STEPPER MOTOR
Frame 1: The top electromagnet (1) is turned on, attracting the nearest teeth of the gear-shaped iron
rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from right electromagnet (2).
Frame 2: The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the
teeth into alignment with it. This results in a rotation of 3.6" in this example.
Frame 3: The bottom electromagnet (3)'is energized; another 3.6" rotation occurs.
Frame 4: The left electromagnet (4) is energized, rotating again by 3.6". When the top electromagnet (1)
is again enabled, the rotor will have rotated by one tooth position; since there are 25 teeth, it will take 100
steps to make a full rotation in this example.
A stepper motor (or step motor) is a brushless DC electric motor that divides a full rotation into a number of
equal steps. The motor's position can then be commanded to move and hold at one of these steps without any
feedback sensor (an open-loop controller), as long as the motor is carefully sized to the application.
Switched reluctance motors are very large stepping motors with a reduced pole count, and generally are
closed-loop commutated.
Fundamentals of operation
DC brush motors rotate continuously when voltage is applied to their terminals. Stepper motors, on the other
hand, effectively have multiple "toothed" electromagnets arranged around a central gear-shaped piece of iron.
The electromagnets are energized by an external control circuit, such as a microcontroller. To make the motor
shaft turn, first, one electromagnet is given power, which magnetically attracts the gear's teeth. When the
gear's teeth are aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when
the next electromagnet is turned on and the first is turned.off, the gear rotates slightly to align with the next one,
and from there the process is repeated. Each of those rotations is called a "step", with an integer number of
steps making a full rotation. In that way, the motor can be turned by a precise angle.
There are four main types of stepper motors
1. Permanent maanet stepper (can be subdivided into 'tin-can' and 'hybrid', tin-can being a cheaper
product, and hybrid with higher quality bearings, smaller step angle, higher power density)
2. Hvbrid svnchronous stepper
3. Variable reluctance stepper
4. Lavet t v ~ este ppina motor
5.
Permanent magnet motors use a permanent magnet (PM) in the rotor and operate on the attraction or
repulsion between the rotor PM and the stator electromagnets. Variable reluctance (VR) motors have a plain
iron rotor and operate based on the principle that minimum reluctance occurs with minimum gap, hence the
rotor points are attracted toward the stator magnet poles. Hybrid stepper motors are named because they use
a combination of PM and VR techniques to achieve maximum power in a small package size.
Two-phase stepper motors
There are two basic winding arrangements for the electromagnetic coils in a two phase stepper motor: bipolar
and unipolar.
Unipolar motors
A unipolar stepper motor has one winding with center tap per phase. Each section of windings is switched on
for each direction of magnetic field. Since in this arrangement a magnetic pole can be reversed without
switching the direction of current, the commutation circuit can be made very simple (e.g., a single transistor) for
each winding. Typically, given a phase, the center tap of each winding is made common: giving three leads per
phase and six leads for a typical two phase motor. Often, these two phase commons are internally joined, so
the motor has only five leads.
A microcontroller or stepper motor controller can be used to activate the drive transistors in the right order, and
this ease of operation makes unipolar motors popular with hobbyists; they are probably the cheapest way to get
precise angular movements.
(For the experimenter, the windings can be identified by touching the terminal wires together in PM motors. If
the terminals of a coil are connected, the shaft becomes harder to turn. one way to distinguish the center tap
(common wire) from a coil-end wire is by measuring the resistance. Resistance between common wire and coilend
wire is always half of what it is between coil-end and coil-end wires. Thisis because there is twice the
length of coil between the ends and only half from center (common wire) to the end.) A quick way to determine
if the stepper motor is working is to short circuit every two pairs and try turning the shaft, whenever a higher
than normal resistance is felt, it indicates that the circuit to the particular winding is closed and that the phase is
working.
Bipolar motors
Bipolar motors have a single winding per phase. The current in a winding needs to be reversed in order to
reverse a magnetic pole, so the driving circuit must be more complicated, typically with an &
bridae arrangement (however there are several off-the-shelf driver chips available to make this a simple affair).
There are two leads per phase, none are common.
Static friction effects using an H-bridge have been observed with certain drive topologies;18g
Dithering the stepper signal at a higher frequency than the motor can respond to will reduce this "static friction"
effect.
Because windings are better utilized, they are more powerful than a unipolar motor of the same weight. This is
due to the physical space occupied by the windings. A unipolar motor has twice the amount of wire in the same
space, but only half used at any point in time, hence is 50% efficient (or approximately 70% of the torque output
available). Though a bipolar stepper motor is more complicated to drive, the abundance of driver chips means
this is much less difficult to achieve.
