Abstract:
A measuring head is provided with a retracting device for a sensing pin, comprising an electric motor-driven feed screw, a nut shifted by the feed screw and an inclined face formed on the nut; a seesaw member to which the sensing pin is fitted is swung by the linear motion of the inclined face to retract the sensing pin; not only can the retracting speed and the returning speed of the sensing pin be controlled as desired but also can the retracting action of the sensing pin be stopped on the way to make possible its fine positioning. Further, the electric motor may be provided with a manual knob, and the sensing pin would be thereby enabled to be manually retracted.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a measuring head, and more particularly to a measuring head which is to be used in surface texture measuring instruments, contour shape measuring machines and the like and has a retractable device for shifting the sensing pin from its measuring position to a predetermined retracting position. 
   2. Description of the Related Art 
   A conventional surface texture measuring instrument, contour shape measuring instrument or the like for measuring the surface roughness or contour shape of a work has a sensing pin at the tip and a measuring head provided with a seesaw member supported to be swingable pivoting on a fulcrum member, a urging member for urging the seesaw member in one direction, and a detector arranged on the other side than the sensing pin with respect to the fulcrum member and detecting the displacement of the sensing pin by detecting the displacement of the seesaw member. By causing this measuring head to traverse along the measured face of the work and the sensing pin to trace the measured face, the surface roughness or contour shape of the work is measured. 
   In a measuring head having such a structure, in order to protect the sensing pin when a work is set or any discontinuous face of the work is measured, there is provided a retracting device for moving the sensing pin. 
   Such a conventional retracting device has a mechanism in which a solenoid is disposed near the seesaw member, and the sensing pin is moved from its measuring position to a prescribed retracting position and vice versa by turning on and off power supply to the solenoid and thereby swinging the seesaw member. 
   Another retracting device has a mechanism in which a cam is turned by an electric motor, the seesaw member is swung by the lift of the cam, and the sensing pin is thereby caused to retract (e.g. see the Japanese Utility Model Application Publication No. 5-75606). 
   SUMMARY OF THE INVENTION 
   However, the conventional retracting device using a solenoid swings the seesaw member by a certain angle by turning on or off the solenoid, and therefore involves a problem that no fine positioning is possible and stopping it on the way is not possible either. Nor does it permit manual retraction. 
   Or the retracting device using an electric motor and a cam described in the Japanese Utility Model Application Publication No. 5-75606, though it can be equipped with a knob for manual operation use, can be stopped on the way only when it is electrically driven, and manual operation, for which the electric motor is released from excitation, cannot always stop the shift on the way. Accordingly it is unsuitable for fine positioning. 
   An object of the present invention, attempted in view of these circumstances, is to provide a measuring head for use in surface texture measuring instruments, contour shape measuring instruments and the like, having a retracting mechanism capable of controlling the retracting speed and the returning speed of the sensing pin as desired, stopping the sensing pin on the way of its escaping action, permitting fine positioning and enabling the sensing pin to be retracted by manual operation as well. 
   In order to achieve the object stated above, a measuring head according to a first aspect of the invention comprises: 
   a sensing pin disposed at the measuring head&#39;s tip, 
   a seesaw member which is supported to be swingable pivoting on a fulcrum member, 
   an urging member which urges the seesaw member in one direction, 
   a detector which is disposed on the other side than said sensing pin with respect to said fulcrum member and detects any displacement of said sensing pin by detecting the displacement of said seesaw member, and 
   a retracting device which moves said sensing pin from its measuring position to a predetermined retracting position, wherein 
   said retracting device comprises: 
   an electric motor, 
   a feed screw which is driven rotationally by the electric motor, 
   a nut which screws onto the feed screw, is obstructed by a stop from turning, and is linearly moved along the feed screw by the turning of said feed screw, and 
   an inclined member which is formed on the nut or coupled to the nut and has an inclined face which is in contact with said seesaw member on the other side than said sensing pin with respect to said fulcrum member, wherein 
   said sensing pin being moved from its measuring position to the predetermined retracting position by linearly moving said inclined face to swing said seesaw member. 
   According to this first aspect of the invention, as the retracting device of the sensing pin of the measuring head swings the seesaw member by linearly moving with the feed screw driven by the electric motor the inclined face in contact with the seesaw member to which the sensing pin is fitted, the retracting speed and the returning speed of the sensing pin can be set as desired, and the retracting action of the sensing pin can be stopped on the way to make possible its fine positioning. 
   In a measuring head according to a second aspect of the invention, one side of the shaft of the electric motor in the configuration according to the first aspect of the invention is linked to the feed screw and the other side is fitted with a manual knob. 
   According to this second aspect, not only can the sensing pin be manually retracted but also can its action be stopped on the way, making possible fine positioning of the sensing pin. 
