Abstract:
This invention discloses a method and apparatus for measuring the weight of a CNC workpiece. As the weight of the workpiece on a loading platform increases, the loading of a driving module which drives the loading platform in constant speed increases accordingly. On the contrary, as the weight of the workpiece on the loading platform decreases, the loading of the driving module which drives the loading platform in constant speed also decreases. This invention determines the weight of the workpiece on the loading platform by measuring the electrical signal which drives the driving module and utilizing a calibration curve data in a preconfigured database.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a method and apparatus for measuring weight, more particularly, a method and apparatus for measuring the weight of a CNC (Computer Numerical Control) workpiece. 
   2. Description of the Prior Art 
   A Computer Numerical Control (CNC) machine tool is used to shape a workpiece by removing a certain amount of unwanted material from the workpiece, thus reducing the weight of the workpiece and changing its inertia. As shown in  FIG. 1 , when certain amount is removed from a workpiece  105  by a conventional CNC machine tool  100 , the workpiece is required to be unloaded from the loading platform and weighed by a weighing scale. The weight information is then entered into the CNC machine tool, so as to adjust relevant control parameters such that the machined contour conforms to a predicted contour  110 , thereby obtaining optimal accuracy of the servo control. However, since there are a variety of machining applications and dynamic conditions (e.g. change of loading), it is difficult to obtain an optimal servo-control result for various kinds of machining applications with only a single set of fixed control parameters. As a result, for example as shown in  FIG. 1 , an error may occur between the actual contour  115  created and the predicted contour  110 . Therefore, there is a need for a method and apparatus that can detect the weight of the workpiece in real time during CNC machining process that enhances the performance and accuracy of the CNC machine tool, thereby, for example, the surface precision of the workpiece is increased and the operating time and tracking error are reduced. 
   SUMMARY OF THE INVENTION 
   In view of the prior art and the needs of the related industries, the present invention provides a method and apparatus for measuring the weight of a CNC workpiece that solves the abovementioned shortcomings of the conventional CNC machining processes. 
   One objective of the present invention is to provide an apparatus for measuring the weight of a workpiece for a CNC machine tool. The weight of the workpiece being machined is derived by determining the magnitude of an electrical signal received by a driving module that drives a loading platform in constant speed. Then, control parameters of the CNC machine tool can be adjusted/calibrated to reduce the complexity of human operations and enhance precision of servo control of the CNC machine tool. 
   Another objective of the present invention is to provide an apparatus for measuring the weight of a CNC workpiece. The apparatus can detect the magnitude of an electrical signal and compare a calibrated curve data in a preconfigured database, thereby deriving the weight of the workpiece. 
   Yet another objective of the present invention is to provide a method for measuring the weight of a CNC workpiece. The method is able to determine the weight of a workpiece on a loading platform by detecting an electrical signal that causes a driving module to drive the loading platform in constant speed. 
   According to the above objectives, the present invention discloses an apparatus for measuring the weight of a CNC workpiece. As the weight of the workpiece on a loading platform increases, the loading of a driving module which drives the loading platform in constant speed increases accordingly. On the contrary, as the weight of the workpiece on the loading platform decreases, the loading of the driving module which drives the loading platform in constant speed also decreases. This invention derives the weight of the workpiece on the loading platform by measuring the electrical signal which drives the driving module and utilizing a calibration curve data in a preconfigured database. 
   According to the above objectives, the present invention discloses a method for measuring the weight of a CNC workpiece. First, a workpiece is provided on a loading platform that includes a driving module. Second, a power supply module supplies an electrical signal to the driving module. Then, the driving module drives the loading platform in constant speed based on the electrical signal. Thereafter, a determining module is provided, wherein the determining module detects a continuous data of the electrical signal and determines the weight of the workpiece based on the continuous data. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the disclosure. In the drawings: 
       FIG. 1  is a schematic diagram illustrating a conventional CNC machine tool during operation; 
       FIG. 2  is a schematic diagram depicting an apparatus for measuring the weight of a CNC workpiece; 
       FIG. 3  is a schematic diagram depicting a CNC machine tool integrated with the apparatus for measuring the weight of a CNC workpiece; 
       FIG. 4  is a flow chart illustrating a method for measuring the weight of a CNC workpiece; 
       FIG. 5  is a graph showing the magnitudes of driving electrical signals of X- and Y-axis fed at 500 mm/min and 4000 mm/min during no-load condition; and 
       FIG. 6  is a graph showing the magnitudes of driving electrical signals of X- and Y-axes fed at 500 mm/min and 4000 mm/min during a 357 g-loading condition. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention is directed to a method and apparatus for measuring the weight a CNC workpiece. Detailed steps and constituents are given below to assist in the understanding the present invention. Obviously, the implementations of the present invention are not limited to the specific details known by those skilled in the art of CNC weight measuring method and apparatus. On the other hand, well-known steps or constituents of digital watermarking are not described in details in order not to unnecessarily limit the present invention. Detailed embodiments of the present invention will be provided as follow. However, apart from these detailed descriptions, the present invention may be generally applied to other embodiments, and the scope of the present invention is thus limited only by the appended claims. 
