Abstract:
The invention relates to a method for calibration of 2-axis high precision digital angle measurement device, particularly for initializing a planar angle measuring device and an apparatus to generate simultaneous two-dimensional resultant planar angles of full 360° rotation. The planar angle measurement device is, typically but not exclusively, used in concurrent two-dimensional angles leveling, setting and alignment tasks for precision machine setup in the fields of precision engineering and metrology applications.

Description:
BACKGROUND OF INVENTION 
     1. Field of Invention 
     This invention concerns leveling and angle measuring devices, apparatus and methods for calibration. 
     2. Description of Prior Art 
     Traditional precision machining utilizing turning lathe, drilling and milling machines were typically operated by skilled machinist through precise adjusting each X, Y and Z axis to complete a machining component or part. These skilled-labor dependent machines has been radically replaced by very high precision, augmented machining speed, multiple axis, fully automatic computer numerical control (CNC) machines. These programmable CNC machines are capable of non-stop running in production lines integrated with automatic robotic manipulators for material input and removing the machined part. 
     Driven by automobile, semiconductor and clean energy of precision engineering industries, the demand for tighter tolerance machining part—higher precision), High speed machining—vibration becomes important issue affecting machine&#39;s accuracy, High volume machining and complex machined part—production yield significantly affecting cost and delivery lead time, Larger size of machined part and harder materials, have emerged as critical variables influencing these advanced CNC machines accuracy performance and machine—part production yield requirements. 
     In contrast, machine leveling and alignment instrument used for manufacturing, installation, set up and maintenance of these advanced CNC machines and metrology equipment remains relatively unchanged. Machinists are still using the traditional single-axis ‘bubble’ spirit level or conventional single-axis digital leveling instrument to perform machine leveling tasks which are unarguably ineffective—time consuming, skilled-operator dependent, and difficult to verify machine leveling status when machine setup activity completed. 
     Current drawbacks associated with using conventional single-axis leveling devices to align precision machines in attaining positional stability and precise leveled state are as follows: 
     First, the task confronted by the machine operator for leveling a machine is a two-dimensional planar surface alignment issue. In contrast, traditional leveling and angle measuring instruments are single axis or one directional. Machine leveling operator is required to adjust a machine-frame footings one axis at a time. Since aligning a machine structure involves planar surface, adjusting one axis of the machine affect the other axis of existing plane. Thus, the operator has to do trial-and-error by going back-and-forth in adjusting each footing until the machine surface plane (i.e. where the leveling instrument is placed) is completely leveled. This is a tedious, time consuming and nonproductive task, yet critical affecting machine accuracy and yield performance. The operator could potentially resort to compromise in facing such lengthy repetitive task of iteration. 
     Second, leveling a machine using traditional spirit level or digital level typically requires two operators. One operator looks at the instrument for current leveling status while the other operator adjusting at the machine footings one at a time. Prolonged iteration to get a machine leveled tends to promote compromised works of the two operators involved and thus increase the risk that the machine is not being optimally leveled to the required specification. 
     Third, unleveled machine would deform machine structure and affect machine surface plane flatness, cause dimension changes and incur additional machine structural vibration that result in the deterioration of machine accuracy performance. Traditional leveling instruments are not equipped with vibration diagnostic sensors to verify machine leveling positional stability when machine operator alignment task has completed. In particularly, if one footing of a machine is not taking its appropriate weight load during machine setup adjustment (i.e. when machine in static state is just touch on the ground), and when the machine is in operating state (i.e. during machine in dynamic state), induced vibration known as machine ‘rocking’ occurs. Machine structure tends to promote ‘rocking’ when fast-moving machine sub-unit driven by motors (such as milling head), generates inertia and the disposition weight shifts the center of gravity to a different location within the machine causing unstable machine positional stability. 
     Fourth, conventional angle calibration apparatus employs single-axis rotary plate and is unable to generate simultaneous 2-dimentional surface planar angle. Calibrating one axis at a time subjects the calibration system to inter-axis offset error when calibrating 2-axis angle measuring device. This offset error is the result of the first axis reference position has been displaced when removing the instrument for calibrating the second axis. It also increases calibration time due to multiple set up procedure on reference zero. 
     Accordingly, improved leveling devices and calibration apparatus are desired that address the forgoing shortcomings of current single-axis leveling devices and calibration apparatus. 
     SUMMARY OF INVENTION 
     One aspect of present invention is to provide a calibration routine consists of multiple steps for determining the sensor of angle measuring instrument in each X and Y axis for a 360° rotation with reference to earth datum using granite table and Master Square. According to an embodiment, a method and apparatus for calibrating of 2-axis precision planar angle measuring device. The method involves the initialization setting for a planar angle measuring device. Said planar angle is the resultant angle of XY planes. The apparatus consists of 2-axis rotary turning plates precisely leveled to earth datum, wherein one plate is assembled in perpendicular to the other plate and attached within a common frame, whereby each rotary plate is equipped with a turning motor to generate a series of planar resultant angles within 360° turning. 
