Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2001-12-03
2004-07-13
Epps, Georgia (Department: 2873)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S220100
Reexamination Certificate
active
06762866
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high speed mechanical laser shutter, and more specifically to a fast mechanical laser shutter having high power handling capability and suitable for continuous operation in conjunction with a high-power laser used in industrial processes such as machining, welding, deposition and other manufacturing operations.
BACKGROUND OF THE INVENTION
Shutters for selectively interrupting (blocking or diverting) or letting pass the optical output of high power lasers used in industrial processes and manufacturing operations are known. In use, the shutter is moved to either block—and receive the energy of—a laser beam or is moved out of the path of the laser beam permitting it and its energy to be applied to a workpiece or work surface.
In the past a solenoid-operated shutter has been driven from a closed (blocking) position to an open (unblocking) position by selectively energizing the solenoid. The return of the shutter to its normal closed position has been effected by springs or gravity. The opening and closing times of such shutters have been found to be unequal and difficult to control. Since the amount of energy applied by the laser to a work surface or workpiece is proportional to the time the shutter is open, this lack of control of shutter opening and closing times results in a lack of control over the amount of laser energy applied.
Iris-type shutters are also known. These camera-like shutters contain a number of interleaved planar members that are simultaneously rotated about their respective axes, that are all spaced from a central axis, to open an expanding diameter light path or to close a diminishing diameter light path. Iris shutters have been found to be unable to withstand the level of energy present in high-power continuous laser outputs and easily become damaged thereby.
Electro-optical shutters have also been used to pass or interrupt laser outputs. These have been found to be unsuitable for use with high-power laser outputs. Specifically, electro-optic shutters have been found even when open to absorb substantial energy from an incident laser beam. When used with a high power continuous laser, this type of shutter either overheat and fails or allows too much energy pass when it is “closed.”
One goal of the present invention is to provide a fast mechanical shutter for use with high-power, continuous lasers, a shutter that can be opened and closed in a highly repeatable and controllable manner—that is, the opening times and the closing times may be selectively adjusted—to repeatably and accurately control the amount of laser energy that is applied to a workpiece and that is suitable for use with continuous laser operation.
SUMMARY OF THE INVENTION
With the foregoing and other goals in view, the present invention in its broadest aspect contemplates an actuator for moving a mechanical shutter between a first position, whereat the shutter blocks the passage of a light beam, such as that produced by a continuous high power laser, and a second position whereat the shutter permits passage of the light beam. The shutter may include a mirror which is highly reflective at the wavelength of the light. In the second shutter position, the mirror, which may be planar or convex blocks the light and reflects away from the path and onto an efficient light absorber.
The actuator includes a bi-directional, preferably rotary drive or actuator, such as a solenoid, a multi-phase AC motor or a brushless driver, a movable member of which, such as an armature or rotor, is both selectively movable and carries the mirror of the shutter. The movable member is movable between respective first and second positions, at which the shutter is in its first and second position. The movable member is selectively positively driven by a selectively energized current source into one of its positions, in which it remains until positively driven into its other position. An important feature of the shutter is that it must be driven positively into both its opened (second) and closed (first) positions. No mechanical (i.e., spring) or magnetic biasing is relied on to move the shutter to its first and second positions or to any “neutral” position therebetween. Further, because the shutter is positively driven, its opening time and speed and its position between the extreme positions may be selected by the user.
In a somewhat narrower vein, the movable member of the rotary actuator is selectively driven by first and second shaped current signals or pulses. The shape of the pulses is such that the rotary member may be very rapidly moved from one position to the other and held there until a subsequent pulse moves it to its other position. The shape of the pulses permits the velocity and the position of the armature to be controlled. This control permits precise control of the duration and the amount of light, and accordingly of the duration and amount of energy.
In other aspects, the present invention relates to a fast mechanical shutter for selectively intercepting or permitting to pass a laser beam. When the beam is intercepted, the shutter deflects it onto an absorber.
The shutter includes a bi-directional rotary actuator or driver, such as a solenoid, or an AC or DC motor. The Movable member of the rotary actuator, such as an armature or rotor is movable between a first position and a second position by energization thereof, specifically the application of selected, respective first and second shaped current signals to the ststor, coil or winding of the of the rotary actuator. A flag, which may comprise or include a mirror that is highly reflective at the frequency of the laser output, is carried by the armature. The flag permits passage of the beam in the first position of the armature and intercepts the beam in the first armature position. If the flag includes the mirror, in the first armature position, the minor reflects the beam towards and onto a light absorber.
A first facility responds to a command—which may be issued in real time, or pursuant to a stored program, by a computer—by applying one or the other of the shaped current signals to the solenoid. If the armature is in its first position while the second shaped current signal is applied to the solenoid, the armature will be quickly moved to its second position at a rate determined by the shape of the signal. Similarly, if the armature is in its second position while the first shaped signal is applied to the solenoid, the armature will be quickly moved to its first position at a selected rate. If the solenoid receives the first or second shaped signal while the armature is already in the first or second position, the armature will not move. Thus, both the opening and closing of the shutter occur quickly, since the shutter must be positively driven into both positions, at rates determined by the character of the shaped signals.
In preferred embodiments, the first facility includes a controller that produces a pulse having a selected shape, and a power amplifier that applies the shaped pulses to the rotary actuator to operate the shutter.
A second facility monitors the position of the armature. The position of the shutter selected by the last-given command to the first facility and the actual position of the armature are continuously compared. If these do not match, a first error signal is produced. Preferably the shutter-position sensors are optical sensors. As with other error signals, the presence thereof effects the application of a first signal or pulse to the solenoid to close the shutter or hold the shutter in its closed position if it is already there.
A third facility continuously measures the temperature of the solenoid and the signal-applying facility. If the temperature of either exceeds a predetermined limit, a second error signal is produced. Again, as with the first error signal, the second error signal effects movement of the shutter to the closed position if it is not already there.
Either error signal may also effect the de-energization of the laser with which the shutter is use
Choi William
Epps Georgia
Jackson & Walker, LLP
Klinger Robert C.
Lockheed Martin Corporation
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