Patent Publication Number: US-7587956-B2

Title: Device for controlling motion

Description:
FIELD OF THE INVENTION 
   This invention relates generally to a motion control device, and more particularly to a device for controlling motion of an object. 
   BACKGROUND OF THE INVENTION 
   Devices for controlling motion of an object have many useful applications. One application for a control device is as a recline mechanism for backrests in aircraft seats as well as other seats. In aircraft seats, recline mechanisms are currently limited to implementation by hydraulic or pneumatic cylinders. 
   A second application is in aircraft seat leg systems. Aircraft seats must have the ability to be attached to a distorted floor and still stay in place in the aircraft cabin. This distortion of the floor can cause distortion of the seat frame and consequently, failure of the seat design. The control device can be used to accommodate distortion of the floor so that the seat frame can adapt as required and still pass the FAA tests. 
   It is an object of the present invention to provide a device for controlling motion of an object using a mechanical control in the above-mentioned situations and other situations where continuous adjustability using a mechanical control is desirable. 
   SUMMARY OF THE INVENTION 
   In an aspect of the present invention, a device for controlling motion of an object includes a housing defining a first cavity and a second cavity each extending from a first longitudinal end to a second longitudinal end of the housing. The housing includes a partition separating the first cavity and the second cavity. A first sliding (controlled) member is movable within the first cavity. The first sliding (controlled) member includes a first extension extending outwardly from the first longitudinal end of the housing for being attached to an object whose movement is to be controlled. A second sliding (controlling) member is movable within the second cavity. The second sliding (controlling) member includes a second extension extending outwardly from one of the first and second longitudinal ends of the housing for being pulled a variably controlled distance away from the housing. A motion limiting member, such as a circular member which can be, for example, spherical or cylindrical, communicates with the first sliding (controlled) member and the second sliding (controlling) member such that movement of the second extension of the second sliding (controlling) member the variably controlled distance in a direction away from the housing causes the first extension of the first sliding (controlled) member to be movable the variably controlled distance in a direction in which the second sliding (controlling) member is pulled. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a cross-sectional, side elevation view of a motion control device in accordance with the present invention. 
       FIG. 1B  is an end view of the motion control device of  FIG. 1A  taken along the line A-A. 
       FIG. 1C  is an end view of the motion control device of  FIG. 1A  taken along the line B-B. 
       FIG. 2A  is a cross-sectional, side elevation view of the motion control device of  FIG. 1A  in a fully extended position. 
       FIG. 2B  is a cross-sectional, side elevation view of the motion control device of  FIG. 1A  in a midpoint position. 
       FIG. 2C  is a cross-sectional, side elevation view of the motion control device of  FIG. 1A  in a fully retracted position. 
       FIG. 3A  is a plan view of a controlled member of a motion control device in accordance with the present invention. 
       FIG. 3B  is a side elevation view of the controlled member of  FIG. 3A . 
       FIG. 3C  is a perspective view of the controlled member of  FIG. 3A . 
       FIG. 4A  is a cross-sectional, side elevation view of a motion control device in accordance with a second embodiment of the present invention. 
       FIG. 4B  is an end view of the motion control device of  FIG. 4A  taken along the line A-A. 
       FIG. 4C  is an end view of the motion control device of  FIG. 4A  taken along the line B-B. 
       FIG. 5A  is a cross-sectional, side elevation view of the motion control device of  FIG. 4A  in a fully retracted position. 
       FIG. 5B  is a cross-sectional, side elevation view of the motion control device of  FIG. 4A  in a midpoint position. 
       FIG. 5C  is a cross-sectional, side elevation view of the motion control device of  FIG. 4A  in a fully extended position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 1-3 , a motion control device embodying the present invention is indicated generally by the reference number  10 . The device comprises a housing  12  defining a first cavity  14  accommodating a first sliding (controlled) member  16  for movement therealong, and a second cavity  18  accommodating a second sliding (controlling) member  20  for movement therealong. The first sliding member  16  serves as a controlled member, and the second sliding member  20  serves as a controlling member. The housing  12  includes a projection  22  such as a mounting lug for attaching the housing to an external support  24 . The first sliding member  16  includes a first extension  26  projecting outwardly from a first longitudinal end  28  of the housing  12  for attaching the first sliding member to an object  30  whose movement is to be controlled. The second sliding member  20  has a second extension  32 , such as a cable or rod extending outwardly from a second longitudinal end  34  of the housing  12  for controlling the movement of the object  30  as explained more fully below. As shown in  FIGS. 1B and 1C , the first and second sliding members  16 ,  20  and associated first and second cavities  14 ,  18  are round or circular in cross-section, but can be square, rectangular or other practical shapes without departing from the scope of the present invention. 
