JPH08110546A - Brake device for shutter - Google Patents

Abstract

PURPOSE: To provide a brake device for a shutter capable of improving the operational durability of a shutter blade and also attaining an effective arrangement in a limited space. CONSTITUTION: The brake device is provided with a shutter operating member which is integrally rotated with the exposure traveling of the shutter member, a brake operating member 10 with a cam surface abutting on a member part to be braked 7a of the shutter operating member and for generating a braking force when the member 10 is rotated and pushed in a direction reverse to that of the shutter operating member in contact with the shutter operating member, the rotational center 9 of the brake operating member 10 lies within a virtual extending track of the moving track of the member part to be braked 7a, and the center 9 is arranged near an intersection of a circle whose center is the rotational center of the shutter operating member and whose radius is an intermediate point in an abuttable extent of the member to be braked 7a and an angular line obtained by adding a brake operating angle from an angular line at the stopping position of the member to be braked 7a within the extent from a brake stopping position of the member to be braked 7a to a position having nearly twice the brake operating angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake device for a shutter of a camera.

[0002]

2. Description of the Related Art In a shutter brake device for a camera, a friction brake device as conventionally known brakes the operation of a shutter blade within a relatively small stroke near the trailing end of the shutter to prevent the blade from bouncing. However, if the frictional force is too strong at the braking start position, the shutter blades will bounce back, causing uneven exposure at the edge of the shooting screen, or stopping the blades without traveling to the end position. However, there is an inconvenience.

Therefore, it is desirable that the braking force of the brake is relatively weak at the start position and gradually increases to surely stop the shutter blades at the end position.

However, in the case of adopting a brake that cannot be configured in this way because of space limitations and the spring force for generating frictional force cannot be changed between the beginning and the end, friction characteristics In addition, since the static frictional force is larger than the dynamic frictional force, the braking force at the braking start position is the maximum and then gradually decreases. Therefore, when trying to obtain an appropriate braking force at the end position, the static friction force that acts initially becomes extremely strong, impacting the shutter blades and impairing durability, and the phenomenon such as the uneven exposure and curtain falling defect as described above. Occurs. Such static friction tends to increase particularly at low temperatures. Further, in a blade type focal plane shutter, the blade (blade) is deformed by the impact at the braking start position, and the trailing blade (leading blade) is formed at the edge of the exposure opening of the partition plate that separates the leading blade and the trailing blade. In some cases, the vehicle may collide with the vehicle, hinder driving, or be damaged.

In order to improve the characteristics of such a friction brake, as shown in FIG. 11, means for changing the braking force by changing the lever ratio is adopted. Generally, the cam shape of the brake lever is set so that the position of the contact point with the brake on the rotating shutter actuating member is increased from the initial stage to the final stage of braking.

In FIG. 11, reference numeral 1 is a shutter base plate having an opening 1a, and reference numerals 51 to 54 are divisions constituting rear blades connected to operating arms 6 and 6'having pivots 6a and 6'a as pivotal fulcrums. The blades 21 are a part of the divided blades that form the leading blades connected to the operating arms 3 (not shown) and 3'having the rotation shafts 3a and 3'a as rotation fulcrums. Reference numerals 4 and 7 denote drive levers for transmitting the driving force of a spring (not shown) to the operating arms 3 and 6 which are rotatably supported around the shafts 3a and 6a. Pins (not shown) planted below are ground plates. It penetrates through the circular arc groove formed in 1 and engages with the operating arms 3 and 6 by pin holes, respectively, and rotates integrally. Reference numeral 10 'indicates a brake lever for the leading blade.

Reference numeral 100 denotes a brake lever for the rear blade, which is rotatably supported about a shaft 90 and is always urged clockwise by a spring. Reference numeral 17 is a set lever that is always urged clockwise by a spring,
When the rotation of the shaft 17a in the clockwise direction is interlocked with the rotation of the charge lever while being in contact with the 0 arm portion 100b and the clockwise rotation is restricted, the arm portion 100b is rotated. Is lifted upward in the figure to release the restriction, and is rotated clockwise to allow the brake lever 100 to rotate counterclockwise. When the drive lever 70 rotates clockwise due to the traveling of the trailing blade, the brake pin 70a implanted at the tip of the drive lever 70 moves to the brake lever 100.
The brake is applied by abutting on the cam portion 100a and rotating the brake lever 100 counterclockwise.

