FASEP Presents

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FASEPPresents

• How Toe is measured on the FASEP wheel alignment
  system

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Some customers are wondering about the "magic"
way FASEP alignment system measures toe without
any cross toe measuring arm. The fact is indeed
quite simple when you think to the way an angle
can be measured on a plane you can measure it
referring to x-axis (horizontal, or across the
car) or y-axis (vertical, or along the car). So
now please give us few seconds to explain how
FASEP (and actually many other manufacturers)
measures toe on a car. In the end, what you are
supposed to do is to align the car to its travel
direction something you may not have done so
far.
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• We will discuss 4 different situations
• The ideal case Rectangle shape chassis, 0 toe.
• A little more complicated Rectangle shape, toe
  is not null.
• Trapezoid shaped chassis, toe is not null.
• And Measuring along the "y-axis".

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The ideal case a rectangle shaped chassisThe
yellow line is the geometric centerline of the
vehicle.Toe of the left front wheel is the angle
between the wheel middle line (red) and the
x-axis or the y-axis.In the case of a car
ideally rectangle shaped, with all wheels at 0
toe, it is very clear how the real toe of the
wheel (red line) and the toe measured on the
sensor (light blue line) are giving the same
value, that is 0.
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A little more complicated rectangle shaped
chassis, toe is not null. In this conditions, if
wheel is with toe-in by 1, it is easy to see
that the sensor measuring toe along the car
(y-axis) that is with respect to the sensor
placed in the rear left wheel (light blue lines),
is also giivng a reading of 1.
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Trapezoid shaped chassis, toe not null In this
picture, the chassis is no longer rectangle
shaped, and become a generic trapezoid shaped
chassis. In this case, we designed a front track
smaller then rear track (usually it is opposite
situation). The difference between front and rear
wheels tracks is evidenced by the green lines.
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Trapezoid shaped chassis, toe not
null Displacement of the left rear wheel with
respect to the green line (or, with respect  to
the ideal position of the rear wheel if the
chassis was rectangle shaped) is called
semi-track difference. The value of toe at the
left front wheel against the centerline (yellow)
is still 1 (red line) but angle "Beta" (light
blue lines) measured by the front left sensor (in
relation with rear left sensor) is not 1 because
the rear left sensor is displaced to the right
with respect to position in figure 2.
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Trapezoid shaped chassis, toe not null However
angle "Alfa",  given by the displacement of the
rear wheel can be easily determined by measuring
the (semi) track difference. Alfa Beta make
then the correct result of toe angle for the left
front wheel.
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Measuring toe "along the car" (or referring to
y-axis).Only with the FASEP System? Approaching
the wheel alignment measures "along the car",
instead of "across the car" (I mean with front
long arms that allow to do a transversal
measure), is not a FASEP exclusive point of
view.Other manufacturers are now doing the same
way, recognizing that measuring along the y-axis
gives consistent advantages in measurement
process and accuracy, not to mention the fact
that a car is traveling exactly in the direction
of the y-axis and there is where we want it to be
aligned. Among others, we can mention -
Policontrol (made in Switzerland, for control
lines)- Powercontrol (made in U.S.A., for
motoring assembling lines)- B-Dyna (made in
Japan, for control lines)- G-Swat (made in
Japan, for control lines)Latest added to the
"y-axis" approach- John Bean 3D (Balco, Sun and
Hofmann are the same machine)- Hunter 3D- Bosch
aligner introduced in Automechanika 2002.
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ConclusionsThe way I described things here is
obviously following very simple cases  and
conditions of the car.More complicated cases can
easily be described just in the same way, but
taking in mind that Thrust Angle becomes
important. However the main point to understand
here is that an angle can be measured always with
reference to a given direction.Traditional
aligners do measure toe from one side the other
on a car, what we defined the direction of
x-axis, in other word left-to-right.FASEP, since
many years, and very recent aligners (3d
generation) are instead using a different
approach, getting the same reading referring to
the y-axis, or , more simply, front-to-rear. Of
course the way to measure the angle does not
change the angle.But in all measuring systems
you have always to take tolerance and accuracy
into your consideration. The question is that
your car is traveling along the y-axis,
front-to-rear.So you are supposed to do this
exactly align the car to such direction. As
simple as that.Now, wouldn't it be better to
place your measuring system in such direction
instead of left-to-right, in order to align your
car exactly where it has to be aligned, that is
the travel direction?
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This Concludes Our Presentation On Toe
Measurement Using The FASEP System Thank You