The present invention relates to a safe laser line
projection system. The system is used for projection of
reference lines on the roller table of a trimming machine,
for the purpose of correct positioning of the plate under
trimming on the roller table in optimum time.
Laser line projection systems for projection of
reference lines on the roller table of trimming machines are
known in the art. Red, visible output of He- Ne laser is
generally being used for the purpose. Sometimes, visible
output from a diode laser is also used.
Laser line projection systems with two different design
concepts are known in the art. These designs are based on:
I Line generation by using a cylindrical lens in the fanning
mechanism, and
II Line generation by using a vibrating mirror in the
scanning mechanism.
In the design based on line generation by using a
cylindrical lens the major components are:
(i) a laser head,
(ii) a high voltage power supply for the laser head, and
(iii) a cylindrical lens.
In this design, a visible laser beam of required power,
is made to fan out, by using a cylindrical lens of
appropriate focal length. This fan out beam generates a line
when intercepted by an opaque plane. As the total energy of
the laser beam gets distributed over the complete length of
the projected line, a relatively small line, which is
visible, can be generated with comparable power of laser
beam.
In the second type of prior art design, based on line
generation by using vibrating mirror, the major components
are:
(i) a laser head,
(ii) a high voltage power supply for the laser head,
(iii) a laser beam focusing optics, and
(iv) a vibrating mirror based on simple electromagnetic
mechanism.
The line is generated by moving a laser spot with the
help of a vibrating mirror at a speed to appear as a
continuous line to the human eye.
These prior art systems are generally designed by
assembling the laser head optics and the vibrating mirror in
a single unit and the high voltcige power supply as separate
unit. Both the units are connected by a high voltage cable
that connects the laser head in one unit to its high voltage
power supply in the other unit.
The following disadvantages are experienced in prior art
laser line projection systems:
(i) Requirement of relatively high power laser in case of
laser line generation by using cylindrical lens and fanning
mechanism,
(ii) Presence of a high voltage cable connecting the laser
head and its power supply outside system enclosures, which is
a potential high voltage hazard.
(iii) Fast deterioration of performance because of exposure
of delicate optical components to dust and fume generally
prevalent in industry.
(,iv) Possibility of the laser beam being projected out as a
soot which is a potential eye hazard.
(v) In some models of prior art. design an electromagnetic
stopper is also used in the path of laser beam as eye safety
device. This stopper is electrically connected in parallel
with the electromagnetic vibrating mechanism. The electro-
mechanical stopper is prone to get stuck in an unpredicted
position.
(vi) Complicated arrangement for adjustment of projected
laser line. The rotation of the projected laser line,
shifting of projected laser line parallel to itself keeping
the laser line projection system in a fixed location and
adjustment of line length, together with their adjustment in
a changed condition of operation are difficult to achieve in
orior art design.
To overcome these problems, more reliable designs having
following features were developed:
(;') Scanning mechanism is adopted thus avoiding the
relatively higher power laser required in the case of laser
line generation using cylindrical lens and fanning mechanism,
(ii) The high voltage cable connecting the laser head and its
power supply are restricted within the same enclosure, as the
laser head, its high voltage power supply, vibrating mirror,
drive circuit of scanning mirror, interlock circuit, etc.
Thus, potential high voltage hazards prevalent in prior art
systems by high voltage cable hanging in open space is
prevented.
(iii) All optical components excluding the outer surface of
the output window (which is uncoated) are housed inside a
dustproof enclosure. Thus, delicate optical components are
not exposed to hazardous industrial environment.
(iv) To obviate the problem of accidental exposure to laser
radiation for a longer period of time, which may cause eye
damage, safety interlock for laser comprising two reliable
alternative interlock circuits were developed and
incorporated.
(v) A specially designed clamp type mounting bracket is
provided for adjustment of laser line.
(vi) The vibrating mirror is driven by an electronic circuit
providing smooth variation of amplitude of vibration over a
specific limit and having means for setting it at a specific
value, thus allowing for projected line adjustment over a
limit and keeping line length constant at a set specific
value.
(vii) A flexible lens assembly is used for adjustment of line
width to a specified value over a wide range of projected
distance and keeping the line width nearly constant over the
length of projected line at any distance within the designed limit.
