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System Level Design Review
P09503 – Electrophotographic Development and Transfer Station
Friday, October 3rd, 2008
10:00AM-1:00PM
Xerox Auditorium
James E Gleason Building
Rochester Institute of Technology
Introduction
Electrophotography (EP) is the base technology that is used in many modern day copiers and printers. Examples of manufacturers that use this technology in their products include Xerox, Canon, Lexmark, and Hewlett-Packard, to name a few. Electrophotography is a six-step process that consists of uniformly charging a photoconductive material. Photoconductive materials allow charge to flow when exposed to light. EP products exploit this property by selective discharging areas on the photoconductor to form what is referred to as a latent image. When this latent image comes close to charged toner particles, these charged particles will transfer onto the latent image to form a developed image. Through the use of electrostatics, the image is ultimately transferred onto a media substrate (such as paper) and fused.
The experimental EP station in this project will contribute to the understanding of current EP technology by allowing for the manipulation of certain input parameters. Some of these inputs can include charging voltage, discharge intensity, development voltage and transfer current to name a few. Different technologies such as Charged Area Development and Discharge Area Development may also be explored. The device must be operation and posses an easy to use interface to allow operators at all levels of expertise to research and understand the EP process.
The objective of this project is to make an existing electrophotographic development and transfer station function and to improve at a minimum its usability and to automate the control of the machine. It is also expected that additional performance improvement opportunities will be identified, designed and implemented.
Table of Contents
Part I – Status of Current Sub-Systems
1.0 System Level Functional Diagram...... 4
2.0 Photoconductor System...... 5
3.0 Charging System...... 6
4.0 Discharging System...... 7
5.0 Development System...... 8
6.0 Transfer System...... 10
7.0 Test Stand...... 11
8.0 High Voltage System...... 12
9.0 Control System...... 13
Part II – System Level Design Improvements
10.0 Paper Delivery System...... 15
11.0 Monitoring Charge on Photoconductor...... 17
12.0 LED Exposure System...... 19
13.0 Directional Ozone Exhaust...... 22
14.0 Labview...... 23
15.0 Measuring Charge Over Corona...... 25
16.0 Monitor Speed of Transfer Roller...... 26
1.0System Level Functional Diagram
Since the high level architecture has already been defined for P09503 concept generation activities involved creating a large list of possible improvement opportunities. The opportunities in this case are in addition to the activities required to have the device functional, since in its current state it is not able to function as intended.
The customer and guide, Dr. Marcos Esterman, provided the functional diagram below. The purpose of providing this diagram was to capture the functional areas of the Electrophotographic and Transfer Station (EDTS) that have opportunities to be improved from the current state that they are in.
2.0Photoconductor System
The purpose of the photoconductor system is to transverse the EDTS while carrying photoconductor material with charge and toner for transfer to a certain medium. The photoconductor system carries a photoconductive material which increases conductivity when exposed to light. The photoconductor directly interacts with the charging system, discharge system, development system and the transfer system. The following is a functional diagram of the photoconductor system.
The current activities that have been undertaken to ensure that this system is functional include attempting to have the Photoconductor Plate transverse the EDTS. An inventory of the current system has also been completed.
The following issues have been discovered during the course of attempting to activate this system.
Issue / Action / OwnerDetermine the functionality of the motor / Apply Voltage / Rachel
Determine how to attach photoconductive material / Talk to Greg / Dave
Determine purpose of optical encoders / Look up Part Number / Sasha
3.0Charging System
The purpose of the charging system is to establish an electrical field within the photoconductor and consists of two parts, the corona and the grid. The corona wires, enclosed by the grid, are subjected to voltages that can range up to 10,000 volts. The purpose of the grid is to ensure that charge uniformity exits on the photoconductor; the potential applied on the grid is closer to what is desired on the photoconductor. The photoconductor does not come into contact with the grid and passes over at distances in the micron range.
Currently the charging system has been determined to be functional, small voltages were applied to the grid which was measured. However the ozone filter functionality is to be determined. An inventory of the current system has also been completed.
4.0Discharging System
The purpose of the discharging station is to expose the photoconductive material to light. Due to the properties of the photoconductive material this light then neutralizes the charged area leaving only an electrostatic latent image on the photoconductive surface.
It has been determined that the projector which produces the light source is functional. However in order to expose the photoconductor with a focused image a pneumatic lift on the system which encases the light is brought barley into contact with the photoconductor from its resting position . However it is not know if the exposure lift is functional and can move.
The shutter is known to work since it has been opened manually. The projector is also known to work since it has been turned on. An inventory of the current system has also been completed.
The following issues have been discovered during the course of attempting to activate this system
Current Issue / Action / OwnerVerifying that the exposure lift functions / Test pneumatics to determine if it is functional / Dan
5.0Development System
The purpose of the development system is to deposit charged toner particles onto the charged surface of the photoconductor. The photoconductor transverses the development system at distances that range in the microns. The following is a functional diagram of the development system.
