Abstract:
The present invention relates to a dynamic height adjusting system and method that uses capacitance for a head assembly of a laser processing system throughout a process cycle. The proposed system and method involves use of a single frequency in which a change in phase is measured and processed to determine changes in height and distance between a work piece with an increased reliability. The system further enables operative computerized processor control and substantial improvements in process control signal and feedback distribution throughout an integrated system and optional remote interfaces.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to dynamic height adjusting system and method preferably for use with a laser processing system. More particularly, the present invention provides a dynamic cutting head height adjusting system involving use of a single frequency in which a change in phase is processed to determine changes in height over a work piece with increased reliability, and enhanced process control. 
         [0003]    2. Description of the Related Art 
         [0004]    Cutting head assemblies for laser processing systems are recognized from Applicant&#39;s innovative developments in U.S. Ser. No. 61/542,156 filed Oct. 1, 2011, the entire contents of which are incorporated by reference. Applicant&#39;s cutting head optionally includes a co-located or remote computerized process controllers for uses as noted therein. This system discusses an operative system for processing of a work piece by means of a laser beam. 
         [0005]    A method for monitoring thermal processing (welding) of a work piece is known from U.S. Pat. No. 5,694,046 (Hillerich). This method employs a requirement to form a complex measured capacitance frequency distribution compared to a reference frequency distribution to determine a thermal processing parameter (welding) for a work piece. It recognized that such complex signal methods employs delays in signal determination, is easily compromised by fluxation in voltage, signal interference errors, and an inability to continuously record measured capacitances over the duration of individual laser pulses during welding. Such a method is ill-suited for continuous adaptation to high speed laser processing in an integrated dynamic production cycle. 
         [0006]    Accordingly, there is a need for an improved dynamic height adjusting system and method for a head assembly of a laser processing system. 
       ASPECTS AND SUMMARY OF THE INVENTION 
       [0007]    In response to at least one of the noted concerns, the present invention provides a dynamic height adjusting system and method for operating a head assembly of a laser processing system. The proposed method and system allows for accurate process control throughout a process cycle that is not limited to the type of laser processing conducted. 
         [0008]    In an alternative refinement of the present invention a process control uses capacitance for a head assembly of a laser processing system throughout a process cycle in which a change in phase of a single frequency is monitored to determine changes in distance between a work piece and a laser nozzle. 
         [0009]    Another aspect of the present invention enables easy and operative integration of alternative work piece shapes, materials, types, coatings, and thicknesses while maintaining a continuous process. 
         [0010]    Another aspect of the present invention enables correction for ambient process temperature to eliminate signal error and enhance process control. 
         [0011]    In yet a further alternative aspect of the present invention, the proposed method and system is operatively adaptable to cutting a wide variety of work pieces, including metals, and more particularly including materials that are coated on one or more sides. 
         [0012]    In a further refinement of the proposed invention the system and method accommodates work pieces which are not flat, or which may be substantially flat but contain non-flat regions with improved accuracy. 
         [0013]    In a further refinement of the proposed invention, multiple continuous cutting heads may be operatively controlled by a central process control unit or by one or more remote process control units. 
         [0014]    The proposed method and system further operatively enables a satisfactory monitoring of one or more cutting heads throughout a continuous process cycle, particularly wherein, a continuous process cycle involves intervals of use-nonuse or wherein a work piece may experience variable rates of thermal expansion. 
         [0015]    Another aspect of the present invention enables operative control of one or more process heads for use with work pieces having same or differing thicknesses, such that an indication of initial thickness per work piece may be adopted by a process controller for operative guidance of an individual process head through a use cycle. 
         [0016]    The proposed system and method involves use of a single frequency in which a change in phase is continuously measured and a continuous process determines changes in height or distance between a work piece within an increased reliability and speedy adaptation. 
         [0017]    The system further enables multiple operative computerized processor controls and substantial improvements in process control signal and feedback distribution throughout an integrated process system and optional remote interface. 
