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Light Sources
Semiconductor Components
Standard Components Sensors and Switches
Clutches, Motors, and Solenoids
Other Electrical Components
Consumables
Light Sources
Our products use a variety of different light sources. These range from intense sources such as
halogen lamps to relatively weak sources such as LED arrays. The light source selected depends on
the function--original exposure, quenching, etc.--and the machine design. The most important light
sources from a design point of view are those commonly used for original exposure (scanning)--the
halogen lamp, the fluorescent lamp, and the xenon lamp. The most basic characteristics of these
three lamps are summarized in the following table.
Halogen Fluorescent Xenon
Light Intensity High Low Low
Spectrum Wide Narrow Narrow
Temperature dependency* Small Large Large
Stability at start-up Good Poor Good
Heat output Large Small Smallest
Cost High Low Lowest
*Dependency of light intensity on temperature of these three lamp types.
1 April 2001 Page 980
Standard Components Light Sources
Halogen Lamp
A Halogen lamp is an incandescent lamp filled with
halogen gas (iodine or bromine). The halogen gas
suppresses filament evaporation using a chemical
regeneration process known as the "halogen cycle"
(see below). Halogen lamps have a long effective
life and strong light output.
Characteristics
ˇ Extensive spectrometric distribution
ˇ High illumination level
halogen.pcx
ˇ Small changes resulting from the temperature of
the light source and small transient changes
ˇ Long lead time to lighting
ˇ Large electricity consumption
ˇ Large heat output
Halogen Cycle
During lamp operation, the halogen gas combines with tungsten molecules that have evaporated off
the filament. The evaporated tungsten molecules are then deposited back onto the filament, instead
of on the lamp wall. Consequently, there is almost no reduction of light output from lamp wall
darkening. Some light reduction from filament degradation does occur, but it is significantly lower
than in other incandescent lamps. The halogen regenerative process requires that tungsten-halogen
1 April 2001 Page 981
Standard Components Light Sources
lamps operate at an extremely high temperature, which slightly increases lamp efficiency, and
produces bright light and high temperatures. To withstand these high temperatures, tungsten-
halogen lamps usually have quartz glass walls. Halogen lamps with quartz walled bulbs must be
handled carefully. Quartz materials are extremely sensitive to oil and dirt from human skin, which can
cause bulb wall deterioration, and premature lamp failure.
Applications
The intense light and wide spectral output of the halogen lamp suit it to color copiers and high-speed
copiers. However, as it consumes a lot of electricity and undergoes drastic rises in temperature, it is
generally not used for low-speed copiers and single scanner models. Since halogen lamps output a
large amount of heat, they are also commonly used as a heat source in fusing units.
1 April 2001 Page 982
Standard Components Light Sources
Fluorescent Lamp
A fluorescent lamp is a closed glass tube that has
electrodes at each end and an internal coated surface of
a phosphorous material. The tube is filled with argon gas
(or argon/krypton gas) mixed with a small amount of
mercury vapor. When a suitable high voltage is applied
across the electrodes, an electric arc forms and the
resulting current ionizes the mercury vapor. The ionized
mercury emits ultraviolet radiation, which strikes and
excites the phosphor coating, causing it to glow and FL operation (Illustration source unknown)
produce visible light.
Characteristics
ˇ Has a medium luminance Lamp heater
ˇ Produces excess heat from filaments
ˇ Short lead time to lighting
ˇ The exact makeup of the phosphor coating determines the color
properties of a fluorescent lamp's light output. Fluorescent lamp
ˇ The intensity of illumination changes depending on the tube
temperature. fluorsnt.pcx
ˇ Uneven illumination at the ends of the tube requires shading
plates.
1 April 2001 Page 983
Standard Components Light Sources
Applications
Fluorescent lamps are suited for use in low-speed color copiers as well as medium-speed black and
white copiers. They are the most commonly used type of lamp in fax machines. However, the light
quantity changes depending on the tube temperature; and a lamp heater may be included to solve
this problem.
Some Ricoh machines use a variation of the fluorescent lamp, called the cold cathode fluorescent
lamp (sometimes called CFL or CCFL), as a quenching lamp or pre-transfer lamp. CFLs are also
sometimes used as the exposure lamp in image scanners.
1 April 2001 Page 984
Standard Components Light Sources
Xenon Lamps
A xenon lamp is a tube filled with xenon gas. When a voltage is applied across the lamp terminals,
the xenon gas ionizes and current flows through the gas, which emits light. The terminals do not
have to be preheated, unlike in fluorescent lamps.
There are different kinds of xenon lamp. The xenon lamps used in black and white digital machines
output a yellowish-green light with a peak at 543 nm. The xenon lamps used with color machines
utilize fluorescence as well as gas discharge to produce white light.
The xenon lamp
used in model A250
1 April 2001 Page 985
Standard Components Light Sources
Characteristics
ˇ Medium brightness light output
ˇ Less expensive than fluorescent or halogen lamps
ˇ Good durability--generally can be expected to last the life of the machine
ˇ Low heat output--exposure cavity cooling isn't required
ˇ More compact than fluorescent lamps
Applications
Xenon lamps can be used as exposure lamps for printers, lower speed copiers, fax machines, and
scanners.
