Retractable stop assembly

A stop assembly includes a drive arm and a stop arm with a backside configured to direct a reaction force applied by the stop arm to the drive arm when the stop arm engages a workpiece. The drive arm pivots between pre-locked and unlocked positions in response to movement of the reciprocatable member between extended and retracted positions. The motion range includes a locked position between the pre-locked and unlocked positions. The stop arm is pivotally mounted to the body and has a front side for engaging a workpiece, while the backside engages the drive arm. The stop arm backside 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 and locked positions, and such that the reaction force is substantially coplanar with the drive arm plane when the drive arm is in the locked position.

TECHNICAL FIELD 
The present invention relates to power operated retractable stop 
assemblies. 
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, the retractable stops are powered by a linear 
actuator such as an air or hydraulic cylinder, or a solenoid actuator. 
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. 
Although these 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. As in some 
applications it may be desirable to provide a cushioned stop, assemblies 
providing a "hard" stop without any cushion may not be desired. Further, 
although a cushion may be desirable in some applications, because such 
assemblies cannot guarantee a stopping of the load after the cushion, 
these assemblies too may be undesirable. Further, assemblies utilizing a 
separate shock absorber mechanism are complex and costly. 
For the forgoing reasons, there is a need for an improved power operated 
retractable clamp assembly. 
DISCLOSURE OF INVENTION 
It is, therefore, an object of the present invention to provide a power 
operated retractable stop assembly with integral cushion and stopping 
mechanisms. 
In carrying out the above object, other objects and features of the present 
invention, a power operated retractable stop assembly is provided. The 
assembly comprises a body, a reciprocatable member, a drive arm, and a 
stop arm. The reciprocatable member extends into the body and is adapted 
to engage a driving means such as a cylinder. The reciprocatable member is 
driveable between an extended position and a retracted position. The drive 
arm is pivotally mounted to the body and drivingly connected to the 
reciprocatable member such that the drive arm is pivotable 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 
receiving a workpiece force on the stop arm front side from a workpiece. 
The stop arm backside 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 backside 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 a preferred embodiment, the assembly further comprises a positioning 
guide defined by the stop assembly body. The positioning guide is located 
near the stop arm and has a sloped portion that directs an oncoming 
workpiece to a portion of the stop arm that is sufficiently spaced from 
the stop axis. Thus, spacing is sufficient to apply a moment to the stop 
arm due to the workpiece force that is sufficient to overcome the driving 
means and results in a cushion stopping of the drive arm in the locked 
position. Once in the locked position, the drive arm is locked due to the 
reaction force being substantially coplanar with the drive arm plane. 
Preferably, the drive arm and the reciprocating member are configured such 
that the drive arm pre-locked position corresponds to the reciprocatable 
member retracted position, and the drive arm unlocked position corresponds 
to the reciprocatable member extended position. Alternatively, the drive 
arm and the reciprocating member may be configured such that the drive arm 
pre-locked position corresponds to the reciprocatable member extended 
position, and the drive arm unlocked position corresponds to the 
reciprocatable member retracted position. 
Preferably, the assembly further comprises a cam roller located at the 
drive arm end and positioned to engage the stop arm backside. The roller 
has an axis of rotation that is substantially parallel to the drive axis 
and is substantially coplanar with the drive arm plane. Alternatively, the 
roller may be located at the stop arm backside and positioned to engage 
the drive arm end. 
Further, in carrying out the present invention, a power operated 
retractable stop assembly comprises a body, a piston and cylinder 
assembly, a reciprocatable member, a drive arm, and a stop arm. The 
reciprocatable member extends into the body and is connected to the piston 
and cylinder assembly. The reciprocatable member is driveable by the 
piston and cylinder assembly over the a stroke range between an extended 
position and a retracted position. The stop arm backside 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. Further, the stop arm backside 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. 
The advantages associated with embodiments of the present invention are 
numerous. For example, power operated retractable stop assemblies made in 
accordance with the present invention use the driving means which may be a 
piston and cylinder assembly to provide a cushion when stopping a load. 
The amount of cushion may be selected by choosing appropriate cylinder 
operating pressure and appropriate lever arm distances between pivot 
points and the force application points. Further, stop assemblies made in 
accordance with the present invention, in addition to providing 
cushioning, provide a "hard" stop at the end of the cushion zone. That is, 
during cushioning, reaction force applied to the drive arm has a component 
normal to the drive arm plane; but, once the drive arm reaches the locked 
position, the reaction force is coplanar with the drive arm plane. As 
such, once the stop assembly has locked, the driving means (such as a 
piston and cylinder assembly) is not needed to maintain the locked 
position. Although finite cylinder pressure holding force may be used to 
resist/cushion movement to the locked position, alternatively, a hydraulic 
cylinder with a pressure relief valve may be used. 
The above object, and other objects, features and advantages of the present 
invention will be readily appreciated by one of ordinary skill in the art 
from the following detailed description of the best mode for carrying out 
the invention when taken in connection with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIGS. 1 through 10 which illustrate a power operated 
retractable stop assembly of the present invention, and primarily to FIGS. 