         [0018]    According to an alternative embodiment of the present invention there is provided a method for adjusting a cutting head height relative to a work piece in a laser processing system, comprising the steps of: positioning a capacitance sensor in the cutting head relative to the work piece, applying at least a first signal having a first frequency to the sensor, monitoring continuously a phase change of the first signal as a capacitance change in the sensor by evaluating the first signal during a use, and comparing the phase change to a measured cutting head height reference range, thereby determining the cutting head height relative to the work piece. 
         [0019]    According to another alternative embodiment of the present invention, there is provided a method for adjusting a cutting head height relative to a work piece in a laser processing system, comprising the steps of positioning a capacitor sensor in the cutting head relative to the work piece, the capacitor sensor including a nozzle and an isolated sensor block, generating a first and a second signal being equal in frequency but different in phase, applying the first signal to the capacitor sensor, monitoring a phase shift in the first signal as a capacitance changes in the capacitor sensor according to a position of the cutting bead relative to the work piece, adjusting the second signal to a fixed value proximate −90° different in phase from the first signal, determining a phase-shifting of the first signal as a capacitance change in the capacitor sensor by evaluating the phase-shifting of the first signal relative to the fixed value different in phase in the second signal, and comparing the capacitance change to a mapped reference of height versus phase change, thereby determining a relative height between the cutting head and the work piece during a use thereof. 
         [0020]    According to another alternative optional embodiment of the present invention, there is provided a system for adjusting a cutting head height relative to a work piece in a laser processing system, comprising: a capacitance sensor in the cutting head relative to the work piece, means for applying a first signal having a first frequency to the sensor, a detector for continuously detecting a phase change of the first signal as a capacitance change in the sensor by evaluating the first signal during a use, and an operative comparison system for comparing the phase change to a measured cutting head height reference range, thereby determining the cutting head height relative to the work piece. 
         [0021]    The above and other aspects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic illustration of an optional system according to the present invention noting a cutting head relative to a work piece. 
           [0023]      FIG. 2  is a schematic illustration of a cutting head and a work piece according to the present invention. 
           [0024]      FIG. 3  is a graphical representation of a single frequency phase signal shift (from a phase detector) causing an amplified output to go to full range, this amplified phase detector output is digitized and the measured phase change represents a capacitance change in the cutting head. 
           [0025]      FIG. 4  is a graphical representation of the non-linear relationship between capacitance (as phase measurement output voltage (mV)) and stand off height (in mm) from a work piece. 
           [0026]      FIG. 5  is a schematic illustration of a cutting head sensor electronics system noting the interrelation between the cutting head nozzle, a process control unit, and various signals and support elements for operative cycle use. 
           [0027]      FIG. 6  is an exemplary process flow diagram for the proposed system and method for a head assembly of a laser processing system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Reference will now be made in detail to embodiments of the invention. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. The drawings are in simplified form and are not to precise scale. For purposes of convenience and clarity only, directional indicators terms may be used with respect to the drawings. These and similar directional terms should not be construed to limit the scope of the invention in any manner. 
         [0029]    Referring to  FIG. 1 , one alternative of the present inventions provides a system  10  for dynamic height adjusting of a head assembly of a laser processing system (incorporated via the shown cutting head). Various elements are in communication and are operatively linked to enable system  10  to operate in a continuous cycle. System  10  includes a base station  1  having at least one and optionally several process controllers  2  operatively linked with a cutting head element  3 , having sensor and controlling processors  3 A, positioned relative to a work piece  4  and controllably linked via an operative control loop represented at  11  with a Z-stage assembly  5  enabling precision positioning in real time of cutting head  3  relative to work piece  4 . 
         [0030]    As will be noted from  FIG. 1 , multiple optional communication arrangements can be provided, including transmission to an optional customer computer  7  or a separate electronic controller package  8  via a variety of communication pathways interlinked as will be understood by those of skill in the art. For the purposes of this discussion it will be understood, per the paragraph below, that all forms of communication are intended to be incorporated by reference in a manner readily understood by one so skilled. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 Table of optional communication pathways between system components. 
               