Recently, xenon lamps have been increasingly used in digital products. This is mainly due to
improvements in the spectral sensitivity of CCDs, which allows use of the more economical xenon
lamp.
1 April 2001 Page 986
Standard Components Light Sources
Xenon Flash Lamp
The xenon flash lamps used in office
machines are basically the same as
the flash lamps used in photography--
only larger. A xenon flash lamp has
main electrodes at both ends of a gas
tube, which contains xenon (Xe) gas.
(Generally, any noble gas will work in a xenon.pcx
flash lamp. However, gases other than
xenon are rarely used.) The lamp also
has trigger electrodes, generally in the
form of a wire, or conductive coating in
the lamp tube wall.
The typical xenon flash lamp circuit consists of four parts: (1) power supply, (2) energy storage
capacitor, (3) trigger circuit, and (4) the flash lamp itself. It operates as follows:
ˇ The energy storage capacitor connected across the flash lamp is charged by the power supply.
(The energy storage capacity is quite large.)
ˇ A separate small capacitor is charged to generate a trigger pulse.
ˇ The charge on the trigger capacitor to is dumped into the primary of a pulse transformer whose
secondary is connected to the trigger electrodes. The pulse generated by this trigger is enough
to ionize the xenon gas inside the flash lamp.
1 April 2001 Page 987
Standard Components Light Sources
ˇ The resistance of the ionized xenon gas is very low and the energy storage capacitor
discharges through the flash lamp, which then emits a brilliant burst of light.
Characteristics
ˇ Produces an intense peak of radiant energy.
ˇ Since flash lamps use a high voltage, precautions must be taken against electric shocks.
Applications
Xenon flash lamps are suited for use in high-speed black-and-white copiers. They are also
occasionally used as the heat source for flash fusing.
1 April 2001 Page 988
Standard Components Light Sources
Neon Lamps
Like the cold cathode fluorescent lamp, a neon lamp uses a cold cathode to excite the atoms of a
gas in an enclosed tube. However, the light is emitted by the neon gas in the tube rather than by a
phosphorous coating inside the tube. The neon gas gives an orangish-red light.
Applications
In Ricoh products, neon lamps are used only as quenching lamps.
1 April 2001 Page 989
Standard Components Light Sources
LED Arrays
LED stands for light emitting diode. As the name
implies, an LED is a diode that emits light when a
small electric current passes through it. LEDs are
commonly used as display devices and indicators
(see the next section), but they can also be
mounted together in an array and used as a light
source.
Characteristics
ˇ LED arrays can be wired so that the LEDs can be
turned on/off in blocks to provide precise
illumination.
ˇ LED arrays are useful where compact components
are required.
Applications
In Ricoh products, LED arrays are used for document
exposure in small fax machines and scanners. They
are commonly used as quenching lamps in analog and
digital copiers. Also, most analog copiers use them for
erase lamps. The illustration to the right shows an LED
array [A] used as an erase lamp in a copier. [A]
1 April 2001 Page 990
Standard Components Semiconductor Components
Semiconductor Components
This section deals with components that are based on semiconductors.
Diodes _
+
Normal Diodes
A diode consists of a p-type semiconductor joined to an n-
type semiconductor. A diode only passes current in one Current
direction. If it is connected up as shown opposite, current
flow
will flow.
However, if the power source is connected up the opposite P N
way around, current will not flow.
Symbol:
1 April 2001 Page 991
Standard Components Semiconductor Components
Zener Diodes
A zener diode is connected the opposite way around
from a normal diode. Normal diodes cannot pass any
+
current if connected up in this way, and may be
destroyed. However, zener diodes connected in V VZ
reverse will pass current, if the voltage across the
diode exceeds a certain value, known as the
breakdown voltage. After the breakdown voltage has
been reached, the voltage across the diode will not Zener Diode
change much, even if the current is greatly increased.
Zener diodes can be used to make sure that the voltage at
a certain point in a circuit (Vz in the above-right diagram)
does not exceed a certain value. The diagram below right
is the typical diode characteristic curve. While normal
diodes should operate below the breakdown voltage and
may be damaged if it is exceeded, the zener diode is
intended to operate at that voltage.
1 April 2001 Page 992
Standard Components Semiconductor Components
Varistors
A varistor acts like two zener diodes connected back
to back. This means that it has positive and
negative breakdown voltages. A single zener diode
only has a negative breakdown voltage. Varistors L
are used in similar ways to zener diodes. They are Vac
also useful in protecting circuits against voltage
spikes. The example to the right shows a varistor
connected across a switch to eliminate sparking.
The illustration below right shows the characteristic
double-breakdown curve of the varistor.
1 April 2001 Page 993
Standard Components Semiconductor Components
Light Emitting Diodes
A light emitting diode (LED) is a kind of diode that emits +
_
photons (light particles) when a small electric current
passes through it. When current flows across the pn Current
flow
junction in diodes, energy is released in the form of P N
P
N
heat. However, the material used to make LEDs is
selected so that some of the energy is emitted as light.
Light emitting diodes have some special characteristics. Symbol:
They convert electrical current directly into light;
therefore, the LED is more efficient than many other
light sources. Also the light emitted by an LED has a
narrow wavelength range.
