Abstract:
A servo control device that displays, by a two-dimensional image, evaluation of control precision of a servo system, includes: an instruction unit that instructs a position instruction having periodicity; a unit that records a track of position data based on a position feedback of a servo system according to the position instruction; and a first drawing unit that draws position data based on the position feedback, data before a quarter cycle or after a quarter cycle of the position data or position data based on the position instruction before a quarter cycle or after a quarter cycle, on a two-dimensional plane including orthogonal two axes, as the axis data of the orthogonal two axes respectively.

Description:
RELATED APPLICATIONS 
   The present application is based on, and claims priority from, Japanese Application Number 2005-040582, filed Feb. 17, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety. 
   FIELD OF THE INVENTION 
   The present invention relates to a numerical control (NC) device. Particularly, the invention relates to an adjusting device that adjusts the control precision of a servo system, and a method of adjusting the servo system. 
   BACKGROUND OF THE INVENTION 
   Conventionally, a machine having plural axes, such as an NC machine tool, gives an arc instruction as orthogonal straight lines having two axes, draws position feedback data of the straight lines having two axes on a two-dimensional plane, and adjusts a servo system using a shape of this track as an evaluation reference, as disclosed in Japanese Patent Application Unexamined Publication No. 4-177408 and Japanese Patent Application Unexamined Publication No. 2002-120128. 
     FIG. 1  graphically expresses an example of a configuration of an NC device. In this example, a servo system is adjusted based on a conventional method using two orthogonal axes. 
   In  FIG. 1 , an NC device  1  can control a servo motor  2  that drives the X-axis and a servo motor  3  that drives the Y-axis, thereby freely moving a position of a work table  4 , fitted to the front end of each axis, within an X-Y plane. 
   In the present example, a control unit  11  of the NC device  1  gives an arc instruction to an X-axis driving unit  12  that controls the position of the work table  4  in the X-axis direction, and gives an arc instruction, of which phase is deviated by 90 degrees from the phase of the above arc instruction, to a Y-axis driving unit  13  that controls the position of the work table  4  in the Y-axis direction. 
   The control unit  11  receives position feedback information from the servo motors  2  and  3  and the work table  4 , and converts the position feedback information into normal polar coordinates (x=sin θ,2 y=cos θ, 0≦θ&lt;π), thereby calculating an actual move position of the work table  4 . In this case, the work table  4  moves along a unit circle (x 2 +y 2 =1). The control unit  11  displays the actual move position of the work table  4  on a monitor  5  using a personal computer or the like, by superimposing the actual move position with the instruction arc (unit circle) as the evaluation reference value of the servo system adjustment. 
     FIG. 2  shows one example of a monitor screen shown in  FIG. 1 .  FIG. 2  shows a superimposition of the evaluation reference value according to the instruction arc, and the position feedback information obtained by actually moving the work table  4  based on the instruction arc. It is clear from  FIG. 2  that an error of the servo system occurs mainly due to quadrant projections  21  to  24  attributable to nonlinearities (frictions) before and after a speed polarity changes. The quadrant projections  21  to  24  appear as shape errors when an arc instruction is given to the orthogonal two axes (X-Y axes). 
   An operator adjusts the servo system so that the quadrant projections  21  to  24  become close to zero (i.e., instruction arc), while watching the drawing track displayed on the monitor  5 . Based on this, the operator can easily evaluate processing precision of the machine tool without actually carrying out a work process. 
   At the time of adjusting a servo system of a single control axis such as a straight line axis and a rotation axis having no adjacent orthogonal axes, a shape error also occurs before and after the speed polarity is changed. However, in this case, because adjacent axes, like the orthogonal two axes which can easily draw an arc, are not present, a visual evaluation standard on which the servo axis is adjusted is not present. Therefore, the servo system cannot be visually adjusted easily. 
   For the above reason, at the time of adjusting a servo system of a single control axis such as a straight line axis and a rotation axis having no adjacent orthogonal axes, a work process is actually carried out to evaluate the processing precision of the machine tool. When this method is used, the work efficiency of adjusting the single control axis such as a straight line axis and a rotation axis having no adjacent orthogonal axes is extremely decreased, and the adjustment cost increases substantially. 