   The first cavity  14  and the second cavity  18  each extend longitudinally within the housing  12  and in parallel relation to one another generally from the first longitudinal end  28  to the second longitudinal end  34 . The housing  12  includes or accommodates a partition  36  generally extending from the first longitudinal end  28  to the second longitudinal end  34  of the housing  12 . The partition  36  generally separates the first cavity  14  and the second cavity  18 . The first cavity  14  is more specifically defined by a first side  38  of the partition  36  and an opposing inner side  40  of the housing  12 . Likewise, the second cavity  18  is more specifically defined by a second side  42  of the partition  36  and an opposing inner side  44  of the housing  12 . As shown in  FIGS. 1-3 , the first side  38  and the second side  42  of the partition  36  face opposite directions relative to each other. 
   The partition  36  defines an opening  46  between the first cavity  14  and the second cavity  18  disposed about longitudinally midway between the first longitudinal end  28  and the second longitudinal end  34  of the housing  12 . As shown in  FIGS. 1-3 , the opening  46  is disposed closer to the first longitudinal end  28  relative to the second longitudinal end  34 . Alternatively, the opening  46  can be disposed midway between the first longitudinal end  28  and the second longitudinal end  34 , or be disposed closer to the second longitudinal end  34  relative to the first longitudinal end  28  without departing from the scope of the present invention. 
   The first sliding member  16  generally defines an outer surface  48  shaped for abutting against and being guided by the first side  38  of the partition  36  and the opposing inner side  40  of the housing  12 . Likewise, the second sliding member  20  generally defines an outer surface  50  shaped for abutting against and being guided by the second side  42  of the partition  36  and the opposing inner side  44  of the housing  12 . The outer surface  48  of the first sliding member  16  has a longitudinal portion defining a first recess  52  relative to and facing the first side  38  of the partition  36 . Likewise, the outer surface  50  of the second sliding member  20  has a longitudinal portion defining a second recess  54  relative to and facing the second side  42  of the partition  36 . 
   As best shown in  FIGS. 3A through 3C , the portion of the outer surface  48  defining the first recess  52  is generally J-shaped as seen in cross-section and includes a straight portion  56  and a curved portion  58  as seen in a direction from the first longitudinal end  28  to the second longitudinal end  34  of the housing  12 . The straight portion  56  defines an inclined plane relative to the first side  38  of the partition  36 . A portion of the outer surface  48  of the first sliding member  16  facing the partition  36  and forming the straight portion  56  or inclined plane is directed away from the first side  38  of the partition  36  in a direction from the first longitudinal end  28  to the second longitudinal end  34  of the housing  12 . A portion of the outer surface  48  of the first sliding member  16  facing the partition  36  and forming the curved portion  58  is directed toward the first side  38  of the partition  36  in a direction from the first longitudinal end  28  to the second longitudinal end  34  of the housing  12 . 
   The portion of the outer surface  50  defining the second recess  54  is generally J-shaped and includes a straight portion  60  and a curved portion  62  as seen in a direction from the second longitudinal end  34  to the first longitudinal end  28  of the housing  12 . The straight portion  60  defines an inclined plane relative to the second side  42  of the partition  36 . A portion of the outer surface  50  of the second sliding member  20  facing the partition  36  and forming the straight portion  60  or inclined plane is directed away from the second side  42  of the partition  36  in a direction from the second longitudinal end  34  to the first longitudinal end  28  of the housing  12 . A portion of the outer surface  50  of the second sliding member  20  facing the partition  36  and forming the curved portion  62  is directed toward the second side  42  of the partition  36  in a direction from the second longitudinal end  34  to the first longitudinal end  28  of the housing  12 . As shown in  FIGS. 1-3 , the inclined planes  56 ,  60  defined by the first and second sliding members  16 ,  20  extend in a parallel direction relative to each other. 
