Patent Publication Number: US-10322486-B2

Title: Grinding machine

Description:
TECHNICAL FIELD 
     The present invention relates to a grinding machine including a manual rotating handle provided with a rotation detector that outputs a rotation detection signal that is an electric signal corresponding to the amount of rotation resulting from an operator&#39;s manual operation so that the position of a grinding wheel with respect to a workpiece can be relatively moved in accordance with the rotation detection signal. 
     BACKGROUND ART 
     Some grinding machines have an automatic operation mode in which a workpiece is automatically machined by automatically moving the position of a grinding wheel relative to the workpiece in accordance with a program stored in a numerical control apparatus or the like and a manual operation mode in which the workpiece is machined by an operator&#39;s manual operation in which the operator operates a manual rotating handle to move the position of the grinding wheel relative to the workpiece. 
     In conventional hydraulic grinding machines with the manual operation mode, the position of the grinding wheel relative to the workpiece is moved by using the manual rotating handle to apply pressure directly to hydraulic oil for oil pressure that al lows movement of the position of the grinding wheel relative to the workpiece. Thus, when the grinding wheel contacts the workpiece, the grinding wheel (or the workpiece) does not move even if is applied to the hydraulic oil. Thus, a rotational torque that is a torque needed to rotate the manual rotating handle is automatically increased, so that the operator can easily feel the contact between the grinding wheel and the workpiece. In the conventional grinding machines, the operator can recognize subtle (delicate) contact based on the increased rotational torque of the manual rotating handle, and can start to finely (delicately) operate the manual rotating handle after the contact to achieve accurate machining. 
     Patent Document 1 describes a CNC grinding machine including a table feeding manual handle (corresponding to the manual rotating handle) and a wheel spindle stock-feeding manual handle (corresponding to the manual rotating handle) and having a manual operation mode. In the manual operation mode, each manual handle causes a pulse generator to generate a pulse corresponding to the amount of rotation, and the pulse is input to a control unit that outputs an amount of control corresponding to the pulse to a servo motor to move the position of the table or the grinding wheel. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent Application Publication No. 2006-123138 (JP 2006-123138 A) 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In recent years, grinding machines have prevailed which, for various purposes such as improvement of controllability, machining accuracy, and maintainability, control the position of the grinding wheel or the table using the servo motor instead of hydraulically controlling the position of the grinding wheel or the table. The CNC grinding machine described in Patent Document 1 also controls the position of the grinding wheel or the table using the servo motor instead of hydraulically controlling the position of the grinding wheel or the table. 
     However, in the grinding machine described in Patent Document 1, when, for example, the operator manually moves the grinding wheel in the manual operation mode by operating the wheel spindle stock-feeding manual handle, the rotational torque of the wheel spindle stock-feeding manual handle is not changed even when the grinding wheel and the workpiece come into contact with each other. Consequently, the operator fails to feel the contact between the grinding wheel and the workpiece. Therefore, even though the grinding wheel and the workpiece are in contact with each other, the grinding wheel may be operated to further cut into the workpiece, possibly precluding accurate machining. 
     The present invention has been developed in view of these circumstances. An object of the present invention is to provide a grinding machine including a manual rotating handle provided with a rotation detector that outputs a rotation detection signal that is an electric signal corresponding to the amount of rotation resulting from an operator&#39;s manual operation so that the position of a grinding wheel with respect to a workpiece can be relatively moved in accordance with the rotation detection signal. The grinding machine allows the operator to feel a state of proximity between the grinding wheel and the workpiece and assists accurate machining based on the operator&#39;s manual operation. 
