Abstract:
In a data collection system for electric discharge machines, multiple electric discharge machines are connected with a computer over a data transmission path. Information on machining conditions of an electric discharge machine is stored in a storage unit of the electric discharge machine, and information sent from the electric discharge machine after completion of machining is collected by the computer. By minimizing monitoring information that is temporarily stored in the storage unit, various kinds of monitoring information can be stored without being affected by a network environment.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a data collection system for electric discharge machines in which a computer is connected with electric discharge machines over a network. 
         [0003]    2. Description of the Related Art 
         [0004]    A known technique for assessing the quality of a machined product manufactured by machining with an electric discharge machine is to measure and assess the surface roughness or dimensional accuracy of the machined product after machining. However, general assessing method of the quality of a machined product is to obtain monitoring information, such as machining voltage, machining current and machining speed which are used for keeping track of machining conditions during machining, and to asses the obtained monitoring information by determining the monitoring information falls within a prescribed range or not. And such obtained monitoring information is stored in a storage device in a numerical controller mounted on the electric discharge machine or transferred to a computer over a network when the electric discharge machine is connected to a network. 
         [0005]    Japanese Patent No. 4137384 (JP4137384B2) discloses a technique for collecting data on machining speed, machining voltage, machining current, on-time and off-time of voltage applied to electrodes, total number of discharges, the number of abnormal discharges, abnormal discharge rate and discharge frequency during machining with an electric discharge machine, and storing the collected data in a numerical controller mounted on the electric discharge machine. 
         [0006]    Such a numerical controller mounted on an electric discharge machine, however, typically has a smaller data storage capacity than a personal computer or a server. This makes it difficult to store multiple kinds of monitoring information over all routes of electric discharge machining that takes a long machining time in terms of storage capacity. Also, mounting a large-capacity storage device on an electric discharge machine for storing various kinds of monitoring information increases costs of the electric discharge machine. 
         [0007]    Another known technique is to continuously transfer various kinds of monitoring information to a network-connected computer and store the information in a storage device in the computer, instead of storing them in the numerical controller mounted on the electric discharge machine. While this scheme avoids the problem of increase in costs of the electric discharge machine caused by mounting a large-capacity storage on the electric discharge machine as in the case of the above-mentioned patent document, constant transfer of data over a network can increase communication load on the network or result in monitoring information not being stored in the computer in the event of a failure on the network. 
         [0008]    Japanese Patent No. 4047544 (JP4047544B2) discloses a system for collecting monitoring information such as variations in machining voltage and/or machining speed during machining via a network connection between a computer and an electric discharge machine. 
         [0009]    The system, constituted by a computer and an electric discharge machine, is able to store monitoring information such as machining speed, machining voltage, and machining current during a machining process in the numerical controller in the electric discharge machine at predetermined time intervals and subsequently transmit the information to an external computer or the like as needed. This scheme, however, has the disadvantage of data volume becoming large because it stores monitoring information at predetermined time intervals. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention addresses the above problems of the prior art technique with the object of providing a data collection system for electric discharge machines that is capable of collecting and storing various kinds of monitoring information during machining without adding a large-capacity storage device to a numerical controller mounted on the electric discharge machine. 
         [0011]    In a data collection system for electric discharge machines according to the present invention, a computer is connected with electric discharge machines over a data transmission path, information on machining conditions of an electric discharge machine is stored in a storage unit of the electric discharge machine, and information sent from the electric discharge machine after completion of machining is collected by the computer. The electric discharge machine includes: a detection unit that detects a physical quantity relating to machining conditions during machining either at predetermined intervals or each time a moving part of the electric discharge machine has traveled a predetermined distance; a determination unit that determines whether the physical quantity detected by the detection unit exceeds a predetermined threshold or not; a storage unit that stores the physical quantity or information indicating the fact that the physical quantity exceeds the threshold when the determination unit determines that the detected physical quantity exceeds the predefined threshold; and a transmission unit that sends the physical quantity or the information indicating the fact that the physical quantity exceeds the threshold, stored in the storage unit, after the machining by the electric discharge machine. The computer includes: a reception unit that receives the physical quantity or the information indicating the fact that the physical quantity exceeds the threshold sent from the transmission unit after the machining by the electric discharge machine; and a storage unit that stores the physical quantity or the information indicating the fact that the physical quantity exceeds the threshold, received by the reception unit. 
