JPH0371999B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention prevents the scale from rotating suddenly in the falling direction due to its own weight due to the inclination of the drawing board when the scale of the universal parallel ruler is set in an equilibrium state and the scale is allowed to rotate freely. The present invention relates to a scale balance device designed to prevent

In this type of device, a disc-shaped eccentric cam is provided on the rotating body that interlocks with the scale, and a roller is provided on the non-rotating side of the head so as to be movable in forward and backward directions with respect to the cam. There is a known configuration in which the scale is brought into elastic contact with the cam, and the balance state of the scale is set by using this elastic contact force to offset the rotational torque of the rotating body due to the weight of the scale or the like.

In the above device, the torque T applied to the cam by the spring is T = S × R (see Figure 7), where S is the force of the spring, and R is the rotation of the cam by the elastic contact force of the rollers. The radius is an element that generates torque. The shape of the cam and the radius R are determined so that the torque T becomes a sine curve when the scale is rotated. When the inclination angle of the drawing board is changed, the rotational torque applied to the cam changes depending on the weight of the scale, etc. When the inclination of the drawing board is made steep, the rotational torque due to the weight of the scale, etc. on the cam increases, and when the inclination of the drawing board is made gentle, the rotational torque due to the weight of the scale, etc. applied to the cam decreases.

When changing the inclination angle of the drawing board, the spring force S is adjusted by a screw feed mechanism. In this case, when the spring force is strengthened, the spring force S becomes S+A, and when it is weakened, the spring force S becomes S-A.

The rotational torque T of the cam due to the spring force when the spring force S is adjusted is as follows: T=(S±A)×R, and the characteristics of this torque T do not form a sine curve. However, the characteristic of the rotational torque of the cam due to the weight of the scale etc. is a sine curve. Therefore, the scale cannot be perfectly balanced unless the rotational torque of the cam due to the spring force used to balance this rotational torque is a sine curve. However, as shown in FIG. 8, if the spring force S is changed proportionally, the rotation torque due to the spring force of the cam becomes a sine curve with respect to the rotation of the scale.

Therefore, the present invention provides a scale in which the spring force can be adjusted so that the spring force changes proportionally, and the rotational torque of the cam maintains the characteristics of a sine curve with respect to the rotation of the scale even when the spring force is adjusted. The purpose is to provide a balance device.

The configuration of the present invention will be described in detail below based on embodiments shown in the accompanying drawings.

Reference numeral 2 denotes a drawing board, which is fixed to a support frame of a tiltable drafting table so that it can be fixed at a desired angle of inclination between horizontal and vertical. 4 is a horizontal rail arranged on the upper side of the drawing board 2, and a horizontal cursor 6 is placed on this rail.
is installed so that it can be moved freely. The upper end of the vertical rail 8 is connected to the horizontal cursor 6. The lower end of the vertical rail 8 is placed on the drawing board 2 via a tail roller so as to be freely movable. 12 is a vertical cursor movably attached to the vertical rail 8;
A support substrate 18 of the head 16 is connected to this via a known double hinge mechanism 14. 22 is a tubular main shaft, the outer peripheral surface of which is connected to the support substrate 1.
It is rotatably inserted into the tube portion 18a of No. 8 via a ball bearing. A disc-shaped cam 36 and a mounting plate 2 are attached to the upper part of the main shaft 22 by means of a nut.
4 is fixed, and a handle 26 is fixed to the mounting plate 24. A scale mounting plate 28 is fixed to the lower end flange of the main shaft 22.
Scales 30 and 32 are fixed to 8. 3
Reference numerals 8 and 40 denote guides formed on the support substrate 18 and have guide surfaces extending along the diameter direction of the cam 36, and a roller support plate 42 is slidably disposed between the guides 38 and 40. Reference numeral 44 denotes five approximately U-shaped springs, each with its middle portion connected to the shaft body 4 fixed to the support substrate 18, as shown in FIG.
6 is rotatably fitted. One of each of the springs 44 is connected to a shaft body 48 protruding from the support plate 42.
is in contact with. A roller 50 is rotatably supported by the support plate 42, and is brought into elastic contact with the cam surface of the cam 36 by the elastic force of the spring 44. Reference numeral 52 denotes five pressing pieces, each intermediate portion of which is rotatably supported by a shaft 54 on the support substrate 18, and each tip is in elastic contact with the other end of the corresponding spring 44. 56 is a stopper shaft, 58 is a stopper spring whose one end is locked to the support substrate 18, and the bent portion of the other end is in elastic contact with each side surface of the spring 44.

The plurality of springs 44 and the plurality of pressing pieces 52 corresponding to each of the springs 44 constitute means for proportionally changing the spring force.

Next, the operation of this embodiment will be explained.

