Abstract:
In a cam actuated brake, an adjustable cam disposable intermediate a pair of following surfaces on first ends of a pair of arms. The arms being rotatable about parallel axes and having a pair of opposing brake surfaces at second ends. The cam comprises a body having a first and second opposite cam surfaces adapted to engage the following surfaces and a bore intermediate the cam surfaces and a piston receivable in the bore. The piston is releasably coupled to the bore. The cam further comprises an adjuster for varying the position of the piston in the bore. The piston may be engaged by an actuator so as to wedge the cam between the following surfaces of the arms so as to rotate the first and second arms about their respective axes thereby frictionally engaging an object between the braking surfaces.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates generally to brakes and in particular to an apparatus for adjusting a cam actuated brake. 
         [0003]    2. Description of Related Art 
         [0004]    Brakes for rotating disks are well known. A common brake for such disks is known as a caliper brake. A caliper brake provides a pair of brake pads disposed on either side of the rotating disk. Each brake pad may be attached to an arm at a proximate end. The arms are rotatable about an intermediate axis and actuated by an actuator between the distal ends thereof. 
         [0005]    An example of a cam actuated caliper brake assembly is shown in U.S. Pat. No. 4,121,697 to Kobelt et. al. the entirety of which is incorporated herein by reference. U.S. Pat. No. 4,212,697 to Kobelt et al. provides a wedge or cam between a pair of followers on the distal ends of the arms. 
         [0006]    A present difficulty with disk brakes arises due to wear of the brake pads. As the brake is used, the brake pads are worn or abraded away. As the thickness of the brake pads is reduced due to wear, the arms of the caliper brake are required to pivot through a greater angle to cause the brake pads to contact the disk. The actuator is therefore required to displace the distal ends of the arms by a greater distance. In the case of a cam actuated caliper brake assembly, the wedge or cam will be required to be displaced by a greater distance by the actuator. Unfortunately, many actuators in use for brakes typically have a relatively short stroke due to the primary design considerations being applicable force and modulation as opposed to stroke length. 
         [0007]    In addition, many actuators have a spring return or release whereby the actuator returns to a fully retracted position when the brake is not being applied. In cam actuated brakes, such as in U.S. Pat. No. 4,212,697 to Kobelt et al., the retraction of the actuator may cause the wedge or cam to be retracted from engagement upon the following surfaces. In this retracted position, the contact surfaces between the following surfaces and the wedge or cam may become fouled or misaligned from each other. 
         [0008]    One solution to the problem of brake pad wear is to provide an actuator having a longer stroke. While this solution will enable the brake pads to contact the disk over a larger range of brake pad wear, this solution will not prevent the disengagement of the wedge or cam from the cam followers. Such actuators may also be more expensive than those traditionally used and suffer from deficiencies in applicable force and modulation. 
         [0009]    Another solution is to provide a link with an adjustable length between the actuator and the wedge or cam. The length of such a link may be adjusted so as to remove any slack caused by brake pad wear. Such an adjustable link requires that the length be adjusted periodically so as to ensure proper operation of the brake. The process of adjusting such a link, however, requires that the brake not be in operation during the time of the adjustment. Because the brake may be used as an emergency safety device in some operations, this will require that all of the surrounding equipment similarly be stopped during the adjustment. The resulting shutdown time may be quite expensive in some industries, such as, for example, oil drilling. 
         [0010]    What is desirable is an adjusting cam actuated brake assembly that may be rapidly adjusted to compensate for brake pad wear. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides an adjustable cam actuated brake assembly that may be rapidly adjusted to compensate for brake pad wear. 
         [0012]    According to a first embodiment of the present invention there is provided a brake actuating cam disposable intermediate a pair of following surfaces on first ends of a pair of arms. The arms are rotatable about parallel axes and have a pair of opposing brake surfaces at second ends. The cam comprises a body having first and second opposite cam surfaces adapted to engage the following surfaces and a bore intermediate the cam surfaces. The cam further comprises a piston receivable in the bore, the piston being releasably coupled to the bore and an adjuster for varying the position of the piston in the bore. The piston may be engaged by an actuator so as to wedge the cam between the following surfaces of the arms so as to rotate the first and second arms about their respective axes thereby frictionally engaging an object between the braking surfaces. 