         [0012]    According to the data collection system for electric discharge machines of the present invention, electric discharge machines do not store all physical quantities that relate to machining conditions during machining but store them only when any physical quantity goes beyond a predetermined range. This minimizes monitoring information to be stored in the storage units of electric discharge machines and enables storage of necessary monitoring information even for electric discharge machining that involves a long machining time. In addition, since physical quantities stored in the storage units of electric discharge machines are sent to the computer after completion of machining instead of being transferred over the network at all times, no problem would occur in information transmission if communication load on the network becomes high or a temporary trouble occurs on the network. 
         [0013]    Note that the language “cross a threshold” used herein is intended to mean a transition from a range defined as “non-defective products” to another range defined as “defective products” in case where a range representing “non-defective products” and a range representing “defective products” are demarcated by a threshold, and is not necessarily used only to mean a transition from the smaller-valued range to the larger-valued range across the threshold. 
         [0014]    The the physical quantity may include one of: a machining voltage, a machining current, a machining speed, a temperature of a place where the electric discharge machine is installed, and a water temperature in a machining tank. 
         [0015]    The threshold may be a range defined by an upper limit and a lower limit of the physical quantity, and a plurality of such ranges are set for the physical quantity to be determined by the determination unit. The electric discharge machine may further include a setting unit that sets one or more items of physical quantities to be stored, from among the physical quantity to be determined by the determination unit and other physical quantities relating to the machining conditions, according to the respective ranges. The determination unit determines one of the set ranges within which the detected physical quantity falls. And the storage unit stores the item of physical quantity, set by the setting unit according to the respective ranges, based on the determination result of the determination unit. 
         [0016]    According to this embodiment, physical quantities to be stored in the storage device of an electric discharge machine are minimized by varying the kinds of physical quantity to be stored in the storage device of the electric discharge machine in accordance with which range a physical quantity is determined to fall within. Thus, various kinds of monitoring information can be stored for a long machining time even in a numerical controller not having a large-capacity storage device. 
         [0017]    The threshold may be a range defined by an upper limit and a lower limit of the physical quantity, and a plurality of such ranges are set for the physical quantity to be determined by the determination unit. The electric discharge machine may further include a setting unit that selects, for each of the set ranges, one of: a storage mode that stores the physical quantity in a form of a measured value and another storage mode that stores the physical quantity in the form of a flag indicating whether the physical quantity falls within or outside the range. The determination unit determines one of the set ranges within which the detected physical quantity falls. And the storage unit stores the physical quantity in the storage mode selected by the setting unit, based on the determination result of the determination unit. 
         [0018]    According to this embodiment, a physical quantity is stored in the storage device of an electric discharge machine in different forms, i.e., either as a flag or a measured value, depending on which range the physical quantity is determined to fall within, thereby minimizing physical quantities to be stored in the storage device. Thus, various kinds of monitoring information can be stored for a long machining time even in a numerical controller not having a large-capacity storage device. 
         [0019]    If the physical quantity or the information indicating that the physical quantity exceeds the threshold, stored in the storage unit of the electric discharge machine, exceeds a predetermined size, the physical quantity or the information indicating that the physical quantity exceeds the threshold may be sent from the electric discharge machine to the computer, and the machining by the electric discharge machine is stopped. 
         [0020]    According to this embodiment, when the physical quantity or data exceeds a predetermined size, the physical quantity or data is sent from the electric discharge machine to the computer and operation of the electric discharge machine is stopped, thereby preventing an overflow of monitoring information that should be stored and a resulting failure to store them. It also can prevent machining from continuing with the physical quantity or data exceeding a predetermined size so that the product in process is not judged as defective and does not result in waste machining if the machining is continued in such a condition. Additionally, since the physical quantity or data in the electric discharge machine is sent to the computer upon exceeding the predetermined size, the physical quantity or data sent to the computer may be analyzed to determine the cause of the defectiveness and the like. 