     Means for Solving the Problem 
     A grinding machine according to an aspect of the present invention includes:
         a grinding wheel that grinds a workpiece;   a moving apparatus that relatively moves a position of the grinding wheel with respect to the workpiece;   a proximity detector that outputs a proximity detection signal corresponding to a distance between the workpiece and the grinding wheel;   a manual rotating handle provided with a rotation detector that outputs a rotation detection signal that is an electric signal corresponding to an amount of rotation resulting from an operator&#39;s manual operation; and   a control apparatus that receives the rotation detection signal to control the moving apparatus by an amount corresponding to the rotation detection signal.   The manual rotating handle is provided with a rotational-torque varying apparatus that varies a rotational torque that is a torque needed to rotate the manual rotating handle.   The control apparatus receives the proximity detection signal to control the rotational-torque varying apparatus in accordance with a state of proximity between the workpiece and the grinding wheel based on the proximity detection signal.       

     In the above aspect, the rotational-torque varying apparatus is controlled in accordance with the state of proximity between the workpiece and the grinding wheel. For example, in the state of proximity immediately before or at a time point when the workpiece and the grinding wheel come into contact with each other, the rotational torque of the manual rotating handle is increased. Accordingly, the operator can feel the contact between the grinding wheel and the workpiece (or a state immediately before the contact) and appropriately avoid operating the grinding wheel to significantly cut into the workpiece without recognizing the contact between the grinding wheel and the workpiece. Therefore, the grinding machine, which includes the manual rotating handle provided with the rotation detector that outputs the rotation detection signal that is an electric signal corresponding to the amount of rotation resulting from the operator&#39;s manual operation so that the position of the grinding wheel with respect to the workpiece can be relatively moved in accordance with the rotation detection signal, allows the operator to feel the state of proximity between the grinding wheel and the workpiece and assists accurate machining based on the operator&#39;s manual operation. 
     According to another aspect of the present invention, in the grinding machine according to the above aspect, upon determining that the state of proximity between the workpiece and the grinding wheel is such that the workpiece and the grinding wheel are in contact with each other, the control apparatus controls the rotational-torque varying apparatus such that the rotational torque of the manual rotating handle increases above the rotational torque exerted when the workpiece and the grinding wheel are not in contact with each other. 
     In the above aspect, when the workpiece and the grinding wheel are determined to be in contact with each other, the rotational-torque varying apparatus is controlled to increase the rotational torque of the manual rotating handle above the rotational torque exerted when the workpiece and the grinding wheel are not in contact with each other. Consequently, the operator can be appropriately and easily feel a timing when the workpiece and the grinding wheel come into contact with each other. Therefore, the operator can appropriately avoid operating the grinding wheel to further cut into the workpiece in spite of the contact between the grinding wheel and the workpiece. The aspect thus allows assistance of accurate machining based on the operator&#39;s manual operation. 
     According to yet another aspect of the present invention, in the grinding machine according to the above aspect, the rotational-torque varying apparatus includes: a handle shaft supported so as to be rotatable around a rotation axis of the manual rotating handle, and a pressing member that is disposed so as to face the handle shaft and that is pressed against the handle shaft facing the pressing member, under a pressing force adjusted by a control signal from the control apparatus. 
     According to still another aspect of the present invention, in the grinding machine according to the above aspect, the rotational-torque varying apparatus has a shaft integral member that rotates integrally with a handle shaft, and a pressing member disposed so as to face the shaft integral member and pressed against the shaft integral member facing the pressing member, under a pressing force adjusted by a control signal from the control apparatus. 
     In the above aspects, the rotational-torque varying apparatus can be appropriately implemented with the handle shaft and the pressing member or the shaft integral member and the pressing member. 
     According to further another aspect of the present invention, the grinding machine in the above aspect includes an air regulating apparatus that enables adjustment of a flow rate of compressed air fed from an air source, and the control apparatus adjusts the flow rate of the compressed air from the air regulating apparatus to adjust the pressing force applied to the pressing member, in accordance with the state of proximity between the workpiece and the grinding wheel. 
     In the above aspects, the pressing force applied to the pressing member can be adjusted simply by controlling the air regulating apparatus using the control apparatus, allowing the rotational torque of the manual rotating handle to be easily varied. 