   A motion limiting member  64  such as, for example, a circular member as shown in  FIGS. 1-3 , is disposed within the opening  46  of the partition  36 . The motion limiting member  64  protrudes at one end into the first recess  52  and abuts the outer surface  48  of the first sliding member  16  forming the straight portion  56  and the curved portion  58 . Likewise, the motion limiting member  64  protrudes at an opposite end into the second recess  54  and abuts the outer surface  50  of the second sliding member  20  forming the straight portion  60  and the curved portion  62 . The partition  36  prevents the motion limiting member  64  from moving in a longitudinal direction with the sliding members  16 ,  20 . As a result, the motion limiting member  64  is limited to movement through the opening  46  and in a direction perpendicular to the direction of movement of the sliding members  16 ,  20 . 
   A resilient member  66  such as, for example, a compression spring is disposed between an inner side  68  of the housing  12  adjacent to the second longitudinal end  34  and an opposing longitudinal end  70  of the second sliding member  20  to urge a portion of the outer surface  50  defining the second recess  54  toward and against the motion limiting member  64  and to cause the motion limiting member to press against the first sliding (controlled) member  16  at the portion of the outer surface  48  defining the first recess  52  when there is no pulling force on the second extension  32  of the second sliding (controlling) member  20 . In effect, the resilient member  66  urges the inclined plane  60  of the second sliding (controlling) member  20  against the motion limiting member  64  which in turn pushes the other side of the motion limiting member into contact with the inclined plane  56  of the first sliding (controlled) member  16 . The motion limiting member  64  is thus wedged between the inclined planes  56 ,  60  so as to prevent the controlled member  16  from moving further beyond this controlled position toward the second longitudinal end  34  of the housing  12 . 
   As shown in  FIGS. 1-3 , a first end  72  of the first recess  52  is longitudinally aligned with a first end  74  of the second recess  54 . Likewise, a second end  76  of the first recess  52  is longitudinally aligned with a second end  78  of the second recess  54 . The surfaces defining the straight portion  56  and the curved portion  58  of the first sliding member  16 , and the surfaces defining the straight portion  60  and the curved portion  62  of the second sliding member  20  cooperate to form a slot or track in which the motion limiting member  64  moves relative to the track as explained more fully below. As seen in cross-section, the straight portion  56  of the first sliding member  16  extends in a direction parallel to the straight portion  60  of the second sliding member  20 . Moreover, the curved portions  58 ,  62  serve as stops for limiting the range of movement of the sliding members  16 ,  20  within the respective first and second cavities  14 ,  18 . For example, the curved portion  58  abuts against the motion limiting member  64  when the first sliding member  16  is in a fully extended position as shown in  FIG. 2A . 
   In operation, the device  10  restricts and allows the movement of the first sliding (controlled) member  16  by the positioning of the second sliding (controlling) member  20 . The motion of the first sliding member  16  can be controlled in one direction so as to provide step-less, continuously variable positioning as well as an arresting of motion. The second extension  32  is configured to be pulled either manually or by an external mechanism a predetermined controlled distance in a direction away from the housing  12 . For example, the second sliding (controlling) member  20  can be moved toward the second longitudinal end  34  of the housing. As the second sliding member  20  moves in the above-mentioned direction, the straight portion or inclined plane  60  of the second sliding (controlling) member  20  abutting the motion limiting member  64  moves away from the opposing surface of the straight portion or inclined plane  56  of the first sliding (controlled) member  16 . The first sliding member  16  is then able to be moved the controlled distance toward the second longitudinal end  34 . As the first sliding member  20  moves over the controlled distance, the straight portion or inclined plane  56  of the first sliding member  16  moves toward the opposing surface of the straight portion or inclined plane  60  of the second sliding member  20  until the motion limiting member  64  simultaneously contacts both straight portions  56 ,  60  of the sliding members  16 ,  20  so as to prevent the first sliding member  16  from moving beyond the controlled distance. If the first sliding member  16  is attempted to be moved beyond the controlled distance, the resilient member  66  forces the straight portion or inclined plane  60  of the second sliding (controlling) member  20  to press against the motion limiting member  64 , and the motion limiting member to in turn press against the straight portion or inclined plane  56  of the first sliding (controlled) member  16 . The motion limiting member  64  becomes wedged against the straight portions or inclined planes  56 ,  60  of the sliding members  16 ,  20  so as to prevent the first sliding member  16  from moving beyond the controlled distance. 
