Abstract:
A fast mechanical shutter for a laser has a reflective flag which either blocks or unblocks the laser output. In the blocking position, the flag reflects the light onto a laser output absorber. The flag is rapidly moved by an electric actuator into which shaped current pulses are forced to determine the velocity, acceleration, deceleration and position of the flag. Absent a current pulse, the flag remains in its extant position. Sensors detect and produce an error signal if (i) the flag is in a selected position or (ii) if the actuator or the laser overheat. The error signal moves the flag to its blocking position, terminates laser operation and produces an alarm. Exemplary actuators include rotary actuators, such as solenoids and AC or DC motors that can be rapidly operated by shaped current pulses. A computer may direct the operation of the shutter and the laser.

Description:
FIELD OF THE INVENTION  
         [0001]    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  
         [0002]    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.  
           [0003]    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.  
           [0004]    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.  
           [0005]    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.” 
           [0006]    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  
         [0007]    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.  
           [0008]    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.  
           [0009]    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.  
           [0010]    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.  
           [0011]    The shutter includes a bidirectional 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 mirror reflects the beam towards and onto a light absorber.  
           [0012]    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.  
           [0013]    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.  
           [0014]    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.  
           [0015]    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.  
           [0016]    Either error signal may also effect the de-energization of the laser with which the shutter is used, as well as disabling the shutter after it has been moved to its closed position. Disabling the shutter may include first operating the first facility to apply the first shaped signal to the rotary actuator to ensure that the shutter is in the closed position wherein it intercepts the beam. The fault signal may also trigger the production of a human-sensible signal, such as a light or alarm that indicates a malfunction of the shutter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0017]    [0017]FIG. 1 is a generalized, perspective representation of a laser machining system which includes a shutter that is usable to pass or intercept a laser beam produced by the system and which also includes facilities for operating the shutter in a predetermined manner; and  
         [0018]    [0018]FIG. 2 is a graphical depiction of current pulses which are applied to the actuator of FIG. 1 to operate the shutter.  
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring first to FIG. 1, a schematic of a laser operating system  100 , including a shutter  102  according to the present, are shown. As can be seen the shutter  102  is used in conjunction with a laser (not shown, but indicated at  104 ), which is preferably a high power (kilowatt level), continuous laser used to machine, weld, deposit materials or perform other manufacturing operations. Suitable lasers include neodynium/yttrium-aluminum-garnet (“YAG”) lasers, though any high power laser suitable for machining, welding, depositing or other manufacturing operation may be used.  
         [0020]    The laser  104  and its associated facilities, including cooling facilities (not shown but indicated at  106 ), are contained within a housing  108 . Shown entering the rear of the housing  108  are power leads  110  to the laser  104  and hoses  112  through which a coolant moves as it is circulated by the cooling facilities  106 , as indicated by the arrows  114  The laser  104  maybe selectively operated to produced a coherent light beam  116  which exits the front of the housing  108 . The light beam  116  maybe focused by a lens system, generally indicated at  118 , to produce a high energy “spot”  120  at a selected site on a work table or stage  122 , the focused light being indicated at  116   a . A workpiece (not shown) to be machined, welded, or have something deposited thereon rests or is held on the stage  122 . As is known, the stage  122  is movable by facilities (not shown) in the “X”, “Y” and “Z” directions to apply the high energy spot  120  on the desired portion of the workpiece, as indicated by the axes  124 . Although the stage  122  is depicted in FIG. 1 as vertically oriented and the light  116 , 116   a  from the laser as horizontally directed, it is clear that the orientation and direction of either may assume any desired orientation.  
         [0021]    The shutter  102  of the present invention either intercepts and blocks the light beam  116   a  produced by the laser  104  or permits passage of the beam  116   a  therepast and onto the workpiece resting on the stage  122 . The shutter  102  achieves the foregoing by occupying either a first position  124  (solid outline) which intercepts the beam  116   a  or a second position  126  (phantom outline) which is located away from the first position  124  so that the beam  116   a  by-passes the shutter  102  and reaches the stage  122 .  
         [0022]    The shutter  102  may comprise a generally planar flag  128  made of or coated with a dielectric material which can withstand the impingement thereon of the beam  116   a  and which blocks the beam  106  when the shutter  102  is in its first position  124 . In preferred embodiments, the flag  128  is a dielectric material coated with a reflective coating  130 . Thus, the coated flag  128 , 130  is a mirror. The coating is selected so that the flag acts as an efficient mirror for light having the wavelength of the light beam  116   a . The mirror  128 ,  130  may be planar or non-planar, such as convex. FIG. 1 depicts a planar mirror  128 , 130 .  