[0008]

However, in the conventional brake device shown in FIG. 11, the brake pin 70a and the cam of the brake lever 100 are cammed due to the constraint of smoothly rotating the brake lever during braking in one direction. Part 1
The following problems have been pointed out in the continuous contact relationship with 00a.

(1) The load on the braked portion is (a) in FIG.
As shown in Fig. 5, it has a characteristic that it is relatively small from the initial stage of braking to the middle stage, and it becomes relatively large from the middle stage to the end of control, so that the impact applied to the shutter blades via the braked part is large in the final stage, For example, when the shutter blade is made of a plastic material, there is a problem in improving durability.

This problem largely depends on the cam shape of the cam portion 100a, but as shown in FIG. 12, the braking pin 70a, which is the braked portion of the drive lever 70 that is the shutter braking member, is the cam of the brake lever 100. A tangent line drawn in the traveling direction of the braking pin 70a from the braking start contact point that starts contact with the portion 100a (braking start direction vector of the braked portion)
And the tangent line drawn from the control end contact point in the traveling direction of the braked portion (direction vector at the time of control termination of the braked portion) to the region (hatched portion in FIG. 12) between the rotation centers of the brake levers. Is not located, which reduces the degree of freedom in designing the cam shape of the cam portion, which in turn reduces the degree of freedom in selecting the load curve for the braked portion, resulting in a two-dimensional load curve. It was the next curve.

(2) As disclosed in Japanese Utility Model Publication No. 5-42423, one having two braking contact portions is also proposed, which is a load characteristic shown in FIG. 13 (b).
As shown in (3), the load cannot be continuously increased at the same rate of change from the start to the end of braking, and there is a drawback that the shock is applied twice. Further, also in this case, the same problem as the above-mentioned problem (1) was encountered.

The object of the present invention is to be relatively weak in the initial stage of braking,
The braking force is continuously and gradually increased from the initial stage of braking at substantially the same rate of change, and a sufficient braking force is obtained at the end of braking to improve the operating durability of the shutter blades, which is effective in a limited space. An object of the present invention is to provide a brake device for a shutter that can be arranged.

[0013]

The structure for achieving the object of the present invention is such that a shutter member composed of a plurality of divided blades travels for exposure as described in claim 1. Shutter operating member that rotates as
A shutter having a cam surface that comes into contact with a braked portion of the operating member, and a brake operating member that is rotationally pushed in a direction opposite to that of the operating member to generate a braking force by coming into contact with the operating member. In the brake device, the center of rotation of the brake operating member is within a virtual extension locus range of the movement locus of the braked portion, from the braking stop position of the braked member to a position approximately twice the braking operating angle. Within the range, a circle whose center is the rotation center of the shutter actuating member and whose radius is the midpoint of the contactable range of the braked member, and a brake operating angle portion from the angle line of the stop position of the braked member It is characterized in that it is provided near the intersection with the added angle line.

In this structure, the center of rotation of the brake actuating member is located on the virtual extension line of the movement track of the braked portion, so that the lever ratio of the braking member can be utilized to the maximum extent.

Further, the rotation center position of the braking member is set within a range from the braking stop position of the member to be braked to a position approximately twice the braking operation angle, so that the braking device is operated in a limited space. It can be stored most efficiently including the range.

Furthermore, a brake operating angle is calculated from a circle centered on the center of rotation of the shutter operating member and having a radius at an intermediate point of the contactable range of the braked member, and an angle line of the stop position of the braked member. The fact that it is provided near the intersection with the added angle line is that it is combined with the cam of the brake operating member described later,
It shows a position which is a design guideline for obtaining an ideal load curve as shown in FIG.

As described above, the brake operating member can be set at the optimum position, the degree of freedom in designing the cam surface of the brake operating member is increased, the entire device including the operating range can be downsized, and the shutter can be released. It is possible to approach the center of rotation of the actuating member.

Another structure for achieving the object of the present invention is, as described in claim 2, in claim 1, wherein the cam surface of the brake actuating member is a cam in the initial stage of the braking range of the shutter actuating member. A cam portion that has a curved portion having a center of curvature on the braked member side of the actuating member with a tangent line of the contact point sandwiched between the curved portion and a straight portion that smoothly connects the curved portions, and that abuts and slides from the middle stage to the end stop. Has a curved portion having a center of curvature on the braking member side across the contact point tangent line and a straight line portion that smoothly connects the curves.The cam portion in the initial braking range and the cam portion in the middle and later stages are tangent to each other. The feature is that they are connected smoothly by connecting straight lines.