The following actions have been completed to activate the development system:
Toning Station 1:
1) Connected ground wires 3, 5, and 7
2) Turned on motor manually from front panel
3) Turned on motor manually from rear panel using variable speed and direction controls
4) Inserted toning station into motor mount and verified roller function
An inventory of the system has been completed.
Toning Station 2:
a) Turned on motor manually from front panel
The following issues have been discovered during the course of attempting to activate this system.
Current Issue / Action / OwnerSkiving blade size / Identify Problem / Ruth
Identify Toner Hazards / Identify Problem / Dave
Check that Magnetic Sensor and Clutch Sensor Engage / Verify if Sensors engage / Andrew
Determine if control Plug is critical to toner operation / Talk to Greg Miller / Andrew
Determine how to modify the toning station so that the photoconductor can traverse
6.0Transfer System
The purpose of the transfer system is to movethe toner on the photoconductor to a charged roller and then onto the desired medium. The photoconductor comes into contact with the transfer roller in this step. The following is a functional diagram of the transfer system.
An inventory of the system has been completed along with voltage measurements from the drum.
The following issues have been discovered during the course of attempting to activate this system.
Issue / Action / OwnerDetermine purpose of unknown white wires / See if we really need them. / Min
Determine Functionality of Drive train motor / Apply Voltage / Rachel
Determine Proper Operation of Pneumatics / Test pneumatics / Dan
7.0Test Stand
The purpose of the test stand is to support all devices needed for EDTS operation and support. The test stand also encompasses the pneumatics system, a functional diagram can be seen below. Safety is included in this section.
An inventory of the system has been completed.
A Failure Modes Effects Analysis (FMEA) has been performed on the EDTS and high risk areas such as human shocks have been identified and documented.
8.0High Voltage System
The purpose of the high voltage system is to provide the high voltage needs of the grid, corona and the transfer roller. The functional diagram can be seen below.
An inventory of the system has been completed.
At this time the high voltage systems are functioning normally.
9.0Control Systems
The purpose of the control system is to monitor and control all aspects of the EDTS. Some of these controls include the translation of the photoconductor, toning station drive control, manual control of the paper feed, manual control of lamp exposure,
etc. The functional diagrams can be seen below.
The following actions have been taken to activate the control systems:
1)Spoke to J. Wellin about possible way to interface LabView to PLC
2)Identified the cable and the adapter for the cable to connect the PLC to the computer
3)Organized a meeting with J. Wellin so team could ask questions about interfacing device to LabView
4)Read through the manual for the PLC
5)Researched LabView online
6)Researched use of HyperTerminal to listen on the serial port for the output/input from PLC
7)Looked up part numbers for the control systems on their manufacturing website.
8)Researched different voltage levels for transfer and toning parts of the system
9)Measured voltage levels on various parts of the device
10)Identified and documented the properties of all electronic parts of the device
11)Tested control boards to identify correct placement
12) Inventory of current system
13) Connected ground wire six to slot in circuit breaker
14) Removed front panel to determine station control port locations
15) Attempted various placements of control circuit boards into ports yielding no response from the system
The following issues have been discovered during the course of attempting to activate this system.
IssueVerify Card Positions / Trace wires and check schematics / Sasha and EEs
Obtain Keyence Cable / Get Cable / Sasha
Determine how to get output on PLC / Talk to Dr. Cockburn / Sasha
Determine if Magnetic Sensors are Functional / Check voltage and use a magnet for testing / Min
Determine if sensors are in the correct position / Operate EDTS / TBD
10.0 Paper Delivery System
Statement of Problem:
Existing system requires manually catching paper after application of toner from the transfer roller, resulting in a risk of marring image quality by handling, as well as hazards to hands including a pinch point at the transfer roll, high voltages, moving parts, and pneumatics.
Design Constraints:
Solution must be able to smoothly guide and hold 4.25” x 5.5” paper samples. It must fit in available space adjacent to the transfer roller. It must be easily and quickly manufactured using appropriate inexpensive, easily obtainable materials. It must be easy to install and remove. If fixed to transfer station, it must be able to handle motion when components are moving, and have sufficient clearance. Tray must be able to withstand high fusing temperatures.
Solution:
Design, model, make, and install a paper delivery system consisting of a durable frame which supports a flat, removable metal tray and guides the paper into the tray.
Future Design Improvements:
Reduce the material used. Minimize the footprint. Simplify for ease in manufacturing.
