Abstract:
A linear stage system is provided. The linear stage system includes a base, a carriage plate, a first shaft, a first air bushing coupled to the base, a first motor coupled to the base and the carriage plate, and a first position encoder. The first air bushing is configured to support the carriage plate via the first shaft, wherein the first air bushing utilizes the first shaft as a guide surface and is configured to support positioning of the carriage plate along an axis. The first motor is configured to create a linear motion parallel to the axis in a first motor element coupled to the carriage plate to position the carriage plate along the axis in response to a first control signal. The first position encoder is configured to determine a position of the carriage plate relative to the base.

Description:
RELATED APPLICATIONS 
     This application hereby claims the benefit of and priority to U.S. Provisional Patent Application No. 61/107,418, titled “AIR BUSHING LINEAR STAGE SYSTEM”, filed on Oct. 22, 2008, and which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL BACKGROUND 
     Linear stage systems are utilized for precision motion in linear directions. Linear stage systems are commonly used in manufacturing processes, such as semiconductor manufacturing. A linear stage system may be used to position a silicon wafer at a specific position so that a mask image is in focus on the wafer surface. In such photolithography applications focus is critical and is accomplished by ensuring that the surface of the wafer is in a precise position for best possible focus. Other applications for linear stage systems may arise in testing semiconductors where a wafer must be lifted against a set of probes. Once again vertical positioning of the wafer is critical since overdriving the probes may damage them. 
     One common linear stage system is a Z wedge design used to create motion in the Z, or vertical, direction. Many versions of Z wedge designs exist but this design inherently has many errors associated with it. The motors typically drive in a horizontal dimension and bearings constrain the stage such that motion results in a vertical direction. Bearings always have some dimensional error or parallelism errors that are included in the motion. Additional errors are induced by machining accuracy errors, which are greater than normal for the angular surfaces required of such a design. Often the encoder measures horizontal motion and the results are calculated into the resulting Z motion. This calculation requires assumptions that add to the Z linear accuracy error. 
     Other Z stage designs use mechanical bearings with encoders and motors oriented vertically. This eliminates some of the errors with the Z wedge design but mechanical bearings still induce errors and are largely dependent on machined surfaces. Additionally stages in this orientation also tend to be large dimensionally in the Z direction. 
     OVERVIEW 
     A linear stage system is provided. The linear stage system includes a base, a carriage plate, a first shaft, a first air bushing coupled to the base, a first motor coupled to the base and the carriage plate, and a first position encoder. 
     The first air bushing is configured to support the carriage plate via the first shaft, wherein the first air bushing utilizes the first shaft as a guide surface and is configured to support positioning of the carriage plate along an axis. 
     The first motor is configured to create a linear motion parallel to the axis in a first motor element coupled to the carriage plate to position the carriage plate along the axis in response to a first control signal. 
     The first position encoder is configured to determine a position of the carriage plate relative to the base. 
     A method for operating a linear stage system is also provided. The linear stage system includes a base, a carriage plate, a first shaft coupled to the carriage plate, a first air bushing coupled to the base, a first motor coupled to the base and the carriage plate, and a first position encoder coupled to the base. The method includes supporting the carriage plate via the first shaft within the first air bushing, wherein the first air bushing utilizes the first shaft as a guide surface and is configured to support positioning of the carriage plate along an axis. 
     The method also includes with the first motor, creating a linear motion parallel to the axis in a first element coupled to the carriage plate to position the carriage plate along the axis in response to a first control signal, and determining a position of the carriage plate relative to the base using the first position encoder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. While several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents. 
         FIG. 1  is a top view of an example of a linear stage. 
         FIG. 2  is a top view of an example of a linear stage. 
         FIG. 3  is a cross sectional view of the air bushings and shafts in an example of a linear stage. 
         FIG. 4  is a top view of an example of a linear stage. 
         FIG. 5  is a block diagram of an example of a linear stage system. 
         FIG. 6  is a perspective view of an example of a linear stage. 
         FIG. 7  is a top view of an example of a carriage plate for a linear stage. 
         FIGS. 8A and 8B  are side views of an example of a linear stage. 
         FIG. 9  is a top view of an example of a base for a linear stage. 
         FIG. 10  is a bottom view of an example of a base for a linear stage. 
         FIG. 11  is a top view of an example of a carriage plate for a linear stage. 
         FIG. 12  is a perspective view of an example of a base for a linear stage. 
         FIG. 13  is a perspective view of an example of a carriage plate for a linear stage. 
