BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates to a lens grinding apparatus in which there can be obtained
a position, i.e., a coordinate of the edge of a lens, which was roughly ground and
held between two lens rotating shafts of a swingable carriage with respect to a V-groove
of a V-beveling or V-edging grinder.
Description of the Prior Art
[0002] There is a conventional lens grinding apparatus as shown in Fig. 8. In this lens
grinding apparatus, a drive shaft 2 disposed within a front portion of a body 1 is
secured thereon with a coarse grinder 3 and a V-edging grinder 4 adjacent to each
other. Also, a supporting portion 5 is disposed on a rear portion of the body 1.
A supporting shaft 6, which is parallel with the drive shaft 2, is rotatably and movably
held by the supporting portion 5 for movement in the axial direction thereof. A carriage
7 is secured at a rear end portion thereof to the supporting shaft 6. Furthermore,
a pair of lens shafts 8,9, which are parallel with the supporting shaft 6 and coaxial
with each other, are rotatably held by a front end portion of the carriage 7. The
lens shaft 9 is adjustable as such that it can be moved forward and backward with
respect to the lens shaft 8. By tightening the lens shaft 9, an ophthalmic lens L
to be ground is fixedly held between the lens shafts 8 and 9. The lens shafts 8,9
can be rotated in synchronism with each other by a pulse motor 10 which is disposed
within the carriage 7. Also, the lens shaft 8 is provided with a template 11 removably
mounted on one end portion thereof.
[0003] Also, when a pulse motor 12 supported on a frame (not shown) is rotated normally
or reversely, a feed screw 13 is rotated. As a result, an arm plate 15, which is supported
by a guide shaft 14, is reciprocally moved in the longitudinal direction parallel
with the lens shafts 8,9 and the supporting shaft 6. Since one end portion of the
supporting shaft 6 is rotatably held by the arm plate 15, the carriage 7 is reciprocally
moved in the axial direction of the supporting shaft 6 by means of activation of
the pulse motor 12 through the arm plate 15. Also, the arm plate 15 is provided with
a contact platform 16 vertically and movably held thereby and with a pulse motor 17
mounted thereon and adapted to move the contact platform 16 in the vertical direction.
The contact platform 16 comprises a body 16a and a contact piece 16b mounted on the
body 16a in such a manner as to be swingable within a predetermined range in the vertical
direction about one end thereof. The contact piece 16b is energized upwardly by spring
means (not shown). In case the lens L is going to be ground using such a lens grinding
apparatus as described, the template 11 is brought to be contact with the platform
16. In that state, the lens shafts 8,9 are rotated and the coarse grinder 3 is driven
to rotate. When the platform 16 is lowered, the lens L is roughly ground into a configuration
identical with that of the template 11 by the coarse grinder 3. The lens L, which
was roughly ground, is different in radius vector ρ
i from the center of rotation thereof to the peripheral surface thereof at each point
in the circumferential direction according to the configuration of the template 11.
Also, since both refractive surfaces of the lens L are three-dimensional curved-surfaces
as shown in Fig. 9, peripheral edges L
f, L
b of the lens L are changed in the axial direction of the lens shafts 8,9. Therefore,
when the edges of the lens L, which was roughly ground as mentioned, is going to be
subjected to V-edging treatment, the lateral moving amount of the carriage 7 is required
to be controlled according to each radius vector ρ
i since otherwise an ideal V-edging treatment cannot be applied to the peripheral portion
of the lens L.
[0004] Therefore, in order to satisfy this point, there is considered the apparatus, as
shown in Fig. 9, in which the lens L, which was roughly ground, is moved to position
above a V-groove 18 of a V-edging grinder 4 and then, the lens shafts 8,9 are repeatedly
lowered by a predetermined amount from position of a predetermined height and the
carriage 7 is repeatedly laterally moved by means of the vertical movement of the
platform 16 in order to measure a movable coordinate of the carriage 7 in the Y-direction
(axial direction of the lens shafts 8,9) when the peripheral edges L
f, L
b of the lens L are abutted against inclined surfaces 18a, 18b of the V-groove 18
and the thickness of the edge of the lens which can be obtained from the coordinate
per radius vector ρ
i at several places beforehand, thereby to determine the amount of lateral movement
of the carriage during the V-edging treatment according to each radius of vector
ρ
i. The specific structure of this apparatus is identical with that described in Japanese
patent application No. Sho 62-335672 filed by the present applicant.
