Proceedings of the Multi-Disciplinary Senior Design Conference Page 7
Project Number: P14473
Project P14473
Proceedings of the Multi-Disciplinary Senior Design Conference Page 7
Programmable Mounting fixture
Chris WilliamsMechanical Engineering / Dennis Roffo
Mechanical Engineering
Chloe Parliman
Industrial and Systems Engineering
Jacky Ruan
Mechanical Engineering / Ben Lawrence
Electrical Engineering
Project P14473
Proceedings of the Multi-Disciplinary Senior Design Conference Page 7
Abstract
Luminaires and electrical enclosures designed for outdoor applications are rated with NEMA and IP waterproof standards, which quantify resistance to drenching. An automated testing procedure is desired for checking the water resistance of the enclosures’ seals, where the enclosures are most vulnerable to water seeping inside. A programmable mounting fixture was designed to hold and rotate the enclosure or luminaire during these automated waterproofing tests. The fixture is able to rotate 360° at an adjustable speed up to 1 rpm and tilt 45° forward and back to ensure the test enclosure gets adequate and consistent water coverage. The aluminum framing and steel supports allow the test fixture to withstand the water pressure from the fire hose used during the test as well as the weight of enclosures up to 1000 pounds. The rotary motion is controlled with a microcontroller programmed to output PWM to a gear motor that drives a chain, which is linked to the fixture’s drive shaft by a sprocket. Hinges under the drive shaft assembly allow the fixture to tilt using a pneumatic cylinder controlled by a solenoid valve which is actuated with a 3-position switch. A gas compression spring allows the fixture to return to its neutral position. In addition the fixture is able to accommodate various mounting configurations for the enclosures with sliding vices. The fixture demonstrated all its functionalities are operational under initial testing at 116 pounds for centric and eccentric loading.
Nomenclature
· IPX6 – Waterproof standard that requires waterproofness for at least 3 minutes with 75 liters per minute of water applied at a pressure of 1000kPa and at a distance of 3 meters away.
· Marine Hose Test – Cooper Crouse-Hinds developed waterproof test that uses a marine hose at a distance of approximately 20 feet for 5 minutes
· NEMA Type 4 – Waterproof standard that requires waterproofness for at least 5 minutes with at least 65 gallons per minute of water from a 1 inch nozzle being sprayed at a distance of 10 feet away.
introduction
Waterproof products must undergo testing to ensure that they perform as advertised. The test setup requires a frame to hold the product in question while it is sprayed with water at a set pressure and for a designated amount of time. While the test is in progress the product must be rotated to ensure adequate water coverage over the entire surface. Existing water test rigs consist of frameworks that must be moved manually or of static frameworks that instead require the hose to be redirected to spray different parts of the product. This project will entail the design and fabrication of a programmable mounting fixture capable of securing and rotating a variety of waterproof lighting fixtures while they are being sprayed with water under pressure to ensure their compliance with NEMA Type 4, IPX6, and Marine Hose test Standards. The fixture should be able to accommodate the sizes and weights of the current line of Cooper Crouse-Hinds products. The fixture should have a control that will allow the operator to rotate the fixture with respect to the X, Y and Z axes at a variable speed. The expected end result is a working fixture that can be used for in-company testing. The fixture will be partially tested before delivery to the customer.
process
Customer Requirements and Engineering Requirements
The mounting fixture has 16 customer requirements that were developed during a teleconference with Cooper Crouse-Hinds. These 16 customer requirements along with the project readiness package led to the development of 15 engineering requirements. Both the customer requirements and the engineering requirements were assigned a value of importance. Using these values, a customer and engineering requirements relationship matrix was implemented to determine the top requirements. Training time, factor of safety, and project budget were found to be the top three engineering requirements. The ability to meet these requirements were used as a metric to determine the success of the project.
Table 1- Customer Requirements
Table 2- Engineering Requirements
Concept development and selection
A functional decomposition was created to breakdown the fixture into managable subsystems. The four main functions and their breakdowns can be seen in Figure 1. This allowed for each function to be researched individually.
