Tuesday, March 27, 2012

Elevator Optimization Challenge: Part 2

Earlier I posted an Elevator Optimization Challenge and asked for feed back on what kinds of questions you might need to ask in order to begin suggesting a course of action to make the elevator's usage more efficient.

If however you missed it, please return to Elevator Optimization Challenge for an overview.

Once you've familiarized yourself, you can continue after the jump.

For this exercise it becomes apparent that you must establish some details about the elevators in a given building.  Specifically, what are their characteristics, how do they operate.  You might even go to the abstract and consider the question of just what is an elevator.  An elevator can be defined two ways:

1. A platform or compartment housed in a shaft for raising and lowering people or things to different floors or levels.

2. A machine consisting of an endless belt with scoops attached, used typically for raising grain for storage.

For the purpose of this exercise we will assume it is definition #1.  An elevator being a platform or compartment housed in a shaft for raising and lowering people or things to different floors or levels.  We can also assume that even if an elevator may possibly be used for transportation of cargo, it is designed with the idea that people may also ride along.  This is an important distinction because now we know that safety issues for an elevator will be related to human tolerances under which the elevator may be operated safely.  You can picture any typical type of elevator you might find in a building.

Once we have an idea of the general function of an elevator, we can think about it's components, or key parts.  Each elevator typically has a control interface, one internal to the elevator lift compartment which is used to select a number of floors (ignore other options for this exercise), and an interface external to the elevator doors which is used to call an elevator for pick up to take its passengers or cargo up or down to another level.

Secondly, each elevator, sometimes pairs of elevators will have a mechanism which is used to raise or lower the elevator lift compartment to the desired level.  While there are many different types of mechanisms used for raising and lowering elevators including but not limited to: Mechanical Gears, hydraulics, or cables, the exact mechanism really isn't of importance for this exercise.  For our purposes, you may assume that all the elevators in a building are of a similar lift type.

There is also a regulator interface which controls the speed and acceleration of the elevator as it accelerates up to its normal speed, and decelerates to stop at the next chosen level.   As you can imagine, different types of elevators may raise or lower at different rates of speed, and may accelerate fast or slow.  However, this difference really isn't going to have much bearing on this exercise because this speed is a function of the mechanism to lower and raise the elevator lift, and is also governed by a limiter which prevents each elevator from exceeding an acceleration or speed threshold that would be unsafe for human passengers.  So you can in effect treat this as a constant for each building, even if elevators in another building might move at a different rate of speed.  While it might be possible to 'boost' the mechanism for an elevator, we will assume that the owners of any given building will require us to remain within prescribed tolerances under which the elevator was installed and that tampering with this aspect of the elevator's motion mechanism could violate or void it's warranty or service agreements.

Now, we may also wish to consider the elevator's size attributes.  Each elevator also has a size factor, the volume or square foot area that encloses the people or cargo it can haul, and more importantly it has a maximum weight tolerance that it can permit before a warning sensor triggers an alarm.  When the alarm is triggered, cargo or passengers must exit the elevator until the weight has fallen below that maximum weight threshold.  The elevator will not move until this has been achieved.

Those are the givens of this and any elevator mentioned in this exercise.  So the question you ask was a very good one, how can you optimize an elevator?  Because of the capital expenditures involved to install, or replace an elevator, and the time factor involved in replacement (and the annoyance to clients as a single or multiple shafts are out of commission), it seems an unreasonable possibility for our situation to increase the capacity either in terms of maximum number of persons carried or weight that the elevator can lift.  Suffice it to say, that's just not reasonable for our clients.  They are hoping we can offer a software solution, a patch to the computer which controls where the elevator goes.  So while changing the physical size of the elevator's lift compartment and shaft could be done, we are not in the elevator 'building' or 'replacement' business.  Think of the us in this exercise as an elevator software 'tuning' company.

So given this detail, what questions need to be asked that will help identify how to 'tune' the elevator to increase its efficiency through out the day.  This tuning won't be related to its hardware, or the parameters we established above, so what can we change? I think the next question is simple, how does the elevator move when it receives commands?  That will spawn a number of questions I'm sure, but one that sticks out to me is what happens after the elevator has answered its last 'order' and the last passenger or cargo has been removed, and the elevator's doors have closed?  What happens?

In my mind there are a few possibilities:

1.  The elevator does nothing, it stays on the floor it last serviced until summoned by another call for service.
2.  It returns to where it started, perhaps the first floor, or some main entrance floor as defined by the building's business rules.
3.  It might return to some other standby floor where it can reduce its travel time to the next pick up floor upon being summoned.  That standby floor could be a fixed position, or could it might change depending upon the time of day or recent elevator activity.

Given this what other information would we need to cull from the usage of the elevator to attempt to suggest a pattern to better optimize it's usage?   Then once you've gotten the answers to those questions, consider whether there are any special cases you might have forgotten.   I'll add more later, because I don't want to give away what I think some of these questions are just yet, but this is how I'd frame the discussion to begin moving towards a solution that we can build and then verify via testing.

It looks like a third post on this Testing Challenge may be forth coming.  I hope this second part has helped peel back a few layers of the onion and get the mind thinking in terms of how you can accomplish the challenge.


  1. Hi Veretax! Very good post and start of discussion.
    Here are my questions for elevator owner:
    1.Are there any customer complaints about elevator usage? What are they?
    2.Do you have any complaint?
    3. Do you have any documentation about elevators program?

    My goal would be to identify the problem about elevator usage.

    Regards, Karlo.

    1. Those would be fair questions to ask. Presumably if you worked for a company that tunes and optimizes elevators, there might be a reason for it, and that reasoning could potentially shed some light on what is bugging the customer.

      Some possible answers that could be given, and not all of them may apply in every situation like this.

      1. Maybe the customer is concerned that it takes him so long to reach his more private suite. (Maybe a direct access to his floor via key would be an easier solution, fix one customer's issue, but wouldn't affect the rest.)

      2. The customer might say, he notices that people spend a lot of time waiting for the elevators to come back down when they come into the building in the morning, and it seems like it takes forever to wait on them in the evening when everyone is trying to leave at the same time. (this would of course be compounded by an elevator that has to stop on multiple floors). In the case of a large Hospital this might be around the time of the Shift Changes (which are easy to find out), or it could be just an issue where too many people and too few elevators to begin with at peak time.

      3. In this case I'd presume that most people who would have responsibility to see that Elevator's are in working order, a building owner wouldn't have much knowledge of the elevator's programming per say. Odds are that's why they called you the 'elevator optimization expert.'

      those are my thoughts anyhows.