FIELD OF INVENTION:
The present invention relates to a method using an industrial six axis
robot for dimensional measurement of large volume machine drilled
circular holes for different sizes of condenser and heat exchanger plates
having varying diameter and number of circular holes.
BACKGROUND OF THE INVENTION:
In a heat exchanger or condenser, particularly for steam generators of
pressurized water stations, large plates are provided with large volume
circular holes (thousands of circular holes) for fixing and supporting the
bundles of tubes. These circular holes are drilled using mechanical
means such as single-spindle or multi-spindle drilling machines. The
circular holes, produced by mechanical machining process have
dimensional tolerances and the circular holes need to be circular and
cylindrical without drift for the insertion of tubes. The diameter of the
holes, pitch, circularity and straightness of holes needs to be within the
assembly tolerances for easier of insertion of tubes and correct assembly
of the equipment. Hence, there is necessity of measurement of the hole
parameters to identify the error.
In the existing art method of inspection of the large volume holes of the
heat exchanger or condenser plates, the measurement is carried out by
'go'- 'no-go' gauge resulting in acceptance or rejection of hole without
knowing its dimensions. This manual method is inaccurate, cumbersome
and time consuming leading to large cycle time.

Some apparatus and methods have been previously employed for
measurement of circular holes but none of the methods have been
employed for large volume circular hole measurement using a robot as
proposed in the current invention.
Patent No. US 4235110 discloses an apparatus and a method has been
proposed for measuring crevice gap clearance between the tubes and
tube supports in a heat exchanger.
Patent number US 201210288336 provides a system comprising a
drilling machine; a capacitive probe; and a probe deployment system,
mounted to the machine, for moving the capacitive probe inside a hole
drilled by the machine to measure the drilled hole at different depths.
Patent number US 2014/0313506 describes an apparatus that is
provided with an optical probe and a robotic transport so adapted to the
optical probe as to move the optical probe inside a drilled hole to
measure the drilled hole at one or more depths.
Patent number US 7,310,889 discloses a method for three-dimensionally
measuring objects, according to which the positions of a measuring
element are determined by means of a locating method (e.g. optically,
electromagnetically, or acoustically), the positions being relative to a
reference system defined by the associated locating system, and desired
dimensions of the object being calculated from the determined positions
of the measuring element. The measuring element can be moved by
means of a robot arm or a flying object (e.g.a type of Zeppelin).

To alleviate the drawbacks of the prior art the invention proposes a
method for dimensional measurement of the large volume circular holes
using a six-axis industrial robot for different sizes of heat-exchanger or a
condenser plates with varying diameters and number of circular holes.
OBJECTS OF THE INVENTION:
It is therefore, an object of the invention to propose a method for
dimensional measurement of the large volume circular holes using a six-
axis industrial robot for different sizes heat-exchanger and condenser
plates having varying diameter and number of circular holes to decrease
the cycle time and improve the accuracy of circular hole measurement
process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only
typical embodiments of the present subject matter and are therefore not
to be considered for limiting of its scope, for the invention may admit to
other equally effective embodiments. The detailed description is
described with reference to the accompanying figures. In the figures, the
left-most digit(s) of a reference number identifies the figure in which the
reference number first appears. The same numbers are used throughout
the figures to reference like features and components. Some
embodiments of system or methods in accordance with embodiments of
the present subject matter are now described, by way of example, and
with reference to the accompanying figures, in which:
Figure 1 shows manual process of using 'go' 'no-go' gauge' in accordance
to the prior art.
Figure 2 shows a prototype condenser plate having large number of
circular holes.

Figure 3 shows the industrial six-axis robot with contact touch probe
and prototype condenser plate being used for dimensional measurement
of large number of circular holes in accordance to the invention.
Figure 4 shows the contact touch probe with insulated contact probe
holder and electrical conductor in accordance to the invention.
Figure 5 shows a robot wrist holding a measurement probe for
dimensional measurement of a circular hole in accordance to the
invention.
The figures depict embodiments of the present subject matter for the
purposes of illustration only. A person skilled in the art will easily
recognize from the following description that alternative embodiments of
the structures and methods illustrated herein may be employed without
departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF DRAWINGS:
Figure 1 illustrates a view of prior art showing manual process of using
'go' 'no-go' gauge'. The figure illustrates a method for dimensional
measurement of the large volume circular holes of different sizes of heat-
exchanger or condenser plates (1) with varying diameter and number of
circular holes. The invention as proposed in the present subject matter is
aimed to replace the existing manual process of circular holes
measurement using ‘go-nogo’ gauge (2).
Figure 3 illustrates the industrial six-axis robot with contact touch probe
and prototype condenser plate being used for dimensional measurement
of large number of circular holes in accordance to the invention.