Figure 1- Functional Decomposition
These breakdowns along with research conducted on current methods of water hose testing was used to form a morphological table (Table 3). Options were developed for each function. Table 3 along with weekly faculty advisement led to the development of five concepts. The five concepts were developed by mixing and matching options from the morphological table. The chosen concept as seen in Figure 2, was selected through the use of a Pugh matrix (Table 4), and team consensus. The selected concept is simple, low cost, and easy to maintain.
Table 3- Morphological Table
Table 4- Pugh Matrix
Figure 2- Selected Concept
Focus on the components of the select concepts yields the following:
Motor Selection
When choosing the motor to provide the rotational force on the fixture, there were several constraints in consideration. The first and most important was that the motor needed to provide enough torque to rotate the largest fixture at 1 RPM. Based on the information gained from the CAD model created in Autodesk Inventor, the rotating assembly had a moment of inertia of 251,778.9 lb-in2. Using a time of 15 seconds to reach full speed, the necessary torque was found to be 30.86 N-m, and adding in a 1.5 safety factor, the final require torque was 45.3 N-m. The second constraint was self-imposed to find a motor that operated on 24 VDC. This is the same voltage used for the other electronics and would allow for a simpler electrical system.
When searching for motors that fit these constraints, as well as physical size and budget requirements, it was determined that additional gearing would be needed to be used on the chain drive to achieve the desired torque. It was determined that a 24 VDC gear motor from McMaster-Carr was the solution. The motor was a 26 Watt mini gearmotor and output 5.65 N-m. When used with additional gearing, it would supply sufficient torque.
Figure 3- Motor
Air Cylinder Selection
To provide the tilting force, a pneumatic cylinder was chosen. When determining the size of the cylinder required to tilt the fixture, several factors needed to be taken into account. The first and least flexible factor is the pressure available at the locations, which was 60 PSI. Using the CAD model in Inventor, the moment of inertia was determined to be 245,638.3 lb-in2. Before a pneumatic cylinder, a compressed gas cylinder was chosen to return the fixture to its neutral position. Taking into account the angle of the cylinder relative to the rotating plate (22.1°) and the distance from the rotational axis (12”) the required force of the compressed gas cylinder was determined to be 88.3 lbs. Based on standard sizes, a cylinder with a force of 120 lbs was chosen. Using this value and the supplied air pressure, the required diameter of the pneumatic cylinder was determined to be 2.5”. Taking into account standard sizes and a safety factor, a dual-action cylinder 3” in diameter was chosen. To make the cylinder last in the test environment, a stainless steel with rod wipers to prevent dirt and moisture from entering the cylinder bore was purchased.
To drive the cylinder, a 24 VDC 3 Watt solenoid valve was chosen. To get the necessary operation out of the solenoid valve, a 5 port, 3 position valve was chosen. This valve allows pressure to be supplied to both sides of the air cylinder.
Figure 4- Pnuematic Cylinder
Clamp Mechanism
The electrical enclosures Cooper-Crouse Hinds manufactures do not have standard mounting hole locations or sizes. In order to encompass all mounting hole configurations, the clamping mechanism must be readily and easily adjustable. A simple solution to the clamp design is to clasp the bolts fitted through an enclosure’s mounting holes with a vice. The vice consists of two 45mm X 32mm extruded aluminum bars from Minitec, held together by 3 M8-1.25 stainless steel threaded rods fitted through both bars. Washers are placed at each end of the threaded rods along with a wing nut and a bolt on opposite ends of each rod. These wing nuts will either increase or decrease the gap between the aluminum bars, so the device functions like a vice. Due to the large load the mounting fixture is expected to carry, two vice devices will share the electrical enclosure’s weight.
Figure 5 - Concept design for the clamping device.