   SUMMARY OF THE INVENTION 
   In the light of the above problems, it is an object of the present invention to provide a method of adjusting a servo system capable of visually adjusting the servo system in a similar manner to that using the conventional orthogonal two axes, at the time of adjusting the servo system of a single control axis such as a straight line axis and a rotation axis having no adjacent orthogonal axes. 
   According to a first aspect of the present invention, there is provided a control device including: an instruction unit that instructs a position instruction having periodicity; a unit that records a track of position data based on a position feedback of a servo system according to the position instruction; and a first drawing unit that draws position data based on the position feedback, data before a quarter cycle or after a quarter cycle of the position data or position data based on the position instruction before a quarter cycle or after a quarter cycle, on a two-dimensional plane including orthogonal two axes, as the axis data of the orthogonal two axes respectively. 
   According to a second aspect of the invention, there is provided the control device according to the first aspect, further including a second drawing unit that draws, in superimposition on the two-dimensional plane, the position data based on the position instruction and data before a quarter cycle or after a quarter cycle of the position data, as axis data of the orthogonal two axes respectively. According to a third aspect of the invention, the control device further includes an adjusting unit that adjusts the servo system so that a shape drawn by the first drawing unit becomes closer to a shape of an evaluation reference, using a shape drawn by the second drawing unit as the evaluation reference. 
   According to a fourth aspect of the present invention, there is provided a method of adjusting a servo system including: instructing a position instruction having periodicity; drawing position data based on a position feedback of a servo system according to the position instruction, data before a quarter cycle or after a quarter cycle of the position data or position data based on the position instruction before a quarter cycle or after a quarter cycle, on a two-dimensional plane including orthogonal two axes, as the axis data of the orthogonal two axes respectively; drawing, in superimposition on the two-dimensional plane, the position data based on the position instruction and data before a quarter cycle or after a quarter cycle of the position data, as axis data of the orthogonal two axes respectively; and adjusting the servo system so that a shape drawn based on the position data based on the position feedback and the data before a quarter cycle or after a quarter cycle of the position data or the position data based on the position instruction before a quarter cycle or after a quarter cycle, becomes closer to a shape of an evaluation reference, using a shape drawn based on the position data based on the position instruction and the data before a quarter cycle or after a quarter cycle of the position data as the evaluation reference. 
   According to the present invention, a sine arc instruction is given to the servo system as a move instruction having periodicity. Position feedback data and data before one quarter cycle or after one quarter cycle or position data based on the position instruction before one quarter cycle or after one quarter cycle are converted into each position data of the X-axis and the Y-axis, and an image obtained is drawn on the two-dimensional plane (X-Y plane). This has the same effect as that of drawing a track of the obtained position feedback data, based on the arc instruction to the orthogonal two axes. Accordingly, it becomes possible to visually adjust the servo system of a single control axis such as a straight line axis and a rotation axis having no adjacent orthogonal axes. 
   Consequently, in the servo system of a single control axis such as a straight line axis and a rotation axis having no adjacent orthogonal axes, it becomes possible to carry out a high-precision evaluation of the machine tool without actually executing a work process. As a result, efficiency of the adjusting work can be increased, and adjustment cost can be decreased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the description as set forth below with reference to the accompanying drawings, wherein: 
       FIG. 1  is an explanatory diagram of one example of a system configuration that can be adjusted using orthogonal two axes; 
       FIG. 2  is an explanatory diagram of a monitoring screen shown in  FIG. 1 ; 
       FIG. 3  is an explanatory diagram of one example of a basic configuration of a servo control system according to the present invention; 
       FIG. 4  shows a graph of an example of a display carried out by a two-dimensional drawing unit shown in  FIG. 3 ; 
       FIG. 5  shows a configuration of a servo control system according to a first embodiment of the present invention; 
       FIG. 6  is a graphical expression of another example of a basic configuration of a servo control system according to the present invention; 
       FIG. 7  shows a graph of an example of a display carried out by a two-dimensional drawing unit shown in  FIG. 6 ; and 
       FIG. 8  shows a configuration of a servo control system according to a second embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3  is an explanatory diagram of one example of a basic configuration of a servo control system according to the present invention. 
   In  FIG. 3 , an arc instruction to adjust a servo system  32  is given to a control axis driving unit  31  of the NC device. With this arrangement, the control axis driving unit  31  outputs an assigned arc position signal to the servo system  32  repetitively in a constant cycle of arcs. A subtracter  35  of the servo system  32  subtracts a position feedback signal sent from a position moving unit  34  that includes a spindle motor, from the position signal sent from the main axis driving unit  31 , and outputs a differential signal, which is the difference of these signals, to a position loop processing unit  33  at the next stage. 