According to an embodiment of the invention disclosed therein, the
apparatus consists of an industrial six axis robot (4), a measurement
contact touch probe (6) with spherical end (7), an electrical conductor
connected to measurement touch probe (6), an electrical conductor
connected to heat-exchanger or condenser plate (5), an audible sound
buzzer (not shown) and a robot controller (not shown).
In another embodiment of the invention disclosed herein, the conducting
measurement probe (7) is made of the material that offers least
resistance to electricity flow. The contact measurement probe (7) is
mounted to the robot (4) flange and is insulated from the robot flange by
using a non-conducting probe holder (3). An electrical conductor (5),
whose one end is connected to robot input and the other end is
connected to heat-exchanger or condenser plate (1). Second electrical
conductor (6), whose one end is connected to positive 24V of the robot
voltage supply and the other end is connected to measurement probe (7),
is used to trigger robot input when the measurement probe (7) touches
the condenser plate (1). A buzzer (not shown) is connected to robot
output and configures such that it generates sound when the
measurement probe touches the condenser plate and a robot input is
triggered.
Figure 5 illustrates a robot wrist holding a measurement probe for
dimensional measurement of a circular hole in accordance to the
invention.
In another embodiment of the invention disclosed herein, the
measurement of circular hole parameters is carried out with double
touch strategy. At the start of the cycle of the proposed method six-axis
robot (4) which measurement probe (7) is mounted, moved from a home
position to a defined position at height Z1 on top of first circular hole (8)

at the approximate position in the center of the circular hole. The robot
(4), extends down and positions the measurement probe (7) at a desired
depth in the circular hole. The measurement probe (7) is then moved at
high speed to a first position in the circular hole till it touches on of the
sides of the circular hole (8) and triggers a signal to the robot controller.
This is indicated by the audio signal from the buzzer (not shown). The
measurement probe (7) is then slightly retracted back and moved to the
previous position at a lower speed till the signal to the robot controller is
triggered. The X11 and Y11 coordinates of the robot position, when the
signal is triggered at slow speed, are stored in robot memory. The
measurement probe (7) is then moved back to center of the circular hole.
The measurement probe (7) is then moved at a high speed to a second
position that is diametrically opposite to first position till it touches the
wall of the circular hole (8) triggers a signal to the robot controller. The
measurement probe (7) is then slightly retracted back and moved to the
previous position at a slow speed till the signal to the robot controller is
triggered. The X12 and Y12 coordinates of the robot position, when the
signal is triggered at slow speed, are stored in robot memory. The
measurement probe is then moved back to center of the circular hole.
This procedure is repeated for the third position which is at
approximately 90 degrees diametrically opposite to the line joining first
and second positions and X13 and Yl3 coordinates of the robot position
are stored in robot memory. Again, the procedure is repeated for the
fourth position which is diametrically opposite to the third position and
Xl4 and Yl4 coordinates of the robot position are stored in robot memory.
The measurement probe (7) is then lowered at a height Z2 that is at lower
depth than Zl and the measurement procedure is repeated for four
positions at height Z2. The coordinates X2l, Y2l, X22, Y22, X23, Y23,

X24 and Y24 are stored in the robot memory for first, second, third and
fourth robot positions respectively.
The measurement operation is repeated for programmed second and
subsequent circular holes till all the holes of the condenser plate 1 are
measured. After the measurement operation of last circular hole is
finished, the robot travels back to a programmed home position.
Based on the measurement data for four positions of the circular hole
hole at height Zl and four positions of the circular holes at height Z2, the
robot controller programmatically calculates the diameter of circular
holes at two desired depth levels, pitch between the circular holes,
circularity and cylindricity of the circular holes.
Although embodiments for the present subject matter have been
described in language specific to structural features, it is to be
understood that the present subject matter is not necessarily limited to
the specific features described. Rather, the specific features and methods
are disclosed as embodiments for the present subject matter. Numerous
modifications and adaptations of the system/device of the present
invention will be apparent to those skilled in the art, and thus it is
intended by the appended claims to cover all such modifications and
adaptations which fall within the scope of the present subject matter.

WE CLAIM:
1. A method of measuring dimension of a machine drilled circular holes
on a metal, the method comprising the steps of:
Step 1 : aligning a six-axis robot (4) coupled to a probe (7) at a predefined
position (P1) within the said machine drilled circular hole at an
elevation (Z1);
Step 2: extending down the probe (7) at an accelerated speed to a first
position (P2); wherein the probe (7) on contact with the base of
the machine drilled circular hole set an audio signal; and the
first coordinates is recorded;
Step 3: retracing the probe to the initial position (P1) at a retarded speed;
wherein a second coordinate is recorded;
Step 4: repeating steps (2) and (3) for a second, third and fourth position
different geometric angles to generate coordinate positions;
Step 5: aligning the said six-axis robot (4) coupled to a probe (7) at a
predefined position (P1) within the said machine drilled circular
hole at an elevation (Z2);
Step 6: repeating the aforesaid procedure to obtain a second set of four
coordinate positions;
wherein the recorded first and second set of coordinates are stored in a
storage device of the six-axis robot (6).

2. The method as claimed in claim 1, wherein the recorded four
coordinate position at height Z1 and four coordinate position at height
Z2 are compared to generate the dimensional parameter of the circular
hole.
3. An apparatus to measuring dimension of a machine drilled circular
hole on a metal comprising a six-axis robot (4), a probe (7) coupled to
robot (4) flange; a first electrical conductor (5) wherein the said
conductor is connected to the robot input at distal end and connected to
a metal plate at proximal end; a second electrical conductor (6)
connected to a power supply at one end and connected to the metal plate
at other end; and an audio alarm means selectively enabled on contact of
the measurement probe with the base of the circular hole and metal
plate thereby triggering the robot input.
4. The apparatus to measuring dimension of a machine drilled circular
hole on metal as claimed in claim 1, wherein the metal plate is a
condenser plate or heat exchanger.