Patent Publication Number: US-2023158601-A1

Title: Handheld laser welding device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 63/281,116 filed on Nov. 19, 2021, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Embodiments of the present invention relate to laser devices. More specifically, embodiments of the present invention relate to handheld laser devices, systems, and methods, for example, for welding and cutting. 
     Description of Related Art 
     Handheld laser devices can be very effective in executing certain types of welding or cutting procedures on workpieces. However, when using such devices, the accidental emission of laser light into free space or in an otherwise unwanted or unintended direction away from the workpiece is generally undesirable. Furthermore, performance improvements with respect to certain aspects of handheld laser devices are desired. 
     BRIEF SUMMARY OF THE INVENTION 
     The following summary presents a simplified summary in order to provide a basic understanding of some aspects of the devices, systems and/or methods discussed herein. This summary is not an extensive overview of the devices, systems and/or methods discussed herein. It is not intended to identify critical elements or to delineate the scope of such devices, systems and/or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. 
     In accordance with one aspect of the present invention, provided is a laser welding system. The laser welding system includes a laser power supply having a controller that controls activation of laser light by the laser power supply. A sense lead is attachable to a workpiece to be welded. A handheld laser welding torch is operatively connected to the laser power supply to receive the laser light from the laser power supply. The handheld laser welding torch includes a nozzle having an electrically insulating outer surface, and a pressure sensor that measures a pressure level applied to the nozzle and generates a corresponding pressure level signal. The laser welding system further includes a proximity sensor that is operatively connected to the sense lead and the handheld laser welding torch and that is configured to determine whether the handheld laser welding torch is adjacent to the workpiece and generate a corresponding proximity signal. The controller receives the pressure level signal from the pressure sensor and the proximity signal from the proximity sensor. The controller is configured to activate the laser light when the pressure level applied to the nozzle meets or exceeds a threshold and the proximity signal indicates that the handheld laser welding torch is adjacent to the workpiece. 
     In accordance with another aspect of the present invention, provided is a laser welding system. The laser welding system includes a laser power supply having a controller that controls activation of laser light by the laser power supply. A sense lead is attachable to a workpiece to be welded. A handheld laser welding torch is operatively connected to the laser power supply to receive the laser light from the laser power supply. The handheld laser welding torch includes a nozzle and a pressure sensor that senses a pressure level applied to the nozzle and generates a corresponding pressure signal. The laser welding system further includes a proximity sensor that is operatively connected to the sense lead and the handheld laser welding torch and that is configured to determine whether the handheld laser welding torch is adjacent to the workpiece and generate a corresponding proximity signal. The controller receives the pressure signal from the pressure sensor and the proximity signal from the proximity sensor. The controller is configured to activate the laser light when the pressure level applied to the nozzle meets or exceeds a threshold and the proximity signal indicates that the handheld laser welding torch is adjacent to the workpiece. 
     In accordance with another aspect of the present invention, provided is a laser welding system. The laser welding system includes a laser power supply having a controller that controls activation of laser light by the laser power supply. A sense lead is attachable to a workpiece to be welded. A handheld laser welding torch is operatively connected to the laser power supply to receive the laser light from the laser power supply. The handheld laser welding torch includes a nozzle and a pressure sensor that generates a pressure signal based on a pressure level applied to the nozzle. The laser welding system further includes means for determining that the handheld laser welding torch is adjacent to a workpiece to be welded and generating a corresponding proximity signal. The controller receives the pressure signal from the pressure sensor and the proximity signal from the proximity sensor. The controller is configured to activate the laser light when the pressure level applied to the nozzle meets or exceeds a threshold and the proximity signal indicates that the handheld laser welding torch is adjacent to the workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other aspects of the invention will become apparent to those skilled in the art to which the invention relates upon reading the following description with reference to the accompanying drawings, in which: 
         FIG.  1    is a system block diagram illustrating one embodiment of a laser welding system; 
         FIG.  2    shows a handheld laser welding torch; 
         FIG.  3    shows a user interface of a laser power supply; and 
         FIG.  4    illustrates a block diagram of an example embodiment of a controller that can be used, for example, in the laser welding system of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to handheld laser devices for welding and cutting. The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It is to be appreciated that the various drawings are not necessarily drawn to scale from one figure to another nor inside a given figure, and in particular that the size of the components are arbitrarily drawn for facilitating the understanding of the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention can be practiced without these specific details. Additionally, other embodiments of the invention are possible and the invention is capable of being practiced and carried out in ways other than as described. The terminology and phraseology used in describing the invention is employed for the purpose of promoting an understanding of the invention and should not be taken as limiting. 