         [0013]    According to a further embodiment of the present invention there is provided a brake apparatus. The apparatus comprises a pair of opposed arms rotatable about parallel axes having first and second ends. The first ends are adapted to be coupled to opposing brake pads to brake a disk therebetween. The second ends have cam following surfaces. The apparatus further comprises an actuated cam disposed intermediate the cam following surfaces. The cam comprises a body having first and second opposite cam surfaces for engaging the cam following surfaces and a bore intermediate the cam surfaces. The cam further comprises a piston receivable in the bore, the piston being releasably coupled to the bore. The cam further comprises an adjuster for varying the position of said piston in said bore. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In drawings which illustrate embodiments of the invention, 
           [0015]      FIG. 1  is a plan view of a first embodiment of an exemplary brake assembly according to the present invention; 
           [0016]      FIG. 2  is a side elevation view of the brake assembly of  FIG. 1 ; 
           [0017]      FIG. 3  is a rear elevation view of the brake assembly of  FIG. 1 ; 
           [0018]      FIG. 4  is a cross sectional view of the brake assembly of  FIG. 1  taken along the line  4 - 4  in  FIG. 3 ; and 
           [0019]      FIG. 5  is a cross sectional view of the wedge of  FIG. 4  taken along the line  5 - 5  of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring to  FIG. 1 , a brake assembly according to a first embodiment of the invention is shown generally at  10 . The brake assembly  10  comprises a frame  12 , supporting a pair of arms  30  and an actuator  80 . The frame  12  comprises a body having a pair of spaced pivots  14  pivotally supporting the arms  30 . 
         [0021]    The arms  30  comprise elongated members having first and second ends  32  and  34 , respectively. Arms  30  are rotatably connected to the frame  12  at pivots  14 . The arms support a brake pad assembly  36  at each first end  32 . The brake pad assemblies include brake pads  38  having brake pad surfaces  40  disposed adjacent and opposite each other to form a passage  42  therebetween. The passage may receive a disk brake (not shown) or other object to be braked or retained. 
         [0022]    Referring now to  FIG. 2 , a side elevation view of the brake apparatus is shown in which the second ends  34  of the arms  30  have a cam following assembly  60 . In the embodiment shown in  FIG. 2 , the arms  30  are forced from first upper and second lower arm portions  44  and  46 , respectively. The second ends  34  of the first and second arm portions  44  and  46  each include a bore  48  able to receive a roller pin  50 . The roller pin  50  is received within a coaxial bore  68  in cam following assembly  60  so as to rotatably connect the cam following assembly to the second end  34  of the arms  30 . 
         [0023]      FIG. 3  shows a rear elevation view of the brake assembly. Cam following assembly  60  comprises a body having a first axis of rotation defined by the roller pin  50 , includes a cam follower or roller  62 . Roller  62  comprises a cylindrical body rotatably connected to the cam following assembly  60  about an axis perpendicular to the first axis. The second ends  34  of the two arms  30  are further biased towards each other by means of springs  64  and  66 . 
         [0024]    The actuator  80  is connected to the frame  12  and includes an actuator rod  82  driving a cam or wedge  84  disposed about the actuator axis  86 . The actuator axis is in planar alignment with the rollers  62  such that the wedge  84  is disposed between the rollers  62 . The cam or wedge  84  comprises a wedge shaped body having first and second angularly disposed cam surfaces  88  and  90 , and a proximate and distal end  92  and  94 , respectively. The first and second cam surfaces are oriented such that they are closer together at the distal end  94  of the wedge than at the proximate end  92 . 
         [0025]    Referring now to  FIG. 4 , a cross sectional view of the cam or wedge  84  is shown taken along line  4 - 4  of  FIG. 3 . The wedge further includes a pair of retaining pins  98  and a central bore  96  coaxial with the actuator axis  86 . The retaining pins  98  are received in opposed transverse slots  102  in the wedge  84 . Slots  102  extend perpendicularly to the central bore  96 . The central bore contains a notched piston  110  moveable longitudinally within in the bore. The notched piston includes a plurality of notches  112  on opposite longitudinal sides oriented so as to be engagable by retaining pins  98 . The retaining pins  98  are biased toward central bore  96  and notches  112  by springs  106 . The retaining pins may also include retraction pins  114 . The retraction pins may be grasped by a user to retract the retaining pins  98  out of engagement with the notches  112  on the notched piston  110 . 