   The first sliding (controlled) member  16  is generally permitted to be moved or returned in a direction toward the first longitudinal end  28  of the housing  12 . As the first sliding member  16  is moved in a direction toward the first longitudinal end  28 , the straight portion  56  of the first sliding member  16  moves away from the opposing surface of the straight portion or inclined plane  60  of the second sliding member  20 . The resilient member  66  pushes against the opposing end  70  of the second sliding member  20  so as to urge the second sliding member  20  toward the first longitudinal end  28  of the housing  12 . The straight portion  60  of the second sliding member  20  contacting the motion limiting member  64  moves toward the opposing surface of the straight portion or inclined plane  56  of the first sliding member  16  until the motion limiting member  64  contacts and wedges against the opposing surface. 
   In sum, any force applied to the device  10  in a direction that would move the extensions  26 ,  32  of the sliding members  16 ,  20  into the housing  12  and toward each other forces the combination of the inclined planes  56 ,  60  and the motion limiting member  64  to wedge in the housing. This wedging restricts relative motion between the parts of the device  10  and provides a positive locking action. If a force is then applied to the device  10  that would move the extensions  26 ,  32  of the sliding members  16 ,  20  apart, the sliding members become freed in the housing  12  and relative motion between the sliding members is allowed. 
   The device  10  is ideal for providing positioning control by restricting movement of some other device or machine element. Typically the device  10  is mounted by attaching the housing  12  in an appropriate location and using the locked position of the second sliding (controlled) member  20  to prevent other elements or equipment attached to the first sliding (controlling) member  16  from moving beyond a certain point. Because the locked position is controllable, the device  10  can stop movement at intervals as needed or at predetermined intervals. As will be explained below, by using two controlling members mounted facing in opposite directions, bidirectional control can be provided. 
   With reference to  FIGS. 4 and 5 , a motion bidirectional control device in accordance with a second embodiment of the present invention is indicated generally by the reference number  100 . The device  100  comprises a housing  102  defining a first cavity  104  accommodating a first sliding (controlled) member  106  for movement therealong, a second cavity  108  accommodating a second sliding (controlling) member  110  for movement therealong, and a third cavity  112  accommodating a third sliding (controlling) member  114  for movement therealong. The first sliding member  106  serves as a controlled member, and the second and third sliding members  110 ,  114  serve as controlling members. The housing  102  includes a projection  116  such as a mounting lug for attaching the housing to an external support  118 . The first sliding member  106  includes a first extension  120  projecting outwardly from a first longitudinal end  122  of the housing  102  for attaching the first sliding member to an object  124  whose movement is to be controlled. The second sliding member  110  has a second extension  126 , such as a cable or rod extending outwardly from a second longitudinal end  128  of the housing  102  for controlling the movement of the object  124  in a first direction. The third sliding member  114  has a third extension  130 , such as a cable or rod extending outwardly from the first longitudinal end  122  of the housing  102  for controlling the movement of the object  124  in a second direction as explained more fully below. As shown in  FIGS. 4B and 4C , the first, second and third sliding members  106 ,  110 ,  114  and associated first, second and third cavities  104 ,  108 ,  112  are round or circular in cross-section, but can be square, rectangular or other practical shapes without departing from the scope of the present invention. 
   The first cavity  104 , the second cavity  108  and the third cavity  112  each extend longitudinally within the housing  102  and in parallel relation to one another generally from the first longitudinal end  122  to the second longitudinal end  128 . The housing  102  includes or accommodates a first partition  132  and a second partition  134  each generally extending from the first longitudinal end  122  to the second longitudinal end  128  of the housing  102 . 