     According to further another aspect of the present invention, in the grinding machine according to the above aspect, the rotation detector attached to an indirect rotating member that is rotated, via a predetermined rotational power transmitting member, by a direct rotating member that rotates integrally with the manual rotating handle. 
     In the above aspects, the rotation detector that outputs the rotation detection signal is attached to the indirect rotating member that is rotated via a rotational-power transmitting member such as a gear and a belt rather than to the direct rotating member that is directly rotated by rotation of the manual rotating handle. Thus, when the rotational torque is changed, delay attributed to play of the gear, the belt, or the like is intentionally caused, so that the operator&#39;s feeling is made similar to a feeling obtained from a conventional mechanical grinding wheel that uses oil pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the appearance of a grinding machine according to an embodiment. 
         FIG. 2  is a plan view illustrating an example internal structure of a cover of the grinding machine. 
         FIG. 3  is an example right side view of  FIG. 2  in which illustration of a main spindle apparatus, a tailstock apparatus, and the like is omitted. 
         FIG. 4  is a diagram illustrating a system that varies the position of a grinding wheel relative to a workpiece and a rotational torque of a manual rotating handle in accordance with a rotation detection signal that is an electric signal from a rotation detector provided on the manual rotating handle. 
         FIG. 5  is a diagram of example distance (between the workpiece and the grinding wheel) vs. rotational-torque characteristics observed when the rotational torque of the manual rotating handle is set to be increased at a time point when the workpiece and the grinding wheel come into contact with each other. 
         FIG. 6  is a diagram of example distance (between the workpiece and the grinding wheel) vs. rotational-torque characteristics observed when the rotational torque of the manual rotating handle is set to be increased before the workpiece and the grinding wheel come into contact with each other. 
         FIG. 7  is a diagram of example distance (between the workpiece and the grinding wheel) vs. rotational-torque characteristics observed when the rotational torque of the manual rotating handle is set to be increased at the time point when the workpiece and the grinding wheel come into contact with each other and to be further increased according to the amount of cut-in. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Modes for carrying out the present invention will be described below with reference to the drawings. In figures illustrating an X axis, a Y axis, and a Z axis, the X axis, the Y axis, and the Z axis are orthogonal to one another. A Y-axis direction represents an upward direction of the vertical direction, an X-axis direction represents a direction in which a grinding wheel  22  cuts into a workpiece W, and a Z-axis direction represents a direction parallel to a workpiece rotation axis ZJ. 
     As depicted in  FIG. 1 , a grinding machine  1  is covered by a cover  81  in order to ensure an operator&#39;s safety and includes a display apparatus  82 , various input apparatuses  83 , and manual rotating handles  84 ,  85 . The display apparatus  82  displays a state of the operator&#39;s input to the grinding machine  1  (setting state), an operational state of the grinding machine  1 , and the like. The various input apparatuses  83  are apparatuses that accept the operator&#39;s input for switching between an automatic operation mode and a manual operation mode, various settings, and the like. The details of the inside of the cover  81  and the like will be described below using  FIG. 2  and  FIG. 3 . 
       FIG. 2  is a plan view of the grinding machine  1  depicting an internal configuration of the cover  81  in  FIG. 1 , and  FIG. 3  is a right side view of the cover  81 . Unlike in  FIG. 2 , in  FIG. 3 , illustration of a spindle apparatus  30 , a tailstock apparatus  40 , and the like is omitted. As depicted in  FIG. 2  and  FIG. 3 , the grinding machine  1  has a base  2 , a slide table  10 , an advancing and retracting table  20 , the grinding wheel  22 , the spindle apparatus  30 , the tailstock apparatus  40 , a control apparatus  50  (corresponding to a control apparatus), and the manual rotating handles  84 ,  85 . 