   Referring to  FIG. 2 , a first embodiment of the present invention is an apparatus for measuring the weight of workpieces  200 , which includes a loading platform  205 , a workpiece  210 , a driving module  215 , a power supply module  225  and a determining module  220 . The workpiece  210  is secured on the loading platform  205 . The driving module  215  is used to drive the loading platform  205  in constant speed, wherein the magnitude of the force with which the driving module  215  drives the loading platform in constant speed depends on an electrical signal  230  provided by the power supply module  225  received by the driving module  215 . The determining module  220  may receive this electrical signal  230  and determine the weight of the workpiece  210  according to the magnitude of the electrical signal  230 . 
   The driving module  215  can be a servo motor. The electrical signal  230  can be a current, voltage or other electrical signal. The electrical signal  230  includes a current for a horizontal servo motor and a current for a vertical servo motor. The electrical signal  230  includes an electrical signal for causing the loading platform  205  to move from a first location to a second location, and an electrical signal for moving from the second location back to the first location. The driving module  215  includes a horizontal servo motor and a vertical servo motor. The power supply module  225  detects the velocity of the loading platform  205 , and outputs the electrical signal  230  that keeps the loading platform  205  moving in constant speed based on the detected velocity. 
   The determining module  220  includes a database for storing weight information about different workpieces  210  and data of the electrical signals corresponding to the weight of the various workpieces  210 . The determining module  220  may include a neural network, which outputs the weight of the workpiece  210  based on the electrical signal. The neural network is trained according to the weights of the different workpieces  210  and the data of the electrical signals corresponding to the weight of the various workpieces  210 . Since the driving module  215  must maintain a constant rotational speed for the precision of machine control and driving the loading platform  205  in constant speed, when the weight of the workpiece  210  changes, the electrical signal  230  received by the driving module  215  will vary accordingly, thus the weight of the workpiece  210  corresponding to the received electrical signal  230  can be determined. 
   Referring to  FIG. 3 , a second embodiment of the present invention is a CNC machine tool  300  that includes an apparatus for measuring the weight of CNC workpieces and a control unit  335 . The CNC machine tool  300  includes a loading platform  305 , a workpiece  310 , a driving module  315 , a power supply module  325 , a milling cutter  340 , a control unit  335  and a determining module  320 . The workpiece  310  is secured on the loading platform  305 . The driving module  315  is used to drive the loading platform  305  in constant speed, wherein the magnitude of the force with which the driving module  315  drives the loading platform in constant speed depends on an electrical signal  330  provided by the power supply module  325  received by the driving module  315 . The determining module  320  may receive the electrical signal  330 , and detect its magnitude and determine the weight of the workpiece  310 . With the weight of the workpiece  310  being inputted into the control unit  335 , the control unit  335  can adjust/calibrate the fine-tuning parameters of the CNC machine tool  300  to reduce complicated human operations and enhance machining precision of the CNC machine tool  300 . 
   The driving module  315  is a servo motor. The electrical signal  330  can be a current, voltage or other electrical signal. The electrical signal  330  includes a current for a horizontal servo motor and a current for a vertical servo motor. The electrical signal  330  includes an electrical signal for causing the loading platform  205  to move from a first location to a second location, and an electrical signal for moving from the second location back to the first location. The driving module  315  includes a horizontal servo motor and a vertical servo motor. The power supply module  325  detects the velocity of the loading platform  305 , and outputs the electrical signal  330  that keeps the loading platform  305  moving in constant speed based on the detected velocity. 