   The first partition  132  generally separates the first cavity  104  and the second cavity  108 . The first cavity  104  is more specifically defined by a first side  136  of the first partition  132  and a first side  138  of the second partition  134 . The second cavity  108  is more specifically defined by a second side  140  of the first partition  132  and an opposing inner side  142  of the housing  102 . As shown in  FIGS. 4 and 5 , the first side  136  and the second side  140  of the first partition  132  face opposite directions relative to each other. 
   The second partition  134  generally separates the first cavity  104  and the third cavity  112 . As mentioned above, the first cavity  104  is more specifically defined by the first side  136  of the first partition  132  and the first side  138  of the second partition  134 . The third cavity  112  is more specifically defined by a second side  144  of the second partition  134  and an opposing inner side  146  of the housing  102 . As shown in  FIGS. 4 and 5 , the first side  138  and the second side  144  of the second partition  134  face opposite directions relative to each other. 
   The first partition  132  defines a first opening  148  between the first cavity  104  and the second cavity  108  and is disposed between the first longitudinal end  122  and the second longitudinal end  128  of the housing  102 . Similarly, the second partition  134  defines a second opening  149  between the first cavity  104  and the third cavity  112  and is disposed between the first longitudinal end  122  and the second longitudinal end  128  of the housing  102 . 
   The first sliding member  106  generally defines an outer surface  150  shaped for abutting against and being guided by the first side  136  of the first partition  132  and the first side  138  of the second partition  134 . Likewise, the second sliding member  110  generally defines an outer surface  152  shaped for abutting against and being guided by the second side  140  of the first partition  132  and the opposing inner side  142  of the housing  102 . Similarly, the third sliding member  114  generally defines an outer surface  154  shaped for abutting against and being guided by the second side  144  of the second partition  134  and the opposing inner side  146  of the housing  102 . The outer surface  150  of the first sliding member  106  has a longitudinal portion defining a first recess  156  relative to and facing the first side  136  of the first partition  132 . The outer surface  152  of the second sliding member  110  has a longitudinal portion defining a second recess  158  relative to and facing the second side  140  of the first partition  132 . Moreover, the outer surface  150  of the first sliding member  106  has a longitudinal portion defining a third recess  160  relative to and facing the first side  138  of the second partition  134 . The outer surface  154  of the third sliding member  114  has a longitudinal portion defining a fourth recess  162  relative to and facing the second side  144  of the second partition  134 . 
   The portion of the outer surface  150  defining the first recess  156  is generally J-shaped as seen in cross-section and includes a straight portion  164  and a curved portion  166  as seen in a direction from the first longitudinal end  122  to the second longitudinal end  128  of the housing  102 . The straight portion  164  defines an inclined plane relative to the first side  136  of the first partition  132 . A portion of the outer surface  150  of the first sliding member  106  facing the first partition  132  and forming the straight portion  164  or inclined plane is directed away from the first side  136  of the first partition  132  in a direction from the first longitudinal end  122  to the second longitudinal end  128  of the housing  102 . A portion of the outer surface  150  of the first sliding member  106  facing the first partition  132  and forming the curved portion  166  is directed toward the first side  136  of the first partition  132  in a direction from the first longitudinal end  122  to the second longitudinal end  128  of the housing  102 . 
   The portion of the outer surface  152  defining the second recess  158  is generally J-shaped and includes a straight portion  168  and a curved portion  170  as seen in a direction from the second longitudinal end  128  to the first longitudinal end  122  of the housing  102 . The straight portion  168  defines an inclined plane relative to the second side  140  of the first partition  132 . A portion of the outer surface  152  of the second sliding member  110  facing the first partition  132  and forming the straight portion  168  or inclined plane is directed away from the second side  140  of the first partition  132  in a direction from the second longitudinal end  128  to the first longitudinal end  122  of the housing  102 . A portion of the outer surface  152  of the second sliding member  110  facing the first partition  132  and forming the curved portion  170  is directed toward the second side  140  of the first partition  132  in a direction from the second longitudinal end  128  to the first longitudinal end  122  of the housing  102 . As shown in  FIGS. 4 and 5 , the inclined planes defined by the first and second sliding members  106 ,  110  extend in a parallel direction relative to each other. 