Accordingly, the present invention provides a safe laser line projection system, based on
line generation by scanning mechanism, comprising:
(i) a laser having a laser head, a high voltage power supply for the laser head, a high
voltage cable to connect said laser head with said high voltage power supply;
(ii) a flexible lens assembly for focusing laser beam from the laser, in a nearly uniform
width over the designed length of the projected line:
iviii) a front surface coated vibrating scanning mirror and a right angle prism placed in front
of said mirror, such that the said laser beam projected through the lens assembly, is caused to fall on
^.aid mirror, after getting deflected by 90° . said scanning mirror being caused to be vibrated by an
electronic drive circuit;
(iv) means for adjustment of the laser line projection, said means being constituted by a clamp
type mounting bracket designed such that the two halves of said bracket clamp the cylindrical
portion of a line generator unit, said line generator unit being adapted to be rotated about its axis by
loosening screws provided in the bracket and subsequently tightening the screws, thereby shifting the
projected laser line parallel to itself, and said bracket also having angle adjustment supports for
micro adjustment of the angle of the laser line projection, so that the line generator unit is capable of
being finally locked at a particular angle by lilting in the vertical plane to adjust the length of the
laser line; and
(v) a safety interlock for laser comprising:
either (a) an interlock circuit to actuate the high voltage power supply for the laser to be
switched on through a relay, which is caused to be actuated in the event of the scanning mirror
receiving a proper input such that laser generation is caused to be interlocked with the scanning
mirror;
or (b) an interlock circuit to actuate the high voltage power supply for the laser to be
witched on through a relay which is caused to be actuated on receiving feedback signal from the
canning mirror, the feedback signal being caused to be generated only in the event of physical
ibration of the scanning mirror;
the high voltage cable connecting the laser head and its high voltage power supply being
oused in the same enclosure together with the vibrating scanning mirror, the drive circuit of the
ibrating scanning mirror and the interlock circuit; and
said enclosure being a dust proof enclosure housing all the aforesaid components, excluding
le outer surface of the output window for the laser beam.
The safe laser line projection system of the present invention will be better understood from
lie following detailed description with reference to the accompanying drawings, wherein:
'ig. 1 illustrates a schematic diagram and component layout of the laser line apparatus for projection
f reference lines on
a surface in accordance with the present invention.
Fig.2 illustrates a schematic diagram of the power
distribution box which also houses a DC power supply.
Fig. 3 illustrates a circuit diagram of the interlock circuit
for input to a high voltage power supply with input to a
scanner, in accordance with a preferred embodiment of the
invention.
Fig. 4 illustrates a schematic Block Diagram of the apparatus
in accordance with the invention
Fig. 5 illustrates a block diagram of interlock circuit based
on feed back signal from the scanner, in accordance with a
preferred embodiment of the invention.
Fig. 6 illustrates prior art laser line projection system
using cylindrical lens.
Fig. 7 illustrates prior art laser line projection system
using vibrating mirror based on electromagnetic mechanism.
Fig. 8 illustrates clamp type mounting bracket of instant
invention.
The laser line system according to the instant
invention has the following components, as illustrated in
Fig. 1 with the corresponding reference numerals given in
brackets:
5mw He- Ne laser (1)
Lens Assembly (2)
Right Angle Prism (3)
Scanning Mirror (4)
PCB I (5)
PCB II (6)
Line Filter and Surge Suppressor (7)
MS Standard Multipin Connector (8)
Bayonet Cap Fuse (250 mA) (9)
HV Power Supply for Laser (10)
Laser Cover (11)
Dust Proof Enclosure for Optical Components (12)
Mounting Bracket (13)
Mounting Shaft (14)
Angle Adjustment Support (15)
Output Window (16)
High Voltage connector for laser (17)
The power distribution box of the system according to
the present invention has the following components as
illustrated in Fig.2 with the corresponding reference
numerals given in brackets:
DC Power Supply (18)
Fuse (1 amp) (19)
Fuse (250 mA)' (20)
Cable Gland (AC/ out) (21)
Cable Gland (DC/ out) (22)
Cable Gland (Mains in) (23)
The system ±n accordance with the present invention
is designed with a 5mw He- Ne laser (1/Fig.l). Depending upon
the visibility condition, the color and power of the laser is
selected. The laser .beam is made to scan by a front surface
coated vibrating mirror (4/Fig.l). Frequency of vibration of
the mirror is selected high enough so that the projected
scanning spot on the surface appears as a continuous line due
to persistence of vision. Care is also taken to choose this
frequency so that it does not resonate with the natural
frequency of vibration of the machine near which the
projector is intended to be mounted.
