19.2.2 Project Descriptions
19.2.3 Previous Project Topics
“GVSU Workcell” (Jenny Agnello, Tom Johnson, Colin Moore, Lisa Nahin, Jeremy Scott) The material handling system at GVSU was designed to produce puzzles. The heart of the system was an Allen Bradley SoftPLC and Devicenet. It controlled a material handling system supplid by Worksmart Systems. The system included a robot for loading/unloading the mill. A CNC mill for cutting the parts. A vision system for inspecting the final parts. Various feeder and fixtures were designed and build by students in EGR450.
“Hole in Sphere Project” (Alex Wong, Robert Krygier, Andre Cargnelli, Ahmed Nensey) A mechanism will be designed and built for orienting spherical balls with small through holes. This will be done with a mechanism that uses three rollers for orientation, and an optical pair to detect the hole. An electromechanical control system will be used.
“Automated Robot Arm” (Lev Mordichaev, Karl Fung, Dennis Ngo, Nikko Chan, Edwin Wen, Elaine Rodrigues) A robot arm will be designed and built that can move up/down, left/right, and has a gripper that will open/close. The robot will be controlled via a computer program, and electrical connections to the robot.
“A Manually Controlled Robot” (Keith Lou, Sue Lee, Richard Dankworth, Phat N. Huynh, Howie Lam, Tarius Makmur) To build a manually controlled robot to perform a certain task using a joystick for control. This small scale robot will be capable of picking up an object, and positioning it in another location. And, for proof of concept, a set of fixtures, jigs or feeders will be constructed for a simple robotic task. Note: This project has too many people for construction of a robot only.
“A Box Sorting System” (Joey Aprile, Don Christie, Gabe Fusco, Mike Poczo) A conveyor based system will be designed and built for sorting boxes by a switched conveyor path. This will include construction of the conveyor, sensors, actuators, and control system.
“Automated Drink Dispenser” (Keith German, Dave Van Den Beld, Jeff Kempson, Brent Rubeli, Michael Staples) Glasses on a conveyor belt will be transported to/from a dispensing station where they will be filled by an automated mechanism. The system will be designed and built, possibly using a PLC, or a PC for control.
“Self Leveling Platform” (Gerard Biasutto, Mario Borsella, Dino Farronato, Marco Gaetano, John Yuem) An actuated system will be designed and built to level a platform under tilting conditions. This will involve actuators positioned at four corners. A control system will be constructed to drive the actuating cylinders.
“Manufacturing Database” (K. Beute, M. Mead) A manufacturing database will be developed that allows operators to call up machine configurations based on part numbers. This system uses an HMI to allow easy operator access.
“Construction and control of Stiquito Robot” (T. Cowan and J. Cummings) A kit for a stiquito robot will be purchased and assembled. The appropriate interface electronics and software will be written to control the robot.
“Computer Based Analysis of Battery Discharge Data” (R. Sietsema) A computer application will be developed using Excel, and a scripting language, to allow a user to do an analysis of battery discharge data.
• The suggested problems Chang and Wysk are recommended to help you examine the basic properties of the problems. the required problems assigned during the semester must be submitted. Doing only the required problems will leave you at a disadvantage.
3.3 There are three significant levels of solid models. The lowest level is the 2D line based model. To represent any real part with this we need two or three views. Mathematically is can be difficult or impossible to relate the lines in the different views. A 3D line based model is a bit better, the lines are all related, but determining where the inside/outside lies can be a problem. 3D solid models are the highest level and are useful because we can exactly determine what parts of space the geometry occupies. The mathematical exactness of the model makes it well suited to supporting other tasks after geometrical design such as finite element analysis, and automatic generation of NC programs.
3.5 Using the definitions of the book the major divisions include Mechanical, Architectural, Electrical/Electronic and Map Making. This list is not complete and can be expanded to include manufacturing (such as CNC milling), process (pipe layouts, etc.), textiles (clothing design and pattern making), etc.
3.6 CAD systems can be of benefit for engineering design when the geometry is to be reused. Examples of reuse include CNC program generation, FEA analysis, paper drawings, shipping drawing to customers, drawings imported into other designs, drawing will be revised. New CAD systems not mentioned in the book also allow designs to be treated like a sketchpad. Think of Pro/E that allows a design to change radically by altering one dimension on the screen. When users become proficient, CAD systems will make them more efficient. After a CAD systems has been in use for some time new designs can be done by modifying old CAD files.
3.7 The major difference between a wire frame and solid model is the mathematical representation. The wire frame model only indicates where edge of the model lay in space. This leads to ambiguity, not knowing where the inside of the part lies. Another major problem is that the wire frame models do not allow curved surfaces to be drawn easily. (This can be with done approximately with difficulty using cross section drawings) Solid models contain a closed mathematical surface model, including all geometrical features.
3.9 We can used Euler’s equation, there are no holes in the part faces so the Euler-Poincare equation is not necessary. Counting the geometrical entities shows that F = 4, E = 6, V = 4. Applying the formula shows that F: E + V = 2. Because this equals 2 the solid model is valid.
6.1 The production volume determines the tradeoff between these solutions. Hard automation works quickly, but retooling is expensive and time consuming. If the cost and downtime can be amortized over a larger number of unit cost drops very low. For smaller volumes and mixed product types the flexible automation can be a better choice.
7.1 Scan time can be critical to applications that have fast changing inputs or outputs. If the scan time is too long then a fast input may be missed. And, slow scans may prevent the system from responding fast enough for outputs.