[0005] In such measurement, if the measuring position of the lens L is changed in the circumferential
direction, the radius vector ρ
i is also changed. Therefore, if the abutting positions of the peripheral edges L
f, L
b of the lens L against the inclined surfaces 18a, 18b are changed in the circumferential
direction, a swing angle ϑ of the carriage 7 at this time is also changed.
[0006] However, the abutting force of the peripheral edges L
f, L
b of the lens L against the inclined surfaces 18a, 18b uses a pivotal moment by the
weight of the carriage 7, if the swing angle ϑ is changed, the abutting force is increased,
and therefore, not constant. In order to obtain a comparatively more accurate measurement,
it is preferable that the abutting force is small enough and always constant under
lens grinding pressure, even if the abutting positions are moved in the circumferential
direction to change the radius vector ρ
i at the abutting points.
SUMMARY OF THE INVENTION
[0007] It is therefore the object of the present invention to provide a lens grinding apparatus
capable of satisfying the above requirement.
[0008] In order to achieve this object, there is provided a lens grinding apparatus including
a V-edging grinder rotatably mounted on a body of the apparatus, a carriage swingably
supported by a supporting shaft parallel with a rotating shaft of the V-edging grinder
in such a manner as to be swung about the supporting shaft and adapted to hold a lens
to be ground with a lens rotating shaft thereof, and means for measuring the radius
vector of the lens, CHARACTERIZED in that the lens grinding apparatus comprises a
carriage base having the supporting shaft and reciprocally movably mounted on the
body in such a manner as to be moved in a direction parallel with the rotating shaft,
a resilient member mounted at one end thereof on either a rear end por tion of the
carriage or the carriage base, abutting force adjusting means interposed between
the rear end portion of the carriage or the carriage base, on which the resilient
member is not mounted, and the other end of the resilient member, and control means
for calculating a swing down moment of the carriage with reference to a swing angle
of the carriage about the supporting shaft when the lens, which was roughly ground,
is abutted against the V-edging grinder and the radius vector of the lens at that
time and drive controlling the abutting force adjusting means as such that a difference
between the swing down moment and a swing down preventing moment by the abutting
force adjusting means becomes constant.
[0009] According to the above-mentioned construction, a swing down moment of the carriage
is calculated with reference to the swing angle of the carriage when the roughly ground
lens is abutted against the V-edging grinder and the radius vector of the lens at
that time, and the abutting force adjusting means is drive controlled by the control
means as such that a difference between the swing down moment and a swing down preventing
moment by the abutting force adjusting means becomes constant. By this, the abutting
force of the lens against the V-edging grinder becomes constant even if the radius
vector of the lens at its abutting position against the V-edging grinder is changed.
[0010] The above and other objects, features and advantages of the present invention will
be well appreciated upon reading of the following description of the invention when
taken in conjunction with the attached drawings with understanding that some modifications,
variations and changes of the same could be made by the skilled person in the art
to which the invention pertains without departing from the spirit of the invention
or the scope of claims appended hereto.
BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS
[0011]
Fig. 1 is a perspective view of a lens grinding apparatus according to the present
invention;
Fig. 2 is a schematic view of a device for maintaining abutting pressure of a lens
against a grinder;
Fig. 3 is a right side view of Fig. 2;
Fig. 4 is a control circuit diagram of the device of Fig. 2;
Fig. 5 through Fig. 7 are schematic views for explaining the operation of the device
of Fig. 1 through Fig. 4;
Fig. 8 is a perspective view showing one example of a conventional lens grinder (prior
art); and
Fig. 9 is a schematic view for explaining the operation of the lens grinder of Fig.
8.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] The embodiment of the present invention will be described hereunder with reference
to Figs. 1 through 7.
[0013] Fig. 1 is a perspective view of a lens grinder including a device for maintaining
abutting pressure against a grinder according to the present invention, in which identical
or similar parts of Fig. 8 are denoted by identical reference numerals and description
thereof is omitted. Also, the measurement of a peripheral edge position of a lens
is performed in the same manner as described in Japanese patent application No.