     Another object of present invention is to provide an apparatus for a continuous routine in setting a 2-axis resultant planar angle within 360° rotation without the need to compensate the inter-axis reference angles on each X and Y planes. 
     A further object of present invention is to provide the instrument with vibration sensors to detect vibration magnitude and frequency, particularly advantageous to verify a leveled-machine structural stability performance. 
     Still another object of present invention is to provide a continuous procedure consisting a predefined multiple moving steps (such as zigzag movements) to excite vibration of a levelled machine while enabling the device to acquire the machine vibration amplitude and frequency patterns for accessing machine structure positional stability. 
     A further object of present invention is to provide the instrument with a wireless communication device to enable another device accessing the planar angles in real time, particularly advantageous when performing remote two-dimensional alignment tasks. 
     A further object of the present invention is to provide the device with an azimuth sensor to detect angular change, particularly advantageous when performing parallelism alignment tasks. 
     Tedious machine leveling and alignment tasks confronted by machine installation operators using conventional single-axis leveling devices encourage compromised works and thus exposing higher risk of having reduced machine accuracy performance during installation resulting in lower machined-part production yields. The advantage of the present invention is its simplification of planar surface leveling task results in faster machine leveling and alignment, improved accountability and significantly reduction of machine installation and setup cost. 
     A further object of the present invention is to provide a system and method for changing a measurement state of a digital level having an orientation sensor. The system and method includes detecting an orientation of the digital level through the orientation sensor and automatically activating a measurement mode of the digital level based on the orientation detected by the orientation sensor. The system and method may further include switching between multiple measurement modes based on different detected orientations of the digital level. 
     Other objects, features and advantages of the present invention would become apparent from the subsequent description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The details of the calibration method and apparatus will be understood more clearly with reference made to the accompanying drawings, in which: 
         FIG. 1  is the calibration method shown the algorithm to configure the sensor reference angular positions. 
         FIG. 2  to  FIG. 9  are illustrations of calibration steps of an embodiment of 2-axis angle measuring device. 
         FIG. 10  is the front perspective view of one embodiment of a 2-axis rotary table for generating a planar angle in the present invention and the embodiment is placed on a granite table supported by a rectangular steel stand; 
         FIG. 11  is a front elevation view of one embodiment of the present invention showing a 2-axis angle measurement instrument is attached on Y-axis turn table and a control panel for operating the rotary table apparatus; 
         FIG. 12  is a back perspective view of the rotary table apparatus showing a precision footing adjustment micrometer mounted; 
         FIG. 13  is a side perspective view of preferred embodiment showing the X-Axis rotary table position is rotated at 45.0122° and the Y-Axis rotary plate position is at 0.0000° displayed by the control panel; 
         FIG. 14  is another side perspective view of preferred embodiment showing the X-Axis rotary table position is rotated at 45.0122° and the Y-Axis rotary plate position is at 47.0833° displayed by the control panel. The combination of XY-plane generates a novel resultant planar angle (RPA) of =28.7897°; 
         FIG. 15A  is a front perspective view of a leveling device in a single-axis leveling orientation; 
         FIG. 15B  is a front view of the leveling device of  FIG. 15A  in the single-axis leveling orientation; 
         FIG. 15C  is a front perspective view of the leveling device of  FIG. 15A  in a two-axis leveling orientation; and 
         FIG. 15D  is a front view of the leveling device of  FIG. 15C  in the two-axis leveling orientation. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The calibration method used for setting the 2-axis digital angle measuring instrument is to configure both X and Y sensors reference angular plane positions as shown in  FIG. 1  to  FIG. 9 . The digital angle measuring instrument or device may include any of a variety of orientation sensors that may be disposed in the device, for example in one or more microelectromechanical systems (MEMS) chips or the like. For example, the orientation sensors may include vibration sensors for detecting vibration magnitude in X, Y and Z directions of the cartesian coordinate system, azimuth sensors for detecting angular position change in one or more directions or in parallelism measurements, weight or pressure sensors, or any other desired orientation sensors such as accelerometers or gyroscopes. According to  FIG. 1 , the 2-axis digital level  1  is preferably placed on a levelled granite table  2  and a granite master square  3  supported by a metal frame  4 . 
     According to  FIG. 2  to  FIG. 9  illustrate each steps involved in setting sensor reference angular plane position for each of the two axis accordingly.  FIG. 2  to  FIG. 3  are illustrating the steps for setting X-sensor in horizontal front-position  5  and back-position  6  respectively, whereas  FIG. 4  and  FIG. 5  are steps for setting Y-sensor in vertical front-right position  7  and vertical back-left position  8  respectively. 
