US 6921056 B2
A mechanical assembly includes an arm and an extension link that rotate about a pivot point, a yoke, and a force generating device. The yoke includes a first slot in which a pin of the link resides. The yoke translates in a plane responsive to rotation of the counterbalance extension link pin about the pivot point. The force generating device is connected between the counterbalance extension link pin and a fixed point on the yoke to exert a force on the counterbalance extension link pin. The orientation and magnitude of the force produced by the force generating device remains constant as the yoke translates. The force generating device and extension link produce a torque that is equal and opposing to the torque produced by the force of gravity acting on the arm so that the arm is in static equilibrium. The static equilibrium condition is independent of the rotational position of the arm.
1. A mechanical assembly, comprising:
a first arm connected to and free to rotate about a pivot point;
a counterbalance extension link connected to and free to rotate about the pivot point;
a yoke including a first slot in which a pin of the counterbalance extension link resides, wherein the yoke is enabled to translate in a plane responsive to rotation of the counterbalance extension link pin about the pivot point; and
a force generating device connected between the counterbalance extension link pin and a fixed point on the yoke to exert a force on the counterbalance extension link pin, wherein the orientation of the force produced by the force generating device remains constant as the yoke translates responsive to the counterbalance extension link pin rotating about the pivot point;
wherein the yoke includes at least a second slot perpendicular to the first slot and a pin attached to a fixed reference through the second slot to guide the motion of the yoke as it translates.
2. The assembly of
3. The assembly of
4. The assembly of
5. The assembly of
6. The assembly of
7. The assembly of
1. Field of the Present Invention
The present invention is in the field of mechanical devices and more particularly in the field of counterbalanced mechanical arms or extension.
2. History of Related Art
In the field of mechanical systems, mechanisms for counterbalancing a rotating or pivoting arm are found in a wide variety of applications from construction equipment to computer displays. Referring to
Counterbalancing mechanical arm 102 is achieved in
An attempt to address the undesirable weight and size of the counterbalance approach of
The objectives identified above are achieved by a counterbalancing assembly according to the present invention. The assembly includes a mechanical arm connected to a fixed point about which the arm can pivot. A first end of a counterbalance link is also pivotally connected to the pivot point while a second end of the counterbalance link includes a pin. The counterbalance pin engages a first slot in a yoke device. The first slot is oriented in a first direction, which is typically either horizontal (0°) or vertical (90°). The yoke device includes second and third slots oriented perpendicularly with respect to the first slot. The second and third slots engage fixed position pins that restrict the motion of the yoke mechanism. The counterbalance pin is connected to a first end of a force generating apparatus such as a spring. The spring is preferably a constant force spring that produces a force that is substantially independent of the spring's displacement. A second end of the force generating apparatus is connected to the yoke wherein the force generating mechanism is oriented in the direction of the first slot. The yoke slots, in conjunction with the constant force spring, produce a force on the counterbalance pin that does not vary, in magnitude or direction, with the rotational position of the counterbalance extension. By adjusting the dimensions of the counterbalance extension and the force produced by the force generating apparatus, the assembly produces a torque or movement on the pivot point that counteracts the movement produced by the force of gravity acting on the mechanical arm regardless of the rotational position of the mechanical arm. The mechanical arm and counterbalance link may be collinear or perpendicular to each other depending upon the implementation. Additional mechanical arm and counterbalance extension links may be connected to the first mechanical arm to produce a multi-segmented or articulated mechanical structure that remains statically balanced independent of the rotational position of any of the mechanical arm segments. In one embodiment, the counterbalanced, multi-segment structure is achieved with a single spring.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description presented herein are not intended to limit the invention to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
Generally speaking, the present invention contemplates a mechanism that provides a substantially constant counterbalancing torque to a mechanical arm free to pivot about a pivot point. A counterbalancing extension link is connected to the pivot point. The orientation of the mechanical arm to the extension link is fixed. A force that is substantially constant in both magnitude and direction is applied to the free end of the extension link. The force is substantially invariant with the rotational positions of the extension link and mechanical arm. The magnitude of the constant force is determined by the length of the extension link and the torque on the pivot pin attributable to the mechanical arm to produce a counterbalancing torque on the pivot pin that maintains the mechanical arm in a state of static equilibrium without restricting the arc in which the arm is free to move.
Referring now to
The assembly 140 as depicted further includes a yoke 150 that includes a first slot 152 having a vertical orientation. A pin 154 affixed to a free end of extension link 146 is engaged or otherwise located within first slot 152. The pin 154 is free to move within slot 152 as the mechanical arm is rotated about pivot point 144.
Yoke 150 is constrained to move in a single direction, which is perpendicular to the orientation of first slot 152 as the link pin 154 rotates about pivot point 144. In the depicted embodiment, yoke 150 is constrained to move in the +/− x-direction by first and second constraining pins 160 and 162 which attach to a fixed reference 165 through second and third slots 164 and 166, respectively, in yoke 150. In this embodiment, the position in the x-direction of yoke 150 tracks the x-direction position of link pin 154 as it rotates about pivot point 144. As depicted in
As shown in the side view detail of
In the preferred embodiment, force generating device 170 is implemented with a constant force spring. As its name implies, a constant force spring is a device that exerts a force that is substantially invariant with spring displacement, at least within a specified range of displacement. If such a constant force spring is constrained by the implementation to maintain its displacement within the substantially constant force range, the corresponding force generating device may be characterized as a constant force generating device.
The combination of the constant force device 170 and the yoke 150, which provides a constant direction mechanism, it will be appreciated that assembly 140 maintains a force on extension pin 154 that is constant in both magnitude and direction. The force of gravity, likewise, provides a constant force on a center of mass 143 of arm 142. These two forces produce countervailing torques about pivot point 144. By manipulating the value of force generated by constant force spring 170 and the dimension (length) of counterbalance extension link 146, the torque attributable to counterbalance extension link 146 and the torque attributable to the force of gravity acting on arm 142 may be made to be equal in magnitude and opposite in direction such that the two forces counterbalance each other such that the mechanical arm is in static equilibrium.
The force generating device 170 may be implemented with a constant force spring as described above. In one embodiment, the constant force spring includes a long and thin rectangular steel strip rolled to form a hollow cylinder. One end of the cylinder is rigidly attached to the yoke pin while the coiled end is loosely centered around an extension of the link pin 154. In other embodiments, force generating device 170 may be implemented with a tension spring, pneumatic cylinder, or other suitable means for providing a constant force.
Referring now to
It will be apparent to those skilled in the art having the benefit of this disclosure that the present invention contemplates a counterbalanced arm mechanism. It is understood that the form of the invention shown and described in the detailed description and the drawings are to be taken merely as presently preferred examples. It is intended that the following claims be interpreted broadly to embrace all the variations of the preferred embodiments disclosed.