The LED is enclosed in a transparent case of epoxy
resin or plastic. The typical LED produces red or
infrared light; however, there are varieties to produce
many colors. Alternately, as shown in the illustration, a
colored case can be used to modify the light output.
LEDs can be used to form large displays and are often
the lighting elements in information displays used in
public places such as highways and airports. In office A small PCB with indicator LEDs on it.
machines, LEDs are used to light indicators on
operation panels, as indicator lights on circuit boards,
and in LED arrays.
1 April 2001 Page 994
Standard Components Semiconductor Components
Laser Diodes
Natural light is a mixture of light of different
wavelengths. However, a laser beam consists of
light at one wavelength, and the waves are all in
phase (the peaks and troughs in the waves all
coincide).
As the waves are all in phase, the light is very
intense (if peaks and troughs do not coincide, they
tend to cancel each other out, reducing the power
of the beam).
Natural light can be focused, but it cannot be
focused to so fine a point as laser light can. This P N
is because a lens at the same angle does not
refract the different components of natural light,
having different wavelengths.
To the right is a simplified diagram of a laser Current
diode. Laser diodes can be considered as similar flow
to LEDs in operating principle; current flowing
across the pn junction causes energy to be + _
emitted in the form of light. LEDs emit light in all
directions. However, the pn junction in laser
diodes has a mirror at each end, reflecting the
light back into the diode. When the current
1 April 2001 Page 995
Standard Components Semiconductor Components
passing through the diode reaches a threshold
value, the light reflected back into the junction
stimulates more atoms in that region to emit more
radiation of the same wavelength. Some of this
light passes out of the diode through one of the
mirrors, which is partially transparent. The light
beams emerge from the mirror parallel to each
other.
The wavelength of the laser depends on the Laser diode LD Unit
composition of the semiconductor material. The
lasers used in most printers emit red light.
Engineers are trying to develop lasers that emit
green or blue light; the shorter wavelengths of this For More Information
light would allow smaller dots to be written to the For a brief introduction to laser theory
photoconductor, leading to higher resolution and more information on laser diodes
printouts. we suggest you reference A Brief
Introduction to Laser Diodes at the
University of Washington web site
(http://www.ee.washington.edu/class/
ConsElec/Chapter6.html)*.
*We have no control over this web page. The content or
location may change at any time.
1 April 2001 Page 996
Standard Components Semiconductor Components
Transistors
Bipolar Junction Transistors
A bipolar junction transistor contains two junctions
between p and n type semiconductor, and three
electrodes (the collector, the base, and the NPN
emitter). The most common use of a transistor is Type
as a switch. They are also used in amplification
and rectification. There are two types of transistor:
the npn transistor, and the pnp transistor. The npn
transistor is the most commonly-used of these.
The diagrams to the right show the symbols for
both types of transistor, their construction, and the
direction of current flow. Notice that the batteries
in the pnp transistor circuit are connected up the
opposite way round from the npn transistor. PNP
Type
(Continued on next page.)
1 April 2001 Page 997
Standard Components Semiconductor Components
In the diagram on the right, an npn transistor is
controlling a lamp. A positive voltage is applied
between the collector and the emitter. The lamp
cannot switch on unless a voltage is also applied
between the base and the emitter.
1 April 2001 Page 998
Standard Components Semiconductor Components
Phototransistors
A phototransistor works like an ordinary bipolar
transistor, except that the transistor is switched on
by light shining on the base region of the
transistor. The diagram on the right shows an npn-
type phototransistor.
In office machines, phototransistors are used in
photointerrupters, optoisolators, and reflective
photosensors.
1 April 2001 Page 999
Standard Components Sensors and Switches
Sensors and Switches
Reflective Photosensors
Reflective photosensors are short range sensors that
have a light emitting element (usually an LED) and a
light sensitive element (usually a phototransistor).
Reflective photosensors work by bouncing light off of
an object.
There are two main types of reflective photosensor.
The simplest type signals the presence or absence
of an object or condition--the presence of paper, the
presence of a belt reference plate, the presence of a
cassette or cartridge. The illustration to the right is an
example. This type of sensor has a binary output; it
is either activated or deactivated.
The other type of reflective photosensor is used to
gather information about the surface being sensed. It
has a variable output that depends on the strength of
the light striking the light sensitive element. The
primary example is the image density sensor (or ID
sensor) used in copiers and other products.
1 April 2001 Page 1000
Standard Components Sensors and Switches
Characteristics
! Small, inexpensive, rugged
! Available in many different types (size, shape,
sensitivity, specifications).
Applications
Reflective photosensors are used for detecting
paper in the paper path, paper size detection,
master belt position detection, and a number of
other functions.
A reflective photosensor
1 April 2001 Page 1001
Standard Components Sensors and Switches
ID Sensor
Drum
The ID sensor is a special application of the
reflective photosensor. Two types of ID sensor are Direct Toner
used as part of the process control system in reflection
ID sensor
photocopiers.
One type is a direct reflection ID sensor. It is
positioned so that light from the LED reflects
directly to the detector. This is the commonly used LED
Detector
type of ID sensor.
The other type is a diffused reflection ID sensor.
In addition to the light reflected at a direct angle,
diffuse light reflects at all angles from the toner on
the drum. This sensor detects image density by Diffused
reflection Drum
receiving some of this diffused light. Using this
ID sensor Toner
type of sensor improves the measurement
accuracy of the sensor pattern densities--
particularly for yellow, cyan, and magenta toners.