     
    
    
     DETAILED DESCRIPTION 
     A linear stage system comprises multiple air bushings, shafts, encoders, motors, and a controller, which are all mounted on a base. The air bushings support a carriage plate. The linear stage system may also comprise pneumatic counter balances to permit easy user adjustment for various applications and a central thru aperture that provides an added capability for additional equipment mounted to the base. The motors, air bushings, and counter balances are all placed symmetrically within the structure to ensure all applied forces and restraint are balanced. Other embodiments may include placing the motors, air bushing, and counter balances asymmetrically within the structure. Depending on how the linear stage system is configured, the carriage plate may move in different linear dimensions from the base. 
       FIG. 1  is a top view of an example of a linear stage  100 . The linear stage  100  of  FIG. 1  is triangular in shape and is comprised of a stationary base (not shown beneath carriage plate  102 ) and a top moving carriage plate  102 . While the linear stage system of  FIG. 1  is triangular in shape, other shapes and configurations may be used. This example linear stage  100  includes a single air bushing  106  located near the center of the linear stage  100 , and air bushing  106  encloses shaft  104 . Air bushing  106  is permanently fixed to the stationary base to ensure system performance and repeatability over time. Air bushing  106  is used to constrain carriage plate  102  and to allow motion along the air bushing guide shaft. 
     Shaft  104  is used as an air bushing guide surface and can be manufactured to very high precision which allows for a precise straightness of motion. Additionally, the high precision allows for the pitch, yaw, and roll errors of the linear stage to be very small. In this example illustration, motion of carriage plate  102  would be in or out of the page. 
     The linear stage  100  of  FIG. 1  also includes motor  108  and position encoder  110 , however any number of motors and position encoders may be used in other embodiments. Motor  108  is a linear actuator, and in this example, a voice coil and a moving element is used for motor  108 , while other linear actuators may be used for motor  108  in other embodiments. In this example embodiment, the voice coil is coupled to the base while the moving element is coupled to carriage plate  102 . When electrical signals are applied to the voice coil, the element is moved up or down along the voice coil. Thus, the voice coil creates a linear motion parallel to the axis of motion of the carriage plate with respect to the base. 
     The voice coil provides positional accuracy on a nanometer level with minimal dither and no backlash. The voice coil allows for speeds that range from less than one micrometer per second to several meters per second (depending on motor size selection). Additionally, the voice coil is a non-contact device that does not add any friction or error into the system. 
     Position encoder  110  provides for high resolution digital output. The encoder scales may be made with Invar® to reduce positional error due to thermal expansion or environmental effects. The encoder design also accommodates Zerodur® or glass scales with zero thermal expansion. Two or three encoders may paired with each motor and located adjacent to the respective motor in some embodiments. The use of multiple encoders per motor allows for accurate feedback, which in turn results in accurate positioning capability as well as no angular errors of the carriage plate during motion or holding position. Additionally, position encoders  110  may be used to determine the position of carriage plate  102  with respect to the base in other configurations. 
     The linear stage system of  FIG. 1  is controlled by a stand-alone controller (illustrated in  FIG. 5 ). The controller communicates with a computer through a RS-232 serial port, an Ethernet, or a USB connection. The controller communicates with the linear stage using component signals. The controller can be used to monitor the air bushing supply pressure for sufficient pressure. The controller has two to three channels of motion control for the different motor/encoder pairs. 
       FIG. 2  is a top view of an example of a linear stage  200 . The linear stage  200  of  FIG. 2  is triangular in shape and is comprised of a stationary base (not shown beneath carriage plate  202 ) and a top moving carriage plate  202 . While the linear stage  200  of  FIG. 2  is triangular in shape, other shapes and configurations may be used. A thru aperture  204  is found at the center of the linear stage system and passes through the base and the carriage plate  202 . The linear stage  200  has air bushings  208  located near each corner and each air bushing  208  surrounds a shaft  206 . Air bushings  208  are permanently fixed to the base to ensure system performance and repeatability over time. The air bushings  208  are used to constrain the carriage plate  202  and allow motion along the air bushing guide shafts. There are three air bushings  208  for kinematic support and constraint of the moving carriage plate  202 . The shafts  206  are used as the air bushing guide surfaces and can be manufactured to very high precision, which allows for a precise straightness of motion. Additionally, the high precision allows for the pitch, yaw, and roll errors of the linear stage to be very small. 