2-4 which are partially in section, the preferred embodiment of the stop 
assembly is generally indicated at 10. Stop assembly 10 has a body 
composed of sides 12. A driving means engages body 12. A suitable driving 
means is a piston and cylinder assembly, generally indicated at 14. Piston 
and cylinder assembly 14 includes a cylinder 16 in which a piston 18 is 
driven. Piston and cylinder assembly 14 has suitable connectors 20 and 22 
for connecting to a source. Piston and cylinder assembly 14 forms a linear 
actuator and may be either powered by air (or other gas) or hydraulic 
media. An air powered cylinder is suitable for providing a cushioning zone 
due to the compressability of gas. Alternatively, a hydraulic cylinder 
with a pressure relief valve may be employed to provide a cushioning zone. 
Of course, it is appreciated that compressed air may be preferred because 
air sources are generally cheaper, and many times are already present at a 
work site. 
A reciprocatable member such as push rod 24 is driven by piston and 
cylinder assembly 14 and extends into stop body sides 12. Reciprocatable 
member 24 is driveable by piston and cylinder assembly 14 over a stroke 
range between an extended position and a retracted position as described 
further, below. Reciprocatable member 24 includes an end 26 that is 
preferably adjustably secured by nut 28 and threaded portion 30 of end 26. 
The nut and threads arrangement allows some adjustment of the extended and 
retracted positions for reciprocatable member 24, which is preferred, but 
not required. 
A drive arm 32 is pivotally mounted to body 12. A pin and bearing 
arrangement 34, preferably of side thrust bearings to prevent side-to-side 
sliding, is used to mount drive arm 32 to body 12. Drive arm 32 is pivotal 
about drive axis 36. Drive arm 32 is connected to reciprocating member end 
26 by intermediate link 50. Link 50 pivotally connects to member end 26 by 
pin 52, and connects to drive arm 32 with pin 34. As pin arrangements 52 
and 54 will move with respect to body 12 during operation, pin 
arrangements 52 and 54 only extend within the clamped sides and preferably 
are needle bearings on hardened shafts. Accordingly, pin and bearing 
arrangement 34 and drive arm 32 are affixed to clamp body 12. 
Drive arm 32 is pivotable about drive axis 36 over a motion range between a 
pre-locked position (reference numeral 56, FIG. 3) and an unlocked 
position (reference numeral 60, FIG. 4). Further, the motion range 
includes a locked position (reference numeral 32, FIG. 2) between the 
unlocked and pre-locked positions. The reciprocatable member is in the 
retracted position 58 (FIG. 3) when the drive arm is in the pre-locked 
position 56 (FIG. 3). The reciprocatable member is in the extended 
position 62 (FIG. 4) when the drive arm is in the unlocked position 60 
(FIG. 4). The reciprocatable member is at an intermediate position 26 
(FIG. 2) when the drive arm is in the locked position 32 (FIG. 2). 
As described above, the drive arm moves over its motion range in response 
to movement of the reciprocatable member. Drive arm 32 has a central axis 
64 passing through drive axis 36 to define a drive arm plane that pivots 
with the drive arm. The drive arm plane is the plane defined by central 
axis 64 and pivot axis 36 that, when viewing FIG. 2, is perpendicular to 
the page. The drive plane rotates as the drive arm rotates, which may be 
observed by referring to FIG. 3. In FIG. 3, the drive plane is again 
perpendicular to the page, but has rotated slightly clockwise from the 
position of the drive plane of FIG. 2. 
Of course, as mentioned previously, although in a preferred embodiment of 
the present invention, the extended reciprocating member corresponds to 
the unlocked position for the drive member, and the retracted 
reciprocating member corresponds to the pre-locked position for the drive 
member, an alternative arrangement is contemplated and is shown in FIG. 
11, later described below. In particular, it is preferred that the 
retracted reciprocatable member corresponds to the pre-locked position 
such that when the drive member is urged to the locked position, maximum 
available force may be applied to piston 18 within piston and cylinder 
assembly 14 to unlock the assembly. That is, in a piston and cylinder 
assembly of a particular operating pressure, more force may be applied 
when extending piston rod 24 than when retracting piston rod 24. This is 
because the attachment of piston rod 24 to piston 18 takes up some of the 
available surface area and resultantly reduces the amount of force 
available to move piston 18 towards the opposite side of where piston rod 
24 is attached thereto for a given operating pressure. 
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 clamp body 
12 and which preferably includes side thrust bearings to prevent 
side-to-side sliding. Stop arm 70 is pivotable about a stop axis 74. Stop 
arm 70 has a front side 76 for engaging a workpiece, such as workpiece 84 
(FIG. 3). Stop arm 70 has a backside 78 for engaging drive arm 32. 