In a state where the drawing plate 2 is limited to the maximum inclination angle, all the tips of the pressing pieces 52 are in elastic contact with one end of the corresponding spring 44. At this time, all the springs 44 act on the roller 50, and the elastic contact force of the roller 50 with respect to the cam 36 becomes maximum. When the scale mounting plate 28 is in a free rotation state, the scale 3
0, 32 and the weight of the scale mounting plate 28 generate a rotation moment in the hour hand rotation direction in the cam 36 via the main shaft 22 in FIG. This rotational moment changes in a sine curve as the scale mounting plate 28 rotates. On the other hand, cam 36 of roller 50
Due to the elastic force, a rotational moment is generated in the cam 36 in the counterclockwise rotational direction in FIG. 6, and the magnitude of this rotational moment is the same as the rotational moment of the cam 36 due to the weight of the scale, etc. The cam shape of the cam 36 is formed as shown in FIG.
Therefore, the above two rotational moments cancel each other out,
The scales 30 and 32 are in a balanced state, and the scales 30 and 32 are in a freely rotatable state and are stationary with respect to the support substrate 18 of the head 16 at a desired rotation angle on the drawing board 2.

When the inclination angle of the drawing board 2 is changed in the horizontal direction, the rotational moment of the cam 36 due to the elasticity of the spring 44 becomes larger than the rotational moment of the cam 36 due to the weight of the scales 30, 32, etc. The balance will be lost.
In this case, a selected predetermined one of the pressing pieces 52 is rotated in the direction of rotation of the hour hand in FIG.
Move away from 4. The spring 44, which is disengaged from the tip of the pressing piece 52, loses its fulcrum. This results in
Since the effective spring among the springs 44 decreases, the roller 5
0's elasticity decreases. This reduced elastic force of the roller 50, that is, the elasticity of the effective spring 44 changes in accordance with the change in the amount of eccentricity of the cam 36, and this change characteristic curve S2 is as shown in FIG. 4
There is a proportional relationship with the elasticity change characteristic curve S1 of No. 4. That is, at any rotation angle of the cam 36, the ratio A:B of the value A of the spring force S1 and the value B of the spring force S2 is constant. From this, cam 36
The rotational torque T due to the spring 44 is S x the number of springs x R = T, where S is the elasticity of one spring 44 and R is the radius of the cam, and the rotational torque T due to the spring 44 after adjustment is It changes in a sine curve as it rotates. Therefore, when the inclination angle of the drawing board 2 is changed, the scale can be adjusted to a perfectly balanced state by selecting and rotating an appropriate one of the pressing pieces 52 to increase or decrease the effective number of springs 44. be able to.

The same effect as in the above embodiment can also be achieved by changing the spring fulcrum for one spring 60, as shown in FIG. When the inclination angle of the drawing board is 10 degrees, only point A of the spring 60 is locked by the pressing piece (not shown), when the inclination angle of the drawing board is 30 degrees, point B, and when it is 90 degrees. Only point C is locked by a separately provided pressing piece (not shown). By changing the locking point or spring fulcrum of the spring 60, the spring constant of the spring 60 changes. That is, for example, the spring force of the spring 60 when the fulcrum is set at point B and the spring force of the spring 60 when the fulcrum is set at point A have a certain proportional relationship.
The other configuration in FIG. 9 is the same as the first embodiment.
The above configuration for changing the fulcrum of the spring 60 constitutes a means for proportionally changing the spring force.

Since the present invention is configured as described above, it is possible to adjust the spring force for scale balance in response to changes in the inclination angle of the drawing board without destroying the sine curve characteristic of the rotational torque for scale balance. There is an effect.

[Brief explanation of drawings]

Fig. 1 is a plan view, Fig. 2 is a sectional view, Fig. 3 is a plan view, Fig. 4 is a sectional view taken along line A-A, and Fig. 5 is B-B.
6 is a plan view, FIG. 7 is an explanatory view, FIG. 8 is an explanatory view, and FIG. 9 is an explanatory plan view showing another embodiment. 2...Drawing board, 4...Horizontal rail, 6...Horizontal cursor, 8...Vertical rail, 12...Vertical cursor, 16
... head, 18 ... support substrate, 22 ... main shaft,
36...Cam, 26...Handle, 28...Scale mounting plate, 30, 32...Scale, 38,4
0... Guide, 42... Roller support plate, 44... Spring, 50... Roller, 52... Pressing piece.

Claims (1)

[Scope of Claims] A head 16, a main shaft 22 rotatably supported on a support substrate 18 of the head 16, a handle 26 fixed to the upper part of the main shaft 22, and the main shaft 22.
a scale mounting plate 28 connected to the lower part of the scale mounting plate 28; a scale 30 mounted on the scale mounting plate 28;
32, a cam 36 rotatable in conjunction with the scale; a roller 50 supported on the support substrate 18 side so as to be movable in forward and backward directions with respect to the cam 36; It consists of a spring that brings the roller 50 into elastic contact with the cam 36 and applies a rotational moment to the cam 36 in a direction opposite to the rotational moment due to the weight of the scales 30, 32, and means for proportionally changing the elasticity of the spring. A scale balance device characterized by: 2. The means for proportionally changing the elasticity of the springs includes a plurality of springs 44 that engage with the rollers 50, and a plurality of pressing pieces 52 that releasably engage with the spring fulcrum of each of the plurality of springs 44. 2. The scale balance device for a universal parallel ruler according to claim 1, characterized in that it is comprised of: 3. The scale balance device for a universal parallel ruler according to item 1, wherein the means for proportionally changing the elasticity of the spring is configured to change the fulcrum position of the spring that engages with the roller 50.