     The slide table  10  can be moved along a Z-axis direction guide GZ provided on the base  2  parallel to the Z-axis direction, by use of a Z-axis direction driving motor  10 M (corresponding to a moving apparatus) provided on the base  2 . The control apparatus  50  controls the position of the slide table  10  (the grinding wheel  22  on the slide table  10 ) on the base  2  in the Z-axis direction based on inputs and command values for the position in the Z-axis direction from an encoder  10 E of the Z-axis direction driving motor  10 M. 
     The advancing and retracting table  20  can be moved along an X-axis direction guide GX provided on the slide table  10  and parallel to the X-axis direction, by use of an X-axis direction driving motor  20 M (corresponding to a moving apparatus) provided on the slide table  10 . The control apparatus  50  controls the position of the advancing and retracting table  20  (and the grinding wheel  22  located on the advancing and retracting table  20 ) on the base  2  in the X-axis direction based on output signals and command values for the position in the X-axis direction from an encoder  20 E of the X-axis direction driving motor  20 M. 
     On the advancing and retracting table  20 , the cylindrical grinding wheel  22  is mounted which grinds the workpiece W, and a grinding wheel driving motor  21  is also mounted which rotationally drives the grinding wheel  22  via a power transmission apparatus such as a belt. Based on the command value, the control apparatus  50  outputs a control signal to the grinding wheel driving motor  21  to rotationally drive the grinding wheel  22 . 
     The spindle apparatus  30  is provided on the base  2  to support a first end of the workpiece W, while rotating the workpiece W around a workpiece rotation axis ZJ. The spindle apparatus  30  has a headstock  31  fixed to the base  2 , a main spindle  32  housed in the headstock  31  and rotationally driven around the workpiece rotation axis ZJ, a spindle center  33  that rotates integrally with the main spindle  32 , and a gripping member  34  that rotates integrally with the main spindle  32  while gripping the workpiece W. The control apparatus  50  controls rotation of the main spindle  32  based on the command value. As depicted in  FIG. 3 , a rotation axis of the grinding wheel  22  and the workpiece rotation axis ZJ of the workpiece W are on the same virtual plane VM (a plane parallel to both the X axis and the Z axis). 
     The tailstock apparatus  40  is provided on the base  2  to support a second end of the workpiece W, while pushing the supported workpiece W toward the spindle apparatus  30  so that the workpiece W is rotatable around the workpiece rotation axis ZJ. The tailstock apparatus  40  has a tailstock stock  41  fixed to the base  2 , a ram  42  that is housed in the tailstock stock  41 , biased toward the spindle apparatus  30 , and that is supported so as to be rotatable around the workpiece rotation axis ZJ, and a tailstock center  43  that rotates integrally with the ram  42 . 
     The manual rotating handle  84  is a handle used to relatively move the grinding wheel  22  in a direction in which the grinding wheel  22  cuts into the workpiece W (the X-axis direction in  FIG. 2 ) in accordance with the operator&#39;s rotating operation in the manual operation mode. For example, the manual rotating handle  84  has a handle shaft  84 S supported so as to be rotatable around a rotation axis XJ 84  and an auxiliary handle  84 H that assists the operator&#39;s rotating operation, as depicted in an enlarged view in  FIG. 1 . The manual rotating handle  85  is a handle used to relatively move the grinding wheel  22  in a direction parallel to the workpiece rotation axis (the Z-axis direction in  FIG. 2 ) in accordance with the operator&#39;s rotating operation. 