     The linear stage  200  of  FIG. 2  also contains two voice coils  210  and two counterbalances  214 , however, more than two voice coils  210  and two counterbalances  214  may be used. The voice coils  210  provide positional accuracy on a nanometer level with minimal dither and no backlash. While voice coils  210  are used as motors in the linear stage system of  FIG. 1 , other linear actuators can be used. The counterbalances  214  support the payload and moving mass with the motors providing the driving force for motion. The voice coils  210  allow for speeds that range from less than one micrometer per second to several meters per second (depending on motor size selection). Additionally, the voice coils  210  are non-contact devices that do not add any friction or error into the system. Multiple voice coils  210  are used to ensure force is applied evenly over the entire carriage plate  202 . 
     Additionally, the linear stage  200  of  FIG. 2  contains three encoders  212 , although, more or fewer encoders  212  could be used. The encoders  212  provide for high resolution digital output. The encoder scales may be made with Invar® to reduce positional error due to thermal expansion or environmental effects. The encoder design also accommodates Zerodur® or glass scales with zero thermal expansion. Two or three encoders  212  may be paired with each separate motor  210  and located adjacent to the respective motor. The use of multiple encoders  212  per motor  210  allows for accurate feedback, which in turn results in accurate positioning capability as well as no angular errors of the carriage plate  202  during motion or holding position. 
     The linear stage  200  of  FIG. 2  is controlled by a stand-alone controller (illustrated in  FIG. 5 ). The controller communicates through a RS-232 serial port, an Ethernet, or a USB connection. The controller can be used to monitor the air bushing supply pressure for sufficient pressure. The controller has two to three channels of motion control for the different motor/encoder pairs. 
       FIG. 3  is a cross sectional view of the air bushings and shafts in an example of a linear stage.  FIG. 3  is an illustration of cross-section A-A from  FIG. 2 .  FIG. 3  illustrates an example of the positioning of the air bushings  208  and shafts  206  relative to each other. In  FIG. 3 , the shafts  206  move up and down while the air bushings  208  are affixed to the base  302 . Such a configuration of a Z motion may provide better than 100 nm of accuracy and better than 90 nm of repeatability, and better than 10 nm of resolution. 
     In this example, two air bushings  208  and two shafts  206  are illustrated within linear stage  300 . Linear stage  300  includes stationary base  302  and moving carriage plate  202 . The two air bushings  208  are coupled to base  302 , and the two shafts are coupled to carriage plate  202 , and configured to move along one axis within the two air bushings  208 . Counter balance  214  is also illustrated as coupled with carriage plate  202  and touching base  302 . Counter balance  214  supports the payload and moving mass against gravity with the motors providing the driving force for motion. 
       FIG. 4  is a top view of an example of a linear stage  400 . Linear stage  400  illustrated in  FIG. 4  is similar to linear stage  300  illustrated in  FIG. 3  with the exception of the addition of another motor/encoder pair and another counterweight. Also, positions of some of the elements of linear stage  400  are different. In this example, linear stage  400  includes carriage plate  402 , three air bushings  408  with their associated shafts  406 , three motors  410  with their associated position encoders  412 . Also shown are three counterweights  414 . 
       FIG. 5  is a block diagram of an example of a linear stage system  500 . This example linear stage system includes linear stage  502  and controller  504 . Controller  504  communicates with a controlling computer through a RS-232 serial port, an Ethernet, or a USB connection  506 . The controller communicates with the linear stage using component signals. Controller  504  can be used to monitor the air bushing supply pressure for sufficient pressure. Controller  504  has two to three channels of motion control for the different motor/encoder pairs. 
       FIG. 6  is a perspective view of an example of a linear stage  600 . This example linear stage  600  includes stationary base  1  and moveable carriage plate  4 . A thru aperture  30  is also shown in the center of linear stage  600  going through both carriage plate  4  and base  1 . 
     Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. While several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents. 
     The linear stage  600  of  FIG. 6  also includes at least one motor and at least one position encoder, however any number of motors and position encoders may be used in other embodiments. The motor is a linear actuator, and in this example, a voice coil and a moving element is used as a motor, while other linear actuators may be used as a motor in other embodiments. In this example embodiment, the voice coil is coupled to the base  1  while the moving element is coupled to carriage plate  4 . When electrical signals are applied to the voice coil, the element is moved up or down along the voice coil. Thus, the voice coil creates a linear motion parallel to the axis of motion of the carriage plate with respect to the base. 
     The voice coil provides positional accuracy on a nanometer level with minimal dither and no backlash. The voice coil allows for speeds that range from less than one micrometer per second to several meters per second (depending on motor size selection). Additionally, the voice coil is a non-contact device that does not add any friction or error into the system. 
