Patent Application
20070175729
1. Field of the Invention
The invention relates to power operated retractable stop assemblies.
2. Background Art
The use of industrial retractable stop products has become wide spread, due at least in part to high demands in the automotive and heavy equipment industries. Conventionally, a retractable stop is powered by a linear actuator such as an air or hydraulic cylinder, a solenoid actuator, or a rotary actuator with a linear worm gear.
A power operated retractable stop assembly typically includes a reciprocatable rod member driven by the linear actuator, and an assembly body secured to the driving cylinder. Some of these existing assemblies, such as those described in U.S. Pat. No. 4,184,579, utilize a stop lever for stopping and releasing loads traveling on a conveyor. In such an assembly, a blocker leg is used to prevent pivoting of the stop arm causing an uncushioned hard stop of loads traveling on the conveyor when the blocker leg is in the blocking position.
Other existing assemblies attempt to provide a cushioned stop by using cylinder pressure to hold the stop arm in the blocking position. However, assemblies such as these may be disadvantageous in that there is no guarantee of a stop, and a heavy load may deflect the stop lever against the biasing cylinder pressure and continue right past the retractable stop without stopping. Sometimes, assemblies utilize a first mechanism for actuating and deactuating the stop and utilize a separate shock absorber mechanism, such as the assembly described in U.S. Pat. No. 5,168,976.
Other existing assemblies use a linear actuator rod interfering at a right angle with the direction of travel of the conveyor load. This has the disadvantage of side loading the actuator which is designed for the loads to be in line with the center line of the actuator. This creates excessive wear of the actuator. Also, excessive side load on a linear actuator can cause the actuator to bind and be unable to release without first releasing the load.
Although the existing retractable stop assemblies that provide a hard stop and those assemblies that attempt to provide a cushioned stop by using cylinder pressure have been used in many applications that have been commercially successful, these assemblies have disadvantages. In some applications, it may be desirable to provide a cushioned stop, and assemblies providing a hard stop without any cushion may not be desired. Further, although a cushion may be desirable in some applications, because assemblies providing a cushioned stop cannot guarantee a stopping of the load after the cushion, these assemblies may also not be desired. Further, assemblies utilizing a separate shock absorber mechanism are complex and costly, so these assemblies may also not be desired.
Power operated retractable stop assemblies with integral cushion and stopping mechanisms are described in U.S. Pat. No. 6,119,843. These power operated retractable stop assemblies provide a cushion when stopping a load and provide a hard stop at the end of the cushion zone. These existing retractable stop assemblies that provide integral cushion and stopping mechanisms have also been used in applications that have been commercially successful.
There is an opportunity for improvement in power operated retractable stop assemblies with integral cushion and stopping mechanisms due to the fact that the parts required to mount and connect the linear actuator have significant costs. Accordingly, there is a need for an improved power operated retractable stop assembly.
It is an object of the invention to provide a power operated retractable stop assembly in which a reciprocating rotary actuator mounts on the side of the stop assembly with a through shaft at the pivot point of the drive arm. This makes it possible to eliminate some internal parts that were previously used to mount and connect a linear actuator, resulting in significant cost reduction.
The invention involves a power operated retractable stop assembly. The assembly comprises a body, a reciprocatable member, a drive arm, and a stop arm. The reciprocatable member extends at least partially into the body and is adapted to engage a rotary driving means such as a motor or rotary actuator. The reciprocatable member is driveable between a first angular position and a second angular position. The drive arm is pivotally mounted to the body and drivingly connected to the reciprocatable member such that the drive arm is pivoted about a drive axis. The drive arm is pivotable over a motion range between a pre-locked position and an unlocked position in response to movement of the reciprocatable member. The motion range includes a locked position between the pre-locked position and the unlocked position. The drive arm has a central axis passing through the drive axis to define a drive arm plane that pivots with the drive arm.
The stop arm is pivotally mounted to the body such that the stop arm is pivotable about a stop axis. The stop arm has a front side for engaging a workpiece and a back side for engaging the drive arm. The stop arm is positioned to apply a reaction force to the drive arm in response to a force exerted on the stop arm front side by a workpiece.