As previously mentioned, the vice devices must be easily adjustable to accommodate all mounting hole configurations for Cooper Crouse-Hind’s electrical enclosures. These vice clamps are situated on the mounting fixture’s top frame where the electrical enclosure is mounted. Each aluminum bar has two Minitec cross connectors attaching the bar’s bottom to the aluminum top frame. The cross connector is an L-shaped block with a set screw hole located at the long leg’s end, the short leg is a rounded edge. The set screw is placed against the vice’s bottom to fasten the connector to the vice, while the rounded edge is placed in the 45mm X 45mm aluminum bar top gaps (these bars make up the top frame assembly). The rounded edges allow the vices to slide around the top frame assembly to ensure all mounting hole configurations are covered.
Figure 6 - Minitec cross connector fastener CAD model.
Electrical components
The microcontroller selected for the test fixture is the Ruggeduino from Rugged Circuits and its accompanying Rugged Motor Driver shield. The Ruggeduino is based on the Arduino Uno, but boasts a high external input voltage range (7-24V), high I/O pin voltage protection(up to 24V), I/O pin current protection with resettable fuses, and reverse voltage protection. Due to the presence of water in the application, it was believed that the Ruggeduino would have a better chance at surviving in the event of a leak in the electronics housing. The Rugged Motor Driver is similarly resilient, rated for up to 30V and 2.8A. The entire circuit is shown in figure 7.
Figure 7- Test Fixture Control Circuit
The motor speed is controlled by using a potentiometer and one of the analog pins on the microcontroller. Based on the analog voltage measured at the input pin, a PWM signal is output to the motor shield. The top speed of the motor is code regulated to a maximum of 1 rpm. The solenoid is controlled with a three position switch. Actuating the switch in either direction sets an input pin and a corresponding output pin on the microcontroller high. The output pin is connected to the base of an NPN power transistor, which allows current to flow through the solenoid.
A 24V 3A LED power supply was used to supply DC power to the fixture. The motor, solenoid valve, and microcontroller have a combined maximum current draw of 1.23A, well under the amount that can be supplied. A custom PCB has been designed in order to regulate down the voltage to the microcontroller. Although the microcontroller is rated for 24V, it was theorized that running the microcontroller at the maximum allowable voltage input might decrease its lifetime. The PCB also holds the transistor circuits for the solenoid actuation.
Results and discussion
Design Analysis
To validate and optimize the design choices for this project, the stress analysis package in Autodesk Inventor was used. The three main area of Finite Element Analysis (FEA) were the hinges, drive shaft assembly, and upper frame.
Figure 8- Hinge Analysis Figure 9- Hinge Analysis
The first part that was put through the FEA program was the hinges that provided the tilt support. When loaded with 750 lbs, which is a 1.5 SF, the minimum simulated safety factor was 1.16 which equates to a total safety factor of 1.75.
Figure 10- Drive Shaft Analysis
The drive shaft was then simulated to ensure it was strong enough. A 1500 lb. load was put on the shaft at 45°. Because the shaft had to be oversized to fit the required bearings, the shaft had a very high safety factor (~5) and almost no displacement (0.015”) when loaded.
Figure 11- Top Frame Analysis
The upper frame assembly was also analyzed to ensure it could withstand the weight on the enclosures it needed to support. When each side was loaded with 750 lbs. to have a total enclosure weight of 1500 lbs, the minimum safety factor was 1.41, which when coupled with the 1.5 safety factor of the load equated to a total SF of 2.115.
Additional FEA was performed on the support posts, and bolts throughout the design. When loaded with the maximum weights, they all had a minimum safety factor above 1.5 and in most cases well above.
Size test
The mounting fixture was size tested using a tape measure. The fixture was measured to be 3’x3’x3’3”. This result is well under the 5’x5’x8’ maximum fixture volume specification.
Function and Failure test
The tilting function of the mounting fixture was tested with the compressed air regulated to 60PSI. The frame was tilted forward and held forward for 30 seconds. The fixture then was tilted back so that the top frame was parallel with the floor. Then the motor was turned on and rotation function was tested at both the parallel and forward tilted positions. These both ran as expected with the tilt reaching 45° and 360° of rotation. The emergency stop button was tested with the motor running in both the forward tilt and parallel positions. In both cases the machine stopped and remained in the same position without any further rotation.