         [0021]    According to the present invention, by minimizing the amount of monitoring information temporarily stored in a numerical controller mounted on an electric discharge machine, various kinds of monitoring information can be stored without being affected by a network environment even if the numerical controller does not have a large-capacity storage device. Further, transfer of such monitoring information temporarily stored in the numerical controller to a computer connected over a network enables storage of a large volume of monitoring information. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    These and other objects and features of the present invention will become apparent from the following description of an exemplary embodiment with reference to the accompanying drawings in which: 
           [0023]      FIG. 1  schematically shows a data collection system for electric discharge machines according to the present invention; 
           [0024]      FIG. 2  schematically shows a numerical controller which is mounted on an electric discharge machine and which constitutes the data collection system of  FIG. 1 ; 
           [0025]      FIG. 3  shows an example of machining voltage values and assessment of machined product quality in the data collection system for electric discharge machines according to the present invention; 
           [0026]      FIG. 4  shows an example of machining current values and assessment of machined product quality in the data collection system for electric discharge machines according to the present invention; 
           [0027]      FIG. 5  shows the relationship between the result of machining voltage assessment and data to be stored in response to the result, where only a machining voltage value obtained by monitoring is stored when the result of assessment is “inspection required”; 
           [0028]      FIG. 6  shows the relationship between the result of machining voltage assessment and data to be stored in response to the result, where a flag value indicating the assessment result is stored when the result is “inspection required”; 
           [0029]      FIG. 7  is a flowchart illustrating a process of storing simple data when the result of machining voltage assessment is “inspection required”; 
           [0030]      FIG. 8  is a flowchart illustrating a process of storing a flag when the result of machining voltage assessment is “inspection required”; and 
           [0031]      FIG. 9  shows an example of machining voltage values and assessment of machined product quality for a case where multiple “inspection required” ranges are defined for machining voltage assessment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Referring to  FIG. 1 , a data collection system for electric discharge machines  10  according to the present invention will be generally described first. 
         [0033]    Multiple electric discharge machines  10  (machines a, b, . . . , n) are connected with a computer  40  via a hub and router  50 . Between the computer  40  and the hub/router  50 , and between the hub/router  50  and each of machines a, b, . . . , and n are connected by LANs  30 . While between the computer  40  and the hub/router  50 , and between the hub/router  50  and the individual machines are connected by LANs  30  in the example of  FIG. 1 , they may be connected by network connection means other than LANs. 
         [0034]    Turning to  FIG. 2 , a numerical controller  11  included in each electric discharge machine  10  (machine n) is described. 
         [0035]    As also shown in  FIG. 1 , the electric discharge machine  10  (machine n) is connected with the computer  40  by a LAN and includes a numerical controller  11 , a discharge device  17 , a servo motor  18 , and a temperature sensor  19 . The numerical controller  11  includes a CPU  12 , a storage  13 , an SRAM  14 , a RAM  15 , a display  16 , a keyboard  21 , and a network interface card (NIC)  20 . 
         [0036]    The storage  13  is a flash memory or a hard disk for example, and the SRAM  14  is a nonvolatile memory backed by a battery or the like. The storage  13  and SRAM  14  store setting data, machining conditions, and machining programs for use in machining, and thresholds for use in performing assessment of monitoring information. 
         [0037]    The display  16  shows monitoring information and other information. The keyboard  21  is used for inputting a monitoring range (an assessment range used for storage of data in the numerical controller  11  as described later) or inputting types of data to be stored in the numerical controller  11  when any monitoring information goes beyond the monitoring range. Although, in the example of  FIG. 2 , monitoring range and data types for storage are manually input using the keyboard  21  with which the numerical controller  11  is equipped, they may instead be set from a network-connected computer or may be input using a machining program. 
         [0038]    Various setting data, machining conditions, machining programs, and stored monitoring information used for assessing the quality of machined products can be obtained by the numerical controller  11  and sent from the numerical controller  11  to the computer  40 , which is connected via the NIC  20  and LAN  30 , to be stored in the computer  40 . While in this embodiment the connection between the machine  10  and the computer  40  is a LAN connection as described above with reference to  FIG. 1 , other network connection means may instead be used for the connection. 
         [0039]    In the data collection system for the electric discharge machine  10 , the numerical controller  11  periodically obtains physical quantities such as machining voltage and machining current, and performs assessment of machined product quality for each kind of physical quantity obtained. For the data collection system for the electric discharge machine  10 ,  FIG. 3  shows the relationship between machining voltage values of the electric discharge machine  10  and assessment of machined product quality; and  FIG. 4  shows the relationship between machining current values and assessment of machined product quality. 