Detector
LED Diffuse light
1 April 2001 Page 1002
Standard Components Sensors and Switches
Photointerrupters
A photointerrupter consists of an LED and a
phototransistor separated by a slot. The sensor
detects when something enters or leaves the slot,
such as an actuator, a part of the machine, or a
sheet of paper.
When there is no actuator in the slot, light from
the LED activates the phototransistor, and current
flows through it. However, if an actuator enters the
slot, light from the LED is blocked and current
cannot pass through the phototransistor.
Photointerrupters have a variety of uses in office
machines. They are commonly used as home
position detectors for moving parts such as lenses
and scanners and to detect paper as it moves
through the paper feed path. In machines such as
photocopiers that handle a variety of feed stock
photointerrupters are generally preferred over
reflective photosensors because photointerrupters
are not affected by the reflectivity of the paper.
Continued on next page.)
1 April 2001 Page 1003
Standard Components Sensors and Switches
Characteristics
! Small, inexpensive, rugged
! Available in many different
types (size, shape, sensitivity,
specifications).
Most photointerrupters that are used as paper detectors
use a "feeler" type plastic actuator. However, a photo-
interrupter is occasionally installed across a paper feed [A]
path, as shown above. This type of photointerrupter may
become dirty and will need cleaning periodically.
A photointerrupter [A] used as a home
position sensor. Notice the scanner drive
wire below the slot of the photointerrupter.
Photointerrupters: The one on the left has a
weight operated actuator built on it.
1 April 2001 Page 1004
Standard Components Sensors and Switches
CCDs Charge transfer
control signals
A CCD (Charge Coupled Device) is a
T1 T2 T3
semiconductor chip with light receiving elements
etched onto it. In a digital machine that scans
documents, the CCD is a row of these elements;
each element on the CCD corresponds to one Charge transfer circuits
pixel on one main scan line across the original. Output
The CCD also contains circuits for transferring the Light sensitive elements
accumulated charges out of the elements and into
the video processing circuits.
The diagram on the right shows a simplified cross-
section of a CCD element. When applying the
appropriate voltage across the element, any light
hitting the element liberates electrons from the
silicon at the boundary between the n and p type
semiconductors. Positive charges can flow out, but
an insulating layer traps the electrons, and gathers
them under the electrodes. The brighter the light _
shining on the element, the more electrons N
generated in that element.
P +
1 April 2001 Page 1005
Standard Components Sensors and Switches
After scanning a line, the charges trapped in
T1 = V1
each element must be moved out of the
CCD and into the video signal processing T2 = 0
circuits so that the next line can be T3 = 0
1 2 3 1 2 3
scanned. The diagram shows how this is
done. __ __
__ __
The diagram shows two adjacent elements.
Each element has three electrodes attached
to it. After scanning a line of data, the T1 = V1
electrons are under electrode 1, as shown T2 = V2
in the top diagram.
T3 = 0
1 2 3 1 2 3
A voltage V2, higher than V1, is then
applied to electrode 2. The electrons are
__ __ __ __
attracted to the area beneath electrode 2, _ _ __ _ _ __
as shown in the middle diagram.
Then, the voltage at electrode 1 switches off T1 = 0
and the voltage at electrode 2 is set to V1, T2 = V1
as shown in the bottom diagram. The
T3 = 0
electrons all gather under electrode 2. 1 2 3 1 2 3
By repeating the above procedure, but
__
__ __
__
using electrodes 2 and 3 instead of
electrodes 1 and 2, the electrons move to
1 April 2001 Page 1006
Standard Components Sensors and Switches
electrode 3. The result of this is that one element shifts all the charges along, and the element
charges at the end of the CCD shift out of the CCD. By continuing this process, all the charges shift
out of the CCD. The series of charges appears on the CCD output line as a serial analog video
signal. This signal passes to the video processing circuits, allowing the next line of the original to be
scanned.
1 April 2001 Page 1007
Standard Components Sensors and Switches
Contact Image Sensors (CIS)
The contact image sensor (CIS) is a compact
image reading assembly containing an LED array,
an array of self-focusing optic fibers (SELFOC),
and a strip of light detectors, such as
phototransistors. The CIS is used instead of the
CCD in the most compact of fax machines.
The illustration to the right (from model H545)
shows a typical CIS. Light from the LED array [A]
reflects off of the document, through a row of self-
focusing optic fibers [B], and onto a strip of
phototransistors [C]. The entire assembly is
located directly below the document, so a long
light path is not necessary. [B]
When using a fluorescent lamp/lens/CCD [A]
arrangement, the light path is typically about 300
to 500 mm. However, with a CIS, the light path
can be reduced to about 15 to 50 mm; with the
most recent types, the CIS is positioned less than [C]
0.1 mm from the surface of the document.
1 April 2001 Page 1008
Standard Components Sensors and Switches
Hall Effect Sensors
Hall effect sensors are used in some network
control units (NCU) of fax machines to detect line
current. The output of a Hall effect sensor is called
the Hall voltage. If a conductor [A] is placed in a
magnetic field [B], and current [C] flows through
this conductor perpendicularly to the magnetic
field, a Hall voltage (VH) is generated across the
conductor.