     In the grinding machine  1 , proximity detectors  51 ,  52  are provided at predetermined positions. The proximity detectors  51 ,  52  are, for example, acoustic sensors, gap sensors, or distance measuring sensors and output proximity detection signals corresponding to a distance between the grinding wheel  22  and the workpiece W. When, for example, the proximity detectors are acoustic sensors, the proximity detectors are attached to a position depicted by reference numeral  52  in  FIG. 2 , in other words, a workpiece-side end of the advancing and retracting table  20  with the grinding wheel  22  mounted thereon, or a position depicted by reference numeral  51 , in other words, on a side surface of the tailstock stock  41 . When the grinding wheel  22  and the workpiece W come into contact with each other in the X-axis direction or in the Z-axis direction, the proximity detectors output the proximity detection signal, which is indicative of the contact. When, for example, the proximity detectors are gap sensors or distance measuring sensors, the proximity detectors are attached to the position denoted by reference numeral  52  or the position denoted by reference numeral  51  in  FIG. 2 , as is the case with acoustic sensors. The proximity detectors detect a distance DX between the grinding wheel  22  and the workpiece W in the X-axis direction or a distance DZ between the grinding wheel  22  and the workpiece W in the Z-axis direction to output the proximity detection signal to the control apparatus  50 . The type, arrangement positions, and the like of the proximity detectors are not limited to these embodiments. 
     In the grinding machine  1  in the present embodiment, when the operator rotates the manual rotating handles  84 ,  85  in the manual operation mode, the rotation detector outputs a rotation detection signal that is an electric signal corresponding to the amount of the rotation. The control apparatus receives the rotation detection signal and controls the X-axis direction driving motor or the Z-axis direction driving motor to change the position of the grinding wheel relative to the workpiece. In the case of a conventional hydraulic grinding machine, rotation of the manual rotating handle allows pressure to be applied to hydraulic oil, and when the grinding wheel and the workpiece come into contact with each other, the rotational torque (the torque needed for rotation) of the manual rotating handle is automatically increased. Thus, the operator feels the contact between the grinding wheel and the workpiece and operates the grinding wheel to finely (delicately) cut into the workpiece from the contact position to achieve accurate machining. However, in recent grinding machines that output a rotation detection signal for the manual rotating handle, instead of applying pressure to the hydraulic oil via rotation of the manual rotating handle, the rotational torque of the manual rotating handle is not changed even when the grinding wheel and the workpiece come into contact with each other. Consequently, the operator has much difficulty in knowing a timing when the grinding wheel and the workpiece come into contact with each other. Thus, the operator may operate the grinding wheel to further cut into the workpiece without recognizing the contact between the grinding wheel and the workpiece and fail to achieve accurate machining. In the grinding machine in the present application, the rotational torque of the manual rotating handle can be varied according to the state of proximity between the grinding wheel and the workpiece as described below. 
     Now, using  FIG. 4 , an example of a system will be described in which the rotational torque of the manual rotating handle  84  can be varied when the grinding wheel  22  is moved in the X-axis direction relative to the workpiece W in accordance with rotation of the manual rotating handle  84 . The control apparatus  50  receives the proximity detection signal from the proximity detector  51  (or the proximity detector  52 ), the detection signal from the encoder  20 E, and the rotation detection signal from an encoder  84 E (corresponding to the rotational torque) corresponding to the amount of rotation of the manual rotating handle  84 . The control apparatus  50  outputs a control al to the X-axis direction driving motor  20 M and also outputs a control signal to a pressure-regulating solenoid valve  61 . 
     The proximity detectors  51 ,  52  output, to the control apparatus  50 , the proximity detection signal corresponding to the state of proximity between the grinding wheel  22  and the workpiece W in the X-axis direction. Based on the proximity detection signal, for example, the control apparatus  50  can determine that the grinding wheel  22  is in contact with the workpiece W or that the grinding wheel  22  and the workpiece W are not in contact with each other. Furthermore, given that the grinding wheel  22  and the workpiece W are not in contact with each other, the control apparatus  50  can determine the distance between the grinding wheel  22  and the workpiece W. For amplification of subtle proximity detection signals from the proximity detectors  51 , the signals may be relayed by amplifiers  51 A,  52 A. 