Sho 62-335672 filed by the present applicant.
[0014] Therefore, the different points from these will be described hereunder in detail.
[0015] A body 1 of the apparatus is provided with a guide shaft 19 extending in a direction
parallel with a drive shaft 2 (rotating shaft) of a V-edging grinder 4 and mounted
to position (not shown) of a rear portion of the body 1. A carriage base 20 is reciprocally
and movably held by the guide shaft 19 in the longitudinally direction thereof. The
carriage base 20 is connected with an arm plate 15 and is reciprocally moved in the
axial direction of the guide shaft 19 by a pulse motor 12 together with the arm plate
15. The carriage base 20 is provided at both ends in its moving direction with supporting
portions 21,21 projecting upward therefrom. Portions in the vicinity of rear end portions
7a,7a of the carriage body or carriage 7 are held by upper end portions of the supporting
portions 21,21 as such that the carriage 7 is vertically pivoted by supporting shafts
22,22 coaxial with each other. The gravity G of the carriage 7 is located in front
of the supporting shaft 22. Between a body 16a of a contact platform 16 and a contact
piece 16b, a contacting sensor S is interposed. This sensor S employs a detector same
to one which is provided to a contact platform of the above-mentioned Japanese patent
application and therefore, detailed description thereof will be omitted.
[0016] The carriage 7 is provided with an abutting force adjusting means 23 mounted on
a rear end portion 7a thereof. The abutting force adjusting means 23 includes a pulse
motor 24 mounted on the rear end portion 7a, a reduction gear 24a interlocked with
the pulse motor 24, a rotating shaft 24b interlocked with the reduction gear 24a,
a circular timing plate 25 and a lever 26 mounted on the rotating shaft 24b, and a
microswitch 27 mounted on the rear end portion 7a. The timing plate 25 is formed with
a V-shaped notch 25a. A roller 27b attached to an actuator lever 27a of the microswitch
27 is abutted against the peripheral surface of the timing plate 25. And, upon engagement
of the roller 27b with the notch 25a, the microswitch 26 is switched off.
[0017] Between the free end portion or lower end portion of the lever 26 and the carriage
base 20, a spring 28 is interposed. The timing plate 25 and the microswitch 27 constitute
means for detecting a pivot starting position of the lever 26.
[0018] Furthermore, the abutting force adjusting means 23 is drive controlled by CPU 29
(central processing unit) as a calculation control circuit (control circuit). In the
CPU 29, power output from the microswitch 26 and a signal from the contacting sensor
S are input. Also, the CPU 29 controls the rotating time of the pulse motor 24 through
a timer 30. The CPU 29 calculates the rotation angle of the lens shafts 8,9 in accordance
with a drive control pulse signal of the pulse motor 10 during rough grinding treatment
of the lens and stores the same therein. An electric power is fed to the pulse motor
24 through the timer 30 when the timer 30 is being activated.
[0019] Also, the CPU 29 employs a measuring device as disclosed in the above-mentioned Japanese
patent application in order to measure a positional coordinate of the peripheral edge
of the roughly ground lens L in such a manner as that a radius vector ρ
i of the lens L abutted against the V-edging grinder 4 is found in accordance with
the shaft rotation angle of the lens shafts 8,9 and a swing angle ϑ of the carriage
7, when the roughly ground lens L is abutted against the V-edging grinder 4 in this
radius vector position, is calculated based on such obtained radius vector ρ
i and a known carriage arm length. Moreover, the CPU 29 determines the operating time
of the timer 30 and the current feeding direction to the pulse motor 24, thereby to
allow the timer 30 to control the current feeding time to the pulse motor 24 and the
current feeding direction. At this time, the controlling of the current feeding time
and the current feeding direction by the timer 30 is started from a position where
the microswitch 27 is switched off due to engagement of the roller 27 with the notch
25a and is performed as such that a difference between a swing down moment by weight
of the carriage acted on the abutting portion from the swing angle ϑ of the carriage
7 and a pivot down preventing moment by the spring 28 becomes constant. In this embodiment,
although the driving time of the pulse motor 24 is determined by the operating time
of the timer 30, it may be designed as such that the number of drive pulse of the
pulse motor 24 is found through the above calculation and such found number of drive
pulse is input into the pulse motor 24 from the CPU 29 so as to drive control the
pulse motor 24 directly by the CPU 29.