         [0026]    Referring now to  FIG. 5 , a longitudinal cross sectional view of the wedge  84  and notched piston  110  is shown taken along line  5 - 5  of  FIG. 4 . As described above, the notched piston  110  is received within bore  96  in the wedge  84  and includes first and second ends  124  and  126 , respectively. The retaining pins  98  are received within opposed, transverse slots  102  and biased against the notches  112  in the notched piston. The notched piston is connected to actuator rod  82  and has a substantially cylindrical shape wherein the notches  112  are disposed on opposite sides of the notched piston. The notched piston also includes semi-circular side regions  118  which are substantially complementary with the shape of the bore  96 . 
         [0027]    The notches  112  include a retaining surface  120  and an advancing surface  122 . The retaining surface  120  is substantially parallel to the retaining pins  98 . The advancing surface  122  comprises a planar surface extending between an inside edge  128  of an retaining surface to the outside surface of the notched piston  110  at a position towards the second end  126  of the notched piston relative to the retaining surface  120 . The retaining pins  98  include retaining surfaces  130  corresponding to the retaining surface of the notches  112 . The retaining pins  98  also include advancing surface  132  corresponding to the advancing surfaces  122  of the notches  112 . 
         [0028]    The bore  96  includes a bottom surface  100  and a fluid supply port  104 . The fluid supply port may be threaded so as to accept a threaded supply line and is operable to supply a fluid supply to the bottom of the bore  96 . The second end  126  of the notched piston  110  includes a sealing means  134  such as for example an O-ring disposed around the notched piston proximate to the second end  126 . The second end  126  of the notched piston  110  and the bottom surface  100  of the bore  96  co-operate to form a chamber  136  for receiving the fluid supply. 
       Operation 
       [0029]    Referring  FIGS. 1-3 , in operation, when the brake apparatus is required to brake the disk in passage  42 , the actuator  80  is supplied with an actuation signal such as for example, a hydraulic, pneumatic, or electrical signal. The actuator  80 , in response to the actuation signal, displaces the actuator rod  82  and the cam or wedge  84  towards the following rollers  62 . As the wedge is driven between the rollers  62 , the rollers and thereby the following assemblies  60  are forced apart by the first and second cam surfaces  88  and  90 . The outward movement of the cam following assemblies  60  correspondingly rotates the second ends  34  of the arms  30  outwardly about the pivots  14 . The rotation of the arms about pivots  14  causes the first ends  32  and thereby the brake pad assemblies to be displaced towards each other to narrow the width of the passage  42 . After a sufficient movement of the brake pads  38 , the brake pad surfaces  40  will frictionally engage the disk therebetween to provide a braking force to the disk. 
         [0030]    Now referring to  FIG. 4 , the actuating movement of the actuator rod  82  is transmitted to the wedge  84  through the notched piston  110 . As the notched piston  110  is moved towards the following rollers  62 , the retaining surfaces  120  of the notched piston bear against the corresponding retaining surfaces  130  of the retaining pins  98 . The retaining pins are further held in engagement in the notches  112  by the springs  106 . 
         [0031]    When the disk pad have become worn or abraded such that adjustment of the brake apparatus is necessary, a pressurized fluid supply is provided to the fluid supply port  104  and thereby into the chamber  136 . The fluid in the chamber  136  will displace the notched piston  110  relative to the wedge  84  out of the bore  96 . The advancing surfaces  122  of the notched piston  110  will cause the advancing surfaces  132  of the retaining pins to retract the retaining pins against the springs  106 . When a sufficient displacement of the notched piston has been achieved, the retaining pins  98  will be engaged in the next pair of successive notches  112  and the slack in the brake assembly will be reduced. 
         [0032]    When new brake pads  38  are to be supplied to the brake apparatus, the brake apparatus will need to be returned to an initial position. The retraction pins  114  may be grasped by a user and pulled away from each other so as to retract the retaining pins  98  into the slots  102 . The retaining surfaces  130  of the retaining pins  98  will then be disengaged from retaining surfaces  120  of the notches  112 . The notched piston  110  may then be displace within bore  96  towards the bottom surface  100  so as to return the brake apparatus to an initial position. 
         [0033]    In an alternative embodiment, the notched piston  110  may be rotated, such that the retaining pins  98  are caused to be displace out of the notches  112  and onto the side regions  118  of the notched piston  110 . When the retaining pins are retracted by the side regions  118  and no longer in engagement with the notches  112 , the notched piston may be displaced with the bore  96  towards the bottom surface  100  so as to return the brake apparatus to an initial position. It will be appreciated that in this alternative embodiment, the retraction pins  114  are not necessary. 
         [0034]    While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.