     The encoder  20 E outputs the detection signal corresponding to the amount of rotation of the X-axis direction driving motor  20 M to the control apparatus  50 . The encoder  84 E is rotated by the manual rotating handle  84  via a gear  84 G and a gear  94 G to output the rotation detection signal corresponding to the amount of rotation of the manual rotating handle  84  to the control apparatus  50 . The encoder  84 E receives a setting signal from a scale changing apparatus  84 B and outputs a rotation detection signal corresponding to a rotation angle and a scale. The control apparatus  50  outputs, to the X-axis direction driving motor  20 M, a control signal based on the rotation detection signal from the encoder  84 E and the detection signal from the encoder  20 E, so as to feedback-control the position of the grinding wheel  22  in the X-axis direction. For amplification of subtle proximity detection signals, the signals may be relayed by the amplifiers  51 A,  52 A. For amplification of a subtle proximity detection signal from the encoder  84 E, the signal may be relayed by an amplifier  84 A. The encoder  84 E is preferably attached to an indirect rotating member (in this case, corresponding to a shaft  94 S) that is indirectly rotated via a rotational-power transmitting member (in this case, corresponding to the gear  84 G and the gear  94 G) rather than to a direct rotating member (in this case, corresponding to the gear  84 G, the handle shaft  84 S, and a plate  84 C) fixed to the manual rotating handle  84  and rotating directly and integrally with the manual rotating handle  84 . 
     In this case, a delay attributed to play of the rotational-power transmitting member (the delay from actual rotation of the manual rotating handle until the rotation detection signal is output) is intentionally caused to allow the operator to have a feeling similar to a feeling obtained using the conventional hydraulic grinding machine. The amplifier  84 A may have a function to cause a delay. Enabling adjustment of a delay time conveniently allows the delay time to be freely adjusted according to the operator&#39;s preferences. 
     A rotational-torque varying apparatus that makes the rotational torque of the manual rotating handle  84  variable includes the pressure-regulating solenoid valve  61 , a regulator  62 , a cylinder  94 Q, a piston  94 P, an elastic member  94 D, a pressing member  94 C, and the plate  84 C. The pressure-regulating solenoid valve  61  (corresponding to an air regulating apparatus) is supplied with compressed air from an external compressed air supply apparatus or an air source such as a cylinder provided in the grinding machine. The valve lift of the pressure-regulating solenoid valve  61  and the like are adjusted based on control signals from the control apparatus  50 . The flow rate of input compressed air is adjusted to convert the pressure of the input compressed air into a desired pressure, and the resultant air is output to the regulator  62 . The regulator  62  outputs the air received from the pressure-regulating solenoid valve  61  to the cylinder  94 Q. When air at a pressure higher than a predetermined pressure is input to the regulator  62 , the regulator  62  limits the pressure to a preset predetermined value before outputting the air to the cylinder  94 Q. This prevents air at a pressure equal to or higher than an allowable pressure from being input to the cylinder  94 Q. In accordance with the state of proximity between the workpiece and the grinding wheel, the control apparatus  50  controls the pressure-regulating solenoid valve  61  to adjust the flow rate of the compressed air and thus a pressing force applied to the pressing member  94 C, thereby regulating the rotational torque of the manual rotating handle  84 . 
     The air input to the cylinder  94 Q presses the piston  94 P to press the pressing member  94 C connected to the piston  94 P against the plate  84 C (corresponding to a shaft integral member), which rotates integrally with the handle shaft  84 S. The pressing member  94 C is biased in a direction away from the plate  84 C by the elastic member  94 D. When the pressing member  94 C is pressed against the plate  84 C, a friction force between the plate  84 C and the pressing member  94 C increases the rotational torque of the manual rotating handle  84 . The control apparatus  50  increases or reduces the pressure of the air from the pressure-regulating solenoid valve  61  to increase or reduce the pressing force and thus the friction force, so that the control apparatus  50  increases or reduces the rotational torque of the manual rotating handle  84 . 
