Overall Project
The main design goal of this project as specified by the course instructors was to create a machine to automatically crush 10 cans. The cans would be loaded in an unorganized manner into the mechanism, and would exit the mechanism at 1/3 of the original can volume. Additionally, we were given the design objective to crush all of the cans in less than two minutes, and a volume constraint of a 2ft x 2ft x 2ft bounding box. Some of our added “coolness factor” design objectives were to be able to sense, count, and display the number of cans that have been crushed. We also wanted our machine to be safe for human users. Throughout the design process, we focused on the machine’s efficiency by limiting the amount of actuators needed to accomplish the task, which led to innovative designs.
Figure 2.2: Overall System Diagram
For our mechatronics project, we built a robotic can crushing mechanism. The mechanism consists of a large hopper and a pneumatically actuated crusher. Cans are agitated in the hopper by the exhaust from the pneumatic crusher and an agitation wheel. The cans are crushed in a crushing chamber by a pneumatic cylinder, and exit the machine by gravity. The electronics in the system allow the user to run different crushing modes, while displaying useful system information such as the number of cans crushed and the time elapsed. The overall system can be broken down into three main subsystems (see Figure B); the hopper, the crusher, and the electronics; which will be explained in detail in the following section of the report.
Figure 3.1: System Block Diagram
The diagram above shows how the three main subsystems (the hopper, crusher, and electronics) interact with one another in terms of energy, signal, and material inputs and outputs. The following sections will describe in detail the design, manufacturing, and functionality of the three subsystems.
The hopper was designed to move cans and orient them into the crusher chamber with limited agitation. The design consists of laser-cut hardboard, which we bolted together (see Figure 3.2).
Figure 3.2: CAD Model of Hopper
The hopper proved to be the most difficult subsystem to design. This was because figuring out optimal geometry to keep the hopper mostly gravity-driven was difficult to model and test. Various stages of prototyping for our hopper are explained in section 4.1.
The final design creatively used the exhaust from the pneumatic cylinder to blow the cans forward down the chute, while the agitation wheel knocked cans over, ensuring the correct orientation when cans exit the chute into the crushing chamber. (See Figure 3.3).
Figure 3.3: Top View of Final Hopper Design
For this subsystem, cans are loaded into the hopper on the sloped shelf, where they move via gravity and collect in the chute. The chute is also sloped downward toward the crushing chamber. Cans are agitated forward by the exhaust agitation from the pneumatic cylinder, and the orientation is corrected by the agitation wheel before loading.
The crusher is arguably the most important subsystem of our crushing device as it is the part of the mechanism that actually crushes the cans. The crusher consists of a pneumatic ram mounted within an aluminum frame. When actuated, the pneumatic ram moves forward crushing cans with over 160lbs of force. The aluminum frame is shown below in Figure 3.5.
Figure 3.5: CAD Model of Crusher Frame
The aluminum frame is constructed in such a way that once crushed, a can will simply fall out of the bottom of the crushing chamber. However, in no orientation could an uncrushed can fall out of the crushing chamber. The final construction of the crusher frame is shown below in Figure 3.6.
Figure 3.6: Completed Crusher Frame with Pneumatic Cylinder
A pneumatic ram has a crushing head attached to it to allow for can crushing. The calculation for selection of the proper pneumatic ram is included in section 4.2. Also included in section 4.2 is a mechanical analysis of the crusher to ensure that it will not fail during operation.
In addition to the frame, the crusher includes a shroud which surrounds the crushing area. This shroud, shown in Figure 3.7 prevents cans from exiting the crushing chamber during crushing causing injury to people around the device. The shroud also helps align cans for crushing when they are loaded into the crushing chamber. Also included in the shroud design are an aluminum backstop which prevents cans that become impinged upon the crushing head to be pulled out of the crushing chamber. This shroud also has a hinged lid to allow for easy access should a jam occur within the crushing chamber. This hinge is shown in Figure 3.8.
Figure 3.7: Crushing Chamber Shroud
Figure 3.8: Crushing Chamber with Hinged Lid
After a can exits the hopper it loads into the crushing chamber. Once in the chamber the pneumatic ram actuates forward crushing the can. Once crushed, the can falls out of the crushing chamber.
The electronics were all controlled using an Arduino ATXmega a 600W desktop PC power supply. We used such a strong power supply as our original design called for an electric motor rather than a pneumatic ram. The power supply had its 5V rail connected solely to the Arduino in order to power it directly as well as to allow the Arduino to distribute power to the rest of the electronics. The 12V rail was connected solely to the power input of the motor driver board. The Arduino connected directly to the motor driver board, the safety and can counting sensors, the control pad, and a small breakout board to extend the Arduino's 5V power rails to the various devices that required a very steady power supply in order to do differential voltage sensing. A high level diagram is shown in Figure 3.10.
