Z-bar security system

A system for locking a door can: (1) lock the door in dead bolt fashion, (2) allow the door to open a limited distance, or (3) allow the door to open freely. The system has a door-mounted latch assembly that includes a base plate, an intermediate link pivoted to the base plate, and a mode selection and latching assembly that is pivoted to the intermediate link. The latch assembly also includes a high strength, "T"-shaped latch member, and camming means to slide the latch member back and forth as a control knob is rotated. A latch plate is mounted on the door frame in juxtaposition to the door-mounted latch assembly. The latch plate has a cylindrical portion with a vertical slot for receiving the "T"-shaped latch member. A cylindrical sleeve fits inside the cylindrical portion of the latch plate. Like the cylindrical portion of the latch plate, the sleeve has a vertical slot for receiving the latch member. The sleeve also has a horizontal slot running perpendicular to and intersecting with the vertical slot. When the latch member is engaged in the cylindrical portion of the latch plate, the cylindrical sleeve can be rotated so that the latch member is engaged with the horizontal slot in the cylindrical sleeve. The latch member then cannot be directly withdrawn from the latch plate.

INTRODUCTION 
The present invention relates to door locks, and more particularly to a 
door lock that can: lock the door shut in dead bolt fashion; allow the 
door to open a limited distance; or allow the door to open freely. 
BACKGROUND OF THE INVENTION 
Many doors, such as household doors, are provided with a dead bolt lock in 
order to maintain security by bolting the door shut. Incidentally, dead 
bolts are normally required to extend one inch into the door frame and 
associated latch plate. Unfortunately, the dead bolt must be released and 
the door opened in order to (1) pass a small object through the doorway, 
such as an envelope or small package, or (2) to view the persons outside 
the door. While a short chain may be used to prevent the door from fully 
opening, such a chain arrangement is often weak. 
An alternative to a standard dead bolt lock is a lock that can operate 
either in a mode similar to a dead bolt or as a latch having a "Z-Bar" 
configuration, which allows the door to open a limited distance. Such a 
lock is disclosed in U.S. Pat. No. 3,924,887. That device employs a 
baseplate which attaches to the door; an intermediate link; an outer link 
with a latch disk and a mode selection handle; and a latch plate mounted 
on the door frame into which the latch disk can latch. 
However, there are at least four problems with the device. First, the 
device employs rounded "ears" to hold the latching assembly together in 
the dead bolt mode. As structural members, these "ears" are weak and can 
compromise the strength of the lock. Second, when the lock is in the dead 
bolt mode or limited-open mode, the latch disk can be pried out directly 
away from the latch, for instance by someone using a crowbar. Third, since 
the latch disk is the primary load-bearing portion of the lock, the latch 
disk should be as thick as possible. However, when the entire latch disk 
of U.S. Pat. No. 3,924,887 is made thick, the entire latch mechanism must 
increase in size to accommodate it. 
Finally, the prior device does not provide for an indicator to inform the 
user what mode the lock is in. Without such an indicator, the user may 
unwittingly believe that the door has been dead bolted shut, when in fact 
it is unlocked or in the limited-open position. 
It is also noted in passing that the related U.S. Pat. No. 3,924,886 
discloses an alternative embodiment in FIGS. 7-10 of the patent, which 
only provides a sketchy and brief description, and does not have an 
intended dead bolt mode of operation. 
SUMMARY OF THE INVENTION 
It is desirable to provide a lock with the advantages of a "Z-Bar" latch 
but with the additional advantages of structural strength, resistance to 
prying, and user convenience. These goals are satisfied by the various 
embodiments of the present invention. 
Generally stated, this invention relates to a "Z-Bar" door security system 
which provides three modes of operation. In the first mode, the system 
allows the door to open freely. In the second mode, the system permits the 
door to open a limited amount. In the third mode, the system locks the 
door to the door jamb with a dead bolt. 
The present invention provides for a "Z-Bar" latch assembly, which includes 
a base plate that secures to the edge of a door. An intermediate link is 
pivoted to the base plate, and a mode selection and latching assembly is 
pivoted to the intermediate link. When the base plate, intermediate link, 
and mode selection and latching assembly are partially unfolded from one 
another, they form the shape of a "Z". The inventors have chosen to refer 
to their security system as a "Z-Bar" system. 