     The configuration and structure of the rotational-torque varying apparatus are not limited to the configuration and structure depicted in  FIG. 4 . For example, instead of being pressed against the plate  84 C (shaft integral member), the pressing member  94 C may be pressed against the handle shaft  84 S. Instead of being pressed in a thrust direction (axial direction) with respect to the rotation axis XJ 84  of the handle shaft  84 S, the pressing member  94 C may be pressed in a radial direction. The plate  84 C and the pressing member  94 C need not be like discs. 
     The control apparatus  50  allows the rotational torque of the manual rotating handle  84  to be freely adjusted in accordance with the state of proximity between the workpiece and the grinding wheel. An example of the state of change of the rotational torque with respect to the state of proximity will be described below using  FIGS. 5 to 7 . 
     For example, based on the proximity detection signal from the proximity detector  51 , the control apparatus  50  closes the pressure-regulating solenoid valve  61  to separate the pressing member  94 C from the plate  84 C while the grinding wheel  22  and the workpiece W are not in contact with each other. Upon determining that the grinding wheel  22  and the workpiece W are in contact with each other based on the proximity detection signal, the control apparatus  50  controls the valve lift of the pressure-regulating solenoid valve  61  to a predetermined value to press the pressing member  94 C against the plate  84 C under a predetermined pressing force. This state is depicted in  FIG. 5 . In  FIG. 5 , the axis of abscissas represents the distance between the grinding wheel and the workpiece. At a “contact” position, the grinding wheel and the workpiece come into contact with each other. An area to the left of the “contact” position indicates that the grinding wheel and the workpiece are separated from each other and that the distance increases leftward. An area to the right of the “contact” position indicates that the grinding wheel cuts into the workpiece and that the amount of cut-in increases rightward. In  FIG. 5 , the axis of ordinate represents the rotational torque of the manual rotating handle  84  and indicates that the rotational torque increases upward. F 1  denotes a rotational torque exerted while the pressing member  94 C and the plate  84 C are separated from each other. Conveniently, a rotational torque F 2  can be freely changed to a desired rotational torque value by the control apparatus  50  adjusting the valve lift of the pressure-regulating solenoid valve  61 . 
     In this case, when the operator rotates the manual rotating handle  84  to make the grinding wheel  22  gradually closer to the workpiece W, the rotational torque of the manual rotating handle  84  is increased at the time point when the grinding wheel  22  and the workpiece W come into contact with each other. Thus, the operator can determine (feel) that the grinding wheel  22  and the workpiece W have come into contact with each other. At the time point of the contact, the operator can start to finely adjust the amount of rotation of the manual rotating handle  84  to achieve more accurate machining. 
     If distance vs. rotational-torque characteristics illustrated in  FIG. 6  are applied, based on the proximity detection signal from the proximity detector  51 , the control apparatus  50  closes the pressure-regulating solenoid valve  61  to separate the pressing member  94 C from the plate  84 C while the grinding wheel  22  and the workpiece W are not in contact with each other (the separation distance is larger than ΔD). Upon determining that the separation distance between the grinding wheel  22  and the workpiece W is equal to or shorter than ΔD (the grinding wheel  22  and the workpiece W are about to come into contact with each other) based on the proximity detection signal, the control apparatus  50  controls the valve lift of the pressure-regulating solenoid valve  61  to a predetermined value to press the pressing member  94 C against the plate  84 C under a predetermined pressing force. 
     In this case, the rotational torque of the manual rotating handle  84  is increased immediately before the grinding wheel  22  and the workpiece W actually come into contact with each other. Thus, the operator can recognize (feel) that the grinding wheel and the workpiece are now close enough to be about to come into contact with each other. Thus, at the position of the grinding wheel immediately before the contact, the operator can start to finely adjust the amount of rotation of the manual rotating handle  84  to achieve accurate machining. Conveniently, the separation distance ΔD can be freely set to a desired value by the control apparatus  50 . 