   In a measuring head according to a third aspect of the invention, the configuration according to the first of second aspect of the invention is further provided with sensors which detect the stroke ends of the nut linearly moving along the feed screw. 
   According to this third aspect, as the stroke ends of the nut having the inclined face are detected by the sensors, the seesaw member to which the sensing pin is fitted can be prevented from swinging beyond its properly operable range, and accordingly the sensing pin is protected from damage. 
   As described above, in the measuring head according to the invention, since the retracting device for the sensing pin has an electric motor-driven feed screw and an inclined face moved by the feed screw and the linear motion of the inclined face swings the seesaw member to which the sensing pin is fitted to retract the sensing pin, not only can the retracting speed and the returning speed of the sensing pin be controlled as desired but also can the retracting action of the sensing pin be stopped on the way to make possible its fine positioning. 
   Further, as the electric motor is provided with the manual knob, not only can the sensing pin be manually retracted but also can its action be stopped on the way, making possible fine positioning of the sensing pin by manual action. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a front view of a contour shape measuring instrument provided with a measuring head according to the present invention; 
       FIG. 2  shows a side sectional view of a state in which the sensing pin of a measuring head, which is a preferred embodiment of the invention, is in its measuring position; 
       FIG. 3  shows a side sectional view of a state in which the sensing pin of the measuring head, which is the preferred embodiment of the invention, is in its retracting position; and 
       FIG. 4  shows a side sectional view of a state in which the sensing pin of the measuring head, which is the preferred embodiment of the invention, is stopped on the way. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A measuring head, which is a preferred embodiment of the present invention, will be described in detail below with reference to the accompanying drawings, wherein like members will be designated by respectively like reference numerals or like reference characters. 
     FIG. 1  shows a front view of a contour shape measuring instrument using a measuring head according to the invention. A contour shape measuring instrument  100  is configured of a measuring section comprising a stool  101 , a column  102  erected on the stool  101 , a measuring head  10  having a sensing pin  15 , a drive unit  103  for driving the measuring head  10  in its measuring direction, a manual inclining unit  104  for inclining the measuring head  10  and the drive unit  103 , and an electric vertically shifting unit  105  for vertically shifting the measuring head  10 , the drive unit  103  and the manual inclining unit  104 , a control unit  110  for controlling measuring actions and analyzing measured data, and an XY recorder  120  for recording the measured results. 
   A work W, which is the object of measurement, is mounted on the stool  101 . In the measuring action, the whole measuring head  10  is linearly driven in the horizontal direction in a state in which the sensing pin is in contact with the work W, and the displaced quantity of the sensing pin is detected by a detector in the measuring head  10 . 
   Where the inclined face of the work W is to be measured, the measuring head  10  and the drive unit  103  are inclined by the manual inclining unit  104 . Detected data are delivered to the control unit  110 , where the data are analyzed and measurements are recorded. 
     FIG. 2  shows a side sectional view of the configuration of the measuring head  10 . The measuring head  10 , as shown in  FIG. 2 , comprises a body  11 , a fulcrum member  12 , a seesaw member  13 , a differential transformer  14  which is the detector, the sensing pin  15 , a tension spring  16  as the urging member, and a retracting device  20  among other elements. 
   The seesaw member  13  comprises a seesaw block  13 A, an arm  13 B, a pin  13 C, a weight  13 D and a leaf spring  13 E. To the tip of the arm  13 B is fitted the sensing pin  15 , while the base end of the arm  13 B is inserted into a fitting hole (not shown) bored in the seesaw block  13 A and pressed in the inserting direction by the leaf spring  13 E. 
   The weight  13 D is fitted to the arm  13 B, and its fitting position is adjustable. In the position of the seesaw block  13 A reverse to the fitting position of the arm  13 B is fitted the pin  13 C. 
   The fulcrum member  12  comprises a fulcrum shaft fixed to the seesaw block  13 A and a bearing (not shown) fitted to the body  11 , and swingably supports the seesaw member  13 . 
   The tip of the seesaw member  13  is urged downward by the tension spring  16  stretching between the body  11  and the seesaw block  13 A as the urging member so that a measuring pressure be given to the sensing pin  15 . This measuring pressure is adjusted by shifting the position of the weight  13 D provided on the arm  13 B. Thus, when the weight  13 D is shifted toward the tip of the arm  13 B, the measuring pressure rises, and when it is shifted toward the base end, the pressure lowers. 
   As the detector for detecting any displacement of the sensing pin  15 , the differential transformer  14  is used. A coil  14 A of the differential transformer  14  is provided in the body  11 , while a core  14 B of the differential transformer  14  is fitted to the seesaw block  13 A. As its fitting position is on the other side than the sensing pin  15  with the fulcrum member  12  between them, the motion of the sensing pin  15  is converted into the motion of the core  14 B, and is detected as an electrical signal of the differential transformer  14 . 
