Proceedings of the KGCOE Multi-Disciplinary Engineering Design Conferencepage 1

Proceedings of the KGCOE Multi-Disciplinary Engineering Design ConferencePage 1

Project Number: P07007

Proceedings of the KGCOE Multi-Disciplinary Engineering Design ConferencePage 1

Adapted home entry system

Meklit Kidane / Tanvir Rasel / Wenbo Chen

Proceedings of the KGCOE Multi-Disciplinary Engineering Design ConferencePage 1

Abstract

The adapted home entry system was designed to give access to the individual with disabilities. With this system, the individuals will be able to enter and exit their home without any assistance. The home entry system utilizes a remote control to open/close and lock the front door to a person’s house.

This paper will look into how this system was designed and implemented by the team. The goal of this team was to redesign a control system for an existing remote control door opener that was designed last year by another senior design team. However the system failed after few days of operation. This paper will look into the reason the original design failed and what was done to correct it so the system will be more robust.

introduction

The adapted home entry system was designed to allow access to people with disabilities to open and close doors. Although systems such as these exist on the market, the goal here is to construct the system with off the shelf product that would cost less than the products on the market.

This year the task of the senior design team is to build a robust control system for the existing hardware. The control system should function according the customer specs and ADA (Americans with Disabilities Act).

Design Process

First the design team met with the costumer andthe advisors for this design team: Dr. DeBartolo and Dr. Phillips. At this point the needs of the costumer were addressed and it also gave the design team a chance to observe the unit after it had failed. This allowed the team to also observe the system in its failure mode.

The costumer designated each of the needs based on the importance. The design team took the needs and developed specifications corresponding to the needs. Some of the highest needs are: ease of use, the unit operates within the requirement specified by the ADA, and a robust system.

From this point the team gathered ideas from benchmark product and through brainstorming sessions. The idea here is to keep the existing hardware as much as possible and design a control system around it.

DESIGN

As stated earlier this project will look into building a system with off the shelf components, the following are the list of component that will be needed in order for the system to function.

Motor
Electromagnetic Clutch
Electric Strike plate
Transmitter and Receiver
Motion sensors
Microcontroller
Push/pull solenoid

The list of parts above is the key components that will make the system work, and all the parts are readily available. The main purpose of the control system will be to make all the parts above in unison to give the user the ability to open, close, and lock a door with a remote control.

The previous team utilized their knowledge in mechanical engineering to build a robust mechanical system. However, the control system designed for the unit failed due to the poor design.

One of the components that fell is the rotary potentiometer. The purpose of this component was to determine the position of the door. It functions the following way: when the motor turns the door in either open or close position the potentiometer would turn in the same direction with the motor. Over time the belt connecting the motor shaft to the potentiometer slipped, causing the door to only open half way when the remote was pressed to open the door.

Another issue that was corrected was the wiring in the system, it posed an electrical as well as fire hazard to people operating the unit and others around it. These problems were also addressed when designing the control system.

Hardware DESIGN

The control system hardware was designed around the existing parts from the previous project as indicated in Figure 2. When designing the control system, the first issue that was addressed was the improper wiring of the unit, by replacing it with a PCB board.

To make all the parts work in unison a central processing component is required. This processor can be programmed to manipulate all thehardware parts to be able to meet the design requirements.

Figure 1: Microcontrollers comparison.

Figure1 shows a comparison between two different microcontrollers: the Basic Stamp II and the PIC16F876A. From the table in Figure 1 it can be concluded that the PIC 16F876A would be the better choice. It has low cost, handles more instruction, and also reduces external components required such as timers and analog to digital converters.

The main idea behind designing the control system is to be able to step a voltage level down to a useable level for the part that is being operated as well as to switcha desired mechanism to turn ON or OFF using the PIC microcontroller.

Figure 2. Block Diagram of the Control system.

The Figure 3 shows an example of how this operates.

Figure 3: Voltage regulated with switching capabilities.

Looking at the circuit in Figure 3, looking from the left,the circuit starts off with 24Vdc, which is available through the power supply used in the last year’s project. Then the 24Vdc is regulated down to a useable value. Some components use 5Vdc while others use a 12- 24Vdc. The same set up is used for the reset of the components, however to vary the output voltage of the regulator the relationships shown in Equation 1 is used.

Equation1

According the equation1 the voltage out can be changed by varying the resistor values connected to the voltage regulator.

The TIP122 is the switching transistor that is being used to either provide power to the component or to turn it off. The base of the Darlington transistor would be connected to an I/O pin of the PIC microcontroller mentioned earlier. In the circuit in Figure3, this I/O pin is represented by a voltage source.

The motor control unit is a little different from the circuit in Figure3. The motor for this project needs to turn in two directions: open position and close position. This task is accomplished by using two relay switches to change the polarity of the motor. The circuit is indicated in Figure 4.