[0020] This relation will now be described with reference to Fig. 5 through Fig. 7, wherein
O denotes the swing center of the carriage 7, G denotes the gravity of the carriage
7, A denotes the length from the swing center O to the axial line O₁ of the lens shaft,
C denotes the length from the swing center O to the gravity G, B₀ denotes the length
from the swing center O to a point f on which the force of the spring is acted, F₀
denotes the spring force acting on the point f, G₀ denotes the weight at the gravity
G, and W₀ denotes the swing down moment which is acted on the abutting point E of
the lens against the V-edging grinder and the axial line O₁ by the swing down moment
due to the weight G₀.
[0021] Fig. 5 shows a case where the carriage 7 is in its horizontal position and where
the swing angle thereof is zero. In this case, if the lens grinding radius vector
is denoted by ρ ₀, the correlation of A·W₀, C·G₀ and B·F₀ becomes as follows;
A·W₀ + C·G₀ = B·F₀
[0022] At this time, the pulse motor is controlled as such that the lever is brought to
its downwardly vertical position.
[0023] Also, Fig. 6 shows a case where the radius vector ρ
i is ρ ₁ which is larger than ρ ₀. In this case, if the length from the swing center
O to the point f₁ on which the force of the spring is acted is represented by B₁ and
the spring force acting on the point f₁ is represented by F₁, the force relation
thereof is arranged as follows;

In this case, therefore, the lever is pivoted toward the side departing from the
swing center O.
[0024] Furthermore, Fig. 7 shows a case where the grinding radius vector ρ ₁ is ρ ₂ which
is smaller than ρ ₀. In this case, if the length from the swing center O to the point
f₂ on which the force of the spring is acted is represented by B₂ and the spring force
acting on the point f₂ is represented by F₂, the force relation is arranged as follows;

In this case, therefore, the lever is pivoted toward the side approaching to the
swing center O.
[0025] Instead of obtaining the swing angle of the carriage by calculation, a swing angle
detecting rotary encoder RE may be provided as shown by the broken line of Fig. 1.
[0026] Also, although the operating point of the force of the spring 28 acting on the carriage
7 is performed by the pivotal lever 26, the present invention is not necessarily
limited to this. For example, it may be designed as such that a spring mounting member
is movably mounted on the rear end portion 7a of the carriage 7 in such a manner as
to move forward and backward with respect to the front end portion of the carriage
7, so that the upper end portion of the spring 28 is held by the spring mounting member
and the spring mounting member is controlled by a pulse motor, a cylinder or the like
in such a manner as to move forward and backward with respect to the front end portion
of the carriage 7.
[0027] According to the present invention, in a lens grinding apparatus including a V-edging
grinder rotatably mounted on a body of the apparatus, a carriage swingably supported
by a supporting shaft parallel with a rotating shaft of the V-edging grinder in such
a manner as to be swung about the supporting shaft and adapted to hold a lens to
be ground with a lens rotating shaft thereof, and means for measuring the radius vector
of the lens, the lens grinding apparatus comprises a carriage base having the supporting
shaft and reciprocally movably mounted on the body in such a manner as to be moved
in a direction parallel with the rotating shaft, a resilient member mounted at one
end thereof on either a rear end portion of the carriage or the carriage base, abutting
force adjusting means interposed between the rear end portion of the carriage or the
carriage base, on which the resilient member is not mounted, and the other end of
the resilient member, and control means for calculating a swing down moment of the
carriage with reference to a swing angle of the carriage about the supporting shaft
when the lens, which was roughly ground, is abutted against the V-edging grinder and
the radius vector of the lens at that time and drive controlling the abutting force
adjusting means as such that a difference between the swing down moment and a swing
down preventing moment by the abutting force adjusting means becomes constant. Accordingly,
even when the abutting position of the peripheral end of the roughly ground lens
against the V-edging grinder is moved in the circumferential direc tion and the radius
vector at the abutting point is changed, the abutting force of the peripheral edge
of the roughly ground lens against the V-edging grinder can be made smaller enough
than the grinding pressure during the lens grinding treatment. Also, this controlling
may be utilized not only in a case where the peripheral edge is abutted and measured
but also in a case where the grinding pressure during the lens grinding treatment
is adjusted.