         [0040]    In  FIG. 3 , the bold solid line denotes a reference value representing a voltage optimal as machining voltage. When the machining voltage falls within “region 1” between the bold solid line and the broken line, representing a predetermined range around the reference value, the machining voltage is assessed as “non-defective products (no inspection required)”. When the machining voltage is in “region 2” between the broken line and the chain line, the machining voltage is assessed as “inspection required”. When the machining voltage is in “region 3” outside the chain line, the machining voltage is assessed as “defective products”. The assessment focuses on whether the machining voltage falls within either region 2 or 3, which are outside the broken line; when the machining voltage falls within region 1 and is assessed as “non-defective products (no inspection required)”, physical quantity values at the time are not stored. When the machining voltage falls within region 2 and is assessed as “inspection required”, only simple data enough to indicate the necessity of inspection is stored, rather than storing many kinds of data. When the machining voltage falls within region 3 and is assessed as “defective products”, the machining voltage as well as other data are stored in order to determine the cause of the defectiveness. 
         [0041]    More specifically, when the machining voltage falls within region 2 and is assessed as “inspection required”, only the machining voltage value obtained by monitoring is stored or a flag value indicating that the result of assessment was region 2 is stored. When the machining voltage falls within region 3 and is assessed as “defective products”, the machining current, machining speed, the current positions of axes and the like at the time are also stored in addition to the machining voltage value obtained by monitoring. 
         [0042]      FIGS. 5 and 6  show the relationship between the result of assessment on machining voltage and data to be stored in response to the result. In  FIG. 5 , only the machining voltage value obtained by monitoring is stored when the assessment result is “inspection required”; while in  FIG. 6  a flag value indicating the assessment result is stored when the result is “inspection required”. 
         [0043]    In addition to measuring the machining voltage of the electric discharge machine  10  and assessing machined product quality based on the measured value ( FIG. 3 ), measuring of the machining current of the electric discharge machine  10  and assessing machined product quality based on the measured value ( FIG. 4 ) is also concurrently performed in a similar manner. 
         [0044]    When the machining current falls within region 1 shown in  FIG. 4  and is assessed as “non-defective products (no inspection required)”, physical quantity values at the time are not stored. When the machining current falls within region 2 shown in  FIG. 4  and is assessed as “inspection required”, only simple data enough to indicate the necessity of inspection is stored, rather than storing many kinds of data. When the machining current falls within region 3 shown in  FIG. 4  and is assessed as “defective products”, the machining current as well as other data are stored in order to determine the cause of the defectiveness. 
         [0045]    More specifically, when the machining current falls within region 2 and is assessed as “inspection required”, only the machining current value obtained by monitoring is stored or a flag value indicating that the result of assessment was region 2 is stored. To make clear which physical quantity was assessed as “inspection required”, the value of the physical quantity that was assessed as inspection required may be stored or different flags may be prepared for the kinds of physical quantities that were assessed as inspection required. When the machining current falls within region 3 and is assessed as “defective products”, machining voltage, machining speed, the current positions of axes and the like at the time are also stored in addition to the machining current value obtained by monitoring. 
         [0046]    Using the flowchart of  FIG. 7 , the process of storing only simple data when the result of machining voltage assessment is “inspection required” will be described per step. 
         [0047]    Step SA 1 : Whether machining has started or not is determined. If machining has started, the flow proceeds to step SA 2 . 
         [0048]    Step SA 2 : Stored monitoring information that has been stored during previous monitoring is cleared. 
         [0049]    Step SA 3 : Monitoring information such as machining voltage and machining current is acquired. 
         [0050]    Step SA 4 : Whether or not data in the acquired monitoring information falls within a predefined range of “non-defective products” is determined. If the data is within the range of “non-defective products” (Yes), the flow proceeds to step SA 9 . If the data is outside the range of “non-defective products” (No), the flow proceeds to step SA 5 . 
         [0051]    Step SA 5 : Whether or not data in the monitoring information acquired in step SA 3  falls within a predefined range of “inspection required” is determined. If the data is within the range of “inspection required” (Yes), the flow proceeds to step SA 7 . If the data is outside the range of “inspection required” (No), the flow proceeds to step SA 6 . 
         [0052]    Step SA 6 : The acquired data is determined to be “defective products”, and the machining voltage as well as the machining current, machining speed, and/or the current positions of axes at the time are stored in the numerical controller  11  as monitoring information. 
         [0053]    Step SA 7 : Only simple data indicative of “inspection required” (e.g., only the values of the physical quantities that were assessed as “inspection required”) are stored in the numerical controller  11 . 