Figure 3.10: Electronics Block Diagram
The motor driver board in turn controlled the solenoid for the pneumatic ram and the agitation wheel, as those both required 12V rather than 5V. It was powered directly from the 12V rail from the power supply, and connected to the Arduino for control. Depending on the input from the Arduino, it would extend/retract the pneumatic ram using one output terminal to control the solenoid, or supply power to the hopper agitation wheel using the other output terminal.
The safety sensor was constructed as a voltage divider using a photoresistor as a switch in series with a 1k ohm resistor. It had two terminals connected to 5V and ground on the breakout board and a middle terminal connected to an analog input pin on the Arduino. It was mounted on the underside of the output from the crushing chamber, directly across from an LED, as shown in Figure 3.11. If the photoresistor had enough light shining upon it, the middle terminal was raised close to 5V and the Arduino would determine that nothing was being pushed into the crushing chamber from the bottom, therefore it was safe to actuate the pneumatic ram. Otherwise, something was clearly blocking the LED and therefore it wasn't safe to actuate the ram. The LED was also supplied with power from the breakout board, and was added so that the signal from the safety sensor would be consistent across environments, allowing us to be very stringent about when it was safe to actuate the ram without needing to fine-tune the code for every location.
Figure 3.11: Safety Sensor
The can counting sensor was another voltage divider powered by the breakout board, however rather than a photoresistor it used a manual switch in series with a 1k ohm resistor. When depressed, the middle terminal would rise to 5V from ground and signal the Arduino that something had fallen out of the crushing chamber. It was mounted underneath the crushing chamber, slightly above the safety sensor so as not to interfere with it.
The control pad consisted of three three-position switches and a pair of dual-digit seven segment displays, as shown in Figure 3.12. The two-position switches were constructed as matched voltage dividers, all powered by the breakout board. When a switch was pushed "up," one signal would be almost 5V and the other pulled to ground, when pushed "down," the opposite would happen. When a switch was in the "middle" position, both signals were pulled to ground. The first switch controlled whether the system was operating in automatic ("up" position) or manual ("down" position) mode. The second switch had different functions depending on whether the system was in automatic or manual mode. In automatic mode, it controlled the number of cans to crush, in manual mode it would directly actuate the pneumatic ram. The "up" position would extend the ram while the "down" position would retract it. The third switch was the start/stop switch. In automatic mode the start, or "up" position would tell the system to begin crushing cans, and the stop, or "down" position would tell it to cease crushing and retract the pneumatic ram. In manual mode the start switch, when pressed, would allow the user to use the second switch to actuate the ram until the stop switch was pressed or the system was taken out of manual mode. This was done both as a safety factor, in that no single inadvertent touch of a switch could actuate the system in manual mode, our testing mode, as well as to allow users to play a game. In manual mode, when the start switch was pressed, a clock would begin ticking, only stopping when the stop switch was pressed. The clock would be displayed on one of the seven segment displays and the best time so far on the other seven segment display. In automatic mode, those displays would show the number of cans the machine would attempt to crush before stopping on one display while the other would show the total number of cans already crushed since it was turned on. The seven segment displays were connected and powered by the digital output pins of the Arduino using ribbon cable. Depending on the number to be displayed, the Arduino would set certain pins high to light up the correct segments. It should also be noted that only the switch for auto/manual mode would stay in the up or down position, all the other switches would spring back to the center once released.
Figure 3.12: Control Pad
The breakout board was mainly constructed as a convenience factor to distribute power, as initially the Arduino was powered through a serial connection to a laptop before we added the power supply. After we added the power supply, we kept it connected to the Arduino as our thresholds for analog sensing were determined using the Arduino's 5V rail rather than the power supply's 5V rail. It had already been determined that the Arduino could supply enough current for accurate analog sensing, so we kept the breakout board powered by the Arduino rather than connecting it directly to the power supply. In total, the breakout board supplied stable 5V and ground signals to the safety sensor's photoresistor circuit and LED, the can counting sensor, and the three three-position switches on the control pad.
Team Members
Wil Hamilton-Mechanical Engineering
Pneumatics Fabrication
Kyle Gee-Mechanical Engineering
Hopper Fabrication
Henry Kung-Mechanical Engineering
Pneumatics and Hopper Design
Steve Williams-Electrical and Computer Engineering
Electronics
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