   The determining module  320  includes a database for storing weight information about different workpieces  310  and data of the electrical signals corresponding to the weight of the various workpieces  310 . The determining module  320  may include a neural network, which outputs the weight of the workpiece  310  based on the electrical signal  330 . The neural network is trained according to the weights of the different workpieces  210  and the data of the electrical signals  330  corresponding to the weight of the various workpieces  310 . Since the driving module  315  must maintain a constant rotational speed for the precision of machine control and driving the loading platform  305  in constant speed, when the weight of the workpiece  310  changes, the electrical signal  330  received by the driving module  315  will vary accordingly, thus the weight of the workpiece  310  corresponding to the received electrical signal  330  can be determined. 
   Referring to  FIG. 4 , a third embodiment of the present invention is a method for measuring the weight of workpieces. First, a workpiece is provided on a loading platform that includes a driving module, as shown in step  405 . Second, a power supply module supplies an electrical signal to the driving module, as shown in step  410 . Then, the driving module drives the loading platform in constant speed based on the electrical signal, as shown in step  415 . Thereafter, a determining module is provided, wherein the determining module detects a continuous data of the electrical signal and determines the weight of the workpiece based on the continuous data, as shown in step  420 . The driving module is a servo motor. The electrical signal can be a current, voltage or other electrical signal. The electrical signal includes a current for a horizontal servo motor and a current for a vertical servo motor. The electrical signal includes an electrical signal for causing the loading platform to move from a first location to a second location, and an electrical signal for moving from the second location back to the first location. The driving module includes a horizontal servo motor and a vertical servo motor. The power supply module detects the velocity of the loading platform, and outputs the electrical signal that keeps the loading platform moving in constant speed based on the detected velocity. 
   The determining module may further include a database for storing weight information about different workpieces and data of the electrical signals corresponding to the weight of the various workpieces. The determining module may include a neural network, which outputs the weight of the workpiece based on the electrical signal. The neural network is trained according to the weights of the different workpieces and the data of the electrical signals corresponding to the weight of the various workpieces. Since the driving module must maintain a constant rotational speed for the precision of machine control and driving the loading platform in constant speed, when the weight of the workpiece changes, the electrical signal received by the driving module will vary accordingly. By receiving the electrical signal and analyzing the relationship between the electrical signal and the workpiece, the weight of the workpiece can be determined based on the value of the electrical signal. A preferred embodiment of the present embodiment further includes a step of entering the weight of the workpiece into a CNC machine tool integrated control unit, wherein the step includes adjust/calibrate the control parameters of the CNC machine tool by inputting the weight of the workpiece into the control unit. 
   EXAMPLE 1 
   When a workpiece is cut, its weight will change. This means control parameters related to the inertia of the CNC machine tool will have to be adjusted. One effect of the present invention eliminates the need of unloading/loading the workpiece and resetting position etc., thus increasing machining efficiency. With a control unit, the machine tool is able to obtain the optimal cutting precision during high-speed operations. 
   One feature of the present invention contemplates the relationship between the electrical signal sent by the power supply module and the workpiece. When the workpiece is heavier, the generated on the loading platform is greater. When the kinetic friction increases, the kinetic torque also increases, this in turns increases the torsion required to be outputted by the driving module for driving the loading platform. Accordingly, the electrical signal received by the driving module increases. As shown in  FIGS. 4 and 5 , driving electrical signals of X- and Y-axes fed, respectively, at 500 mm/min and 4000 mm/min are measured for a loading platform with no-load and with a 357 g load, respectively. When analyzing the relationship between the continuous output data of the electrical signals and the workpiece, the loading platform with no or some load is driven by the driving module in the positive X-axis, negative X-axis, positive Y-axis and negative Y-axis directions, and the continuous output data of the corresponding electrical signals are measured. Based on the data, the determining module may then correlate the workpiece and the continuous output data of the electrical signals corresponding to the loading platform having any load and driven in any two-dimensional direction, and determine the weight of the workpiece. 
   The parameter-optimized result is stored in the database. The parameters of the control unit are adjusted according to the load of the loading platform before operation is performed. This eliminates the tracking error attributed to a load with varying weights when the CNC machine tool is feeding in high speed. 
   The foregoing description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. In this regard, the embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the inventions as determined by the appended claims when interpreted in accordance with the breath to which they are fairly and legally entitled. 
   It is understood that several modifications, changes, and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.