In this structure, as shown in FIG. 6, the friction moment around the rotation center of the brake lever 10 received by the brake lever 10 as the brake operating member from the friction member is M, the brake lever 10 and the braked member 7a. The contact point is P, the distance from the rotation center of the brake lever to the point P is 1, the distance from the rotation center of the shutter operating member to the point P is L, the friction coefficient of the contact portion is μ, and the contact pressure angle is α. Then, the braking moment around the rotation center of the shutter operating member at point P in FIG. 6 is approximately F = (l / L) × ((μ + tanα) / (l−μ · tanα)) × M (1) Then, an arbitrary load curve can be obtained by using the cam shape in which the shape of the contact portion of the brake operating member with the shutter operating member is set using the braking load obtained by the above equation (1).

Further, the friction force stabilizing means such as rollers is used for the braked member to stabilize the frictional force (friction coefficient μ) due to the vertical reaction force acting on the abutting portion. Thus, the load moment F obtained by the above equation (1) can be stabilized.

[0021]

【Example】

(First Embodiment) FIGS. 1 to 3 are operational plan views showing a part of a blade type focal plane shutter to which the present invention is applied. FIG. 1 shows a state in which the shutter is charged, and FIG. The state, FIG. 3 shows the state at the end of exposure. In the figure, reference numeral 1 denotes a shutter base plate which forms the base of the shutter, and is fixed at a constant distance from another base plate (not shown) of substantially the same shape, and a shutter front blade and a shutter each having a plurality of divided blades therebetween. Holds the rear blade. As is known from Japanese Patent Publication No. 54-19175, the front and rear blades are pivotally supported by two operating arms to open and close the exposure opening 1a by a parallel link motion. And the opening provided in the middle of the two main plates is 1
A partition plate (not shown) having an opening corresponding to a is provided so that it can operate without interfering with each other.

Numerals 21 to 24 are divided blades constituting the leading blade, and are rotatably supported by the operating arms 3 and 3 ', respectively.

Reference numerals 3a and 3'a denote rotation axes of the arm. 5
Numerals 1 and 54 are divided blades which constitute rear blades, and are rotatably supported by the operating arms 6 and 6 ', respectively.

Reference numerals 6a and 6'a indicate the rotation axes of the arms. 4,
Reference numeral 7 denotes a drive lever for transmitting the drive force of a spring (not shown) to the actuating arms 3, 6, which is rotatably supported around the shafts 3a, 6a, and a pin (not shown) planted on the lower surface thereof is a base plate 1. It penetrates through the circular arc groove provided in the above and engages with the operating arms 3 and 6 through pin holes, respectively, and rotates integrally.

Reference numerals 9 and 9'indicate brake shafts fixed to the main plate 1. FIG. 5 is a cross-sectional view showing the structure of the rear-blade brake around the rear-blade brake shaft 9, and 10 is the shaft 9.
A brake bar that is rotatably fitted to the friction member 12 is stacked in a state of being sandwiched between the friction members 12, and the pressure of the leaf spring 15 is applied via an upper fixed plate 14 that is fitted non-rotatably around the shaft 9. I'm supposed to receive it. Reference numeral 7a is a roller that is planted on the lower surface or the upper surface of the drive lever 7 (either may be used depending on the space) and engages with the brake lever 10. Reference numeral 8 is a torsion spring for returning the brake lever 10 in the direction opposite to the braking direction and against the frictional force. Reference numeral 13 is an intermediate plate fitted to the shaft 9 and stopped rotating. Reference numeral 16 is a fastening means such as a nut or a screw for fastening. Reference numeral 11 is a ring for setting the charge amount of the leaf spring 15 by tightening the fastening means 16, and the leaf spring 15 is formed by a combination of at least two pieces.
Is set and the pressure of the leaf spring 15 is adjusted. Further, the ring 11 also plays a role of guiding the sitting of the torsion spring 8.

FIG. 4 is a cross-sectional view showing the structure of the leading blade brake around the leading blade brake shaft 9 '. Like the structure of the trailing blade brake, 10' is a brake lever.
Reference numeral 4a is a pin which is planted on the lower surface or the upper surface of the drive lever 4 and which engages with the brake lever 10 '. 14 'shows an upper fixing plate.