         [0023]    The flag  128  is carried by an arm  132 . The arm  132  is, in turn, carried by and rotated with a rotatable output shaft  134  of a rotary, bi-directional actuator, such as the solenoid  136  depicted in the Figure. Other rotary actuators  136 , such as a multi-phase AC motor, a brushless DC motor or their functional equivalents to these actuators and solenoid actuators may also be used, in which event the shaft  134  may be connected to or integral with the relevant rotary output member, such as a motor rotor or armature.  
         [0024]    The shaft  134  is rotated by and with the rotor (not shown) of the rotary actuator  136 . The shutter  102 , as well as the lens system  118 , may be contained within the housing  108  instead of being located outside thereof as shown in FIG. 1. Selective energization of power leads  138  to the rotary actuator  136  effects rotation of the shaft  134  and, accordingly, of the arm  132  and the flag  128 , between the respective first and second positions  124  and  126  and in either direction relative to the axis of the shaft  134 , as indicated by the double-headed arrow  140 .  
         [0025]    The flag  128  may assume varying orientations relative to the plane of rotation of the arm  132 . In FIG. 1, the flag  128  is not parallel to the plane of rotation of the arm  132 . Rather, the flag  128  is angularly displaced relative to such plane of rotation. This angular displacement is of little consequence when the flag  128  is in its second position  126 , but when it is in its first position  124 , light  116   a  striking the angled reflective flag  128  is reflected thereby onto a light- and energy-absorbing body  142 , as shown by the light beams  144 . It is preferred that the flag  128  both block the light  116   a  and reflect it, as at  144 , onto the light absorber  142  whenever the laser  104  is energized and the flag is in the first position  124 . The light absorber  142  may be outside (as seen in FIG. 1) or inside the housing  108 .  
         [0026]    In FIG. 1 the plane or rotation of the flag  128  is depicted as normal to the light path  116   a . This in combination with the angularity of the flag  128  relative to the plane of rotation of the arm  132  directs reflected light onto the light absorber  142  when the flag  128  is in its first position. This same end maybe realized by using a planar mirror  128 , 130  that is parallel to or coplanar with the plane of rotation of the arm  132 , with such plane of rotation being not normal to the light path  116   a . Further, the mirror  128 , 130  may be non-planar, the degree and type of non-planarity, the point of intersection between the mirror  128 , 130  and the orientation of the plane of rotation of the arm  132  to the light path  116   a  all being selected to direct the reflected light  144  as desired to the absorber  142 . In some embodiments, the mirror  128 , 130  is convex.  
         [0027]    As diagrammatically shown in FIG. 1, the system  100  also includes sensors  150  and  152  that detect the presence or absence of the arm  132  and, thus, indirectly detect the position of the mirror  128 , 130  which is fixed to the arm  132 . The sensors may also directly detect the position of the flag  128 , or may indirectly detect the position of the flag  128  by sensing the position of the shaft  134  via markings or projections thereon.  
         [0028]    These sensors  150 , 152  produce a first output when the flag  128  is adjacent thereto and a second output when the flag is absent therefrom. Specifically, when the flag  128  is in the first position  124 , the sensor  150  produces the first output and the second sensor  152  produces the second output. The outputs are reversed when the flag  128  is in the second position  126 . When the flag is traveling between the positions  124 , 126 , both sensors  150 , 152  produce the second output.  
         [0029]    A power amplifier  154  is operable to selectively energize the solenoid or other rotary actuator  136  to positively drive the flag  128  into its first or second position, as described more fully below. Proximately located with respect to the power amplifier  154  is a thermal sensor  156 , that produces a first output if the temperature of the power amplifier  154  is within an acceptable range and a second output if that temperature becomes too high. Similarly, a thermal sensor  158  is proximately located relative to the solenoid  136  to the same end. A first output is produced by the sensor  158 , unless the solenoid  136  becomes too hot, in which event a second signal is produced.  