     According to  FIG. 6  to  FIG. 7  are illustrating the steps involved for setting Y-sensor in vertical front-left position  9  and back-right position  10  respectively. 
     According to  FIG. 8  to  FIG. 9  are illustrating the steps involved for simultaneously setting XY-sensor in horizontal-front position  11  and horizontal-back position  12  respectively. 
     A significant feature of the calibration method according to the invention is the condition that both X and Y sensors configured independently for each vertical and horizontal direction of reference planes and the measured quantities are simultaneously integrated to form an inter-planar origin. The preferred arrangement removes inter-planar offset quantities at origin with reference to the earth datum by taking multiple reference planes in determining both horizontal and vertical planes. 
     An embodiment of a 2-axis rotary table apparatus can best be appreciated by referring to  FIG. 10  to  FIG. 14 . According to  FIG. 10 , the apparatus consist of a frame  13  placed on top surface of a levelled granite table  14 . The frame houses an X-axis rotary plate  15  precisely attached perpendicularly to a Y-axis rotary turning plate  16 . A 2-axis digital levelling device  17  is attached on the top surface of the Y-axis rotary plate for calibration. The Y-axis rotary plate is driven by a precision motor  18  to generate an angle along the Y-axis direction. Similarly, the X-axis rotary plate is driven by another precision motor located in the frame  13  to generate an angle along the X-axis direction. Driving both motors in any specific direction and quantity by using the control panel  19  generates a precise two-dimensional angle of a plane within 360 degrees rotations. The planar angle generated is used to calibrate the 2-axis digital levelling device  17 . 
     According to  FIG. 11 , two front-micrometer adjustment footings  20  and one back-micrometer adjustment footing  21  are used for initial setting on the 2-axis rotary table apparatus to attain a levelled X-Y plane with reference to earth datum. According to  FIG. 12 , the back view of the 2-axis rotary table apparatus showing the electrical power socket point  22 . According to  FIG. 13 , the front view of the 2-axis rotary table apparatus showing the X-axis is rotated to an angle of +45.0122° with a positive direction  23  while the Y-Axis turn plate position is maintained at 0.0000°. This feature is used for generating a single X-axis independent to Y-axis. 
     According to  FIG. 14 , the front view of the 2-axis rotary table apparatus showing the X-axis is rotated to an angle of +45.0122° while the Y-Axis turn plate position is set to an angle of +47.8331° with a positive direction  24  as shown in the control panel. This novel feature utilizes the X=+45.0122° and Y=+47.0833° to generate a combination XY-plane having a resultant planar angle of RPA=28.7897°. The resultant planar angle is fed to the device using cable  25  to compensate device sensor readings enabling auto calibration of the entire set of device readings over full 360°. Although communication between the device and the 2-axis rotary table apparatus is shown using cable  25 , in some embodiments, the device may be in wireless communication with the 2-axis rotary table apparatus, for example, using Bluetooth, WiFi, a cellular data network, or any similar system for wireless communication, as should be understood by those skilled in the art. 
     A significant feature of the apparatus according to the invention is the apparatus ability to generate continuous XY plane of set angles within 360° rotational directions for calibrating a 2-axis digital angle measuring device. This simultaneous X and Y axis angles generating feature enables the calibration of a t-axis digital angle measuring device to be performed quickly, accurately and lower cost. 
     The method and apparatus for calibrating a 2-axis planar angle measuring device advantageously enables a machine installation operator to level a machine faster, reduces setup cost and enables the use of vibration diagnostics to enhance machine setup quality. The calibration apparatus advantageously ensures the simultaneous 2-axis angle measuring device is concurrently calibrated for both axis without the need to calibrate one axis at a time as experienced when using a current single-axis calibration apparatus. 
     Referring to  FIG. 15A-15D , in an embodiment, the leveling device  17  may include a system for automatically transitioning the leveling device  17  between multiple measurement states. For instance, the leveling device  17  may automatically transition from a one-axis level mode, shown in  FIG. 15B , to a two-axis level mode, shown in  FIG. 15D , depending upon a detected orientation of the leveling device  17  as detected by the orientation sensors of the leveling device  17 . In particular, when the leveling device  17  is in operation and the orientation sensors detect that the leveling device  17  is in a first orientation for single axis leveling, relative to a surface  28 , shown in  FIG. 15A , the leveling device  17  automatically displays the one-axis leveling mode  29 , shown in  FIG. 15B , on a display  30 . In the one-axis leveling mode  29 , shown in  FIG. 15B , the leveling device  17  operates to detect angular orientation along a single axis to level in a single axis measurement plane and displays leveling data on the display  30 , shown in  FIG. 15B , in the single axis measurement plane. 