               
                 Communication Types 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Digital &amp; Analog 
               
               
                   
                 Wired, Wireless and Optical 
               
               
                   
                 Ethernet, Internet (various), Cellular - digital, Satellite 
               
               
                   
                 (This disclosure intends to encompass all forms of 
               
               
                   
                 communication pathways, without limitation) 
               
               
                   
                   
               
             
          
         
       
     
         [0031]    It will be understood that the electronics for height sensing are used with a cutting head designed for integration into a laser system as noted earlier, and preferably for use with a flat bed laser system for cutting sheet materials, pipe materials etc. This system is readily adaptive to variable cutting, arrangements and in any orientation relative to the gravity field. 
         [0032]    A standoff height is understood to be a distance of the cutting head above a cutting surface and may be optionally understood to include a pre-set correction factor. Precise control and maintenance of the standoff height is critical to performance. Different cutting head designs (longer nozzles) may be used in robotic based cutting systems and will be understood as within the scope of this disclosure. Typically, a desired standoff height is 0.5 mm to 2.0 mm, preferably 1.0 mm with a desired error of ±0.1 mm, but may be any range based upon a number of operational factors, materials, surface coatings focus spot, cutting or thermal treat speed and other operational variables. 
         [0033]    Cutting head  3  may be of any operative construction effective to function as discussed herein and will be understood as operative with any connector, power consumption, or communication elements known to those of skill in the art. 
         [0034]    As discussed particularly, cutting head  3  includes a height sensor PCB, alternatively discussed as a capacitance sensor, and process controller package included as  3 A for effective operation. The cutting head sensor interface is power over Ethernet with a suitable current draw, for example of 48v between 8.3 mA and 30Ma. A compliant interface uses a standard PD interface and is programmed to limit an inrush current to a value acceptable for use with a passive power source thus creating a functional delay between plugging in the device and accepting it as a PD into system  10 . Further components may include an isolated converter provides internal isolation, and optionally sensing components may be positioned below or even on the work piece being treated to provide further process feedback. 
         [0035]    Base station  1  includes a dedicated Ethernet to communicate with cutting head  3 , and external customer systems  7  and  8 . Communication links may be provided without limit. Suitable electronics are provided to enable operation as discussed herein. A series of required signal inputs and outputs are available to the user through Ethernet or other forms of communication (above). The minimum required inputs-outputs are discussed below. 
         [0000]    
       
         
               
             
               
             
           
               
                   
               
               
                 Table of Input-Output types/results involving selected process variables 
               
               
                 and controller sense functions in a non-limited summary. 
               
               
                 INPUT-OUTPUT TYPES 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Tip height (0.10 mm to 15.00 mm, or more, in resolution ±0.05 mm) 
               
               
                 Tip Touch 
               
               
                 Body Touch 
               
               
                 Tip Lost (Nozzle Fell Off) 
               
               
                 Pierce - senses when pierce is complete to reduce time 
               
               
                 Signal/Cable Link Cut/Unplugged/Disconnection 
               
               
                 Out of height range 
               
               
                 In range/position reached 
               
               
                 Temperature reported 0-100° C. ± 4° C. (thermal sensing) 
               
               
                 LED (head) Status Indicator 
               
               
                 Speed - variable, at least 0.05 sec. resolution possible 
               
               
                 Acceleration/Accelerometer 
               
               
                   
               
             
          
         
       
     