   Above the seesaw block  13 A of the body  11  are disposed a lower stopper  17  and an upper stopper  18  so as to regulate the stroke ends of the seesaw action of the seesaw member  13 . 
   In order to protect the sensing pin when a work is set or when any discontinuous face of the work is measured, the retracting device  20  which shifts the sensing pin from its measuring position to a predetermined retracting position and vice versa is built into the measuring head  10 . 
   The retracting device  20  comprises a feed screw  21 , a nut  22  to screw onto the feed screw  21 , an inclined member  23  formed on the nut  22  and an electric motor  24  to drive the feed screw  21 . 
   One end of the feed screw  21  is supported by the body  11  via a bearing (not shown) while its other end is connected to the shaft  24 A of the electric motor  24  into which a decelerator  25  is incorporated via a coupling  29 . To the other side of the electric motor  24  than the shaft  24 A is fitted a manual knob  26 . 
   A stop  27  is fitted to the nut  22  and, as the stop  27  is loosely fitted into a long hole bored in the body, driving the feed screw  21  rotationally causes the nut  22  to shift linearly along the feed screw  21 . As sensors for detecting the two stroke end positions of the nut  22 , two proximity switches  28  and  28  are disposed in the body  11 . Being actuated by an approach of the stop  27 , they detect one or the other of the stroke ends. 
   While the measuring head  10  is shielded by a cover  11 A, the sensing pin  15 , the arm  13 B, the weight  13 D and the manual knob  26  are exposed outside the cover  11 A. 
   Next will be described the actions of the measuring head  10  configured as described above. The sensing pin  15  comes into contact with the face to be measured of the work W in a measuring position M shown in FIG.  2 . The whole measuring head  10  is driven by the drive unit  103  in the measuring direction (the X—X direction in the drawing), and the face to be measured of the work W is traced by the tip of the sensing pin  15 . The quantity of the displacement of the sensing pin  15  in the vertical direction is converted by the seesaw member  13  into the shift quantity of the core  14 B of the differential transformer  14 , and this quantity is supplied as an electrical signal. The measuring pressure in this process is set to an appropriate level by adjusting the tension spring  16  and the weight  13 D. 
   When the sensing pin  15  is to be retracted from the measuring position M to the retracting position R, the feed screw  21  is turned with either the electric motor  24  or the manual knob  26  to shift the nut  22  leftward in the drawing. When the nut  22  is shifted leftward in the drawing, the inclined face  23 A of the inclined member  23  formed on the nut  22  comes into contact with the pin  13 C of the seesaw member  13 . As the nut  22  is further shifted, the pin  13 C is shoved by the inclined face  23 A to swing the seesaw member  13 , and the shifting of the nut  22  is discontinued at the point of time when the proximity switch  28  on the left side of the drawing has detected the stop  27 . 
   This causes the tip of the sensing pin  15  to retract to the retracting position R shown in FIG.  3 . When the feed screw  21  is turned in the reverse direction and the nut  22  is returned rightward in the drawing, the tip of the sensing pin  15  is returned to the measuring position M shown in FIG.  2 . 
   As the retracting device  20  of the sensing pin  15  functions by shifting in this way the inclined face  23 A with the feed screw  21  driven by the electric motor  24 , the retracting speed and the returning speed of the sensing pin  15  can be set as desired by controlling the revolving speed of the electric motor  24 . It is possible to set the retracting speed high and the returning speed low or to set either speed high in the initial phase of the pertinent action and low in its final phase. 
   It is also possible to stop the sensing pin  15  in any desired position on the way between the measuring position M and the retracting position R.  FIG. 4  shows a state in which the tip of the sensing pin  15  is stopped in an intermediate position P between the measuring position M and the retracting position R. 
   As the tip of the sensing pin  15  can be finely positioned as desired, it has been made possible to measure inner faces of thin holes, which was impossible by the prior art. 
   Also, as the retracting device  20  has the manual knob  26 , it is possible to manually retract the tip of the sensing pin to any desired position or to finely position it, enabling even complex shapes to be measured easily. 
   To add, although the inclined member  23  has only one inclined face  23 A in the embodiment of the invention described above, there may as well be disposed two inclined faces  23 A and  23 A with the pin  13 C of the seesaw member  13  between them. In this case, the sensing pin  15  can be retracted upward with the upper inclined face  23 A and downward with the lower inclined face  23 A. Downward retraction is used when the sensing pin  15  is fitted upward to measure the upper face of a hole. 
   While it was stated that the retracting speed and the returning speed of the sensing pin  15  are set by controlling the revolving speed of the electric motor  24 , the speeds can as well be set by altering the lead of the feed screw  21  or the inclination angle of the inclined face  23 A or by the combination of the alteration of the lead of the feed screw  21  or the inclination angle of the inclined face  23 A and the control of the revolving speed of the electric motor  24 .