Figure 4: motor control circuit with two relays.

Figure4 shows the two relay module that will control the direction of the motor. Here the 100Vdc represents the power supply for the motor, which is a 120Vac to 90-100 Vdc converter. This voltage will be applied to each potential of the motor. The software will insure that the two relays never turned on at the same time.

Software DESIGN

All the hardware mention earlier will work in unison because of the program. The complexity of the software was kept to a minimum. The flow of the program is indicated in the flowchart in Figure 5.

The default mode for the door is to be in the closed position. When a user activities the remote to open the door, first the inner sensors are turned on to check if any person is in the path of the door, therefore the system will not activate in that case. If no person is in the path of the door, the sequence follows: the electric strike plate releases, the motor starts turning toward the open position. The door will not be moving fast enough to harm any person. The speed of the door is 20 degrees per second, and force of the door should be less then 15 lbs as defined by the ADA. When the door reaches the open position, the motor arm reaches an opto switch. The processor starts a counter to wait 45sec. and after the 45 second the closing sequence begins. Before the door actually moves to the close position, the sensors recheck for any obstructions, if any obstruction is sensed the door re-opens. If no obstruction is seen by the sensor, the door continues to the close position until the motor arm reaches the close position opto-switch. At which point the system goes to standby mode.

During the standby mode, when the person clicks the button, it will go into an ISR or interrupt service routine which tells the system to wake up from sleep and go to start the system. Some of the problems that we have faced are that the register was not able to read the inputs right away so that if the motion sensor picks up some one, it won’t do anything until the values are written into the registers. There were two different causes for this problem, one was that the user has to set the pin 7 of the ADCON1 so that PORTA pins can be read as digital inputs instead of analog inputs.

Figure 5: Control System software

Proceedings of the KGCOE Multi-Disciplinary Engineering Design ConferencePage 1

The other major cause was using CMVRON register and CMCON register to activate comparator module. This module compares the analog input from PORTA1 with the set voltage reference on PORTA 2. The CMCON controls which comparator mode the user wants and reads the output from CMCON pin 7. When the current sensor picks up a spike, the voltage is suddenly increased. The comparator module checks PORTA1 and compares it to PORTA2. If the PORTA1 input has a higher voltage, the system will recognize that something is blocking the door’s path and automatically go to TIMER if the door was in opening process or goes to SLEEP mode if the door was in closing operation. However, for the PORTA pins to continue work as digital inputs, one needs to load B’00000111’ into the CMCON register so that the comparator module is turned off.

One of the more obscure problems involved with this particular program is that when the bits are loaded to CMCON register, even when the inputs are changed, the input registers do not record those changesinputs are changed, the input registers do not record those changes. The programmer solved this problem by setting up few extra unnecessary instructions. These changes can be spotted in the program easily.

The entire program was created in assembly. The reason for that is that it is easier to manipulate bit level with assembly and should keep the program simple compared to higher level language.

Enclosure DESIGN

The enclosure uses a type of cast aluminum alloy. It is ½ inch thick in the back piece of the box, which is also the side mounted on the wall, in order to handle the amount of stress from the 350 in-lb of torque produced by the motor. The top part of the box has about 2 inch diameter hole which supports a fan that cools the system. It is carefully placed close to the PCB’s which produce great amount of heat. It is placed on the top of the box since heat travels upward. The left side of the box supports the motor control PCB and the receiver PCB. The AC to DC power supply sits on the bottom piece of the box as it delivers power to the rest of the system. The motor itself sits on the back piece of the box. It is attached by threaded hex screws with half inch thread. The bottom of the clutch sits on a aluminum bushing which also connects to a metallic strip that functions as the optical switch breaker. The bushing is attached to the bottom rod by 2 set screws. The rod then extends down to the bottom of the box through a linear ball bearing and connects to the arms that open the door. The ball bearing is strategically located on the bottom piece of the box to reduce stress on the rod when it tries to open the door. The bearing will reduce tension and twist caused by the resistant torque by the 500 lb. door. The bottom piece also has 2 optical switches that actually tells the system when the door is opened or closed. The aluminum casing is chosen to increase heat dissipation and increase durability and robustness. It is an improvement in all aspects compared to the wooden casing designed by the previous design team.

COnclusion

The mechanical design of the enclosure was successful. The box should able to sustain the stress from opening and closing the door repeatedly. The hardware design still needs to be implemented and thoroughlytested. Some of the components The software workedas expected when testing with a standard manufacturer evaluation board, however, the compatibility with the design hardware remains to be seen.

ACKNOWLEDGEMENTS

This material is based upon work supported by the National Science Foundation under Award No. BES-0527358. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.