The mode selection and latching assembly includes a control knob, which the 
user rotates to select the mode of operation. The mode selection and 
latching assembly also includes a high-strength latch member, which may be 
a thick steel bolt member, which slides back and forth as the control knob 
rotates. To complement the latch member, the invention has a latch plate 
that is mounted on the frame of a door opposite the base plate. There is a 
vertical slot in the latch plate for receiving the latch member. 
The invention also has a structurally sound locking device extending from 
the control knob to secure together the baseplate, intermediate link, and 
mode selection and latching assembly when the latch is in the dead bolt 
mode of operation, and also, if desired, in the free-opening mode. 
Two additional aspects of the invention achieve the goals of user 
convenience and resistance to prying. To achieve the goal of user 
convenience, one aspect of the present invention has an indicator on the 
mode selection and latching assembly to inform the user whether the lock 
is on the dead bolt, limited-open, or fully-open setting. To achieve the 
goal of resistance to prying, another aspect of the invention involves the 
provision of a special cylinder within the latch plate that the user can 
rotate to lock the latch inside of the latch plate. 
In accordance with another feature of the invention the latch or bolt is 
shifted in position by camming arrangements intercoupling the control knob 
and the latch or bolt. 
Other objects, features, and advantages of the invention will become 
apparent from a consideration of the following detailed description and 
from the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
This Description consists of three parts. The first part is a detailed 
definition of the components that make up the invention. The second part 
describes how the invention operates in each of its three modes: 
free-opening, inspection, and dead bolt. Finally, the third part describes 
a second embodiment of the invention that adds additional security. 
I. Components of the Invention 
The "Z-Bar" door security system is composed of four major components: the 
base plate, the intermediate link, the mode selection and latching 
assembly, and the latch plate. 
a. The Base Plate 
FIGS. 1 through 9 illustrate an embodiment 20 of the "Z-Bar" security 
system. FIG. 1 illustrates each of the four major components of the 
system, including the base plate. 
Base plate 22 comprises base 42 which has suitable screwholes with screws 
63 mounted therein for secure attachment of base 42 onto door 24. Base 
plate 22 has upturned flange edges 36. These flange edges have a pivot pin 
hole at the end of the base toward the door edge, and pivot pin 48 extends 
through this hole. A bias spring 46 is coiled around pivot pin 48 and 
bears at one end onto base 42. Base plate 22 further comprises an aperture 
44, through which locking flange 66 (FIG. 5) can pass. 
b. The Intermediate Link 
Intermediate link 38 has at one end a pair of flanges 70 through which 
pivot pin 48 passes. Intermediate link 38 also has downturned, tapered 
flange edges 68. The narrow end of tapered flanges 68 begins near the 
flanges 70 and increases in width along the length of intermediate link 
38. The wide end of each of the flanges includes an aperture 72 (FIG. 5) 
through which passes pivot pin 74. 
c. The Mode Selection and Latching Assembly 
Mode selection and latching assembly 40 has a control knob 54, which 
includes a mode indicator including a view window 56 and symbols 58 (FIG. 
9). A central post has three parts of different diameters, including outer 
portion 76 (FIG. 5) embedded in control knob 54, portion 78, which passes 
through washer 80, and portion 82, at the end of which is flange 66. 
Mode selection and latching assembly 40 also has a T-shaped latch bar 60, 
comprised of a long neck portion 62 and a relatively narrower crossbar 64 
at the outer end thereof. Latch bar 60 is positioned in channel 116 (FIG. 
7), along which the latch bar can slide. Opening or slot 84 (FIG. 6) in 
the long neck portion 62 of latch bar 60 allows control knob post 78 to 
pass through. 