The conductive material in Hall effect sensors is
normally a semiconductor, as the Hall effect is too
small to measure accurately in metallic
conductors.
1 April 2001 Page 1009
Standard Components Sensors and Switches
Thermistors
A thermistor is a device that undergoes a very
large change of resistance with temperature. The
name is derived from thermally sensitive
resistor. Typically, a thermistor is made from a
semiconductor or sintered metal oxides.
Most types have a negative temperature
coefficient--that is, the resistance decreases as
the temperature increases. However, some
positive temperature coefficient varieties are also
available. The material can be formed into rods or
small beads, but for sensing purposes the small
bead shape is generally used in order to get the
fastest possible response.
[A]
Thermistors have a large variety of uses. In office
machines, they are used mainly to measure the
temperature at critical points--for example inside
fusing units or optic cavities.
Thermistors [A] used to measure the
temperature of fusing rollers (model G024)
1 April 2001 Page 1010
Standard Components Sensors and Switches
Microswitches
Microswitches are electromechanical devices,
which contain two contacts. They are modular,
inexpensive, resistant to dust and contamination
as well as metered. This means that any time the
actuator is depressed, the contacts of the switch
will close at the same point each time. These
switches have a characteristic sound or click when
the contacts close. The main advantage of a
microswitch is its durability and its consistency.
The "normally open"
terminal of this switch
has been removed so
that it cannot be
connected incorrectly.
FP = Free Postion
OT = Overtravel
OP = Operating Position
PT = Pretravel
RP = Release Position
MD = Movement Differential
OF = Operating Force
Above pictures courtesy of Zippy USA Inc.
1 April 2001 Page 1011
Standard Components Sensors and Switches
Reed Switches
Reed switches are magnetically operated
components with contacts hermetically sealed in a
glass capsule. Bringing a permanent magnet to
the switch or placing the switch in or near an
electromagnet causes the contact "reeds" to flex
and touch, completing the circuit. Either protective
inert gas or a vacuum within the capsule keeps
the contacts clean, protecting them for the life of
the device.
Due to their lack of mechanical parts, reed
switches are maintenance-free and remain
unaffected by temperature change, moisture,
chemicals, dust, abrasive fluids and other hostile
surroundings.
Features:
ˇ Reliable
ˇ Non-mechanical
ˇ Long operating life
ˇ Compact
ˇ Rugged
1 April 2001 Page 1012
Standard Components Sensors and Switches
Thermoswitches
As the name implies, a thermoswitch (also known as
thermal switch or thermostat) is a temperature
controlled switch.
Thermoswitches have contacts made of two
dissimilar metals molecularly bonded together.
These are called bi-metal contacts. The two metals
expand and contract at different rates with changes
in temperature. As the temperature rises the bi-metal
contacts start to flex, and at a certain temperature,
the contacts will open. At a lower, temperature, the
contacts will close again.
The difference between the opening and closing
A collection of thermoswitches.
temperature of a thermoswitch is the "hysterisis" or (Photo courtesy of Elmwood
"differential" of the device. Some thermoswitches, Sensors, Inc.)
such as those used in deep fat cookers or popcorn
Note: Thermoswitch and thermostat are often
machines, have a narrow hysterisis. However, In used interchangeably. In fact, thermostat is the
Ricoh products, thermoswitches are usually term used in our parts catalogs. However, here
overheating safety devices with a large hysterisis. we use thermoswitch to avoid confusion with
For example, the thermoswitch used in the 1st adjustable control devices such as room
scanner of model A257 opens at 140ēC but will not temperature thermostats.
close again until its temperature drops to -35ēC!
1 April 2001 Page 1013
Standard Components Clutches, Motors, And Solenoids
Clutches, Motors, And Solenoids
Clutches
Torque Limiter Clutches
In Ricoh products, torque limiter clutches are often
in reverse rollers of feed and reverse roller paper
feed mechanisms. In concept, torque limiter
clutches (also called slip clutches) are simple.
They transmit rotation to a drive component
(usually a roller, pulley, or gear mounted on a
rotating shaft). As long as the resistance to
rotation is less than the torque (twisting force)
limitation of the clutch, the roller turns with the
shaft. If the resistance exceeds the torque
limitation, the roller stops turning--it slips. In fact,
it may turn in the opposite direction if sufficient
counter force is applied.
Torque limiter structures vary: some use springs
as slip mechanism, while others use magnetic
force or powder filling. Compared to those that
use springs, torque limiters that use magnets
and/or powders do not need to be lubricated with
1 April 2001 Page 1014
Standard Components Clutches, Motors, And Solenoids
grease or other lubricants, so that they are easier
to maintain. In addition, the magnet-type torque
limiter does not generate much heat, even after
extended use, because it does not come in
contact with other components. Consequently, it
ensures stable torque. The torque limiter of the
model A112 reverse roller, shown on the previous
page, is a magnetic type.
Model A084 (magnet)
Here are some other examples of torque limiter
clutches: Outer Inner
magnet Casing magnet
The clutch used in Model A084, illustrated to the
right, uses two coupled magnetic type clutches.
(Two coupled clutches have a stronger total
torque than a single clutch.)
Continued on the next page.
