Building a solution through the iterative process of enquiry

Building a solution is an iterative process of enquiry and detailing. Let us say we want to design an automated lift door control system.

Let us explore the questions that need answered before we embark on building the solution. For the current discussion we will limit our exploration to electronics and software areas. As would be evident later, building a solution would involve an integration of diverse engineering and domain understanding.

Typically, the enquiry process would be driven by three question areas – the “What”, The “Why” and the “How”. The answers are for illustration purpose and could have different variations

• What would be the key processes that the system has to control?
• Opening the Door
• Closing the Door
• Display and alerts

• What would the various stable states that the system would be in?
• Open
• Close
• What would be the trigger for opening the door?
• Push the open door button
• Reaching the requested floor
• What would be the trigger for closing the door?
• Pushing the close door button
• Time out after the door was opened

• What will be the transitory states of the system? Why – Some actions need to be taken during this state which is different than actions during open state and close state.

• How does the door opening process start?
• Sense the door open button is pressed
• Floor Reached Signal
• How does the door open? – Switch on the door motor to rotate in opening direction
• How do we end the door opening process? – Switch off the door motor
• Sense that the door is completely open
• Stop it after a pre-determined time
• Optional – stop it when the stop button is sensed.
• How does the door closing process start?
• Sense the door close button is pressed.
• Time-out after the door is fully opened
• How does the door close? – Switch on the door motor to rotate in closing direction.
• How do we end the door closing process? – switch off the door motor
• Sense that the door is completely closed.
• Stop it after a pre-determined time
• When an obstruction is detected in the door closing path – start the door opening process.
• Sense the door open button is pressed

Is there a need for different intermediate states for opening and closing? Why – some actions are not the same as can be seen above

• What are the exception handling, safety, regulatory and other conformance requirements?
• Stop closing of door if there is an obstruction
• Open button de-activated when lift is in between floors – this means none of the door operations are active if the lift is moving. So we need to sense this before enabling the open door process
• Handle – power supply shut down, door slider jam, motor failure, button, sensor failure etc.
• What are the key elements of the system to cater to the above?
• Doors
• Door gliding system
• Motors with three switching possibilities – off; open – rotating in opening direction; close – rotating in closing directions 
• Sensors to indicate fully open state, fully closed closed state, obstruction sensing; lift moving sensing
• Optional – Alarms – LEDs, Buzzers, signals, remote maintenance alarms
• Anything else?
• What are the control interfaces?
• To control motor?
• To sense door open/close complete sensors
• To sense lift at the floor and stationary
• To sense the open/close button press
• Which controller to choose? What are the options
• How do we integrate and represent the complete system architecture?

 

As can be seen through this journey of iterative enquiry, a simple process of opening and closing a door can unravel the complex system requirements. We have not captured in the above illustration the floor request and stationary state sensing.