     As used herein, “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. Any disjunctive word or phrase presenting two or more alternative terms, whether in the description of embodiments, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” should be understood to include the possibilities of “A” or “B” or “A and B.” 
     While embodiments of the present invention described herein are discussed in the context of laser welding, other embodiments of the invention are not limited thereto. For example, embodiments can be utilized in laser cutting operations. As used herein, the terms “welding” or “laser welding” are intended to encompass both laser welding and cutting. In the interest of efficiency, the term “welding” is used below in the description of exemplary embodiments, but is intended to include both welding and cutting. 
       FIG.  1    is a system block diagram illustrating one embodiment of a laser welding or cutting system  100  (referred to hereinafter as a laser welding system for ease of explanation). The laser welding system  100  includes a handheld laser welding/cutting torch  130  or gun and is configured to manual operation by an operator. The laser welding system  100  includes, among other things, a laser power supply  110  having a laser oscillator  112 , a controller  114  and a user interface  116 . The controller  114  is operatively connected to the laser oscillator  112  to control activation of laser light  118  by the laser power supply  110 . The controller  114  is also operatively connected to the user interface  116 . The user interface  116  allows an operator to set and observe various operating parameters of the laser power supply  110 . The structure and operation of laser power supplies are known in the art and need not be described in detail herein. 
     The certain embodiments, laser welding system  100  also includes a wire feeder  120 . The wire feeder  120  feeds a consumable wire  122  to the torch  130 . The consumable wire  122  can act as a filler wire that is melted by laser energy during welding. In certain embodiments, the consumable wire  122  can be a so-called hot wire that is preheated by the wire feeder  120  or torch  130  prior to discharge from the torch toward the weld zone on a workpiece W. The preheated consumable wire  122  is subsequently melted by the laser light  118 . If an electric arc is produced between the heated consumable wire  122  and the workpiece W, the laser light  118  can be automatically disabled. Similarly, the hot wire power supply and wire feeder  120  can be disabled when the torch  130  is removed from the workpiece W. 
     The handheld laser welding torch  130  is operatively connected to the laser power supply  110  to receive the laser light  118  from the laser power supply. The torch  130  can include laser optics to direct and/or focus the laser light from the laser power supply  110  toward the weld zone. The laser welding system  100  can further include a welding work clamp  140  and sense lead  142 , a cylinder of shielding gas  150 , a protective helmet  160 , and laser shielding glasses  170  configured to be worn under the protective helmet  160 . Laser energy (e.g., laser light  118 ) is provided from the laser power supply  110  to the torch  130  via the wire feeder  120 , in accordance with one embodiment. Alternatively, laser energy is provided from the laser power supply  110  directly to the torch  130  via appropriate optical cabling. Even though various aspects are discussed herein in terms of laser welding, applications to laser cutting are valid as well. 
       FIG.  2    shows the handheld laser welding torch  130  in further detail. The torch  130  can include a trigger  132  for activating and deactivating the laser light during welding. In certain embodiments, the torch  130  can include a laser light guard  134  that blocks reflected laser light (e.g., reflected from the workpiece during welding). The laser light guard  134  can be mounted at a distal end of the torch  130 , such as near a nozzle  136  of the torch. In certain embodiments, the laser light guard  134  can attenuate or filter laser reflections while allowing an operator to view the weld zone through the laser light guard, such as through a lens on the guard. The laser light guard  134  can help protect the operator&#39;s eyes from laser reflections during welding/cutting. The protective helmet  160  and/or laser shielding glasses  170  can provide additional eye protection for the operator. If desired, the laser welding system  100  can include barriers/curtains around a welding work area to provide further protection against laser light  118  emitted from the torch  130 . 