Drive Rotor
shaft
1 April 2001 Page 1015
Standard Components Clutches, Motors, And Solenoids
Model A133 uses a magnet and ferrite powder Model A133 (magnet + ferrite powder)
type slip clutch.
Magnetic
ring Output
hub
Input
Ferrite
hub
powder
Ferrite
ring
1 April 2001 Page 1016
Standard Components Clutches, Motors, And Solenoids
Electromagnetic Clutches
[E] [F]
The illustration to the right diagrams the basic
parts of an electromagnetic clutch. Gear [A] is [D]
[A] [B]
driven by a motor. This gear is an idle gear; it
does not drive the roller shaft [B]. Shaft [B] is
attached to the rotatable part [C] of the clutch, and
held in place by an E-ring [D].
When the clutch is switched on, current flows
through the coil [E]. The magnetic field generated
by this coil attracts plate [F], which is connected to [C]
gear [A]. The motor is still turning gear [A], and
when plate [F] comes into contact with the rotating
part of the clutch [C], the roller shaft begins to
turn.
A typical application is shown to the right, where a
clutch [A] switches on to connect shaft [B] to the
drive from motor [C].
Continued on the next page.
1 April 2001 Page 1017
Standard Components Clutches, Motors, And Solenoids
An electromagnetic clutch requires + 24 or + 12
volts to drive it, but a CPU cannot output this high
a voltage, so the CPU controls the clutch through
a driver. When the clutch is off, the driver is
holding the control signal to the clutch high,
preventing current from going to ground. When
the CPU drops the control signal low, + 24V flows
through the coils in the clutch, and through the
driver to ground.
1 April 2001 Page 1018
Standard Components Clutches, Motors, And Solenoids
Spring Clutch Spring Sleeve
A spring clutch is purely mechanical clutch. It is a tail projection
simple device that consists of two separate pieces fitted
inside a coiled spring. One piece called the drive hub,
supplies rotation from a motor. The other piece, called
the output hub, delivers the rotation of the drive hub to
a shaft. Under normal circumstances, the spring grips
both pieces very tightly, so they function as one unit Output
Drive Hub
and pass on the rotation from the motor. The clutch's Hub
release mechanism is a sleeve that surrounds the Sleeve
spring. The sleeve is attached to one end of the
spring--the clutch spring tail. The other end of the
spring is engaged with the output hub. When the sleeve
is kept from turning, the spring expands away from the
drive hub, disengaging the drive.
The sleeve of a spring clutch either has a ratchet
surface for a pawl to engage with or one or more
projections for a stopper to engage with.
Typically, spring clutches are engaged and disengaged
by some kind of electronic control--usually a solenoid.
1 April 2001 Page 1019
Standard Components Clutches, Motors, And Solenoids
Magnetic Spring Clutch
A magnetic spring clutch is a hybrid of the
electromagnetic clutch and the spring clutch.
Unlike the normal spring clutch, the spring is loose
while idling. When the electric coil is energized, it
causes the spring to tighten around the output
element.
1 April 2001 Page 1020
Standard Components Clutches, Motors, And Solenoids
DC Motors
Electric motors are based on the following two
observations:
ˇ When current flows along a wire, a magnetic
field develops about that wire.
ˇ When two magnetic fields are close to each
other, an attractive or a repulsive force is felt.
So, if a wire carrying current is placed in a
magnetic field, a magnetic field develops around
the wire, and a force is exerted on the wire. The
force is strongest if the wire is at 90° to the
magnetic field. The force is also at 90° to the wire.
If there is no angle between the wire and the field,
there is no force. This is summarized in the
diagram opposite; the wire would be forced
directly upwards, away from the plane of the
paper.
If a loop of wire is placed in a magnetic field, the
current direction is opposite on each side of the
loop. This means that one side has an upward
force on it, and the other side has a downward
1 April 2001 Page 1021
Standard Components Clutches, Motors, And Solenoids
force on it. This causes the loop to rotate, as
shown opposite.
The part of the motor containing the loop of wire is
called the armature. It is normally in the form of a
drum, with many loops of wire wound around it for
increased motor power.
The armature is connected to the drive current by
a split metal ring called the commutator, and a
pair of brushes made from a low-resistance
material such as graphite.
Each segment of the commutator is insulated from
the other. The commutator is split in a dc motor so
that the polarity of the current flowing through the
loop is reversed every 180° of rotation. This allows
the rotation of the coil to continue; if there were no
reversal of current, the coil would not rotate
constantly.
1 April 2001 Page 1022
Standard Components Clutches, Motors, And Solenoids
Brushless DC Motors
In the dc motor described above, the magnet is
stationary while the coil rotates. In the brushless
dc motor, the coil is stationary and the magnet
moves.
In a typical example, nine coils are attached to the
motor drive board, arranged in a circle around the
shaft. A circular magnet, com-posed of eight
alternating north and south polarized segments,
fits around the outside of these coils. The magnet
is bonded to a metal cover, which is bolted to the
motor shaft.
As shown in the diagram, the coils are wired up so
that there are three north poles, three south poles,
and three neutral positions around the center. To
rotate the magnet, the motor drive board switches
the positions of the poles in such a way that the
magnet is always pulled around in the same
direction.
Ricoh products primarily use two types of
brushless dc motors--servomotors and stepper
motors.