The lower fixing plate 13 is replaced with the flange portion 9'a of the shaft 9'and eliminated from the construction.

6 to 9 are detailed plan views of the rear blade brake, in which one arm 10a of the brake lever 10 of the rear blade brake is provided so as to engage with the roller 7a at the end of the rotation of the drive lever 7. The engaging portion of the one arm 10a with the roller 7a is a curve having a center of curvature on the side of the roller 7a across the contact point at the beginning of the braking range of the drive lever 7, the curves, and a straight line connecting the curves smoothly. The part that comes into contact and slides from the middle stage to the end stop is composed of a curve having a center of curvature on the brake lever 10 side across the contact point and a straight line connecting these curves smoothly. The cams are smoothly connected by a straight line connecting the curves with a tangent line. Further, the center of the diameter of the shaft 9 is an extension range of a two-dimensional (plane) range in which the pin 7a rotates (a ring having the shaft 6a as the center and the outer diameter of the roller 7a as the width as shown by the chain double-dashed line in FIG. 6). In a flat plane range) and within a range (2θ) from the outer shape operation end of the roller 7a to twice the braking operation angle (θ) of the drive lever 7 in a fixed manner with respect to the main plate 1.

Further, the center position of the diameter of the shaft 9 is set to the roller 7a.
An intersection between a locus circle of the shaft center and a tangent line connecting the outer shape of the braking end of the roller 7a and the center of the shaft 6a to the straight line passing through the center of the shaft 6a at the braking operation angle β of the brake lever 10. It is desirable to place it fixedly in the vicinity with respect to the main plate 1.

However, depending on the degree of freedom of design, FIG.
The center position of the shaft 9 is arbitrarily set within the range indicated by the shaded area.

As shown in FIG. 2, when the winding operation is started from the state where the shutter travel is completed, the drive lever 4 of the front blade and the drive lever 7 of the rear blade charge the shutter drive spring (not shown) by the rotation of the charge lever (not shown). While rotating in the counterclockwise direction around the shafts 3a and 6a, respectively, the operating arms 3, 3'and 6, 6'rotate around the respective shafts to move the leading and trailing blades. The rear blades 51 to 54 are housed in a state of being folded above the opening 1a, and the leading blades 21 to 24 are locked while the opening 1a is covered as shown in FIG. Is ready to run.

At this time, the tip 10'b of the brake lever 10 'of the leading blade brake is pushed by the pin 4b planted in the drive lever 4, and the lever 10' is rotated clockwise about the shaft 9 '. When the shutter charge is completed, the front blade brake is also set to the operation start state. Further, the set lever 17 is connected to the shaft 1 in conjunction with the rotation of the charge lever.
By rotating counterclockwise around 7a, the brake actuating lever 10 of the trailing blade brake moves the arm portion 10 thereof.
By pressing b, the shaft 9 is rotated clockwise around the shaft 9 and is set in the operation start state similarly to the leading blade brake. Reference numeral 18 is a stopper made of a flexible elastic member such as plastic or rubber, and is a brake lever 10
Has a cushioning function by contacting the outer end surface of the brake lever 10 at the time of brake operation. When the shutter charge is completed, the set lever 17 is rotated and returned in the clockwise direction by the force of the spring 17b, and comes out of the rotation range of the arm portion 10b.

Next, the operation of the brake will be described with reference to FIGS.

When the locking of the drive lever 4 is first released from the state shown in FIG. 1 by the release operation, the drive lever 4 is rotated around the shaft 3a in the clockwise direction by the stored force of the drive spring, and is actuated accordingly. The arms 3 and 3'rotate around the shafts 3a and 3'a in the same (clockwise) direction, and the shutter leading blades move downward in the figure to start exposure. When the leading shutter blade travels a certain distance and the drive lever 4 rotates from the initial position shown by the chain double-dashed line in FIG. 3 to the position shown by the solid line, the braking pin 4a on the lever 4 hits the brake operating lever 10 '. When the lever 10 'is rotated counterclockwise against the frictional force with the friction member 12 and the force of the torsion spring 8', the shutter leading blade operating mechanism (driving lever 4, operating arm) is started. 3 and 3 ', blades 21-2
Braking of 4) is started. At this time, the position of the leading blade is such that the outer shape end surface of the blade 21 facing the opening end portion 1b of the blades 21 to 24 and opposite to the slit forming end surface is outside the opening 1a. When the braking is started, the lever 4 increases in a quadratic curve due to the increase of the lever ratio of the distance between the contact point of the pin 4a with respect to the lever 10 'and the respective rotation centers of the lever 4 and the lever 10'. While being received, it is rapidly controlled while rotating to the position shown in FIG. 2 to completely stop the leading blade at a predetermined position.