     If a user then rotates the leveling device  17  relative to the surface  28 , as shown by arrow  32  of  FIG. 15A , from the first orientation for single axis leveling, shown in  FIG. 15A , to a second orientation for two-axis leveling, shown in  FIG. 15C , the leveling device  17  automatically displays the two-axis leveling mode  33 , shown in  FIG. 15D , on the display  30 . In the two-axis leveling mode  33 , shown in  FIG. 15D , the leveling device  17  operates to detect angular orientation along two orthogonal axes to level in a dual axis measurement plane and displays leveling data on the display  30 , shown in  FIG. 15D , in the dual axis measurement plane. Similarly, if the user rotates the leveling device  17  from the second orientation for two-axis leveling, shown in  FIG. 15C , to the first orientation for single axis leveling, shown in  FIG. 15A , the leveling device  17  automatically transitions back to display the one-axis leveling mode  29 , shown in  FIG. 15B , on the display  30 . 
     Thus, the leveling device  17  may advantageously automatically transition from the one-axis leveling mode  29 , shown in  FIG. 15B , to the two-axis leveling mode  33 , shown in  FIG. 15D , and vice versa, based on the orientation of the leveling device  17  as detected by the orientation sensors of the leveling device  17 . This allows the user to seamlessly transition the leveling device  17  between level modes, as desired, by only changing the orientation of the leveling device  17  and without requiring further input from the user (e.g. through a button, switch or the like). The first and second orientations may advantageously be predefined or preset orientations of the leveling device  17  that are programmed into the leveling device  17 . 
     The leveling device  17  has the necessary electronics, software, memory, storage, databases, firmware, logic/state machines, microprocessors, communication links, displays or other visual or audio user interfaces, and any other input/output interfaces to perform the functions described herein and to achieve the results described herein. For example, the leveling device  17  may include a processor and memory, which may include system memory, including random access memory (RAM) and read-only memory (ROM). The leveling device  17  may be connected to one or more external devices through wired or wireless communication, as discussed above. Suitable computer program code may be provided for executing numerous functions, including those discussed herein in connection with the system for automatically transitioning the leveling device  17  from a one-axis level mode to a 2-axis level mode. 
     The leveling device  17  may include one or more conventional microprocessors and one or more supplementary co-processors such as math co-processors or the like. The one or more conventional microprocessors may be in communication with device memory, which may comprise an appropriate combination of magnetic, optical and/or semiconductor memory, and may include, for example, RAM and ROM. The processors and the device memory each may be, for example, located entirely within leveling device  17 . 
     The device memory may store, for example, one or more databases and other information required by the leveling device  17 , an operating system for the leveling device  17 , and one or more other programs (e.g., computer program code and/or a computer program product) adapted to direct the one or more processors to provide the leveling device  17  with the various attributes discussed herein. The operating system and/or other programs may be stored, for example, in a compressed, an uncompiled and/or an encrypted format, and may include computer program code. The instructions of the computer program code may be read into a main memory of one or more processors from the memory. While execution of sequences of instructions in the program causes the one or more processors to perform the process steps described herein, hard-wired circuitry may be used in place of, or in combination with, software instructions for implementation of the processes of the present invention. Thus, embodiments of the present invention are not limited to any specific combination of hardware and software. 
     The programs discussed herein may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. Programs may also be implemented in software for execution by various types of computer processors. A program of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions, which may, for instance, be organized as an object, procedure, process or function. Nevertheless, the executables of an identified program need not be physically located together, but may comprise separate instructions stored in different locations which, when joined logically together, comprise the program and achieve the stated purpose for the programs such as providing the leveling device  17  with the system for automatically transitioning the leveling device  17  from a one-axis level mode to a 2-axis level mode. In an embodiment, an application of executable code may be a compilation of many instructions, and may even be distributed over several different code partitions or segments, and among different programs. 
     The term “computer-readable medium” as used herein refers to any medium that provides or participates in providing instructions to one or more processors of the leveling device  17  (or any other processor of a device described herein) for execution. Such a medium may take many forms, including but not limited to, non-volatile media and volatile media. Non-volatile media include, for example, optical, magnetic, or opto-magnetic disks, such as memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes the main memory. Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the one or more processors of the leveling device  17  (or any other processor of a device described herein) for execution. 
     In operation, the leveling device  17  may be calibrated and used according to the various embodiments described herein. For instance, the leveling device  17  may be operated in the one-axis leveling mode  29 , shown in  FIG. 15B , the two-axis leveling mode  33 , shown in  FIG. 15D , and may be seamlessly transitioned between the leveling modes as discussed above. 
     The invention has been described with reference to the illustrated preferred embodiments. The invention is not unduly limited by this disclosure of the preferred embodiment described, instead it is intended that the invention be defined as their equivalents, set forth in the following claims.