         [0036]    It is understood for proper cutting of good quality that the stand off height be maintained during movement of the cutting head relative to the surface. Unfortunately surface height variation may exist due to imperfections in flatness, thickness, coating, physical distortion (bending), and thermal distortion (expansion). Such variations may occur in process may change during a process). A typical cutting height is noted above, but proposed system  10  is operative to measure standoff height, report the result to a process controller (in the head  3  or remote from head  3  or both) and is operative to trigger a system action, including trigger a Z-axis controller and Z-stage  5  via link  11 . 
         [0037]    Referring now to  FIG. 2 , an operative cutting head  3  includes a main housing member  16  having microcontroller electronics (arranged in any operative form, including annular, flat, multi-profiled (three dimensioned), etc.), and in series off a work piece  4 , a copper nozzle member  15 , an insulator  14 , an isolated sensor block  13 , and a further insulator  12  to operatively enable a capacitance measuring system as will be discussed. 
         [0038]    Nozzle  15  and isolated sensor block  13  of head  3  form a capacitor and have a capacitance that is affected by the distance to the material being cut. This capacitance varies approximately 4 pF as the height of the nozzle changes from 0.1 mm to 10 mm. Similarly, it will be understood that the nozzle  15  touching the work piece makes a significant change in the signal (flagged as a ‘touch’), isolated sensor block  13  hitting an object also provides a change in signal (flagged as a ‘collision’), and nozzle  15  falling off also creates a cognizable signal. 
         [0039]    In operation a 10 MHz sign wave is applied across the capacitor formed by nozzle  15  and isolated sensor block  13 . Small changes in capacitance cause a small (several degrees) phase shift in the signal. The signal and a reference wave form are measured, for example by an Analog Devices AD8302 gain and phase detector. The phase signal is amplified over a range of interest by a buffer amp with high gain. It will be understood that the phrases capacitance sensor, height sensor, and cutting head sensor may be used adaptively and interchangeably without departing from the scope and spirit of the present invention, and will be understood as such by those of skill in the art. 
         [0040]    Referring now to  FIG. 3 , a simulation of 10 degrees of phase shift (delta 100 mV from phase detector) (V(v-phase)) causes an amplifier output (V(phaseout)) to go full range. The amplified phase detector output is digitized and this measured phase change represents a capacitance change in head  3 . 
         [0041]    Referring now to  FIG. 4 , the capacitance change in head  3  is not linear. By calibrating cutting head  3  to measured height(s), using any operative means such as optical measurement, the capacitance change can be mapped to a height for a particular operative system.  FIG. 4  is an example of the phase measurement output voltage vs. standoff height from the proposed method and system. It will be understood that the process of mapping a height for a particular laser system relative to a work piece can occur prior to operation, or in a dynamic process cycle using any measurement method known to those of skill in the art including optical, some (transducer), or mechanical methods. For example, while the exemplary system employs a single mapping process for  FIG. 4 , it will be understood that a continuous mapping process may be employed by adding a mapping or measuring system to cutting head  3  with a feed back to a process controller for continuous adjustment. As a result, the proposed method and system will be understood as adaptively dynamic. 
         [0042]    Referring now to  FIG. 5 , an example of the electronics schematic in cutting head  3  is discussed and remains substantially unnumbered as the references will be understood by those of skill in the art. As a non-limiting example, cutting head  3  may include an LPC17xx microcontroller (shown as an LPC1768) to communicate the height and other data back to base station  1  and further process controller  2  via Ethernet. An accelerometer is incorporated to separate motion by cutting head  3  from relative motion of work piece  4 . Base station  1  allows a broad array of analog, digital, and bus input/output to adapt to differing use demands. Base station  1  may have one or multiple micro controllers. 
         [0043]    In further explanation, the proposed capacitance sensor, height sensor, or cutting head sensor as  3 A employs a two-carrier coherent synthesizer (from a 312.50 MHz system clock) to create two carrier signals equivalent in frequency but different in phase. Here, one signal (signal one) is phase-shifted by the 40 pF-average capacitive head (noted as a 400-ohm environment at 10 MHz) as the capacitance changes by +5 pF. A 1:8 transformer changes this to 50-ohm 320 pF. The second signal (signal two) is adjusted to a fixed value that creates as close to −90° between the two carrier signals as can be realized with 0.175° phase steps. 
         [0044]    Phase detection is determined by an AD8302ARUZ gain-phase detector IC shown at having two outputs (as shown). One output of the phase detector is 10 mV/° phase. The second output of the phase detector is 10 mV/dB relative magnitude. The phase detector is adjustable, here having an adjustment range of ±33° around the initial adjustment position and a granularity (into it 3.3V 12-bit ADC known in the art) of 0.003°. Thus making an initial adjustment accuracy of about ±30 quantization levels and rendering substantial accuracy following adjustment. 