When the lock of the drive lever 7 is released, the drive lever 7 rotates clockwise around the shaft 6a by the stored force of the drive spring, and accordingly, the operating arms 6 and 6'are respectively rotated by the shaft 6a. And 6′a in the same (clockwise) direction, the rear shutter blades stored outside the opening 1a move downward in the figure to start light shielding. When the rear blade of the shutter travels a certain distance and the drive lever 7 rotates from the initial position shown by the alternate long and short dash line in FIG. 7 to the position shown by the solid line, the control roller 7a on the lever 7 starts contacting the brake operating lever 10. Then, by rotating the lever 10 counterclockwise against the frictional force with the friction member 12 and the force of the torsion spring 8, the shutter trailing blade actuation mechanism (driving lever 7, actuation arms 6 and 6 ′) is rotated. , The blades 5a to 5d) are started to be braked. At this time, the position of the rear blade is such that the outer end surface of each blade facing the opening end surface 1b of the blades 51 to 54 has the opening 1
It is in a. If the brake contact starts, the braking roller 7a
If the vibration of the blade working arm 6'following the vibration due to the impact transmitted through the (braked portion) 7a, the drive lever 7 and the blade working arm 6 and the traveling of the blade is large, the blade, particularly the slit forming blade, undulates. When the blade travels toward the opening end face 1b as it is, the blade collides with the opening end face 1b of the shutter base plate 1 or the opening end face of another base plate having substantially the same shape and is damaged. Further, if the initial braking is insufficient and an attempt is made to make a sudden braking in the final stage, a shock is applied to the link joint of the blade mechanism, and the link joint is broken earlier.

However, in this embodiment, when braking is started, the contact point and the braking roller 7 provided on the drive lever 7 are
Therefore, the braking roller 7a receives a braking load that linearly increases due to an increase in the lever ratio of the distance between the rotation center a and the center of rotation of the brake lever 10 and an increase in the contact angle (pressure angle) at the contact point. While sliding the cam portion 10a formed on the brake lever 10 to the position shown in FIG. 2, the brake is gradually braked so that the rear blade does not give a sudden impact force at a predetermined position. To stop.

In the above structure, as shown in FIGS. 4 and 5, the frictional force of the brake is the brake levers 10 and 10 '.
And the lower fixing plate 13 and the lower fixing plate 13 and the flat portion 9′a of the shaft 9 ′, which are not rotatable about the shafts 9 and 9 ′. It can be adjusted to a fixed value by sandwiching the ring 11 and changing the height dimension of the ring 11 and changing the pressing force of the leaf spring 15 to fix the ring 11, and a member group that rotates around the shafts 9 and 9 '. Since the pressure adjusting member group is separated by the upper fixing plates 14 and 14 'which are non-rotatably provided around the shafts 9 and 9', the fastening amount of the fastening means 16 can be adjusted and fixed. It is possible to adjust the brake friction force to a substantially constant value. Further, it is possible to change the frictional force during braking by changing the tightening amount during braking by interlocking the fastening means with the brake lever or the drive lever.

As described above, according to the embodiment, the braked portion of the drive lever 10 is constituted by the roller 7a, and the position of the rotation center of the brake lever 10 is arranged on the operation locus of the roller 7a, and the brake is applied. Roller 7 which is the braked portion of lever 10
At the beginning of the braking range of the drive lever 7, the contact portion with a is composed of a curve having a center of curvature on the roller 7a side and a straight line connecting these curves smoothly with the contact point tangent line in between, and contacts until the end of the middle stage until stop. The sliding cam is composed of a curve having a center of curvature on the brake member side and a straight line connecting the curves smoothly with the contact point tangent interposed, and the initial cam and the cams in the middle stage or later connect the curves with tangents. Since it is composed of straight and smoothly connected cams, a relatively weak braking force is applied before the slit forming edge reaches the edge of the exposure opening near the end of travel of the shutter blades, and continuous braking is provided from the beginning of braking. The braking force was gradually increased at almost the same rate of change so that sufficient braking force was obtained at the end of braking (the braking load diagram shown in FIG. 10) was obtained, so the impact on the shutter blades was extremely reduced. , Braking wings Deformation is less of. This allows
It is possible to remarkably improve the durability of the shutter blade and prevent the edge of the rear blade of the shutter from being damaged by the edge of the opening colliding with the edge of the opening. Also,
Since the brake can be arranged in a space where the rotation center position of the brake cannot be provided conventionally, the space of the shutter can be saved.