     The laser welding system  100  can include various features to help ensure that the laser light  118  is only activated when the torch  130  is near or adjacent to or pointed toward a workpiece W. Such features can prevent the accidental emission of laser light into free space or in an otherwise unwanted or unintended direction (e.g., toward the operator or toward a bystander). In one embodiment, the outer surface of the nozzle  136  of the torch  130  is electrically insulating. The nozzle  136  could be made of a non-conductive material (not electrically conductive), such as ceramic for example, or have an electrically insulating coating. The laser welding system  100  can include a sense lead  142  from the laser power supply  110 . The sense lead  142  has the work clamp  140  at its distal end. The work clamp  140  can be used to attach the sense lead  142  from the laser power supply  110  to the workpiece W. The work clamp  140  can include jaws or a bolt device to clamp to the workpiece W. The laser welding system  100  can also include a proximity sensor  138  that is operatively connected to the sense lead  142  and the handheld laser welding torch  130 . The proximity sensor  138  is configured to determine whether the torch  130  is adjacent to the workpiece W and generate a corresponding proximity signal, so that the laser light will not be activated while the torch is at a distance from the workpiece. The proximity signal is sent to the controller  114  in the laser power supply  110 , so that the controller knows when the torch  130  is near or adjacent to the workpiece. Example types of proximity sensors can include, but are not limited to, magnetic proximity sensors, inductive proximity sensors, capacitive proximity sensors, etc. The proximity sensor  138  is shown schematically as being located in or on the torch  130  in  FIG.  2   . The proximity sensor  138  is intended to work in conjunction with the sense lead  142  and work clamp  140  to determine whether the torch  130  is adjacent to the workpiece W. For example, the work clamp  140  must be attached to the workpiece W for the proximity sensor  138  to detect that the torch  130  is adjacent to the workpiece. The electrically insulating material or outer surface of the nozzle  136  can prevent the work clamp  140  from being directly connected to the nozzle in order to defeat the system&#39;s capability of detecting the proximity of the torch  130  to the workpiece W. A ceramic or otherwise electrically insulating cover on the nozzle  136  can prevent connecting the sense lead  142 /work clamp  140  directly to the torch  130  instead of to the workpiece W, and can also prevent the nozzle from becoming too hot. In certain embodiments, the sense lead  142  can include a magnet at its distal end rather than the work clamp, to attach the sense lead to the workpiece W. In this case, the nozzle  136  can be made from a nonmagnetic material (e.g., aluminum, brass, ceramic, certain stainless steels, etc.) so that the magnet from the sense lead  142  cannot be attached to the nozzle  136  in order to defeat the system&#39;s capability of detecting the proximity of the torch  130  to the workpiece W. 
     In certain embodiments, the torch  130  can include a pressure sensor  139  to allow the torch to operate with a pressure contact nozzle similar to the nose of a nail gun, such that the laser light  118  will not be activated unless the operator is pressing the nozzle  136  against the workpiece W. The pressure sensor  139  can sense or measure or otherwise respond to an axial pressure level applied to the nozzle  136 , and generate a corresponding pressure or pressure level signal based on the axial pressure applied to the nozzle by the workpiece. In one example embodiment, the pressure sensor  139  includes a strain gauge for measuring the pressure applies to the nozzle  136 . In another example embodiment, the pressure sensor  139  includes a switch that is actuated (e.g., closed or opened) when the axial pressure level applied to the nozzle  136  meets or exceeds a threshold level. One of ordinary skill in the art will appreciate other types of pressure sensors that could be used to provide the torch  130  with functionality similar to the nose of a nail gun, such as piezoelectric or capacitive pressure sensors, solid state sensors, optical sensors, or MEMS devices for example. 