1 April 2001 Page 1023
Standard Components Clutches, Motors, And Solenoids
Servomotors
Servomotors use feedback to maintain a constant
rotating speed. To check that a dc servomotor is
running at the correct speed, the drive board
contains a circuit known as a phase-locked loop.
An oscillator generates a reference frequency.
The circuit board contains a detector that converts
the motor's rotation into another frequency signal.
The phase detector compares both signals; a
feedback signal is sent to the motor drive board to
adjust the motor speed until it reaches the correct
value. When the motor is at the correct speed, the
two frequencies are the same.
Rotor Stator
A servomotor mounted on its controller board. The same motor disassembled to show stator
and rotor.
1 April 2001 Page 1024
Standard Components Clutches, Motors, And Solenoids
Stepper Motors
Stepper motors are used whenever accurate
positioning of a component is required.
The outer shell of the motor is stationary. Coils are
wound around teeth attached to this shell. The
core of the motor, made of iron, can rotate. The
arrangement of the teeth is such that, if pulses are
applied to the coils in the correct timing sequence,
the core of the motor can be rotated in stepwise
increments of a few degrees.
In the example shown here, when phase 1 is
energized, two of the teeth on the motor core will
align with the coils on the outer shell, but the other
four teeth will be out of alignment. Then, if phase
2 is energized, the core rotates by 15 ° to align
two of the other teeth. If phases 1, 2, 3, and 4 are
energized in sequence continuously, the motor will
drive the shaft in increments of 15 °. The order of
activating the coils can be varied to give different
effects, such as reverse motion, or coarser steps.
1 April 2001 Page 1025
Standard Components Clutches, Motors, And Solenoids
The stator
A typical stepper
motor
The Rotor
1 April 2001 Page 1026
Standard Components Clutches, Motors, And Solenoids
Solenoids
The solenoid is one of the oldest, simplest and
most commonly used electromagnetic devices. It
consists of a hollow electromagnet (coil) and a Plunger
movable plunger that fits inside. When an electric
current energizes the coil, it creates an electro-
magnetic force around the coil. This force causes
the plunger to move into the coil. The picture to
the right shows a disassembled solenoid. Coil
The amount of force created by a solenoid is in
direct proportion to the amount of current applied.
Some other factors, such as the number of turns
in the coil, the magnetic character of the steel, Direction of motion
and the stroke of the solenoid affect the amount of
force produced.
The solenoid drive circuit is similar to the drive
circuit for and electromagnetic clutch as explained
on an earlier page.
Continued on the next page. Coil Plunger
1 April 2001 Page 1027
Standard Components Other Electrical Components
A typical application is shown to the right, where
the solenoid's plunger is activating a mechanical
paper feed mechanism. A pawl [A] is gripping the
ratchet sleeve of a spring clutch [B], preventing
motor drive from reaching the feed rollers [C].
When the solenoid [D] turns on, the plunger pulls
the pawl away from the ratchet sleeve, and the [B]
rollers start to rotate.
[C]
For More Information [D]
For more information on solenoid theory,
operation, and design, we suggest you [A]
reference What is a Solenoid at the web
site of the Detroit Coil Company.
(http://www.detroitcoil.com/whatis.htm)*.
*We have no control over this web page. The content or
location may change at any time.
1 April 2001 Page 1028
Standard Components Other Electrical Components
Other Electrical Components
Thermal Heads
Operation
The thermal head is the central component of the thermal printer. A thermal head consists of a row
of heating elements. If a heating element is turned on, it will heat up. The heat from the element will
make a dot on the thermosensitive printer paper.
Roughly speaking, each element on the thermal head reproduces what was scanned by the
corresponding element of the CCD at the transmitter.
There are 8 heating elements for each mm across the thermal head. A4 [8.5"] thermal heads have
1728 elements, B4 [10.1"] thermal heads have 2048 elements, and A3 [11.7"] thermal heads have
2368 elements.
Basically, the CPU clocks a line of data into a shift register in the thermal head. When the line is
complete, the CPU sends a latch signal, then prints the line. Then the paper is fed forward one line,
and the next line is printed in the same way.
When printing a line, the CPU divides the line into 4 blocks. It prints the blocks one at a time. Each of
these blocks is transferred to the printing elements using a strobe signal. Each block has a separate
strobe signal.
1 April 2001 Page 1029
Standard Components Other Electrical Components
The blocks are usually adjacent on the thermal
head, but they do not have to be. In fact it is
even possible to interleave the blocks, having
an element from block 0 next to an element
from block 1, then one from block 2, followed by
one from block 3, then back to block 0 again,
and so on across the thermal head.
Data, latch, and strobe signals reach a decoder
in the thermal head from the CPU. The + 24VD
supply comes directly from the power supply; it
is a separate channel from the + 24VD supply
used by the rest of the machine.
Serial data comes from the CPU on pin A (see
the diagram on the previous page). In most
models, for a black dot, A is high. The data is
clocked into the shift registers (the clock is on
pin B).
When a line of data has been fed to the shift
registers, the CPU sends a latch pulse (pin C)
and the data moves into the latches.
