Measuring device

While a ball 14 is inserted into a hole WA of a workpiece W and is moved in the longitudinal direction of the hole WA while automatically centripetally moved, a change of back pressure of a gas injected into the hole WA is detected by a converter 30, and at the same time reflected light from a reflection member 18 provided on the ball 14 is received by a light receiving unit 22 and a change of peak position A of an amount of the received light is calculated, so as to calculate an inner diameter, straightness, and cylindricity of the hole WA, thus providing an inexpensive noncontact measuring apparatus 10 which measures the inner diameter, the straightness, and the cylindricity of the hole WA.

TECHNICAL FIELD

The present invention relates to a measuring apparatus which measures a hole formed in a workpiece, and more particularly to a measuring apparatus which measures an inner diameter, straightness, and cylindricity of a hole without contact.

BACKGROUND ART

Generally, an inner diameter, straightness, and cylindricity of a hole of a cylindrical component often used as an automobile component or a machine tool component are measured by a method in which a roundness measuring apparatus or the like is used, an object to be measured (hereinafter referred to as a workpiece) is secured, and a contact detector is rotated along an inner surface of the hole and moved in the longitudinal direction of the hole for measurement. For a small workpiece, a roundness measuring apparatus which rotates the workpiece for measurement is used.

However, these roundness measuring apparatuses are general-purpose measuring apparatuses, which have various functions and are expensive. The roundness measuring apparatuses are of contact type, and a scratch or a trail of a contact may remain on a surface to be measured. Further, if measuring pressure is reduced to prevent a scratch on the surface to be measured, the contact is caught by a burr or a groove, if any, in an inner peripheral portion of the hole, which causes variations in measurement values.

The present invention is made in view of such circumstances, and has an object to provide an inexpensive measuring apparatus which can measure an inner diameter, straightness, and cylindricity of a hole formed in a workpiece without contact.

SUMMARY OF THE INVENTION

In order to attain the above described object, the present invention is directed to a measuring apparatus which measures a hole formed in a workpiece, comprising: a holding mount which holds a workpiece and has an injection port for injecting a gas into the hole formed in the workpiece; a ball which is inserted into the hole formed in the workpiece; an elastic member which elastically supports the ball; a converter which converts back pressure of the gas injected from the injection port into an electrical signal; and a control unit which calculates an inner diameter of the hole according to the electrical signal outputted from the converter while the ball is inserted into the hole formed in the workpiece and the gas is injected into the hole.

According to the present invention, the gas is injected into a gap created between an inner peripheral surface of the hole and the ball, and the back pressure of the injected gas is detected by the converter to calculate the inner diameter of the hole, thus providing an inexpensive noncontact measuring apparatus of an inner diameter.

The present invention is also directed to a measuring apparatus which measures a hole formed in a workpiece, comprising: a holding mount which holds a workpiece and has an injection port for injecting a gas into the hole formed in the workpiece; a ball which is inserted into the hole formed in the workpiece; an elastic member which elastically supports the ball; a reflection member which is mounted to the ball and reflects light supplied from a light source; a light receiving unit which receives the light reflected by the reflection member; a moving device which moves the elastic member and the ball along a longitudinal direction of the hole; and a control unit which calculates straightness of the hole by calculating a change of peak position of an amount of light received by the light receiving unit while the ball is inserted into the hole formed in the workpiece and the ball is moved while automatically centripetally moved with respect to the hole by injecting the gas into the hole.

According to the present invention, while the ball inserted into the hole is moved along the longitudinal direction of the hole while automatically centripetally moved, the reflected light from the reflection member provided on the ball is received by the light receiving unit, and the change of peak position of the amount of received light is calculated, so as to calculate the straightness of the hole, thus providing an inexpensive noncontact measuring apparatus of straightness.

The present invention is also directed to a measuring apparatus which measures a hole formed in a workpiece, comprising: a holding mount which holds a workpiece and has an injection port for injecting a gas into the hole formed in the workpiece; a ball which inserted into the hole formed in the workpiece; an elastic member which elastically supports the ball; a converter which converts back pressure of the gas injected from the injection port into an electrical signal; a reflection member which is mounted to the ball and reflects light supplied from a light source; a light receiving unit which receives the light reflected by the reflection member; a moving device which moves the elastic member and the ball along a longitudinal direction of the hole; and a control unit which calculates cylindricity of the hole according to the electrical signal outputted from the converter and data of a change of peak position of an amount of light received by the light receiving unit while the ball is inserted into the hole formed in the workpiece and the ball is moved while automatically centripetally moved with respect to the hole by injecting the gas into the hole.