         [0054]    Step SA 8 : Whether or not the data stored in the numerical controller  11  has exceeded the storage capacity is determined. If the storage capacity has not been exceeded (No), the flow proceeds to step SA 9 . If the storage capacity has been exceeded (Yes), the flow proceeds to step SA 11 . 
         [0055]    Step SA 9 : Whether machining by the electric discharge machine has completed is determined. If machining has completed (Yes), the flow proceeds to step SA 10 . If machining has not completed yet, the flow returns to step SA 3  to continue monitoring. 
         [0056]    Step SA 10 : In response to completion of machining, monitoring information stored in the numerical controller  11 , such as machining voltage, machining current, machining speed, the current positions of axes, are sent to the computer  40  from the numerical controller  11 , whereupon the process ends. 
         [0057]    Step SA 11 : As the data storage capacity of the numerical controller  11  has been reached, monitoring information stored in the numerical controller  11 , such as machining voltage, machining current, machining speed, the current positions of axes, are sent to the computer  40  from the numerical controller  11 . 
         [0058]    Step SA 12 : An alarm indicating that data in the numerical controller  11  goes beyond the storage capacity is displayed on the display  16  of the numerical controller  11 , the machining operation of the electric discharge machine is stopped, and the process is terminated. 
         [0059]      FIG. 8  is a flowchart illustrating the process of storing a flag value indicative of the assessment result when the result of machining voltage assessment is “inspection required”. 
         [0060]    While processing in steps SB 1  through SB 12  shown in the flowchart of  FIG. 8  is substantially the same as processing in steps SA 1  through SA 12  in the flowchart of  FIG. 7 , the processing in step SB 7  in  FIG. 8  is different from the processing in step SA 7  of  FIG. 7 . Specifically, in  FIG. 7 , when data is determined to fall within a range of “inspection required” in step SA 5  and then the flow proceeds to step SA 7 , only simple data indicative of “inspection required” (e.g., only the values of the physical quantity that were assessed as “inspection required”) is stored in the numerical controller  11 ; whereas in  FIG. 8 , when data is determined to fall within a range of “inspection required” in step SB 4  and then the flow proceeds to step SB 7 , a flag value indicating which physical quantity was assessed as “inspection required” is stored in the numerical controller  11  as data indicative of “inspection required”. 
         [0061]    In the examples shown in  FIGS. 3 and 4 , monitoring information for machining voltage and machining current is sorted into three ranges, namely “region 1” (with assessment result “non-defective products”), “region 2” (with assessment result “inspection required”), and “region 3” (with assessment result “defective products”). Alternatively, the range of “region 2” (with assessment result “inspection required”) may be subdivided into a range of “region 2A” (with assessment result “inspection required 1”) and a range of “region 2B” (with assessment result “inspection required 2”) as shown in  FIG. 9 , and different data may be stored in the numerical controller  11  depending on whether the level of “inspection required” is “inspection required 1” or “inspection required 2”, such as storing a flag value in the numerical controller  11  when the machining voltage or current falls under region 2A and storing the machining voltage value when the machining voltage or current falls under region 2B. 
         [0062]    In the above-described example, the monitoring range is specified by defining a reference value for the machining voltage or current and setting predetermined widths above and below the reference value to establish assessment regions. Instead of setting such a reference value, the monitoring range may be specified by establishing upper and lower limit values. 
         [0063]    In the above-described example, when the assessment result is “defective products”, the machining voltage and all of other monitoring information including machining current, machining speed, and current positions of axes are stored in the numerical controller  11 . It is not necessarily required to store all kinds of monitoring information, however; different data may be stored according to the type of data that falls outside the predetermined range. For example, in a case where monitored data is water temperature, only the time at which the water temperature fell outside its monitoring range may be stored. 
         [0064]    Also, in the above-described example, as long as the data stored in the numerical controller  11  does not exceed the storage capacity, the data is sent from the numerical controller  11  to the computer  40  when machining has finished, which is advantageous in that data for the whole machining process can be sent after the machining ends. The invention is not limited thereto however; data may be sent during a machining operation from the numerical controller  11  to the computer  40  through an operator&#39;s control or an instruction from a program, or in a case of multiple machining operations for multiple shapes, data may be sent on each performance of a certain number of machining operations for each of the shapes.