   The portion of the outer surface  150  defining the third recess  160  is generally J-shaped as seen in cross-section and includes a straight portion  172  and a curved portion  174  as seen in a direction from the second longitudinal end  128  to the first longitudinal end  122  of the housing  102 . The straight portion  172  defines an inclined plane relative to the first side  138  of the second partition  134 . A portion of the outer surface  150  of the first sliding member  106  facing the second partition  134  and forming the straight portion  172  or inclined plane is directed away from the first side  138  of the second partition  134  in a direction from the second longitudinal end  128  to the first longitudinal end  122  of the housing  102 . A portion of the outer surface  150  of the first sliding member  106  facing the second partition  134  and forming the curved portion  174  is directed toward the first side  138  of the second partition  134  in a direction from the second longitudinal end  128  to the first longitudinal end  122  of the housing  102 . 
   The portion of the outer surface  154  defining the fourth recess  162  is generally J-shaped and includes a straight portion  176  and a curved portion  178  as seen in a direction from the first longitudinal end  122  to the second longitudinal end  128  of the housing  102 . The straight portion  176  defines an inclined plane relative to the second side  144  of the second partition  134 . A portion of the outer surface  154  of the third sliding member  114  facing the second partition  134  and forming the straight portion  176  or inclined plane is directed away from the second side  144  of the second partition  134  in a direction from the first longitudinal end  122  to the second longitudinal end  128  of the housing  102 . A portion of the outer surface  154  of the third sliding member  114  facing the second partition  134  and forming the curved portion  178  is directed toward the second side  144  of the second partition  134  in a direction from the first longitudinal end  122  to the second longitudinal end  128  of the housing  102 . As shown in  FIGS. 4 and 5 , the inclined planes defined by the first and third sliding members  106 ,  114  extend in a parallel direction relative to each other. 
   A first motion limiting member  180  such as, for example, a circular member as shown in  FIGS. 4 and 5 , is disposed within the first opening  148  of the first partition  132 . The first motion limiting member  180  protrudes at one end into the first recess  156  and abuts the outer surface  150  of the first sliding member  106  forming the straight portion  164  and the curved portion  166 . Likewise, the first motion limiting member  180  protrudes at an opposite end into the second recess  158  and abuts the outer surface of the second sliding member  110  forming the straight portion  168  and the curved portion  170 . The first partition  132  prevents the first motion limiting member  180  from moving in a longitudinal direction with the first and second sliding members  106 ,  110 . As a result, the first motion limiting member  180  is limited to movement through the first opening  148  and in a direction perpendicular to the direction of movement of the first and second sliding members  106 ,  110 . 
   A second motion limiting member  182  such as, for example, a circular member as shown in  FIGS. 4 and 5 , is disposed within the second opening  149  of the second partition  134 . The second motion limiting member  182  protrudes at one end into the fourth recess  162  and abuts the outer surface  154  of the third sliding member  114  forming the straight portion  176  and the curved portion  178 . Likewise, the second motion limiting member  182  protrudes at an opposite end into the third recess  160  and abuts the outer surface  150  of the first sliding member  106  forming the straight portion  172  and the curved portion  174 . The second partition  134  prevents the second motion limiting member  182  from moving in a longitudinal direction with the first and third sliding members  106 ,  114 . As a result, the second motion limiting member  182  is limited to movement through the second opening  149  and in a direction perpendicular to the direction of movement of the first and third sliding members  106 ,  114 . 
   A first resilient member  184  such as, for example, a compression spring is disposed between an inner side  186  of the housing  102  adjacent to the second longitudinal end  128  and a longitudinal end  188  of the second sliding member  110  to urge the second sliding member toward and against the first motion limiting member  180  and to cause the first motion limiting member to press against the first sliding member  106  at the portion of the outer surface  150  defining the first recess  156  when there is no pulling force on the second extension  126  of the second sliding (controlling) member  110 . In effect, the first resilient member  184  urges the inclined plane  168  of the second sliding (controlling) member  110  against the first motion limiting member  180  which in turn pushes the other side of the first motion limiting member into contact with the inclined plane  164  of the first sliding (controlled) member  106 . The first motion limiting member  180  is thus wedged between the inclined planes  164 ,  168  so as to prevent the controlled member  106  from moving further beyond this controlled position toward the second longitudinal end  128  of the housing  102 . 