According to the present invention, while the ball inserted into the hole is moved along the longitudinal direction of the hole while automatically centripetally moved, the back pressure of the gas injected into the hole is detected by the converter, the reflected light from the reflection member provided on the ball is received by the light receiving unit, and the change of peak position of the amount of received light is calculated, so as to calculate the cylindricity of the hole, thus providing an inexpensive noncontact measuring apparatus of cylindricity.

Preferably, the reflection member comprises a corner cube. This causes an entering angle and an emitting angle of the light projected from the light source and reflected by the reflection member to be always equal, and allows accurate detection of the change of peak position of the amount of light received by the light receiving unit, even if the ball is inclined when the ball is moved.

Preferably, the elastic member comprises at least three linear elastic bodies which are parallel to each other. This prevents the inclination of the ball even if an axis of the hole is curve, and allows accurate detection of the change of peak position of the amount of light received by the light receiving unit.

The present invention is also directed to a measuring apparatus which measures a hole formed in a workpiece, comprising: a holding mount which holds a workpiece and has an injection port for injecting a gas into the hole formed in the workpiece; a ball which is inserted into the hole formed in the workpiece; an elastic member which elastically supports the ball; an optical fiber which is attached to the ball and carries and projects light supplied from a light source; a light receiving unit which receives the light projected from the optical fiber; a moving device which moves the elastic member, the ball, and the optical fiber along a longitudinal direction of the hole; and a control unit which calculates straightness of the hole by calculating a change of peak position of an amount of light received by the light receiving unit while the ball is inserted into the hole formed in the workpiece and the ball is moved while automatically centripetally moved with respect to the hole by injecting the gas into the hole.

According to the present invention, while the ball inserted into the hole is moved in the longitudinal direction of the hole while automatically centripetally moved, the projected light from the optical fiber provided on the ball is received by the light receiving unit, and the change of peak position of the amount of received light is calculated, so as to calculate the straightness of the hole, thus providing an inexpensive noncontact measuring apparatus of straightness.

The present invention is also directed to a measuring apparatus which measures a hole formed in a workpiece, comprising: a holding mount which holds a workpiece and has an injection port for injecting a gas into the hole formed in the workpiece; a ball which is inserted into the hole formed in the workpiece; an elastic member which elastically supports the ball; a converter which converts back pressure of the gas injected from the injection port into an electrical signal; an optical fiber which is attached to the ball and carries and projects light supplied from a light source; a light receiving unit which receives the light projected from the optical fiber; a moving device which moves the elastic member, the ball, and the optical fiber along a longitudinal direction of the hole; and a control unit which calculates cylindricity of the hole according to the electrical signal outputted from the converter and data of a change of peak position of an amount of light received by the light receiving unit while the ball is inserted into the hole formed in the workpiece and the ball is moved while automatically centripetally moved with respect to the hole by injecting the gas into the hole.

According to the present invention, while the ball inserted into the hole is moved along the longitudinal direction of the hole while automatically centripetally moved, the back pressure of the gas injected into the hole is detected by the converter, and at the same time the projected light from the optical fiber provided on the ball is received by the light receiving unit and the change of peak position of the amount of received light is calculated, so as to calculate the cylindricity of the hole, thus providing an inexpensive noncontact measuring apparatus of cylindricity.

THE PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

Now, preferred embodiments of a measuring apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals designate like components.

FIG. 1is a sectional view of a concept of a measuring apparatus which measures a hole formed in a workpiece according to the present invention. As shown inFIG. 1, a measuring apparatus10includes a holding mount12which holds a workpiece W, a ball14having a diameter slightly smaller than an inner diameter of a hole WA formed in the workpiece W, an elastic member16having a tip to which the ball14is attached, a lifting device26to which the other end of the elastic member16is connected and which vertically moves the elastic member16and the ball14, an A/E (air/electricity) converter30, a reflection member18mounted to a top of the ball14, a light source20, a light receiving unit22, a semitransparent mirror24, a control unit40, or the like.

A steel ball having good sphericity is used as the ball14, and a piano wire is used as the elastic member16which has the tip attached to the ball14and supports the ball14. The lifting device26includes a linear guide, a ball screw, a stepping motor, or the like, which are known, and is controlled by the control unit40to vertically move the elastic member16and the ball14.

The holding mount12is formed with an injection port12A which injects air toward the hole WA to be measured of the workpiece W, and an air supply port12B communicating with the injection port12A. Compressed air is supplied to the air supply port12B via the A/E converter30, and the supplied air is injected from the injection port12A toward the hole WA of the workpiece W. The A/E converter30is a device which converts back pressure of the air supplied to the air supply port12B into an electrical signal using, for example, a bellows and a differential transformer, and the obtained electrical signal is sent to the control unit40.