Theory
A step motor can be viewed as a synchronous AC motor with the number of poles (on both rotor and stator)
increased, taking care that they have no common denominator. Additionally, Soft magnetic material with many
teeth on the rotor and stator cheaply multiplies the number of poles (reluctance motor). Modern steppers are of
hybrid design, having both permanent magnets and soft iron cores.
To achieve full rated torque, the coils in a stepper motor must reach their full rated current during each step.
Winding inductance and reverse EMF generated by a mov,ing rotor tend to resist changes in drive current, so
that as the motor speeds up, less and less time is spent at full current - thus reducing motor torque. As
speeds further increase, the current will not reach the rated value, and eventually the motor will cease to
produce torque.
FOUR BAR LINKAGE
A four-bar linkage is the simplest movable closed chain linkaae. It consists of four bodies, called bars or
links, connected in a loop by four joints. Generally, the joints are configured so the links move in parallel
planes, and the assembly is called a planar four-bar linkage.
If the linkage has four hinged joints with axes angled to intersect in a single point, then the links move on
concentric spheres and the assembly is called a spherical four-barlinkage. Bennett's linkage is a spatial
four-bar linkage with hinged joints that have their axes angled in a particular way that makes the system
movable.
Planar four-bar linkages are important mechanisms found in machines. The kinematics and dvnamics of
planar four-bar linkages are important topics in mechanical enqineerinq.
Planar four-bar linkages are constructed from four links connected in a loop by four one deqree of
freedom joints. A joint may be either a revolute that is a hinged joint, denoted by R, or a prismatic, as
sliding joint, denoted by P. The planar quadrilateral linkage is formed by four links and four revolute m, denoted RRRR. The slider-crank linkage is constructed from four links connected by three revolute
and one prismatic ioint, or RRRP. The double slider is a PRRP linkage.
Planar four-bar linkages can be designed to guide a wide variety of movements.
Planar quadrilateral links
Planar quadrilateral linkage, RRRR or 4R linkages have four rotating joints. One link of the chain is
usually fixed, and is called the ground link, fixed link, or the frame. The two links connected to the frame
are called the grounded links and are generally the input and output links of the system, sometimes called
the input link and output link. The last link is the floating link, which is also called a coupler or connecting
rod because it connects an input to the output.
Assuming the frame is horizontal there are four possibilities for the input and output links
A crank: can rotate a full 360 degrees
A rocker: can rotate through a limited range of angles which does not include 0" or 180"
A 0-rocker: can rotate through a limited range of angles which includes 0" but not 180"
A n-rocker: can rotate'through a lim'ited range of angles which includes 180" but not 0"
FOUR BAR LINKAGE
Some authors do not distinguish between the types of rocker.
Grashof condition
The Grashof condition for a four-bar linkage states: If the sum of the shortest and longest link of a planar
quadrilateral linkage is less than or equal to the sum of the remaining two links, then the shortest link can
rotate fully with respect to a neighboring link. In other words, the condition is satisfied
if S+L S P+Q where S is the shortest link, L is the longest, and P and Q are the other links.
Classification
The movement of a quadrilateral linkage can be classified into eight cases based on the dimensions of its
four links. Let a, b, g and h denote the lengths of the input crank, the output crank, the ground link and
floating link, respectively. Then, we can construct the three terms:
TI = g + h - a - b , T 2 = b + g - a - h , T a = b + h - a - - g .
The movement of a quadrilateral linkage can be classified into eight types based on the positive and
negative values for these three terms, TI, T2, and TS .
/+ I + I+ l~rashof / crank / Rocker
i I I
Non-Gras hof
""_ .-"
FOUR BAR LINKAGE
r . 3 !+ 1 - i+ I Non-Grashof a n-Rocker 1 1 i 1 0-Rocker 1
I.. . " 4-. ...... .$ ... ... . . . . ..... . . .
i I i i . ! I
The cases of TI= 0, T2=0, and T3=0 are interesting because the linkages fold. If we distinguish folding
quadrilateral linkage, then there are 27 different cases.'