         [0045]    In practice, base station  1 , via process controller  2 , regularly samples the high-gain phase and the relative magnitude (for example by a second microcontroller type LPC1768 known in the art). The high-gain phase and relative magnitude are offset by the ±30 quantization levels of the initial adjustment inaccuracy. The high-gain phase and relative magnitude are then compared to tables of height vs. phase and short versus magnitude, and the height and short information are sent out for further use, for a non-limiting example, to a target customer interface at  8 . 
         [0046]    As introduced above, proposed system  10  enables adjustment for temperature sensitivity. The proposed phase detector system has a temperature coefficient in phase output versus ambient temperature which results in a height error estimated to be ±10-20 μm/°C. Thus, by managing circuit-sensor temperature error is managed by one or more of the process controllers in the cutting head  3 , base station  1 , or in remote systems  7  or  8 . As proposed, a heater thermal sensor and heater circuit is provided to elevate the proposed phase detector (chip) to around 50° C. and to maintain this temperature (although other temperatures may be used without limitation). A target set point enables the heater circuit to maintain temperature, for example ±5° C. from a control set point of ±2.5° C. 
         [0047]    As a non-limited example, a plurality of cutting heads  3 , each with internal sensors and controllers  3 A may be jointly operated by a single base station  1  through a production cycle, wherein a work piece may change height substantially through a cycle path. Thus by managing the above-noted features a continuously operative height adjustment is readily achieved according to the present invention. 
         [0048]    Referring now to an exemplary process flow at  FIG. 6 , wherein a process operation  100  includes a step of inputting initial process cycle data  101  to a process controller  102  in any form noted above and storing selected inputs in a data storage  103  operatively linked with a data calculator  104  all in communication with an input/output feature  105 . In use a start operation step  106  begins with a surface approach  107  and confirmation of an initial height  108  and then beginning of a desired laser treatment process (of any kind). Thereafter a continuous height sensing step  109  is performed throughout the continuous process. If system  100  is within range in a determination step  111 , the process continues to operate and monitor in step  114  until a completion of cycle  115 . 
         [0049]    However, if an out of range step is determined  110  then a cycle of height adjustment  112  and optionally a stop step  113  is initiated to ensure only in range operation. As is noted, input/output step  105  (and thus process controller interaction step  302 ) is continuously in communication with each operative step in system  100 , through a step (via continuous reading step  109 ) or via a direct link, for example initial height determination step  108 . It will be understood that data storage step  103  and data calculator step  104  are used continuously throughout each operation cycle as may be modified by an operational control. 
         [0050]    It will be understood that focus is the distance below the nozzle tip that a laser is in focus. A focus spot is often desired to be below the surface of a material being cut, and potentially may extend through the material. It will also be understood that the phrase PoE (or Power over Ethernet) is an Ethernet connection that includes power. 
         [0051]    It will be understood that the proposed system and method may he operated continuously throughout a process cycle and across different work pieces without limitation, and that such understanding of continuous includes pre- and post-laser use, such that the entire system and method will be understood as being operative ‘in situ’ or throughout the entire use of the system. Those of skill in the art, having studied the entire disclosure, will further recognize the broad application of the proposed system and method and that the system and components employed may be modified, removed, substituted, edited, or changed and that all such actions will be understood as within the scope of the invention. 
         [0052]    As a non-limiting example, the proposed invention employs one or more microcontrollers or process controllers in operatively preferred locations. However, nothing in the disclosure so limits such controllers to a particular number, shape, or location, or type. Indeed, those of skill in the art will recognize that a single controller, in any location, may suffice here operatively sufficient communications loops are established between the system components. 
         [0053]    As a further non-limiting example, the proposed communication pathways between the cutting head, base station, customer PLC or optional PC&#39;s etc, will be understood as exemplary. A single base station may suffice, or the proposed system may be substantially autonomous (without continuous signal external to the cutting head), or such communications may be fully remote from the cutting head in communication solely by wireless signal. in this manner, those of skill in the art will recognize the breadth of the invention and that all such modifications are intended to be within the scope and spirit of the present invention. 
         [0054]    Having described at least one of the preferred embodiments of the present invention with reference to the accompanying drawings, it will be apparent to those skills that the invention is not limited to those precise embodiments, and that various modifications and variations can be made in the presently disclosed system without departing from the scope or spirit of the invention. Thus, it is intended that the present disclosure cover modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.