     Position encoders provide for high resolution digital output. The encoder scales may be made with Invar® to reduce positional error due to thermal expansion or environmental effects. The encoder design also accommodates Zerodur® or glass scales with zero thermal expansion. Two or three encoders may paired with each motor and located adjacent to the respective motor in some embodiments. The use of multiple encoders per motor allows for accurate feedback, which in turn results in accurate positioning capability as well as no angular errors of the carriage plate during motion or holding position. Additionally, position encoders may be used to determine the position of carriage plate  4  with respect to base  1  in other configurations. 
     The linear stage  600  of  FIG. 6  is controlled by a stand-alone controller (illustrated in  FIG. 5 ). The controller communicates through a RS-232 serial port, an Ethernet, or a USB connection. The controller can be used to monitor the air bushing supply pressure for sufficient pressure. The controller has two to three channels of motion control for the different motor/encoder pairs. 
       FIG. 7  is a top view of an example of a carriage plate  4  for a linear stage  600 . This example carriage plate  4  includes a number of apertures and bolts used for attaching internal elements of linear stage  600  to carriage plate  4 . Other embodiments may use other configurations and other means for coupling of elements to carriage plate  4 . A thru aperture  30  is also shown in the center of linear stage  600  going through carriage plate  4 . 
       FIGS. 8A and 8B  are side views of an example of a linear stage  600 .  FIG. 8A  illustrates linear stage  600  in a lowered or closed position. In this position, carriage plate  4  is at its lowest elevation and rests against base  1 .  FIG. 8B  illustrates linear stage  600  is a fully risen or open position. In this position carriage plate  4  is at its highest elevation. Note that carriage plate  4  moves in the Z axis, in the same direction as the motors move. In some embodiments, linear stage  600  may be rotated such that the motion occurs on a different axis. However, the motion of carriage plate  4  will always be along an axis parallel to the motion of the one or more motors or voice coils and moveable elements used in constructing linear stage  600 . 
       FIG. 9  is a top view of an example of a base for a linear stage  600 . In this example embodiment stationary base  1  is illustrated with a number of its associated elements. This example assembly includes three air bushings  2 , three shafts  5  each with a socket head cap  15 . Also included are two actuators used as counterbalances  8 , loop straps  17  used to route tubing to the air bushings  2 . Two voice coils  6  with their assembly screws  22  are illustrated along with two position encoder heads  7  and their respective scales  9 . A thru aperture  30  is also shown in the center of linear stage  600  going through base  1 . 
       FIG. 10  is a bottom view of an example of a base for a linear stage  600 . This view illustrates the various fittings and connections present on the bottom of the base  1  of linear stage  600 . These fittings include a plurality of pneumatic fittings  19  used for supplying air to their associated air bushings, along with three hard stops  11  affixed to their respective shafts by screws  10 . These hard stops  11  constrain the maximum motion along the Z axis that the carriage plate is allowed to move. Other embodiments may use other methods of limiting the travel of the carriage plate. Also illustrated are a plurality of screw holes  14 , and screws  23  for affixing the motors to the base. Other embodiments may use other configurations and means for connecting supply hoses and wires to linear stage  600 ,  FIG. 10  is simply used for the illustration of one possible embodiment. A thru aperture  30  is also shown in the center of linear stage  600  going through base  1 . 
       FIG. 11  is a top view of an example of a carriage plate  4  for a linear stage  600 . In this example, carriage plate  4  includes a number of features used for connecting various elements of linear stage  600  to carriage plate  4 . A thru aperture  30  is also shown in the center of linear stage  600  going through carriage plate  4 . Other embodiments may use other configurations for connecting these various elements to carriage plate  4 ,  FIG. 11  is simply used for the illustration of one possible embodiment. 
       FIG. 12  is a perspective view of an example of a base  1  for a linear stage  600 . In this example embodiment, base  1  includes a number of elements of linear stage  600 . Base  1  includes three air bushings  2 , two actuators used as counterbalances  8 , two motors or voice coils  6 , along with two encoders  7 . A thru aperture  30  is also shown in the center of linear stage  600  going through base  1 . 
     Base  1  of linear stage  600  of  FIG. 12  includes two motors and two position encoders, however any number of motors and position encoders may be used in other embodiments. The motor is a linear actuator, and in this example, a voice coil and a moving element is used as a motor, while other linear actuators may be used as a motor in other embodiments. In this example embodiment, the voice coil is coupled to the base  1  while the moving element is coupled to carriage plate  4 . When electrical signals are applied to the voice coil, the element is moved up or down along the voice coil. Thus, the voice coil creates a linear motion parallel to the axis of motion of the carriage plate with respect to the base. 