   The position loop processing unit  33  drives the position moving unit  34  at the next stage so that the input differential signal becomes zero. The servo system  32  is controlled so that a move position assigned by the arc instruction coincides with a position actually moved by the position moving unit  34 . 
   On the other hand, a quarter cycle time delay unit  37  outputs a position feedback signal of a delay of one quarter cycle (i.e., phase delay of 90 degrees) of a circle assigned by the arc instruction. When a position feedback signal which is synchronous with the arc instruction is expressed as a function of sin θ, a position feedback signal of which phase is delayed by 90 degrees is expressed as a function of cos θ (=sin (θ−π)). 
   When the position feedback signal is x (=sin θ) and also when the position feedback signal of a phase delay of 90 degrees is y (=cos θ), the relationship of x 2 +y 2 =1 is obtained as explained in the conventional example in  FIG. 2 . When this x 2 +y 2 =1 is drawn on the two-dimensional plane (X-Y plane) of the two-dimensional drawing unit  38 , a unit circle is obtained. As can be easily analogized from this explanation, drawing both the position feedback data based on the sinusoidal wave instruction and the data of a quarter cycle delay on the two-dimensional coordinates is equivalent to giving an arc instruction to one straight line axis (X-axis) and giving an arc instruction having the same servo characteristic of which phase is delayed by 90 degrees to the axis (Y-axis) orthogonal with the X-axis, and drawing the track of the position feedback data (see  FIG. 1 ). 
     FIG. 4  shows one example of a feedback signal displayed by the two-dimensional drawing unit shown in  FIG. 3 . A portion (a) of  FIG. 4  shows one example of a position feedback signal (x) drawn based on an arc instruction in one straight line axis (X-axis). A portion (b) of  FIG. 4  shows one example of a position feedback signal (x, y) drawn on a two-dimensional plane (X-Y plane) by converting the position feedback signal (x) shown in  FIG. 4(   a ) into the two-dimensional drawing. 
   As is clear from  FIG. 4 , according to the one-dimensional display in the portion (a) of  FIG. 4 , it cannot be decided whether the feedback signal (x) moves correctly along the arc based on the arc instruction, and it is not possible to distinguish between the arc and quadrant projections  41  and  43 . On the other hand, according to the two-dimensional display in the portion (b) of  FIG. 4 , it can be easily understood that the feedback signal (x, y) moves along the arc based on the arc instruction, and it is possible to distinguish between the arc and the quadrant projections  41  and  43 . 
   Therefore, in adjusting a servo system of a single control axis such as a straight line axis and a rotation axis having no adjacent orthogonal axes, the servo system can be also adjusted using the same visual method as that conventionally used. According to the present invention, the quadrant projections  41  and  42  have mutually similar shapes, and quadrant projections  43  and  44  have mutually similar shapes. 
     FIG. 5  shows a configuration of a servo control system according to a first embodiment of the present invention. 
   In  FIG. 5 , a control unit  50  is configured by a central processing unit (CPU) circuit. During the operation, the control unit  50  refers to a parameter table  51  disposed on a random access memory (RAM), obtains move speed/current data of a servo motor  54  corresponding to the position data of an arc instruction (x=sin θ) in one direction, and gives the move speed/current data to an X-axis driving unit  53 . With this arrangement, the servo motor  54  is driven, and position data, such as a rotation number/angle and a move position that are output from a pulse coder not shown inside the servo motor  54  and a linear scale not shown fitted to a work table  55 , is fed back to the control unit  50 . 
   The control unit  50  receives the position feedback data, and compares the position feedback data with the position data that the control unit  50  has given to the X-axis driving unit  53 , and obtains the difference between the two data. The control unit  50  negatively feeds back the difference to the X-axis driving unit  53  so that the difference becomes zero. In the present invention, the control unit  50  further converts the received position feedback data into X-axis position data (x=α sin θ, α=1+Δ (θ)). 
   On the other hand, the position data output from the pulse coder and the linear scale is also input to a quarter delay memory  52  configured by a first-in and first-out (FIFO) memory. The input data is output after a lapse of a quarter cycle (i.e., after a phase delay of 90 degrees) of the arc instruction. In the present invention, the control unit  50  converts the reception data into virtual Y-axis position data (x=β cos θ, β=1+Δ (θ−π/2)). The phase advance of 90 degrees can be also used as the Y-axis position data. 