To make optimum use of the scan angle of the vibrating
mirror, the laser beam is allowed to fall on it after getting
deflected by 90* with the help of a right angle prism
(3/Fig.l). A lens assembly (2/Fig.l) is used to process the
beam to have nearly uniform width of the projected line over
the desired range of length at a definite distance. All these
optical components excluding the output window are housed
inside a dustproof enclosure (12/Fig.l). This is to protect
the delicate optical components from getting exposed to
ha2ardous industrial environment.
For ease of mounting and adjustment, the system, in accordance with the
invention, is provided with a specially designed clamp type mounting bracket (13/Fig 1,
Fig.8) Mich that two halves of the said bracket clamp firmly the cylindrical portion of
the line generator unit, the laser cover (Il/F'ig.l. Fig.Sf by tightening four screws
(24/Fig-S). The mounting bracket allows the unit containing the laser, vibrating mirror
etc. to rotate around the axis of the laser cover (1 1/Fig.l, Fig\S) by loosening the four
screws (24,Fig.8) provided in the mounting bracket (J3/Fig.l, f'ig.S) and subsequently
fixed at a desired position b\ tightening die four screws (24/Fig.8j. This makes shilling of
projected laser line parallel to i be If an extreme!} easy job. Angle adjustment supports
(15/Fiu.l. Fig.81 provide facility for micro adjustment of angle and final locking of the
sysiem at a particular angle as well. This is achieved by adjusting the relative lengths of
the two angle adjustment support (15/Fig. 1. Fig.8) and subsequently locking them at the
desired angle. Here, in this ease, the axis of rotation is the axis of the stud (1'5/f ig.8j. The
length of the projected line can be adjusted with angle adjustment mechanism also.
The scanning mirror used in this particular design works
on ± 15V DC input and is provided by the DC power supply
(18/Fig.2).
The drive circuit of the scanning mirror PCB-I (5/Fig.l)
and high voltage power supply for laser (10/Fig.l) are also
housed inside the enclosure. This arrangement restricts the
high voltage cable inside the enclosure, thus avoiding
possibility of accident due to high voltage exposure.
Laser radiation in general, is a potential eye hazard,
while the permissible maximum power for accidental exposure
of visible laser to human eye depends on wavelength and power
of the laser. In the case of steady visible laser an exposure
duration not exceeding 0.25 seconds is taken, which is
aversion response time of a common viewer. Use of a higher
power (within a limit) visible laser in open space is
possible if the risk of accidental exposure for a longer
period is kept under control as with a scanning a beam.
For safety of the eye, an interlock system was
incorporated in the system Qf tne present invention, so as
to allow the laser beam to get projected out of the system in
scanning mode only. It could be achieved by incorporating a
solenoid operated stopper as was done in some prior art
design, in the path of laser beam before being allowed to
fall on the scanning mirror. The solenoid is connected in
parallel with the drive circuit, to function simultaneously.
However, the design suffers from serious reliability problem
as electro-mechanical stoppers are prone to get stuck.
To obviate this problem, the following two more reliable
alternatives were developed and incorporated in the system
in accordance with the invention:
I Input to HV power supply for laser is switched on
through a relay which is actuated only when the scanner is
also receiving proper input.
II Input to HV power supply for laser is switched on
through a relay which is actuated on receiving feedback
signal from the scanning mirror.
The interlock PCB-II (6/Fig.l) provided for the purpose
is also mounted inside the dust proof enclosure along with
the other optical components and the high voltage power
supply.
Fig.3 is the circuit diagram (PCB-II) of the first
scheme of interlock. ± 15VDC input to this circuit actuates
the relay RL, which in turn connects the high voltage power
supply of the laser to its required input (Fig.4). The input
(± 15VDC) to this interlock circuit is connected in parallel
with the input to the drive circuit PCB-I of the scanner
(Fig.4). Absence of any of the ±15VDC supply or both will
keep the laser input line open. Thus the laser is interlocked
with the scanning mirror. The design thus meets the necessary
eye safety requirement.
Fig.5 is the block diagram of the second alternative. In
this scheme the controlling signal to actuate the re Lay to
connect the input to high voltage power supply of the lciser
is picked up from the feedback signal (FS) of the scanning
mirror making it a fail-safe safety device.