   A second resilient member  190  such as, for example, a compression spring is disposed between an inner side  192  of the housing  102  adjacent to the first longitudinal end  122  and a longitudinal end  194  of the third sliding member  114  to urge the third sliding member toward and against the second motion limiting member  182  and to cause the second motion limiting member to press against the first sliding (controlled) member  106  at the portion of outer surface  150  defining the third recess  160  when there is no pulling force on the third extension  130  of the third sliding (controlling) member  114 . In effect, the second resilient member  190  urges the inclined plane  176  of the third sliding (controlling) member  114  against the second motion limiting member  182  which in turn pushes the other side of the second motion limiting member into contact with the inclined plane  172  of the first sliding (controlled) member  106 . The second motion limiting member  182  is thus wedged between the inclined planes  172 ,  176  so as to prevent the controlled member  106  from moving further beyond this controlled position toward the first longitudinal end  122  of the housing  102 . 
   As shown in  FIGS. 4 and 5 , a first end  196  of the first recess  156  is longitudinally aligned with a first end  198  of the second recess  158 . Likewise, a second end  200  of the first recess  156  is longitudinally aligned with a second end  202  of the second recess  158 . The surfaces defining the straight portion  164  and the curved portion  166  of the first sliding member  106 , and the surfaces defining the straight portion  168  and the curved portion  170  of the second sliding member  110  cooperate to form a first slot or track in which the first motion limiting member  180  moves relative to the first track as explained more fully below. As seen in cross-section, the straight portion  164  of the first sliding member  106  extends in a direction parallel to the straight portion  168  of the second sliding member  110 . Moreover, the curved portions  166 ,  170  serve as stops for limiting the range of movement of the first and second sliding members  106 ,  110  within the respective first and second cavities  104 ,  108 . For example, the curved portion  166  abuts against the first motion limiting member  180  when the first sliding member  106  is in a fully extended position as shown in  FIG. 5C . 
   As shown in  FIGS. 4 and 5 , a first end  204  of the fourth recess  162  is longitudinally aligned with a first end  206  of the third recess  160 . Likewise, a second end  208  of the fourth recess  162  is longitudinally aligned with a second end  210  of the third recess  160 . The surfaces defining the straight portion  176  and the curved portion  178  of the third sliding member  114 , and the surfaces defining the straight portion  172  and the curved portion  174  of the first sliding member  106  cooperate to form a second slot or track in which the second motion limiting member  182  moves relative to the second track as explained more fully below. As seen in cross-section, the straight portion  176  of the third sliding member  114  extends in a direction parallel to the straight portion  172  of the first sliding member  106 . Moreover, the curved portions  174 ,  178  serve as stops for limiting the range of movement of the first and third sliding members  106 ,  114  within the respective first and third cavities  104 ,  112 . For example, the curved portion  174  abuts against the second motion limiting member  182  when the first sliding member  106  is in a fully extended position as shown in  FIG. 5C . 
   In operation, the device  100  restricts and allows the movement of the first sliding (controlled) member  106  by the positioning of the second sliding (controlling) member  110  or the third sliding (controlling) member  114 . The motion of the first sliding member  106  can be controlled in either direction so as to provide step-less, continuously variable positioning as well as an arresting of motion. The second extension  126  is configured to be pulled either manually or by an external mechanism a predetermined controlled distance in a direction away from the housing  102 . For example, the second sliding (controlling) member  110  can be moved toward the second longitudinal end  128  of the housing. As the second sliding member  110  moves in the above-mentioned direction, the straight portion or inclined plane  168  of the second sliding (controlling) member  110  abutting the first motion limiting member  180  moves away from the opposing surface of the straight portion or inclined plane  164  of the first sliding (controlled) member  106 . The first sliding member  106  is then able to be moved the controlled distance toward the second longitudinal end  128 . As the first sliding member  106  moves over the controlled distance, the straight portion or inclined plane  164  of the first sliding member  106  moves toward the opposing surface of the straight portion or inclined plane  168  of the second sliding member  110  until the first motion limiting member  180  simultaneously contacts both straight portions or inclined planes  164 ,  168  of the first and second sliding members  106 ,  110  so as to prevent the first sliding member  106  from moving beyond the controlled distance. 