   The control unit  50  outputs the received X-axis position data and the received Y-axis position data to a monitor terminal  56  configured by a personal computer via a serial interface of the Recommended Standard 232 version C (RS232C) or a Universal Serial Bus (USB). The monitor terminal  56  displays the X-axis position data and the Y-axis position data on the two-dimensional plane (X-Y plane) as shown in  FIG. 4  ( b ). It can be also arranged such that the X-axis position data and the Y-axis position data are calculated and displayed on the monitor at the monitor terminal  56  side. 
   The operator rewrites parameters of speeds and currents corresponding to positions in the parameter table  51  so that the levels of the quadrant projections  41  to  44  become equal to or below predetermined permissible values, while watching two-dimensional position data. The monitor terminal  56  instructs the control unit  50  to rewrite these data via the serial interface, and the control unit  50  updates the parameters of the parameter table  51  after receiving the instruction. 
     FIG. 6  is a graphical expression of another example of a basic configuration of a servo control system according to the present invention.  FIG. 7  shows an example of a feedback signal displayed by the two-dimensional drawing unit  38  shown in  FIG. 6 . 
     FIG. 6  is different from  FIG. 3  as follows. While the position feedback signal of the servo system is input to the quarter cycle time delay unit  37  in  FIG. 3 , the arc position signal output from the control axis driving unit  31  is directly input to the quarter cycle time delay unit  37  in  FIG. 6 . As a result, in the present example, the position data based on the arc instruction in the X-axis direction is directly converted into position data in the Y-axis direction delayed by 90 degrees. 
   With the above arrangement, in the present example, the quadrant projections  42  and  44  in the Y-axis direction shown in  FIG. 3  (i.e., virtual quadrant projections obtained by turning the quadrant projections  41  and  43  of the position feedback signal by 90 degrees) do not occur as shown in  FIG. 7 . On the other hand, the servo adjustment in one direction (i.e., X-axis direction) and the content of display on the monitor screen coincide with each other. Therefore, the operator can carry out one-axis adjustment based on a visual confirmation that coincides with the actual adjustment work. 
     FIG. 8  shows a configuration of a servo control system according to a second embodiment of the present invention. 
   According to the present embodiment, a parameter table  61 , an instruction data storage area  62 , and a position data storage area  63  are provided by using a memory  60  incorporated in the CPU that constitutes the control unit  50  within the NC device. The parameter table  61  corresponds to the parameter table shown in  FIG. 5 . In the present embodiment, arc instruction data output from the X-axis driving unit  53  are sequentially stored in the instruction data storage area  62 . Corresponding position feedback data from the servo system are sequentially stored in the position data storage area  63 . 
   The control unit  50  receives the position feedback data from the position data storage area  63 , and converts the position feedback data into X-axis position data (x=α sin θ, α=1+Δ (θ)). The controller  50  obtains arc instruction data of which phase is different by 90 degrees, from the instruction data storage area  62 , and converts the arc instruction data into virtual Y-axis position data (y=cos θ). The control unit  50  outputs the position data (x, y) obtained by the conversion, to the monitor terminal  56  configured by the personal computer via the serial interface of the RS232C or the USB. The monitor terminal  56  displays the position data (x, y) as an image on the two-dimensional plane (X-Y plane) as shown in  FIG. 7 . Alternatively, the X-axis position data and the Y-axis position data can be converted at the monitor terminal  56  side. 
   The operator rewrites parameters of speeds and currents corresponding to positions in the parameter table  61  so that the levels of the quadrant projections  41  and  43  become equal to or below predetermined permissible values, while watching two-dimensional position data. The monitor terminal  56  instructs the control unit  50  to rewrite these data via the serial interface, and the control unit  50  updates the parameters of the parameter table  61  after receiving the instruction. 
   As explained above, according to the present invention, feedback track data of a single control axis and a virtual axis orthogonal with the single control axis are drawn on a two-dimensional plane. Based on this, a visual servo adjustment that is conventionally carried out on two orthogonal axes can be also carried out to a single control axis. While the single straight line axis is taken up as an example in the present embodiment, a visual servo adjustment can be also carried out on a control axis which is a rotation axis.