The figure shows examples of the various cases for a planar quadrilateral linkage
i
',* , % 1
hrU rrvoluuw m - l z n k ~k~ Dwblrmdrrr %allrla$rm Lm*glr
w 1mks .+r. p+q S+I < p+q I*IIF+~ *+I -p*q
(oonunuarr -on) (uml~nuown ww) Inaarntlnuw nw-8 (arnln~uuusd o n )
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Types of four-bar linkages, s = shortest link, I ='longest link '
The configuration of a quadrilateral linkage may be classified into three types: convex, concave, and
crossing. In the convex and concave cases no two links cross over each other. In the crossing linkage
two links cross over each other. In the convex case all four internal angles are less than 180 degrees, and
in the concave configuration one internal angle is greater than 180 degrees. There exists a simple
geometrical relationship between the lengths of the two diagonals of the quadrilateral. For convex and
crossing linkages, the length of one diagonal increases if and only if the other decreases. On the other
hand, for non convex non-crossing linkages, the opposite is the case; one diagonal increases if and only
if the other also increases
FOUR BAR LINKAGE
Design of four bar mechanism
The synthesis- or design, of four bar mechanisms is important when aiming to produce a desired output
motion for a specific input motion. In order to maximize cost and efficiency, a designer will choose the
simplest mechanism possible to accomplish the desired motion. When selecting a mechanism type to be
designed, link lengths must be determined by a process called dimensional synthesis. Dimensional
synthesis methodoloclv which in certain circumstances can be an inefficient process; however, in unique
scenarios, exact and detailed procedures to design an accurate mechanism .
Examples of symmetrical motion mechanisms include:
Windshield wipers
Engine mechanisms or pistons
~utomobilew indow crank
Other applications require that the mechanism-to-be-designed has a faster average speed in
one direction than the other. This category of mechanism is most desired for design when
work is only required to operate in one direction. The speed at which this one stroke
operates is also very important in certain machine applications. In general, the return and
work-non-intensive stroke should be accomplished as fast as possible. This is so the
majority of time in each cycle is allotted for the work-intensive stroke. These quickreturn
mechanisms are often referred to as offset
FIELD OF THE INVENTION
The present invention relates to track sun position in a day in any place
on earth.
BACKGROUND OF THE INVENTION
A solar tracker is a device for orienting one or more solar panels
according to the sun, for example, photovoltaic panels. Tracking can
substantially improve the amount of power produced by a solar energy
system. Compared to the photovoltaic solar panels, trackers can be
relatively inexpensive. This makes trackers particularly advantageous
for photovoltaic systems using high-efficiency panels. The required
accuracy of the solar tracker depends on the application.
Photovoltaic devices are a leading technology to convert solar energy
into electricity. Technologically, photovoltaic power systems are
capable of providing energy for any purpose, their main drawback
being cost and efficiency. The sun's position in the sky varies both with
the seasons (elevation) and time of day as the sun. moves across the
sky. Solar powered equipment works best when pointed directly or
nearly directly toward the sun. Thus, a solar tracker can increase the
effectiveness of such equipment over a fixed position panel, and at a
relatively low cost.
Four bar linkages are leading technology to provide motion in any
direction they are designed according to motions like ( double crank,
double rocker, crank rocker ) according to GRASHOFF'S LAW in class-1
and class-11 .
In this tracker first four bar and second four bar linkage produced
double crank mechanism. And their lengths are calculated by
FREUDENSTEIN'S EQUATION.
Current tracker devices are usually built as a sail with mechanical
systems activated by electrical motor actuators. For economical
reasons this tracking device are small in size to allow panel to move
.This may prevent harm by various problems like wind effect, adverse
landscape impact and mechanical and installation problems.
In large plants mounting panels used have to withstand considerable
force even at low wind velocities due to the sail effect created by the
large area of mounted panels.
In large production for any plant it matters in which state or place we
make a plant so according to sun position linkages are designed and
which have same design so transportation does not face any problem.
Recently, as the cost of fossil fuel has increased and the adverse effect
of fossil energy is clear, the market for solar energy systems has
increased dramatically. In addition, other characteristics such as
reliability, simplicity, low maintenance and freedom from pollution
have increased their popularity even further.
Concentrators equipped with solar cells are still an evolving technology
for increasing efficiency of collection but are not yet mature due the
high cost involved in building efficient collectors and trackers.
SUMMARY OF THE INVENTION
The present invention relates to a mechanical approach for tracking the
sun where solar panel is moved along with four bar linkages by both
motors.
The focus of the invention is to provide a device having cost effective
tracking elements to efficiently track the sun and increase the energy
that can be converted into electricity. The invention is a simple and
reliable system powered by relatively small electric motors for efficient
radiation conversion using significantly less electrical power and fewer
motors. The present tracker device lowers the overall system cost by
reducing the number of motors in the system and optimizing the
position of moving panels..
The present invention addresses the problems of high cost of solar
trackers by activating several panels with one motor for each panel
moving along its approximate center of mass, thus, in its optimal
position.
It is an object of this invention to provide a solar tracker with
improvements in terms of cost, complexity, limited angle, large
dimensions, wind sensitivity and so on.