7.3 The advantages of a PLC over a microcomputer is that the PLC is more compact and rugged, the PLC costs less, PLCs can be repaired and replaced faster, PLCs have features designed for the factory floor, etc.
8.5 These problems will commonly occur when the sending and receiving computers do not have the same settings. The settings that can be baud rate and data bits. By changing baud rate and data bits the machines can be made to work correctly.
8.6 The pro-light mill is built around a normal PC, so it has an RS-232 port, but this is not being used for the CNC machine. The EMCO lathe has an RS-485 port that is connected to a dedicated RS-485 card in a computer. Programs are passed to the lathe using a DNC network.
medium-access control: this covers a variety of methods for controlling which network client can talk. If the clients all share a common wire this requires some effort to decide when to listen and when to be quiet.
packet: This is a collection of bits that is transmitted. In simple schemes a packet will hold a single byte. In more complex methods, the packet will consist of hundreds or thousands of bits that can transmit hundreds of bytes.
8.11 CSMA/CD: When multiple clients share a common data wire. When a client sends a message it will also listen to make sure that what was sent is what it hears back. If they don’t match there is a conflict with another client. When this happens they stop for a random time and then start again. When the network is being used lightly this is efficient, but as the network traffic become heavy the conflicts tend to interrupt transmissions more often, and then network slows down quickly.
8.12 The ISO/OSI model for networking layers allows networking software to be split into logical levels. It can be applied when specifying network standards, formats, protocols, and software. It is especially useful when comparing or interfacing different network standards.
9.4 CNC machines can be controlled by a number of power sources. The typical sources are electric motors. Servo motors allow fast positioning with high torques. Stepper motors are used for smaller machines. They allow accurate positioning without feedback, but they are quite weak. Hydraulics and pneumatics are also used, but they are not well suited to positioning, so they are typically used for opening/closing doors, tool holders, etc.
9.12 An open loop CNC system does not use feedback. If the system uses stepper motors then this is typical. If the system uses servo motors, then an encoder is needed to measure the position, thus closing the loop (a closed loop feedback system).
11.2 The three first dof in a robot primarily provide positioning. The last three degrees of freedom provide orientation. This sound quite definite, but in truth these interact, and changes in the last three will often change position slightly, and changing position often changes orientation.
a) Palletizing of 3 lb boxes: I would recommend a servo motor based system with point to point positioning (the book defines point to point in a more restricted manner). I would look for a Cartesian robot with built in palletizing functions.
b) Spray painting in flammable environment: The robot should provide continuous path functions. For a drive system I would suggest either a servo motor system with sealed motors (to prevent sparking). Another alternative (not common) would be to use pneumatic actuators. Programming should also provide the ability to follow continuous smooth paths.
11.9 A compliant robot will help implementing this application, but a significant problem will be the necessity to mate the square shoulders of the pegs and holes. This would require that the peg be brought in at an angle and then stood up. This motion is difficult for a robot, even a compliant one. It is recommended that the pegs and holes be chamfered to allow self location.
11.10 Consider the task. The pallet sets out a 2 dimensional array, for this we need 2 dof. The orientation of the boxes on the conveyor and the pallet are rotated by 90deg., thus requiring 1 dof. If we assume the task is all performed on a single plane we can use a minimum of 3 dof total.
11.11 An accumulator will store hydraulic power (like a capacitor) when the fluid flow is low, and then deliver it when required. A hydraulic robot will not use power continuously, and the accumulator allows power in the robot to be more continuous, and make the robot more efficient.
11.12 As a task I select a record/CD changing arm in a juke box. For this task the arm must move to a linear rack position, pick a disc from the rack, lift it out rotate it and place it on a turn-table. A cylindrical robot can perform the task easily. The height can go to the rack position, the radial distance can move in then out to pick the disk, and the rotation can be used to turn from the rack to the turntable. The tooling could be in a few forms. A set of curved fingers could hold the edges of the disc, with care not to touch the face. The disc could also be picked up with a suction cup. This would only cause trouble when it is closely packed with other discs in the rack.
If you have done drafting by hand, or used simple CAD programs such as Autocad you are used to a different approach to technical drawing. In drafting based programs you picture the part in your mind, and then draw lines and arcs for two, three or more views that represent the edges of the part. For example to draw a cube you draw three squares (front, top, right side views) using four lines for each square. The line dimensions must be correct, and then dimensions can be added after. When you are done the only major use is to print/plot the drawings.
With solid modeling based systems you start by entering the geometry of the object. For example a cube is a cube, not a set of lines. The solid modeler stores this geometry internally as a mathematical model of the surface and volume of the part. After entering the geometry it can be used for various tacks such as creating 3 view drafted drawings, creating NC codes so that it may be machines, doing finite element analysis. Most CAD packages now offer some level of solid modeling, including Autocad.
Pro/Engineer has its own method for entering the geometry that tends to focus on cross section profiles. You draw a profile of the part and then extrude or rotate it. This approach is well suited to parts that will be manufactured. The creation of the profile is the most like traditional drafting. For example to create a cube, you would first draw a square, and then extrude it into a cube. If the same square was rotated it would produce a cylinder. After the base part has been created, it can be added to or features can be cut out. The geometry of the part is not fixed, and it can be changed and manipulated at any time.
1. Use the book “Pro/Engineer Tutorial and Multimedia CD” by Toogood and Zecher. Insert the CD and follow through a few until you feel comfortable. Then work through the book up to and including lesson 8.
2. Create a geometry for a die cavity (a simple box shaped cavity is sufficient). Use the Pro/E machining module to convert this to CL values. Look at the text file that was produced. This file is not yet ready for an NC mill. It requires post processing, which we will do later.