   If the first sliding member  106  is attempted to be moved beyond the controlled distance, the first resilient member  184  forces the straight portion or inclined plane  168  of the second sliding (controlling) member  110  to press against the first motion limiting member  180 , and the first motion limiting member to in turn press against the straight portion or inclined plane  164  of the first sliding (controlled) member  106 . The first motion limiting member  180  becomes wedged against the straight portions or inclined planes  164 ,  168  of the first and second sliding members  106 ,  110  so as to prevent the first sliding member  106  from moving beyond the controlled distance. 
   The third extension  130  is configured to be pulled either manually or by an external mechanism a predetermined controlled distance in a direction away from the housing  102  such that the third sliding (controlling) member  114  moves toward the first longitudinal end  122  of the housing. As the third sliding member  114  moves in the above-mentioned direction, the straight portion or inclined plane  176  of the third sliding (controlling) member  114  abutting the second motion limiting member  182  moves away from the opposing surface of the straight portion or inclined plane  172  of the first sliding (controlled) member  106 . The first sliding member  106  is then able to be moved the controlled distance toward the first longitudinal end  122 . As the first sliding member  106  moves over the controlled distance, the straight portion or inclined plane  172  of the first sliding member  106  moves toward the opposing surface of the straight portion or inclined plane  176  of the third sliding member  114  until the second motion limiting member  182  simultaneously contacts both straight portions or inclined planes  172 ,  176  of the first and third sliding members  106 ,  114  so as to prevent the first sliding member  106  from moving beyond the controlled distance. 
   If the first sliding member  106  is attempted to be moved beyond the controlled distance, the second resilient member  190  forces the straight portion or inclined plane  176  of the third sliding (controlling) member  114  to press against the second motion limiting member  182 , and the second motion limiting member to in turn press against the straight portion or inclined plane  172  of the first sliding (controlled) member  106 . The second motion limiting member  182  becomes wedged against the straight portions or inclined planes  172 ,  176  of the first and third sliding members  106 ,  114  so as to prevent the first sliding member  106  from moving beyond the controlled distance. 
   In sum, any force applied to the device  100  in a direction that would move the extensions  120 ,  126  of the first and second sliding members  106 ,  110  into the housing  102  and toward each other forces the combination of the inclined planes  164 ,  168  and the first motion limiting member  180  to wedge in the housing. This wedging restricts relative motion between the parts of the device  100  and provides a positive locking action. If a force is then applied to the device  100  that would move the extensions  120 ,  126  of the first and second sliding members  106 ,  110  apart, the sliding members become freed in the housing  102  and relative motion between the first and second sliding members is allowed. 
   Moreover, any force applied to the device  100  in a direction that would move the extensions  120 ,  130  of the first and third sliding members  106 ,  114  into the housing  102  forces the combination of the inclined planes  172 ,  176  and the second motion limiting member  182  to wedge in the housing. This wedging restricts relative motion between the parts of the device  100  and provides a positive locking action. If a force is then applied to the device  100  that would move the extensions  120 ,  130  of the first and third sliding members  106 ,  114  away from the housing, the sliding members become freed in the housing  102  and relative motion between the first and third sliding members is allowed. 
   The present invention as described above permits motion to be controlled in very small increments relative to the load being carried. The precision of control is very high relative to the precision needed for the components of a control device embodying the present invention. The control devices in accordance with the present invention can be constructed using conventional low cost methods, and can be assembled and disassembled without tools. The components of the control device can be made of a wide variety of materials that are chosen to meet the demands of the intended application, and various size models can be made to accommodate different conditions of use. 
   The control device of the present invention is easily adapted and integrated with other machine elements. Attachments to the device housing can be made at many different points. The exterior shape of the housing is not critical to function. Moreover, the motion limiting member having a spherical or cylindrical shape contacting flat surfaces permits the control device to inherently tolerate a significant degree of inaccuracy in the component parts. This allows low cost versions of the control device to be produced that can function well where conventional devices requiring precision parts are not as effective. 
   As will be recognized by those of ordinary skill in the pertinent art, numerous modifications and substitutions can be made to the above-described embodiments of the present invention without departing from the scope of the invention. Accordingly, the preceding portion of this specification is to be taken in an illustrative, as opposed to a limiting sense.