serial.println(voltage);
  //
  //    Put code to apply voltage to the brake
  //
}

void loop() {
  float rate = descentRate();
  int   braking = brakeVoltage(rate);
  applyBrake(braking);
  //
  delay(1000);                               // Wait 1 second and then go again                                       
}

@davee I am a little mystified by the proposed solution, although my experience with dumb waiters is smaller and very long ago. Emergency systems don't work anything like the proposal, they involve hardened steel knife edge parts on a strong spring and a mechanical release mechanism involving an overspeed clutch and springs etc. Now I can't say for sure that system was used on dumbwaiters, in fact it sounds like overkill except you have a slippery slope situation as to at what size does it become a one or two person people mover in a luxury house.

I think what the OP really wants is a better safer hoist system. All I can tell you is what I have seen. They typically involve steel rope wound many times around a grooved drum to provide friction in order that the rope can't slip. There are many types of motors both AC and DC and gear/belt/direct drives. These typically have a large wheel with a very thick brake shoe wrapped around it. It is spring loaded and is electrically driven away from the braking surface. This way in a power failure the normal brakes are applied. Old style speed control involved rotating steel balls and all kinds of mechanical devices. Of course today most will be electric at least and more and more electronic/computer style.

Just going from memory, these motors slowed nicely if you just reduced the power to them due in part to all the friction in the mechanical layout.

I think the OP is close to a solution, but my main quibble is that instead of applying a mechanical brake just use some sort of electronic brake (in the old days it was called plugging, basically turned the motor into a generator). Apply the mechanical brake at during the last few feet but it can not remain on while positioning (making the exit floor and cab floor level)

Sorry, maybe too much history, but I think you will get my direction of thought.

@davee Here is a picture of a very typical hoist motor and brake. The small device on top of the brake is the electromagnet thet deactivates the brake. In a power failure, the spring-loaded brakes are automatically applied. You can see the grooves in the hoist pulley. It appears to be a right-angle geared drive using a 440VAC motor. I think speed control including very slow levelling is done electronically. These are often AC induction motors and use some form of variable frequency controller to control the speed. That sounds a lot like PWM.