     The pressure or pressure level signal from the pressure sensor  139  and the proximity signal from the proximity sensor  138  are both sent to the controller  114  in the laser power supply  110 . The controller  114  receives these signals to determine whether the torch  130  is proximate or adjacent to the workpiece W and pressed against the workpiece. The controller  114  is configured to activate the laser light  118  when the pressure level applied to the nozzle  136  meets or exceeds a threshold pressure level and the proximity signal indicates that the torch  130  is adjacent to the workpiece. A further condition for activating the laser light  118  can be the pulling of the trigger  132  on the torch  130 . However, in certain embodiments, pulling of the trigger  132  is not necessary to activate the laser light  118 , and merely pressing the nozzle  136  against the workpiece W with the sense lead  142  attached to the workpiece will cause the controller  114  to activate the laser light. The controller  114  can compare the pressure level signal from the pressure sensor  139  to a stored threshold pressure level to determine whether the torch  130  is pressed against the workpiece W. Alternatively, the comparison can be done mechanically via a bias mechanism in the torch  130 . For example, pressing the nozzle  136  against the workpiece W with sufficient force meeting or exceeding the threshold can actuate a switch in the torch  130  that then generates the pressure level signal. In this case, the controller  114  would not have to compare the pressure level signal to a stored threshold because the presence of the pressure level signal would indicate that sufficient pressure has been applied to the nozzle  136 . The controller  114  can also compare the proximity signal from the proximity sensor  138  to a stored threshold proximity level to determine whether the torch  130  is adjacent to the workpiece W. 
     In certain embodiments, the laser power supply  110  can include software lockouts that prevent unauthorized individuals from operating the laser torch  130 . In one embodiment, an operator must first go through a safety training class, pass the safety training class, and then receive an operator code which the operator uses to enable the laser welding system  100 . The operator does not receive the operator code until passing the safety training class. The code may be provided in one of any number of different ways (e.g., in a text message, in an email, encoded in an RFID tag, or an encoded badge, etc.). The user interface  116  of the laser power supply can be configured to receive an input of the operator code, such as by scanning an RFID tag or QR code associated with the operator, or receiving a manual input of the code by the operator (e.g., manual input of an alphanumeric code). The controller  114  verifies the operator code and enables the activation of laser light only after the operator code is verified. 
     As can be seen in  FIG.  3   , in certain embodiments, the user interface  116  can be configured to display a checklist. The controller  114  verifies a plurality of acknowledgement inputs from the operator corresponding to respective elements of the checklist and enables the activation of laser light only after the plurality of acknowledgment inputs are verified. In  FIG.  3   , the example checklist displayed on the user interface  116  has three elements (checklist items A, B, and C), of which the first two have received acknowledgement inputs. The elements of the checklist can correspond to steps or actions that the operator must perform before performing laser welding. In one embodiment, an entire safety kit is provided which can be set up to provide various safety features around the laser welding work area. The safety kit may include safety PPE, barriers, and sensors, for example. The checklist displayed on the user interface  116  can be provided so that the operator has to go through and acknowledge each item in the checklist (e.g., by pressing a button to touch sensitive display area) before the laser welding operation can proceed. The checklist may require the operator to acknowledge that laser safety PPE (e.g., laser safety glasses (or equivalent), laser safe gloves) are being properly worn, and that a laser safety officer is present, for example. In one embodiment, the checklist may require that an anti-reflective coating be applied to the workpiece. The anti-reflective coating goes on the work piece as a liquid and dries before welding is started. The anti-reflective coating mitigates the reflection of infrared energy (produced by the laser beam) from the workpiece. Similarly, the checklist may require use of an anti-reflective shielding gas (e.g., water vapor, CO2). The anti-reflective shielding gas mitigates the reflection of infrared energy (produced by the laser beam) at and near the weld puddle. 
     In some embodiments of the laser welding system, the system can include an area scanner that scans for RFID tags around the welding area to ensure safety from reflections of laser energy. For example, if a person enters an area where laser welding is taking place, a scanner of the laser welding system will detect an RFID tag worn by the person and shut down the laser of the laser welding device. In such an embodiment, persons who have access to the laser welding facility are required to wear such RFID tags as part of the safety process. In certain embodiments, the laser welding system  100  can include non-operator proximity sensors to keep non-laser operators away from an active laser. This may be accomplished by having a video monitoring system to detect any humans in the welding area. When a non-laser operator is detected in or near the welding area, the laser light may be automatically shut down (e.g., via wireless communication between the video monitoring system and the laser power supply  110 ). Other monitoring systems may be employed in a similar manner, in accordance with other embodiments, including for example a thermal monitoring system, a touch sensing monitoring system, or an RFID monitoring system. 
