Abstract:
A disc brake which is particularly designed for arcuate travel of less than 360 degrees has pie shaped segments, i.e. segments which are not complete circles which are interleaved. Some segments are rotatable about an axis and others are stationary and have friction brake material carried on them at a position remote from the axis of rotation.

Description:
BACKGROUND OF INVENTION 
   This invention relates to electromagnetically actuated mechanical brakes, and more particularly, to such brakes arranged in interleaved stacks. 
   In the prior art, electromagnetically actuated mechanical brakes having multiple discs are known. These may be operated as follows: normally the discs are forced together by a spring. When current is applied, an armature is attracted toward a magnetic body, thereby compressing the spring and releasing the discs; thus allowing them to be rotated. When current is discontinued to the coil, the spring pushes the armature into engagement with the discs, forcing them together to stop the movement of the load. Thus the device holds the load with the power off. 
   The discs are complete circles and are generally acted upon by a centrally disposed spring and armature. This configuration is both bulky and heavy. For example, a 360 degree brake to produce 90 foot pounds of torque would have a diameter of approximately 7 inches and weigh approximately 30 pounds. 
   It is desirable to make such breaks lighter and more compact; so that they can fit into small mechanical devices. 
   SUMMARY OF INVENTION 
   I have invented a new and improved disc brake which is particularly designed for arcuate travel of less than 360 degrees. In such devices, I use segments of discs which segments are not complete circles. I interleave these disc segments. Some segments are rotatable about an axis and have friction brake material carried on them at a position remote from the axis of rotation. 
   I have also invented such a brake wherein some segments have holes there through to make them lighter. Also, I provide friction material on some segments which material is circular in plan view. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of parts of one embodiment of my invention; 
       FIG. 2  is a side elevation of the parts shown in  FIG. 1 , reoriented to the vertical and assembled with additional parts; 
       FIG. 3  is a section of an electromagnetically actuated armature and spring assembly of my device (as shown in  FIG. 2 ), shown mounted to a frame; 
       FIG. 4  is a plan view of an inner disc segment shown in the prior figures; 
       FIG. 5  is a plan view of an outer disc segment assembly shown in the prior figures; and 
       FIG. 6  is an enlarged cross section of a portion of the outer disc assembly shown in  FIG. 5 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the figures,  FIG. 1  shows a plurality of pie shaped segments of discs. A plurality of these are arranged in an interleaved disc pack designated generally  10 ,  FIG. 2 . The inner disc segments  12  are spaced from the outer disc segments  14  by spacers  16 . All are arranged about a shaft  20 . The inner disc segments  12  rotate with the shaft. The outer disc segments are stationary. In operation, the shaft is mounted in a working device (not shown in greater detail) for movement with a portion thereof. 
   A electromagnetically actuated armature and spring assembly is designated generally  18 . The armature  26  engages the disk pack  10 . This is shown in elevation in  FIG. 2  and in section in  FIG. 3 . It comprises an outer body  22 , a coil  24 , an armature  26  and a spring  28 . The outer body  22  is designed to be fixedly mounted to the frame  30  of the working device (referred to above). 
   An inner disc segment  12  is shown in  FIG. 4  and has a plurality of holes  32  there through to make it lighter in weight without sacrificing its strength. The material may be hard anodized aluminum to reduce wear. 
   The outer disc segment  14  is fixedly mounted on the working device as at  34 . It has a plurality of holes  36  there through to make it lighter in weight without sacrificing its strength. The material may be clear anodized aluminum. The segment  14  carries a disc friction puck  40  on each side (see  FIG. 6 ) positioned near the end remote from the shaft  20 . These pucks are, most preferably, retained by adhesive on the surface of the disc segments; but may also be retained by any suitable means, such as, molding in place or riveting. 
   In operation, the spring  28  exerts a force against the armature  26  which engages and exerts a force upon the disc pack  10  to force the interleaved disc segments toward one another and engage the other friction pucks  40 . This is the normal at-rest condition in which the brake is locked. When an electricity is applied to the electromagnet, the armature  26  retracts against the spring  28  and compresses it, thereby allowing the segments to move. This allows repositioning of the working device. 
   Breaking action is a function of the number of pucks, the coefficient of friction of the puck material, the spring force and the moment arm between the axis of rotation (at the shaft  20 ) and the radial position of the puck on the disc segment. 
   In one embodiment of my invention, the inner disc segments  12  can be rotated 15 degrees in each direction for a total travel of 30 degrees. The brake is stopped by mechanical stops in the working device which limit the travel of the brake. The surface area identified generally as “A” in  FIG. 1 , must be sufficient to engage the pucks a various positions throughout the expected range of travel of the discs. While 30 degrees is preferable for some devices, it will be understood that this invention may be applied to other ranges (more or less than 30 degrees) for working devices such as x-ray machines, CT scanners, MRI&#39;s, ultrasound apparatuses and the like. But for 30 degrees, in the example given above, my arc brake would be 5 inches (as opposed to 7 inches) and the weight would be 1.1 pounds (rather than 30 pounds) for 90 foot pounds of torque. 
   Although this design is for a normally off device, it will be understood that it can also be operated as a power on brake or a bi-stable pulse operated brake.