Based upon a variety of design parameters, such as cylinder operating 
pressure or pressure relief valve configuration, it is usually desirable 
that when a workpiece contacts stop arm 70, that workpiece contacts stop 
arm 70 at a point sufficiently spaced from pivot axis 72. A sufficient 
spacing from pivot axis 72 assures that a reasonable moment is applied to 
stop arm 70 to push drive arm 32 over the cushioning zone against the bias 
of piston and cylinder assembly 14. Of course, positioning guide 80 is 
preferred but not required. Positioning guide 80 is part of body assembly 
12 and is affixed to the stop sides by bolts 82. 
By appropriately implementing a positioning guide, it is to be appreciated 
that, as best shown in FIG. 3, workpiece 84 contacts stop arm 70 at a 
contact point sufficiently spaced from pivot axis 74. The sloped portion 
of the positioning guide, which is located near stop arm 70, directs an 
oncoming workpiece (shown in phantom at 86, FIG. 3) to a contact point 
sufficiently spaced from stop axis 74. As such, a cushion stopping of the 
drive arm in the locked position occurs. Stop arm 70 is positioned to 
apply a reaction force to drive arm 32 in response to receiving a 
workpiece force on front side 76 from a workpiece 84. 
As best shown in FIG. 3, stop arm backside 78 is configured such that a 
reaction force applied by stop arm backside 78 to drive arm 56 in response 
to the force of workpiece 84 on stop arm 70 has a component 100 that is 
normal to the drive arm plane when the drive arm is between the pre-locked 
position and the locked position. Because drive axis 36 lies in the drive 
arm plane, forces normal to the drive arm plane urge the drive arm toward 
the locked position. As such, configuring stop arm backside 78 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, 
causes the drive arm to be urged to the locked position, whenever a 
workpiece contacts stop 70 and the drive arm is between the pre-locked 
position 56 and the locked position 32. 
As best shown in FIG. 2, when the drive arm reaches the locked position 32, 
the configuration of stop arm backside 78 causes the reaction force 102 
applied by stop arm backside 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 pin 
and bearing assembly 34, and do not cause drive arm 32 to rotate out the 
locked position. 
Advantageously, pin and bearing assembly 34 hold the stop assembly in the 
locked position against the force of any load or workpiece, and if 
desired, piston and cylinder assembly 14 need not be relied on to maintain 
the locked position for the retractable stop. After drive arm 32 and stop 
arm 70 have remained in the locked positions for a desired amount of time, 
piston and cylinder assembly 14 may be actuated to urge the drive arm to 
the unlocked position 60 (FIG. 4), allowing stop arm 70 to pivot and allow 
workpiece 84 to pass. 
Advantageously, embodiments of the present invention provide 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, utilization of a positioning guide, and selection 
of actuator operating pressures or pressure relief valve configuration. 
Further, it is to be appreciated that embodiments of the present 
invention, after the cushioning zone, provide a "hard" stop. 
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 pin and bearing assembly 34 almost in its entirety. 
In a preferred embodiment of the present invention, a cam roller 90 is 
located at the end of the drive arm and is positioned to engage stop arm 
backside 78. Roller 90 has an axis of rotation 92 that is substantially 
parallel to drive axis 36 and is substantially coplanar with the drive arm 
plane. Of course, alternatively, the roller may be provided on stop arm 
70, instead, if desired, but it is preferred that roller 90 be located at 
the end of the drive arm. Preferably, in compressible gas type cylinder 
embodiments, backside surface 78 includes a portion 108 that is configured 
to follow a radius from the drive arm axis 36 that extends to the contact 
point of roller 90 and backside surface 78. As such, the drive arm may 
slightly bounce or overshoot as the stop arm moves to the locked position 
without disturbing the stop arm. A small bump 110 marks the end of the 
overshoot roll zone. In a construction using an air cylinder (to allow gas 
compressability), the inventor has observed bounce or overshoot of about 
0.50 in (1.3 cm) to 0.75 in (1.9 cm). As such, in that example, a radiused 
portion (overshoot roll zone) that extends over an arc length of about 
0.75 in (1.9 cm) is suitable to allow recovery from reverberations in the 
air column. 
With reference now to FIG. 11, several alternatives for implementing 
specific features of the present invention are described. A power operated 
retractable stop assembly having several alternative features is generally 
indicated at 120. Assembly 120 has a body 122 connected to a piston and 
cylinder assembly 124. Reciprocatable member 126 and drive arm 128 are 
configured such that the extended position for retractable member 126 
corresponds to the pre-locked position for a drive arm 128, and the 
retracted position for reciprocatable member 126 corresponds to the 
unlocked position for the drive arm 128. This is achieved by connecting 
reciprocatable member 126 to drive arm 128 with a link 130 to a pivot pin 
connection 132 that is on an opposite side of pin and bearing assembly 134 
and pivot axis 136 than stop arm backside 138. In another alternative 
feature, a roller 140 having an axis of rotation 142 is connected to stop 
arm 144, as suggested previously. Further, an alternative, long stop arm 
is shown in phantom at 112. Further, preferably in all embodiments, 
radiused portion 114 on the stop arm rides on the drive arm to lift the 
stop arm from the unlocked position. 
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.