         [0030]    A controller  160  supervises the operation of the system. The controller  160  may be programmed to automatically effect such operation, but in some embodiments may itself be under the control of a PC  162  or similar device, as indicated by an input path  163 . An operator can select various modes of operation of the system  100 , particularly as such operation relates to the laser  104  being turned on and off and the position of the shutter  102 , the condition of both items being dependent on the nature of the workpiece and the type of operation to be performed thereon.  
         [0031]    The controller contains facilities which receive the outputs of the sensors  150 , 152 , 156 , 158 . If the sensors  150  and  152  indicate that the shutter  102  is in a position that is different from the last position directed by the PC  162  and/or the controller  160 , an error or fault signal is produced on an output  164  of the controller  160 . Specifically, if the sensor  150  is producing a first output and the sensor  152  is producing a second output, both indicating that the shutter  102  is “closed”  124 , and the PC  162  has directed that the shutter  102  be closed, no error signal is present on the output  164 . If the sensor  150  is producing a second output and the sensor  152  is producing a first output—the shutter  102  is in the “open” position  126 —but the PC  162  has directed that the shutter be closed, an error signal is produced on the output  164 . If both sensors  150  and  152  are producing a second signal, indication that the shutter  102  is moving between its two positions  124 , 126 , but the shutter  102  has not been directed by the PC  162  to so move, an error signal will be present on the output  164 .  
         [0032]    An important time in the operation of the system  100  as regards the function of the position sensors  150 , 152  occurs during the time that (i) the laser  104  is energized or remains energized if being continuously operated, (ii) the shutter  102  is moved from its first or closed position  124  to its second or open position  126 , and (iii) the shutter  102  is then moved back to its closed position  124 . The laser  104  may be de-energized following phase (iii), but may also continue to be energized, if it is operated continuously, as it awaits the next opening and closing of the shutter  102 . Ideally, the total radiant energy received by the workpiece during the time that the shutter  102  is open is just sufficient to perform the desired work on the workpiece. If the shutter  102  does not close after a laser machining or other operation, too much radiant energy may be received by the workpiece to its detriment.  
         [0033]    The operation of the thermal sensors  156 , 158  is similar to that described in the previous two paragraphs. If either the solenoid  136  or the power amplifier  154  become overheated or otherwise exceed their permissible operating temperatures, the appropriate sensor  156 , 158  will cease sending its first output and begin sending its second output to the controller  160 . This will result in the production of an error signal on the output  164 . Thermal sensors may also be located on or near other potentially temperature-sensitive items, such as the housing  108  or the laser  104  therewithin.  
         [0034]    [0034]FIG. 1 depicts the controller  160  as enabling a laser power supply  166  to energize the laser  104  via the power leads  110 , which originate at the power supply  166 . Such enabling is effected via a link  168  between the controller  160  and the power supply  166 . Connected to the power leads  110  between the power supply  166  and the laser  104  are normally closed circuit interrupters, which are not shown, but which are indicated by the reference numeral  170 . These interrupters normally permit the power supply  166  to energize the laser  104  whenever the controller  160 —as directed by the PC  162 —so directs. The interrupters  170  are selectively operable to open, thereby opening the power leads  110  and de-energizing the laser  104 . The controller output  164  is connected to the interrupters  170  so that if an error signal is present on the output  164 , the interrupters  170  immediately open. Immediate termination of energization of the laser  104  in response to an error signal on the output  164  prevents untoward damage caused by the laser  104  being energized too long or at inappropriate times.  
         [0035]    Whenever an error signal appears on the output  164 , the controller may also apply a first signal to the solenoid  136  through the power amplifier to initiate closing of the shutter  102 . If the shutter  102  is already closed—in its first position—the first signal will effect no movement of the shutter  102 . If the shutter  102  is between its extreme positions or is fully open, it is immediately closed by the first signal. This action helps to ameliorate damage to the workpiece and the system in the event that power to the laser  104  is not interrupted or is interrupted after some delay.  
         [0036]    The solenoid  135  is energized by shaped current pulses (FIG. 2) produced by the controller  160 . These shaped current pulses are sent by the controller  160  to the power amplifier  154 , operating as a controlled current source, where they are amplified to current magnitudes that effectively and efficiently operate the solenoid  136  to produce rapid, controllable rotation of the shutter  102 .  