     In some embodiments, the helmet  160  can sense the presence of laser light. Reflecting laser light (laser energy) can cause damage to the head and eyes of a user during a laser welding process. A sensor capable of detecting the laser energy can be incorporated into the user&#39;s protective welding helmet  160  (e.g., on the inside of the helmet, which also has a laser light filter). The welding helmet  160  is further configured to communicate with the laser power supply  110  or torch  130 . In one embodiment, when the sensor in the welding helmet  160  detects laser energy during a laser welding process, a signal is sent to the laser power supply  110  (e.g., to the controller  114 ) or the torch  130  and shuts down the laser. An error symbol or text may be presented on a display of the welding helmet  160  or of the laser power supply  110  to indicate the issue to the user. If laser light manages to get into the interior of the helmet  160 , such as around the neck portion of the helmet, the laser light sensor within the helmet can shut off the laser light. The laser welding system  100  can also include at least one sensor configured to sense laser energy which occurs outside of the immediate work area, and shut down the laser welding system accordingly for safety reasons. 
     In one embodiment, the laser beam of the torch  130  is used to track the weld joint. If the laser beam drifts out of the weld joint, the system can shut down the laser beam and/or provide a warning to the user. 
     In certain embodiments, the torch  130  can include one or more light-emitting diodes (LEDs) to illuminate a weld puddle during the welding operation, to improve visibility of the weld and weld puddle to the user. The torch  130  can also include an Emergency-Stop (E-Stop) device to disable the laser, in particular if the torch lacks a trigger to activate the laser light. In one embodiment, a visible (e.g., red) laser guide light in the torch  130  is activated first upon pulling the trigger  132  to a first trigger position. The guide light turns off when the laser is activated upon pulling the trigger  132  to a second trigger position. The red laser guide light can be used to help find and align the tip of the handheld laser device with a joint on a workpiece to be welded. Use of a visible laser or LED to illuminate the weld puddle, or to constantly illuminate the actual direction of welding with respect to the joint during welding may also be incorporated into the torch  130 . 
     In certain embodiments, the torch  130  can include mirrors to wobble the laser beam and provide a wider and/or adjustable weld puddle. Adjustable wobble settings can be provided on the torch  130  via suitable control devices. Alternatively, the laser beam can be defocused to provide a wider laser beam. The torch  130  can also include different interchangeable nozzle types and sizes, corresponding to different types of welds to be formed. 
     One embodiment of a handheld laser welding system includes an angle monitor and vision system to ensure that a handheld laser device is being used safely. For example, an angle monitoring device is programmed or “taught” (e.g., via a dry run of the weld using the handheld laser welding torch with the laser off) proper angle and position of the handheld laser device for a particular application to ensure safety. In one embodiment, a vision system (having a camera, etc.) is used to ensure proper use of the handheld laser device by the user. The laser is shut off if the handheld laser device gets out of position (within some tolerance) for a particular welding procedure (via position monitoring using cameras or inertial sensors, for example). 
     In one embodiment, the torch  130  includes an optical port mount that allows a digital camera to be mounted to the optics of the laser, allowing a user to see the weld puddle area better without having to weld up close. The torch  130  further includes a display device operatively connected to the digital camera to allow the user to view the imagery (e.g., video) collected by the digital camera. In this manner, the user does not have to be overly close to the weld puddle area to see what is happening. In a further embodiment, the torch  130  includes a camera mounted at the front or distal end of the torch, functioning as a laser view finder, to be able to view the weld puddle. The torch  130  further includes a display device operatively connected to the camera to allow the user to view the imagery (e.g., video) collected by the camera. 