The stop arm back side is configured such that the reaction force has a component normal to the drive arm plane when the drive arm is between the pre-locked position and the locked position. The normal component of the reaction force urges the drive arm toward the locked position. Further, the stop arm back side is configured such that the reaction force is substantially coplanar with the drive arm plane when the drive arm is in the locked position to cause the drive arm to remain at the locked position.
In accordance with the invention, the rotary driving means and the reciprocatable member cooperate to form a reciprocating rotary actuator that drives the drive arm. In the preferred embodiment of the invention, the rotary actuator mounts on the side of the stop assembly with a through shaft at the pivot point of the drive arm.
Referring to
The rotary driving means 14 and a reciprocatable member such as shaft 34 cooperate to form a reciprocating rotary actuator drivable between a first angular position and a second angular position.
A drive arm 32 is pivotally mounted to body 12. Shaft 34 and a suitable bearing arrangement 35 mount drive arm 32 to body 12, and prevent rotational and side thrust friction and wear. Drive arm 32 is pivotable about drive axis 36.
As best shown in
Shaft 34 is in a first angular position when drive arm 32 is in the pre-locked position, and is in a second angular position when drive arm 32 is in the unlocked position. Shaft 34 moves to an intermediate position when drive arm 32 is in the locked position.
With continuing reference to
Stop assembly 10 also includes a stop arm 70. Stop arm 70 is affixed to body 12 by pin and bearing assembly 72, which extends through body 12 and prevents rotational and side thrust friction and wear. Stop arm 70 is pivotable about a stop axis 74. Stop arm 70 has a front side 76 for engaging a workpiece and a back side 78 for engaging drive arm 32. Stop arm 70 is arranged to apply a reaction force to drive arm 32 in response to a force exerted on front side 76.
As best shown in
Further, when drive arm 32 reaches its locked position, the configuration of stop arm back side 78 causes the reaction force applied by stop arm back side 78 to drive arm 32 to be substantially coplanar with the drive arm plane. Because drive arm axis 36 lies in the drive arm plane, substantially coplanar reaction forces are opposed by shaft 34 and bearing assembly 35, and do not cause drive arm 32 to rotate out of the locked position.
Advantageously, shaft 34 and bearings 35 hold the stop assembly 10 in the locked position against the force of any load or workpiece. After drive arm 32 and stop arm 70 have remained in the locked positions for a desired amount of time, rotary driving means 14 may be actuated to urge drive arm 32 to the unlocked position causing stop arm 70 to pivot and allow the workpiece to pass.
The illustrated embodiment provides a cushioning zone between the pre-locked and locked positions in which the amount of cushion may be determined by selecting appropriate lever arm lengths, pivot point positions, and actuator resistance torque. After the cushioning zone, a hard stop is provided. Advantageously, the hard stop directs all force from the workpiece in a direction coplanar with the drive arm plane such that this reaction force is received by shaft 34 and bearing assembly 35 almost in its entirety.
Cam roller 90, located at the end of drive arm 32, is positioned to engage stop arm back side 78. The freely rotating roller eliminates friction that could prevent release of the mechanically locked arms while under load from conveyor travel. This roller 90 also reduces friction between the arms when moving from release positions to ready or pre-locked positions and from ready or pre-locked positions to locked positions during shock absorbing action.
With continuing reference to
In more detail, drive arm 32 has a bore 102 at the pivot point to accommodate shaft 34. Key way 104 is cut to match key 37 in the actuator shaft 34. In the preferred embodiment, drive arm 32 has deformations at each end of the key way 104 so that key 37 cannot slide laterally past the end of the key way 104 in drive arm 32. Bore 102 has a diameter to slip fit on the shaft 34. Bearings 35 have an inside diameter to slip fit with the rotary actuator shaft 34 and an outside diameter to press fit in the pivot holes of side plates 12. The rotary driving means may be mounted to either side plate 12 by providing, for example, four tapped holes around the drive arm pivot point. Because the actuator could mount interchangeably on either side of the stop assembly 10, varied application conditions may be accommodated.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