In accordance with embodiments of one aspect of the present
invention there is provided a linkage mechanism as defined in for
tracking the sun comprising: a singuilarity of photovoltaic panel
connected by both four bar linkages arranged in three dimensional
motion in morning as sun rise both motor runs both four bar linkages
they move solar panel according to sun, and plate face always normal
to sun's rays in a day when sun sets both linkages move panel towards
east direction for sun rise for next day .
BRIEF DESCRIPTION OF THE DRAWINGS
*The present invention will be understood and appreciated
more fully from the following detailed description-taken in conjunction
with the appended drawings in which:
FIG. 1 is a schematic layout of an embodiment of the present tracking
device; and
FIG. 2 is a mechanism of double crank while moving.
The following detailed description of embodiments of the invention
refers to the accompanying drawings referred to above. Dimensions of
components and features shown in the figures are chosen for
convenience or clarity of presentation and are not necessarily shown to
scale. Wherever possible, the same reference numbers will be used
throughout the drawings and the following description to refer to the
same parts.
DETAILED DESCRIPTION OF THE INVENTION
Illustrative embodiments of the invention are described below. In the
interest of clarity, not all features of an actual implementation are
necessarily described.
FIG. 1 shows a schematic layout of an embodiment of the present
tracking device having panel 201. panel 201 is connected by both four
bar linkages through joints by first four bar linkage arms in 202 and 203
. first four bar linkage input and output arms are 204 and 205, input
arm 204 is connect with motor 206 . this motor 206 runs first four bar
linkages arms and they move panel in Z direction it track sun Z
direction.
Similarly panel 201 is connected by second four bar linkage arms
through joints in 302 and 303 .second four bar linkage input and output
arms are 304 and 305, input arm 304 is connect with motor 306, this
motor 306 runs second four bar linkage arms and th'ey move panel in X
direction with increasing heights of sun to tract sun elevation and
depression . Motors 206 and 306 are active by indexers and drivers.
FIG. 2 is a mechanism of double crank while working.
In this tracker linkages are designed according to places because sun
trajectory is different for different places linkages are designed
according to places and in four bar linkages designing FREUDENSTEIN'S
EQUATION is used which is : - klcos(phi) + k2cos(theta) + k3 =
cos(theta-phi)
Where, k l = d/a , k2 = -d/c, k3 = (a)2 - (b)2 + (c)2 + (d)2 / 2ac
: in which a is length of input link,
b is coupler link length
c is output link length
d is fixed link length
where (theta) is input angle
and (phi) is output angle.
After finding lengths check GRASHOF'S LAW
Where a + d < b +c show class 1 mechanism
In which d is fixed, a is input, b is coupler, c is output link p,
This show DOUBLE CRANK mechanism where a and c shows double
crank.
M is the panel's mass.
It should be understood that the above description is designing four bar
linkages according to sun trajectory which is different for different
places.
MERITS OF INVENTION
I. This invention is low in cost, light in weight & small in
size.
2. In this SOLAR TRACKER electricity produced very good
because solar panel moves ( with respect to ) sun or it's
plate always perpendicular or normal to sun's rays in a
day in any place.
3. In this we produced electricity in very good amount in
those places where electric crisis occur.
4. Installation of plant is easily because every plate
attached with linkages and they take less space for
installing.
5. Installing as a plant may prevent harm by various
problems like wind effect, adverse landscape impact
and mechanical & installation problem .

1. A solar tracker device for tracking the sun comprising:
a panel which is move according to sun in a day from east to west viasouth
and in night it travel from west to east .
in this mechanism panel is connect directly with two four bar linkages
in coupler positions and both are designed according to sun position in
a day using FREUDENSTEIN'S EQUATION.
both four bar linkages connected by a motor.
Both motors runs simultaneously to moves four bar linkages to panel to
provide three dimensional motion to panel .
Panel moves parallel to sun or sun' rays always normal to panel plate
rs mcontrol the first and second motors to
i n K Q ~
2. The device according to claim 1, wherein the center of gravity of the
panel is close to the linkages.
3. The device according to claim 1, wherein the two four bar linkages
are arranged in a manner to provide three dimensional motion to panel
and they are run by motors by electrical means according to sun
positions which are changed according to seasons.
FlELD OF THE INVENTION
The present invention relates to track sun position in a day in any place
on earth.
BACKGROUND OF THE INVENTION
A solar tracker is a device for orienting one or more solar panels
according to the sun, for example, photovoltaic panels. Tracking can
substantially improve the amount of power produced by a solar energy
system. Compared to the photovoltaic solar panels, trackers can be
relatively inexpensive. This makes trackers particularly advantageous