Like previous schemes, in this case also a scanning
mirror of required dimension and frequency is selected but
with an additional coil to pick up signal from vibration of
the mirror and provide feedback signal of peak voltage of the
order of 5mV. Hence, the feedback signal generates only when
the mirror physically vibrates.
The input of the laser is switched on (Fig.5) with the
help of a special relay, which in its turn acts on receiving
signal (FS) from the feedback circuit of the scanning mirror.
As the signal from the pick up coil is the true response
of the physical vibration of the scanning mirror, laser can
switch on and get projected in scanning mode only.
It is to be understood that the present invention has
been described in relation to some preferred embodiments with
reference to accompanying drawings, but is not limited to
such preferred embodiments and drawings and includes possible
legitimate developments within the purview of what has been
described herein before and claimed in the appended claims.
WE CLAIM:
1. A safe laser line projection system, based on line generation by scanning mechanism,
comprising:
(i) a laser having a laser head, a high voltage power supply tor the laser head, a high
voltage cable to connect said laser head with said high voltage power supply;
(ii) a flexible lens assembly tor focusing laser beam from the laser, in a nearly uniform
width o\er the designed length of the projected line;
(iii) a front surface coated vibrating scanning mirror and a right angle prism placed in front
of said mirror, such that the said laser beam projected through the lens assembly, is caused to fall on
said mirror, after getting deflected by 90° . said scanning mirror being caused to be vibrated by an
electronic drive circuit:
(iv) means for adjustment of the laser line projection, said means being constituted by a clamp
type mounting bracket designed such that the two halves of said bracket clamp the cylindrical
portion of a line generator unit, said line generator unit being adapted to be rotated about its axis by
loosening screws provided in the bracket and subsequently lightening the screws, thereby shifting the
projected laser line parallel to itself, and said bracket also having angle adjustment supports for
micro adjustment of the angle of the laser line projection, so that the line generator unit is capable of
being finally locked at a particular angle by tilting in the vertical plane to adjust the length of the
laser line; and
(v) a safety interlock for laser comprising:
either (a) an interlock circuit to actuate the high voltage power supply for the laser to be
switched on through a relay, which is caused to be actuated in the event of the scanning mirror
receiving a proper input such that laser generation is caused to be interlocked with ihe scanning
mirror;
or (b) an interlock circuit to actuate the high voltage power supply for the laser to be
switched on through a relay which is caused to be actuated on receiving feedback signal from the
scanning mirror, the feedback signal being caused to be generated only in the event of physical
vibration of the scanning mirror;
the high voltage cable connecting the laser head and its high voltage power supply being
housed in the same enclosure together with the vibrating scanning mirror, the drive circuit of the
\ ibrating scanning mirror and the interlock circuit; and
said enclosure being a dust proof enclosure housing all the aforesaid components, excluding
the outer surface of the output window for the laser beam.
2. A sale laser line projection system, substantially as herein described, particularly with
reference to the figures.

There is disclosed a safe laser line projection system, based on line generation bv scanning
mechanism, and for the purpose of correct positioning of a plate under trimming on a roller table in
optimum time, said system comprising:
(i) a laser (1) having a laser head, a high voltage power supply( 11) for the laser head.
(ii) a flexible lens assembly (2) for focusing laser beam from the laser, in a nearly uniform
width over the designed length of the projected line;
(iii) a front surface coated \ ibrating scanning mirror (4) and a right angle prism (3) placed
in front of said mirror, such that the said laser beam projected through the lens assembly, is caused to
fall on said mirror, after getting deflected by 90° , said scanning mirror being caused to be \ i bra led
by an electronic drive circuit(5);
(iv) a clamp type mounting bracket (13) for clamping the cylindrical portion of the line
generator unit (1,4) such that said line generator unit is adapted to be rotated about its axis, said
bracket also having angle adjustment supports (15) for micro adjustment of the angle of the laser line
projection; and
(v) a safety interlock circuit (6) for the laser ; a high voltage cable (17) connecting the laser
head and its high voltage power supply (10) being housed in the same enclosure (12) together with
the vibrating scanning mirror, the drive circuit of the vibrating scanning mirror and the interlock
circuit; and
said enclosure being a dust proof enclosure housing all the aforesaid components, excluding
the outer surface of the output window (16) for the laser beam.