If the brake device of the present invention is adopted, it is possible to use an ultra-light shutter blade made of a plastic material, and the driving force can be reduced thereby, so that the load at the time of charging can be reduced. It is possible to realize a shutter that can be obtained at high speed without increasing the size.

[Brief description of drawings]

FIG. 1 is a plan view of a brake device for a shutter according to a first embodiment of the present invention, showing a shutter charge state.

FIG. 2 is a plan view of the brake device for a shutter according to the first embodiment of the present invention, showing a state after the traveling of the shutter is completed.

FIG. 3 is a plan view of the brake device for a shutter according to the first embodiment of the present invention, showing a state when the brake is in contact while the shutter is traveling.

4 is a cross-sectional view around the front brake shaft in FIG.

5 is a cross-sectional view around the rear brake shaft in FIG.

FIG. 6 is a diagram for obtaining a locus of a cam surface of the brake lever of FIG.

FIG. 7 is a partial plan view showing details of the trailing blade brake of FIG. 1, showing an initial operation state.

8 is a partial plan view showing details of the trailing blade brake of FIG. 1, showing a mid-operation state. FIG.

9 is a partial plan view showing details of the trailing blade brake of FIG. 1, showing an operation stopped state.

10 is a diagram showing an operation curve of the drive lever of the embodiment of FIG.

FIG. 11 is a plan view showing a conventional brake device for a shutter.

FIG. 12 is a plan view showing details of a conventional brake lever.

FIG. 13 is a braking curve diagram of a conventional drive lever.

[Explanation of symbols]

1 ... Base plate 2, 5 ... Shutter blade 3, 3 ', 6, 6' ... Blade operating arm 4, 7 ... Shutter drive arm 8, 8 '... Brake return spring 9, 9' ... Brake shaft 10, 10 '... Brake Lever 11 ... Brake spring guide 12 ... Friction member 13 ... Lower fixing plate 14, 14 '... Upper fixing plate 15 ... Leaf spring 16 ... Tightening member 17 ... Set lever shaft 17a ... Set lever shaft 17b ... Set lever return spring 18, 18 '... Brake stopper 18a, 18'a ... Brake stopper shaft

Claims (3)

[Claims] 1. A shutter actuating member that rotates integrally with a shutter member composed of a plurality of divided blades that travels for exposure, and a cam surface that abuts against a braked portion of the actuating member. A brake actuating member that generates a braking force by being rotationally pushed in the direction opposite to that of the actuating member when it comes into contact with the actuating member, and the rotation center of the brake actuating member is Within the range of the virtual extension locus of the movement locus of the braking portion, and within the range from the braking stop position of the member to be braked to the position approximately twice the braking operation angle, the center of rotation of the shutter operation member is the center. It is provided in the vicinity of an intersection of a circle having a radius at an intermediate point of the contactable range of the braked member and an angle line obtained by adding a brake operation angle from the angle line of the stop position of the braked member. Shutter shutter device 2. The cam surface of the brake actuating member according to claim 1, wherein the cam portion at the initial stage of the braking range of the shutter actuating member has a center of curvature on the braked member side of the actuating member with a tangent line of the contact point interposed therebetween. A curved portion having a curved portion and a straight portion smoothly connecting the curved portions, and a cam portion that abuts and slides from the middle stage to the end stop has a center of curvature on the braking member side across the contact rolling tangent line and this curved line And a cam portion in the middle of the braking range and the cam portions in the middle and later stages are smoothly connected by a straight line connecting tangents to each other. 3. The brake device for a shutter according to claim 1, wherein the member to be braked is constituted by friction or stabilizing means that makes rolling contact with a cam surface of the brake operating member.