[0028] Also, there can be considered to adopt a method for adjusting the pivot down preventing
moment of the carriage by changing the length of a spring instead of the present invention.
In this case, however, since it is required to use a spring having a large spring
constant and also required to have means for changing a spring length of large torque
in order to change the length of a spring, the apparatus is anticipated to become
large and to be of energy consuming type. Also, since the adjusting range of the preventing
moment is small merely by the adjustment of a spring length, it would be impossible
to control, for example, the abutting force adjustment during the measurement of
the thickness of the peripheral edge of a lens and the grinding pressure adjustment
during the lens grinding treatment by one construction.
[0029] On the contrary, since the present invention employs a method for changing the position
of the operating point of a spring, the adjusting device becomes small and easy to
handle. Furthermore, it is of energy saving type. In addition, the adjusting range
of the carriage pivot preventing moment can be taken large and one adjusting mechanism
can be used both for adjusting the abutting force during the measurement of the thickness
of the peripheral edge of a lens and for adjusting the grinding pressure during the
grinding treatment of a lens.
1. A lens grinding apparatus including
a V-edging grinder (4) rotatably mounted in a body (1) of the apparatus;
a carriage (7) swingably supported by a supporting shaft (6) parallel with a rotating
shaft (2) of said V-edging grinder (4) in such a manner as to be swung about the supporting
shaft (2) and adapted to hold a lens to be ground (L) with a lens rotating shaft (8,9)
thereof; and
means (10,11,12,16,17) for measuring the radius vector of the lens;
CHARACTERIZED IN THAT
said lens grinding apparatus comprises
a carriage base (7a,7a) having the supporting shaft (2) and reciprocally movably mounted
on the body (1) in such a manner as to be moved in a direction parallel with the rotating
shaft (2);
a resilient member (28) mounted at one end thereof on either a rear end portion (20)
of the carriage (7) or the carriage base (7a);
abutting force adjusting means (24,25,26,27,30) interposed between either the rear
end portion (20) of said carriage (7) or said carriage base (7a), on which said resilient
member (28) is not mounted, and the other end of said resilient member (28); and
control means (29) for calculating a swing down moment (W₀,W₀cosϑ) of said carriage
with reference to a swing angle (ϑ) of said carriage about the supporting shaft (2)
when the lens (L), which was roughly ground, it abutted against said V-edging grinder
(4) and the radius vector (ρ i) of the lens (L) at that time and drive controlling said abutting force adjusting
means (24,25,26,27,30) as such that a difference between the swing down moment and
a swing down (W₀,W₀cosϑ) preventing moment (F₀,F₁cosϑ,F₁cosϑ′,F₂cosϑ,F₂cosϑ′) by said
the abutting force adjusting means becomes (24,25,26,27,30) constant.
2. A lens grinding apparatus of claim 1, wherein said swing angle (ϑ) can be obtained
with reference to the radius of vector (ρ i) of the lens (L) and a swing diameter (A) of said carriage (7).
3. A lens grinding apparatus of claim 1, wherein said swing angle (ϑ) is determined
by a rotary encoder (RE) which is interposed between the supporting shaft (6) and
said carriage (7).
4. A lens grinding apparatus according to any of claim 1 through claim 3, wherein
said abutting force adjusting means (24,25,26,27,30) comprises a pulse motor (24)
mounted on a rear end portion (7a) of said carriage (7), and a lever (26) mounted
on said carriage (7) and being pivoted by said pulse motor (24), said lever (26) being
provided on a free end por tion thereof with said resilient member (28).
5. A lens grinding apparatus of claim 4, wherein there is provided pivot starting
position detecting means (25,27) for detecting a pivot starting position (25a) of
said lever (26).
6. A lens grinding apparatus of claim 5, wherein said pivot starting position detecting
means (25,27) comprises a timing plate (25) secured to a rotating shaft (24b) interlocked
with the pulse motor (24) and provided at a peripheral portion thereof with a notch
(25a), and a microswitch (27) mounted on said carriage (7) in such a manner as to
be adjacent to said timing plate (25), a roller (27b) on a front end of an actuator
lever (27a) thereof being abutted against the peripheral surface of said timing plate
(25).