         [0037]    Referring now to FIG. 2, FIG. 2 a  generally depicts a shaped second or opening signal  200  applied by the controller  160  and the power amplifier  154  to the solenoid  136  via its power leads  138 . The Y-axis is the magnitude of the current applied by the power amplifier  160  to the solenoid; the X-axis is time. The shape, duration and magnitude of the signal  200  may be preset in the controller  160  but are preferably directed by the PC  162  following appropriate manipulation by a human operator or storage of an appropriate program. The second or opening signal  200  is intended to move the shutter  102  from its closed position  124  to its open position  126 , to permit the output of the laser  104  to impinge for a selected time on a workpiece on the stage  122 .  
         [0038]    Prior to t 0 , a small negative current I hc  (“hold closed current”) is applied to the solenoid  136  which current is sufficient to hold the shutter in the closed position  122 . As noted above, if the position sensor  150  is producing a second output, or if the position sensor  152  is producing a first output, or if both sensors  150 , 152  are producing a second output, the shutter  102  is not in the closed position  124  as it should be. As a consequence, the controller  160  senses the discrepancy, produces an error signal on the output  164  to open the relays  170 , thereby de-energizing the laser  104  and/or preventing it from becoming energized. At to, and continuing through t 1 , a rapidly increasing current is applied to the solenoid  136  to accelerate the shutter  102  toward the open position  126 . The shutter  102  reaches maximum velocity at t 1 , when the current has a value of +I 1 . Between t 1  and t 2 , the current is maintained at +I 1  and the shutter  102  is maintained at its maximum velocity. Between t 2  and t 3  a rapidly decreasing current, which ultimately reaches a value of −I 2  is applied to the solenoid  136  to decelerate the shutter  102 . Between t 3  and t 4 , a constant negative current −I 2  is applied to the solenoid  102 ; during this time period, the shutter  102  or the armature of the solenoid  136  abuts a mechanical stop (not shown) defining the open position  126  of the shutter  102  (just as it abuts a similar mechanical stop in its closed position  124 ). This abutment occurs as the shutter  102  is moving at a low velocity—as the current nears −I 2 —to prevent impact damage to the shutter  102  and the solenoid, and to avoid unwanted vibrations in the system  100 . At or before t 4  is reached the shutter  102  is fully open. Between t 4  and t 5  the current increases to a small positive value I ho  (“hold open current”) which is sufficient to hold and maintain the shutter  102  fully open.  
         [0039]    An operator or a stored program may manipulate and operate the PC  162  to effect the production by the controller  160  of a variety of open pulses  200 . The slopes of the current from t 0  to t 1 , from t 2  to t 3  and from t 4  to t 5  may be adjusted by adjusting the time periods t 0 -t 1 , t 2 -t 3  and t 4 -t 5 , and the magnitudes of +I 1  and −I 2 . The time periods t 1 -t 2  and t 3 -t 4  are also adjustable. In this way the acceleration, velocity and position of the shutter  102  at any time during its movement between the closed and open positions  124 , 126 —or vice versa—may be adjusted to deliver a selected amount of energy over a selected amount of time from the laser  104  to the workpiece.  
         [0040]    The current signal  202  applied to the solenoid  136  by the power amplifier  154  as the shutter  102  is moved from the open position  126  to the closed position  124  is the mirror image of that which is applied during the opening operation, with the polarities of FIG. 2 a  being reversed, as may be seen in FIG. 2 b . In preferred embodiments, an Open Cycle and a Close Cycle—each depicted in FIG. 2—both occur in about 5 milliseconds, although other cycle times are clearly obtainable. The absolute value of +I 1 , −I 1 , +I 2  and −I 2  is, in one embodiment, about 4 amps, and the absolute value of the holding currents applied before to in FIGS. 2 a  and  2   b  and after t 5  in both Figures is about 100 milliamps, although, again, these values are also adjustable. For example, FIG. 2 depicts the absolute value of +I 1  and −I 1  being slightly greater (about 100 milliamps) than the absolute value of +I 2  and −I 2 . The laser  104  may be continuously on, with the shutter  102  being responsible for opening and closing to effect the serial application of selected amounts of radiant energy to the workpiece. The laser  104  may also be pulsed. The reflective flag  128  and the light absorber  142  are responsible for directing the light in a benign manner, as discussed earlier, when the shutter  102  is closed as the laser remains energized. Although certain embodiments of the present invention are described herein, it is understood that the scope of the invention is to be determined by the appended claims and that equivalents of specific elements described herein are understood to be covered by such claims.