To print the line of data, the CPU sends strobe
signals to the thermal head. First, the strobe
signal for block 0 (pin D goes low) is sent to
1 April 2001 Page 1030
Standard Components Other Electrical Components
block 0, and the data in the block 0 elements passes from the latch to the heating elements (for a
black dot, the element is heated). After all elements for block 0 have been printed, pin D goes high
again. Then blocks 1 (pin E), 2 (pin F), and 3 (pin G) are sent in sequence, in the same way as block
0.
The duration of the strobe pulse determines how much an element is heated to make a black dot.
The CPU monitors the thermistor on the thermal head (see section 3-5-4). The CPU calculates the
strobe pulse width based on the thermistor reading and on the value for the pulse width entered
using service mode when the head was installed.
NOTE: In most models, the pulse width must be programmed using a service function
after installing a new thermal head or system RAM board (called the MBU in
most fax models). In a few models, the pulse width is programmed
automatically.
1 April 2001 Page 1031
Standard Components Other Electrical Components
1728 Heating Elements
Internal Structure Block 0 Block 1 Block 2 Block 3
The internal structure of the thermal head varies
from model to model. However, two basic types
have been used so far. These are the discrete-
element control type and the block control type.
In a thermal head using discrete-element control,
each element has its own discrete clock, latch,
and switching circuits. Each element also receives
the strobe signal.
CPU
FCU
24V
Heating Element
Circuit Element
Latch
Shift Register
STROBE LATCH DATA CLOCK
1 April 2001 Page 1032
Standard Components Other Electrical Components
In a block control type thermal head, driver ICs 1728 Heating Elements (27 driver ICs, 64 elements/driver IC) 24V
control a group of elements. For example, one
driver IC may control 64 elements. The decoder Block 0
7 Driver
Block 1
7 Driver
Block 2
7 Driver
Block 3
6 Driver
sends a clock, latch, and strobe signal to each ICs ICs ICs ICs
driver IC. Each driver IC contains shift register,
latch, and switching circuits for the elements that it
controls.
A good thermal head will have a conductive cover
that is grounded to prevent build-up of static,
which would damage the driver ICs inside the
thermal head.
CPU
FCU
Driver IC
STROBE
64 Heating Elements
LATCH
Latch
DATA CLOCK
Shift Register
1 April 2001 Page 1033
Standard Components Other Electrical Components
LCDs
LCD is an abbreviation for Liquid Crystal Display. An
LCD is a digital display that consists of two sheets of
glass separated by hermetically sealed liquid crystal
material. The liquid crystal is normally transparent.
The outer surface of each glass sheet has a
transparent conductive coating, forming front and
back electrodes. On the viewing side, the conductive
coating is arranged as either a matrix of dots (for
example for a computer display) or character forming
segments (for example the 7-segment display
elements of a calculator). Leads at the edge of the
display attach to the segments or the lines of the
matrix. A voltage applied between the front and back
electrodes, causes the liquid crystal molecules to
change alignment and thus become reflective. The
reflectivity of the liquid crystal segments can vary
depending on the amount of voltage applied.
Some LCDs depend on the reflection of ambient light
for viewing. However, most larger displays use a
backlight. The illustrations to the right show LCD
displays used on model A201 (upper picture) and
model A246 (lower picture).
1 April 2001 Page 1034
Standard Components Other Electrical Components
Characteristics
ˇ Lightweight and thin construction
ˇ Not naturally radiant, a light source is required.
ˇ More expensive than CRTs (Still true ... but prices are dropping.)
Applications
LCDs are used as display screens.
For More Information
For more information on LCD theory, operation, and design, we
suggest you reference the following web pages:
LCD Frequently Asked Questions.
(http://margo.student.utwente.nl/el/misc/lcd_faq.htm)*
Liquid Crystal And Other Non Emissive Displays
(http://itri.loyola.edu/displays/c3_s1.htm)*
*We have no control over these web pages. The content or location may change at any time.
1 April 2001 Page 1035
Standard Components Consumables
Consumables
Photoconductors
The photoconductor--a photoconductive drum or belt is the heart of most imaging processes. The
photoconductor's surface is where the latent image is formed and then developed. Photoconductors
have the following characteristics:
ˇ They are able to accept a high negative electrical charge in the dark. (The electrical resistance
of a photo-conductor is high in the absence of light)
ˇ The electrical charge dissipates when the photoconductor is exposed to light. (Exposure to
light greatly increases the conductivity of a photoconductor.)
ˇ The amount of charge dissipation is in direct proportion to the intensity of the light. That is,
where stronger light is directed to the photo-conductor surface, a smaller voltage remains.
Our products use two types of photoconductors. One type is a selenium based inorganic
photoconductor. That type was used in the past for analog copiers. The other type is an organic
photoconductor (OPC) that is used for analog and digital copiers, plain paper facsimiles, and laser
printers. Recently, all such products use OPCs instead of inorganic photoconductors.
1 April 2001 Page 1036
Standard Components Consumables
Organic Photoconductors (OPC)
An OPC consists of a CTL (charge transfer layer), Cross section of OPC layer
CGL (charge generation layer), electrode layer,
and a substrate to which the layers are bonded. Charge transfer layer
(The electrode layer is also called the under
layer.)
Charge generation layer
Ricoh made OPCs have charge generation
pigments and charge transfer compounds
Electrode
imbedded in the charge generation layer. These
materials greatly improve the response
characteristics of the OPC.