     In one embodiment, vision sensing and RFID technology are used to sense a position of an operator&#39;s head while welding. The position can be compared to a laser line-of-sight and/or angles of laser light reflections associated with using a handheld laser device. Warnings can be provided and/or the laser can be shut down when the comparison indicates potential danger to the operator. Also, in one embodiment, a non-operator proximity sensor having a camera that is aligned with a line-of-sight of a handheld welding gun during welding is provided. When a non-operator comes into that line-of-sight, the laser is shut down. Furthermore, the operator and other persons in the area may be monitored for personal protective equipment (PPE), and the laser can be shut down and alarms activated when someone is not in compliance with PPE regulations. 
     In one embodiment, a welding helmet  160  with augmented reality (AR) capability is provided which displays an AR symbol on a head-up display (HUD) of the welding helmet, indicating a location of the weld joint. Another system that actually finds/tracks the weld joint and communicates with the welding helmet to display the AR symbol in the proper location in the field of view may also be provided. For example, in one embodiment, the laser from the torch  130  tracks the weld joint and the torch communicates the tracking information to the welding helmet  160 . For example, in another embodiment, an angle monitoring device is programmed or “taught” (e.g., via a dry run of the weld using the laser welding torch  130  with the laser off) the path of the weld joint which the helmet  160  uses to display the location of the weld joint via AR. 
       FIG.  4    illustrates a block diagram of an example embodiment of a controller  114  that can be used, for example, in the handheld laser welding system  100  of  FIG.  1   . For example, the controller  114  is located within the laser power supply  110  as shown in  FIG.  1   . Referring to  FIG.  4   , the controller  114  includes at least one processor  314  (e.g., a microprocessor, a central processing unit, a graphics processing unit) which communicates with a number of peripheral devices via bus subsystem  312 . These peripheral devices may include a storage subsystem  324 , including, for example, a memory subsystem  328  and a file storage subsystem  326 , user interface input devices  322 , user interface output devices  320 , and a network interface subsystem  316 . The input and output devices allow user interaction with the controller  114  and correspond to the user interface  116  shown in  FIG.  1   . Network interface subsystem  316  provides an interface to outside networks and is coupled to corresponding interface devices in other devices. 
     User interface input devices  322  may include a keyboard, pointing devices such as a mouse, trackball, touchpad, or graphics tablet, a scanner, a touchscreen incorporated into the display, audio input devices such as voice recognition systems, microphones, and/or other types of input devices. In general, use of the term “input device” is intended to include all possible types of devices and ways to input information into the controller  114  or onto a communication network. 
     User interface output devices  320  may include a display subsystem, a printer, or non-visual displays such as audio output devices. The display subsystem may include a cathode ray tube (CRT), a flat-panel device such as a liquid crystal display (LCD), a projection device, or some other mechanism for creating a visible image. The display subsystem may also provide non-visual display such as via audio output devices. In general, use of the term “output device” is intended to include all possible types of devices and ways to output information from the controller  114  to the user or to another machine or computer system. 
     Storage subsystem  324  stores programming and data constructs that provide some or all of the functionality described herein. For example, computer-executable instructions and data are generally executed by processor  314  alone or in combination with other processors. Memory  328  used in the storage subsystem  324  can include a number of memories including a main random access memory (RAM)  330  for storage of instructions and data during program execution and a read only memory (ROM)  332  in which fixed instructions are stored. A file storage subsystem  326  can provide persistent storage for program and data files, and may include a hard disk drive, a solid state drive, a floppy disk drive along with associated removable media, a CD-ROM drive, an optical drive, or removable media cartridges. The computer-executable instructions and data implementing the functionality of certain embodiments may be stored by file storage subsystem  326  in the storage subsystem  324 , or in other machines accessible by the processor(s)  314 . 
     Bus subsystem  312  provides a mechanism for letting the various components and subsystems of the controller  114  communicate with each other as intended. Although bus subsystem  312  is shown schematically as a single bus, alternative embodiments of the bus subsystem may use multiple buses. 
     The controller  114  can be of varying types. Due to the ever-changing nature of computing devices and networks, the description of the controller  114  depicted in  FIG.  4    is intended only as a specific example for purposes of illustrating some embodiments. Many other configurations of a controller are possible, having more or fewer components than the controller  114  depicted in  FIG.  4   . 
     It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.