     The voice coil provides positional accuracy on a nanometer level with minimal dither and no backlash. The voice coil allows for speeds that range from less than one micrometer per second to several meters per second (depending on motor size selection). Additionally, the voice coil is a non-contact device that does not add any friction or error into the system. 
     Position encoders provide for high resolution digital output. The encoder scales may be made with Invar® to reduce positional error due to thermal expansion or environmental effects. The encoder design also accommodates Zerodur® or glass scales with zero thermal expansion. Two or three encoders may paired with each motor and located adjacent to the respective motor in some embodiments. The use of multiple encoders per motor allows for accurate feedback, which in turn results in accurate positioning capability as well as no angular errors of the carriage plate during motion or holding position. Additionally, position encoders may be used to determine the position of carriage plate  4  with respect to base  1  in other configurations. 
     The linear stage  600  of  FIG. 12  is controlled by a stand-alone controller (illustrated in  FIG. 5 ). The controller communicates through a RS-232 serial port, an Ethernet, or a USB connection. The controller can be used to monitor the air bushing supply pressure for sufficient pressure. The controller has two to three channels of motion control for the different motor/encoder pairs. 
     Other embodiments may use other configurations and different quantities of elements in constructing linear stage  600 .  FIG. 12  is simply used for the illustration of one possible embodiment. 
       FIG. 13  is a perspective view of an example of a carriage plate  4  for a linear stage  600 . In this example embodiment, carriage plate  4  includes a number of elements of linear stage  600 . Carriage plate  4  includes three shafts  5 , each with a corresponding hard stop  11  attached to their respective shafts by screws  10 , along with two motors or voice coils  6  and two encoder scales  9 . In this embodiment, travel of the carriage plate  4  with respect to base  1  is limited by hard stops  11 . However, other embodiments may use other structures or means for limiting the travel of carriage plate  4 . Each voice coil  6  is associated with a moveable element  31  affixed to carriage plate  4 , shown here as a cylindrical sleeve around the voice coil. When electricity is applied to a voice coil  6 , the moveable element  31  moves along the axis of the voice coil. In other words, the motion of the motor is parallel to the axis of the motion of the carriage plate. 
     Carriage plate  4  of linear stage  600  of  FIG. 13  includes two motors and two position encoders, however any number of motors and position encoders may be used in other embodiments. The motor is a linear actuator, and in this example, a voice coil  6  and a moving element  31  is used as a motor, while other linear actuators may be used as a motor in other embodiments. In this example embodiment, during assembly the voice coil  6  is coupled to the base  1  while the moving element  31  is coupled to carriage plate  4 . When electrical signals are applied to the voice coil  6 , the element  31  is moved up or down along the voice coil  6  along the Z axis. Thus, the voice coil creates a linear motion parallel to the axis of motion of the carriage plate with respect to the base. 
     The voice coil provides positional accuracy on a nanometer level with minimal dither and no backlash. The voice coil allows for speeds that range from less than one micrometer per second to several meters per second (depending on motor size selection). Additionally, the voice coil is a non-contact device that does not add any friction or error into the system. 
     Position encoders provide for high resolution digital output. The encoder scales may be made with Invar® to reduce positional error due to thermal expansion or environmental effects. The encoder design also accommodates Zerodur® or glass scales with zero thermal expansion. Two or three encoders may paired with each motor and located adjacent to the respective motor in some embodiments. The use of multiple encoders per motor allows for accurate feedback, which in turn results in accurate positioning capability as well as no angular errors of the carriage plate during motion or holding position. Additionally, position encoders may be used to determine the position of carriage plate  4  with respect to base  1  in other configurations. 
     The linear stage  600  of  FIG. 13  is controlled by a stand-alone controller (illustrated in  FIG. 5 ). The controller communicates through a RS-232 serial port, an Ethernet, or a USB connection. The controller can be used to monitor the air bushing supply pressure for sufficient pressure. The controller has two to three channels of motion control for the different motor/encoder pairs. 
     Also, other embodiments may differ in configuration and quantity of elements used in constructing linear stage  600 .  FIG. 13  is simply used for the illustration of one possible embodiment. 
     It should be emphasized that the above-described embodiments are merely possible examples of implementations, merely set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure. 
     The above description and associated figures teach the best mode of the invention. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Those skilled in the art will appreciate that the features described above can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described above, but only by the following claims and their equivalents.