The semitransparent mirror24reflects substantially half of light projected from the light source20and projects the light onto the reflection member18, and transmits substantially half of the reflected light from the reflection member18and projects the light onto the light receiving unit22. A CCD is used as the light receiving unit22, and a peak position of the amount of received light can be detected. Alternatively, four divided photocells may be used as the light receiving unit22instead of the CCD, to arithmetically operate the peak position of the amount of received light in the control unit40. The light source20includes a laser or a halogen lamp, and projects narrowed collimated light.

The injection port12A formed in the holding mount12is a through hole, into which the elastic member16supporting the ball14is inserted. To a bottom end of the injection port12A, a gasket29is mounted to prevent air leakage from a gap between the elastic member16and the injection port12A. To a top surface of the holding mount12, a gasket28is similarly mounted to fill a gap between the workpiece W and the top surface of the holding mount12, when the workpiece W is pressed and secured on the holding mount12by a pressing device (not shown).

The control unit40controls operations of the parts of the measuring apparatus10, arithmetically operates a signal from the A/E converter30and a signal from the light receiving unit22to calculate a measurement value.

Next, operations of the measuring apparatus10thus configured will be described.

The workpiece W to be measured is placed on the holding mount12. At this time, the gap between a bottom surface of the workpiece W and the top surface of the holding mount12is filled with the gasket28. Then, the ball14is lifted by the lifting device26to be inserted into the hole WA of the workpiece W, and placed in a predetermined position. Next, the compressed air is supplied to the air supply port12B of the holding mount12via the A/E converter30, and is injected from the injection port12A into the hole WA of the workpiece W. The injected air is discharged upward through a gap formed between the hole WA and the ball14. At this time, the ball14supported by the elastic member16is simply cantilevered by the elastic member16, and is thus automatically centripetally moved to the center of the hole WA by the action of air flowing through the gap.

The A/E converter30converts a change of the back pressure of the air, caused by a difference in size of the gap formed between the hole WA and the ball14, into an electrical signal, and sends the obtained electrical signal to the control unit40. The control unit40calculates an inner diameter of the hole WA of the workpiece W from the signal obtained by the A/E converter30. Before the measurement, two types of masters, having known accurate inner diameters of holes, are used to calibrate a multiplying factor of the A/E converter30.

Then, the ball14is moved by the lifting device26, and the inner diameters of the hole WA in a plurality of positions are measured to calculate simple cylindricity of the hole WA.

The reflection member18mounted to the top of the ball14is circular, and the collimated light is projected from the light source20onto the reflection member18via the semitransparent mirror24. The projected light is reflected onto the light receiving unit22by the reflection member18. The light receiving unit22includes the CCD or the four divided photocells, thus a peak position A of the amount of received light is calculated as shown inFIG. 2.

FIG. 3shows a state where the light is reflected from the reflection member18onto the light receiving unit22when the four divided photocells22A are used as the light receiving unit22. A peak position A of the amount of received light is calculated from output distribution of the four photocells. Specifically, the center of a circle having an area ratio corresponding to a ratio of the outputted values of the photocells is determined as the peak position A of the amount of received light.

The ball14is moved in the longitudinal direction of the hole WA of the workpiece W while using automatic centripetal action of the ball14by the air, so that displacement of the peak position A of the amount of received light is measured, thereby calculating straightness of the hole WA. The cylindricity including a straightness component of the hole WA is calculated from the straightness data and inner diameter data obtained from the A/E converter30in longitudinal positions of the hole WA, when the ball14is moved in the longitudinal direction of the hole WA. These measurement values are all arithmetically operated and calculated by the control unit40.

FIG. 4shows an example where a corner cube19is used as the reflection member mounted to the ball14. As shown inFIG. 4, when the hole WA of the workpiece W is curved, the ball14is slightly inclined since it is cantilevered by the elastic member16and is automatically centripetally moved. When the reflection member is a plane mirror18, the slight inclination of the ball causes slight inclination of the plane mirror18, and the peak position of the amount of received light on the light receiving unit22is slightly displaced to cause a slight error in measurement of the straightness of the hole WA. On the other hand, when the reflection member is the corner cube19as shown inFIG. 4, an entering angle and a reflecting angle of the light with respect to the corner cube19are always equal, and the peak position of the amount of received light on the light receiving unit22is not displaced even if the corner cube19is inclined, thus allowing calculation of the straightness of the hole WA with higher accuracy. InFIG. 4, the A/E converter30, the light source20, and the control unit40are not shown.