Risk Assessment
Risk / Severity (1-5) / Corrective ActionsTray too heavy / 1 / Reduce amount of material needed
Choose lightweight, sturdy, heat resistant material
System gets in the way of camera system / 2 / Minimize footprint by reducing size
Determine minimum size necessary
Paper gets caught / 3 / Reposition tray to position of least interference with paper and transfer station but where it most effectively catches paper
Difficulty in manufacturing / 2 / Simplify design and use off-the-shelf parts wherever possible
Balance / 4 / Make sure proper supports are in place
Redesign if this is an issue
11.0 Monitoring Charge on the Photoconductor
The charge on the photoconductor can be measured by using the Trek 344 (Fig. 1.) electrostatic voltmeter. It allows the measurement of potential present on the photoconductor plate without touching it. As of now, the team is still waiting for the probe (Fig. 2) for this meter from Greg Miller.
Figure 1Figure 2
The probe has to be placed 2mm from the surface of the photoconductor. It cannot be held by hand since it will charge itself up with respect to the object being measured; therefore, it also has to be positioned by some sort of fixture.
I propose to use the one of the existing camera station (Fig. 3) as the probe fixture. Since it can be easily placed, removed, and repositioned and it sort of has a circular thing that can hold on to the probe. Another nice thing about the camera station is that it has two degrees of freedom. It can move along and across the photoconductor so that the distance can between the probe and the photoconductor can stay fairly accurate.
Figure 3
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Fig. 4 is what it might look like when the probe is attached to it. The fixture will be able to move up/down and left/right according to Fig. 4.
The fixture itself will most likely not be moved very often since it will be easier to move the photoconductor back and forth. The clear brick holding the probe will be more likely to be moved around to measure the charge across the photoconductor. This will be done by first stopping the movement of the photoconductor, and manually move the brick around.
F
Figure 4
Risk AssessmentIssue / Severity / Action
Allowing the probe to be moveable will introduce a loose wire / 2 / tighten unnecessary length
Manually moving the brick might result in a shock or short / 4 / be very careful, wear gloves even though not surrounded by high voltage
Variable distance between probe and photoconductor will result in poor measurement / 2 / lubricate the two bar so that the fixture will not move as much
12.0 LED Exposure System
Overview of Current Exposure System
Currently, the exposure of the photoconductive material is done with an incandescent light source, specifically a projector bulb. The projector is mounted underneath the exposure system with the light source projected upwards to the exposure lift. Some of the draw backs to the current system are that projector bulbs to not have a long life time, are expensive to replace, and have a tendency to overheat. This type of system also takes up a significant amount of space. The replacement of this system with an LED exposure system would prove to me a more reliable and versatile light source.
Implementation of an LED Exposure System
The LED exposure system could sit relatively in the same position in which the projector sits now. A mount could easily be built to support the smaller, more compact system. By allowing the LED system to sit farther down from the where the actual exposure of the photoconductive material takes place, the more uniform the distribution of light will be. Although the farther away the exposure system is the less intense the light source will become. The LEDs will be arranged in an array to achieve maximum uniformity of light distribution. The use of an array instead of a line of LEDs would be more efficient because the center will emit the greatest light intensity, therefore a greater concentration of LEDs will be a better light source. A 2x2 array will be a good starting point to test if this system is better or worse than the current one. One of the factors that affects density and resolution of the image is the intensity of the light exposure. A device that measures light intensity , such as a Lux meter would aid in determining the number of LEDs needed and their position. LEDs provide a steady light source that does not fluctuate, thus producing an even exposure. They also provide more light per watt than an incandescent bulb thus making it a power efficient choice, and do not require an external focusing device to collect the light and direct it in a usable manor.
Luxeon emitter LED, model number LXHL-BB01 has a turn on voltage of 3.42VDC with a maximum at 3.99VDC. LEDs can be bought individually or in an array. Voltage can be provided by an adapter that steps down 120VAC to an appropriate voltage that can be used or a small power supply could be used.
Difficulties of Implementation
Resolution of the spatially modulated exposure needs to be an order of magnitude better than the photoconductor we are testing. Currently the resolution is unknown but can be measured at a lower resolution. Dr. Jon Arney has volunteered to help with this measurement.
The dynamic range is the range of values between light and dark areas, or the contrast ratio. This would be the maximum contrast divided by the minimum contrast. If we decide to modulate exposure intensity with a mask the dynamic range of the mask will have a maximum and minimum transmittance. A computer could possibly be used to modulate exposure because the monitor has a maximum and minimum brightness. Neutral density filters could also be used to modulate the intensity of because they reduce light of all wavelengths.
Figure 1: Current System vs. Led System- This is a figure of the Current System vs. the LED system courtesy of Dr. Jon Arney. The incandescent light source uses a collimating lens to collect the light and direct it towards the modulating masks. The LEDs provide a more direct source of light to the modulating masks.
Proof of LED Exposure Design and Risk Assessment
LED print heads are used in copiers, duplicators, and printers to expose a photoconductive member or photosensitive film in the apparatus in such a manner that a latent image is formed on the surface or film. This is a technology commonly used in industry to expose photoconductive material and this is much research backing the use of this technology.