     If distance vs. rotational-torque characteristics illustrated in  FIG. 7  are applied, based on the proximity detection signal from the proximity detector  51 , the control apparatus  50  closes the pressure-regulating solenoid valve  61  to separate the pressing member  94 C and the plate  84 C while the grinding wheel  22  and the workpiece W are not in contact with each other. Upon determining that the grinding wheel  22  and the workpiece W is in contact with each other based on the proximity detection signal, the control apparatus  50  controls the valve lift of the pressure-regulating solenoid valve  61  to a predetermined value to press the pressing member  94 C against the plate  84 C under a predetermined pressing force to adjust the rotational torque at the time point of the contact to F 2  (a predetermined rotational torque larger than F 1 ). Moreover, upon detecting that the amount of cut-in of the grinding wheel has increased based on the proximity detection signal from the proximity detector  51 , the control apparatus  50  controls the pressure-regulating solenoid valve  61  by increasing or reducing the valve lift of the pressure-regulating solenoid valve  61  according to an increase or a decrease in the amount of cut-in so as to increase the rotational torque as the amount of cut-in increases. 
     In this case, the rotational torque increases and decreases as the amount by which the grinding wheel cuts into the workpiece increases or decreases. Thus, the operator can feel a variation in load on the grinding wheel corresponding to the amount of cut-in, and can achieve accurate machining while checking the load on the grinding wheel. Conveniently, the control apparatus  50  enables free setting to a desired value, regarding a characteristic such as the rate of increase (gradient) at which the rotational torque is increased with respect to the amount of cut-in of the grinding wheel. 
     The above description describes, movement of the grinding wheel  22  relative to the workpiece W in the X-axis direction by use of the manual rotating handle  84  and the X-axis direction driving motor  20 M. The above description also applies to movement of the grinding wheel  22  relative to the workpiece W in the Z-axis direction by use of the manual rotating handle  85  and the Z-axis direction driving motor  10 M (a contact feeling system the Z-axis direction is similar to the system in  FIG. 4 , and characteristics are similar to the characteristics in  FIGS. 5 to 7 ). Thus, descriptions for the Z-axis direction are omitted. 
     Various changes, additions, and deletions may be made to the configuration, structure, appearance, characteristics, and the like of the grinding machine  1  in the present invention to the extent that the spirits of the present invention remain unchanged. 
     The configuration in which the grinding wheel is moved with respect to the workpiece in the X-axis direction is not limited to the configuration described in the present embodiment. Any configuration may be used so long as the grinding wheel can be moved relative to the workpiece in the X-axis direction. Similarly, the configuration in which the grinding wheel is moved with respect to the workpiece in the Z-axis direction is not limited to the configuration described in the present embodiment. Any configuration may be used so long as the grinding wheel can be moved relative to the workpiece in the Z-axis direction. 
     Or more (≥)or less (≤)more than (&gt;), less than (&lt;), and the like may or may not include an equal sign. 
     DESCRIPTION OF REFERENCE NUMERALS 
       1 : grinding machine,  2 : base,  10 : slide table, 
       10 M: Z-axis direction driving motor (moving apparatus),  20 : advancing and retracting table, 
       20 M: X-axis direction driving motor (moving apparatus),  22 : grinding wheel, 
       30 : spindle apparatus,  40 : tailstock apparatus,  50 : control apparatus (control apparatus), 
       51 ,  52 : proximity detectors,  61 : pressure-regulating solenoid valve (air regulating apparatus), 
       62 : regulator,  84 ; manual rotating handle, 
       85 : manual rotating handle,  84 C: plate (shaft integral member), 
       84 E: encoder (rotation detector),  84 G: gear (rotational-force transmitting apparatus), 
       94 G: gear (rotational-force transmitting apparatus), 
       84 S: handle shaft (direct rotating member), 
       94 C: pressing member (rotational-torque varying apparatus), 
       94 S: shaft (indirect rotating member), W: workpiece, ZJ; workpiece rotation axis