FIGS. 5(a) and5(b) show an example where a parallel spring17constituted by three piano wires evenly spaced on a circle in parallel is used as the elastic member.FIG. 5(a) shows a state where the hole WA of the workpiece W is straight, andFIG. 5(b) shows a state where the hole WA of the workpiece W is curved. InFIGS. 5(a) and5(b), the A/E converter30, the light source20, and the control unit40are not shown.

The elastic member which holds the ball14is the parallel spring17constituted by the three piano wires, thus even if the hole WA of the workpiece W is curved as shown inFIG. 5(b), the reflection member18is not inclined, and even if the reflection member18is the plane mirror, no error occurs in detection of the peak position of the amount of received light on the light receiving unit22, thus allowing calculation of the straightness of the hole WA with higher accuracy like the case inFIG. 4.

Next, a preferred embodiment of a measuring apparatus according to a second embodiment of the present invention will be described.FIG. 6is a conceptual sectional view of a measuring apparatus100which measures a hole formed in a workpiece according to the second embodiment. Like reference numerals designate like components as in the measuring apparatus10according to the first embodiment, and descriptions thereof will be omitted.

As shown inFIG. 6, the measuring apparatus100includes a ball15having a diameter slightly smaller than an inner diameter of a hole WA formed in a workpiece W, an optical fiber21having a tip attached to the ball15through a core of the ball15, a collimating lens25which is mounted to a top of the ball15and faces the tip of the optical fiber21, a light receiving unit22placed above the collimating lens25, a light source20connected to the other end of the optical fiber21, an elastic member23having a tip to which the ball15is attached, a lifting device26to which the other end of the elastic member23is connected and which vertically moves the elastic member23, the ball15, and the optical fiber21, an A/E converter30, and a control unit40.

A steel ball having good sphericity is used as the ball15, a hole through which the core passes is formed in the ball15, and the tip of the optical fiber21is inserted into the hole and fastened with an adhesive. The collimating lens25is mounted to the top of the ball15. The elastic member23whose tip is attached to the ball15and supports the ball15is a hollow straw-like elastic body, and the optical fiber21is inserted through the hollow portion. Light projected from the light source20is carried through the optical fiber21, collimated by the collimating lens25, and projected onto the light receiving unit22. Instead of providing the collimating lens25as a separate component, an optical fiber having a lens formed at a tip thereof may be used.

The measuring apparatus100according to the second embodiment thus configured has the same configuration and operation as the measuring apparatus10according to the first embodiment, other than a difference in that the light from the light source20is projected onto the light receiving unit22via the optical fiber21instead of being reflected onto the light receiving unit22via the reflection member18or19.

Next, a variation of the second embodiment will be described.

When the hole WA of the workpiece W is curved, the ball15is slightly inclined since it is cantilevered by the elastic member23and is automatically centripetally moved. The slight inclination of the ball15causes inclination of a projecting direction of the light from the optical fiber21, and the peak position of the amount of received light on the light receiving unit22is slightly displaced to cause a slight error in measurement of the straightness of the hole WA. Thus, there is proposed a variation as shown inFIG. 7for measurement of straightness with higher accuracy.

FIG. 7shows a case where a parallel spring17constituted by three piano wires evenly spaced on a circle around the optical fiber21in parallel is used as an elastic member. The elastic member which holds the ball15is the parallel spring17constituted by the three piano wires, thus even if the hole WA of the workpiece W is curved as shown inFIG. 7, the ball15is not inclined, and no error occurs in detection of the peak position of the amount of received light on the light receiving unit22. InFIG. 7, the A/E converter30, the light source20, and the control unit40are not shown.

Although the compressed air is used as the gas for measurement of the inner diameter of the hole to be measured, and for automatic centripetal action of the ball in the above described embodiments according to the present invention, the present invention is not limited to this, and N2gas, Ar gas, or the like can be appropriately selected.

INDUSTRIAL APPLICABILITY

As described above, according to the measuring apparatus of the present invention which measures the hole, the change of the back pressure of the gas by the difference in size of the gap between the hole and the ball inserted into the hole is detected to measure the inner diameter of the hole, the straightness of the hole is measured from the automatic centripetal action of the hole and the ball by the flow of the air, and the displacement of the peak position of the amount of received light from the member mounted to the ball, when the ball is moved along the hole, and the cylindricity of the hole is calculated from measurement data of both of them, thus providing an inexpensive measuring apparatus of the hole which can measure the inner diameter, the straightness, and the cylindricity with no contact.