A portion of control knob 54 acts as a camming means which drives latch bar 
60 along channel 116. Control knob 54 has a groove 113 consisting of 
groove segments 86 and 88. Groove 112 overlies an assembly consisting of 
pin 104, spring 106 and sleeve 114, as shown in FIGS. 6 and 6A. Sleeve 114 
passes through latch bar 60. The bottom portion of spring 106 rests along 
the top of channel 116. Pin 104 is situated inside of sleeve 114 and is 
biased into groove 118 by spring 106. As control knob 54 rotates, pin 104 
travels along groove 118. When pin 104 travels along groove segment 88, 
the contour of the groove pushes latch 60 either forward or backward, 
depending on the direction of rotation of the control knob. When pin 104 
travels along groove segment 86, the contour of the groove does not affect 
the position of latch 60, and permits rotation of the knob and locking 
control flange 66 without shifting the position of the latch. 
Groove 118 has indentations 112 that serve as stopping points or detents 
for pin 104. The location of each indentation 112 corresponds to the 
proper control knob position for the free-opening, inspection, and dead 
bolt modes of operation. When pin 104 reaches a groove indentation 112, 
spring 106 forces pin 104 into the indentation. The user must apply 
additional rotational force to dislodge pin 104 from the indentation 112 
in which it is located. 
d. The Latch Plate 
Latch plate 30 comprises base 26 which has suitable screwholes in which 
screws 85 are mounted for secure attachment of base 26 onto door jamb 28. 
Latch plate 30 is rolled into a substantially cylindrical configuration 32 
at one end. Base 26 has a "t"-shaped aperture 34 such that the lower 
portion of the "t" runs along the flat portion of the base, and the 
crossbar of the "t" crosses one edge of cylinder 32. The upper stem 
portion of the "t" follows a curved path along a portion of the surface of 
the cylinder. A tongue 86 extends from the edge of the cylinder to fill 
the lower portion of t-shaped aperture 34. Tongue 86 has at least one 
suitable screwhole 87 in which a screw is mounted for secure attachment of 
cylinder 32 and latch plate 30 to door jamb 28. 
II. How the "Z-Bar" Door Security System Operates 
The "Z-Bar" door security system operates in three modes. In the 
free-opening mode, the door is freely opened and shut without any 
interference from the system. In the inspection mode, the door can open 
only a limited distance. In the dead bolt mode, the system prevents the 
door from opening at all. The following is a detailed description of how 
the system operates in each mode. 
a. Operation in the Free-Opening Mode 
In the free-opening mode, base plate 22, intermediate link 38, and mode 
selection and latching assembly 40 lay flat against each other and are 
latched together, as in FIG. 7. Post 82 and flange 66 have passed through 
rectangular base plate aperture 44. Control knob 54 has been rotated into 
the free-swing position, thereby rotating flange 66 into the locked 
position, as in FIG. 8, with portions of flange 66 overlying the sides of 
rectangular opening 44. Rotation of control knob 54 has also put latch 
plate 60 in the retracted position, disengaged from latch plate 30, so 
that the security system does not prevent the door from swinging open 
freely. 
b. Operation in the Inspection Mode 
To position the security system in the inspection mode from the free-swing 
mode, the user rotates control knob 54 to disengage flange 66 from base 
plate aperture 44. Simultaneously, latch bar 60 extends to engage with 
latch plate 30 through aperture 34, by operation of cam section 88. As 
door 24 swings open, base plate 22 and intermediate link 38 unfold from 
the latched position in FIG. 7 to the extended position of FIGS. 4 and 5. 
Once base plate 22 and intermediate link 38 have fully extended, door 24 
cannot swing open any further. Incidentally, the laterally extending 
portions of the crossbar 64 of the latch are held within the cylinder 32 
of the latch plate, and the reduced width portion 62 of the latch swings 
up into the reduced width outer zone of the opening in the latch plate. 
c. Operation in the Dead Bolt Mode 
To put the security system in the dead bolt mode from the inspection mode, 
the user shuts the door so that bias spring 46 causes intermediate link 38 
and mode selection and latching assembly 40 to fold together over base 
plate 22. The user then rotates control knob 54 to the dead bolt position, 
such that flange 66 is positioned perpendicular to the length of base 
plate aperture 44. The shape of groove 118 is such that latch 60 does not 
retract as the user rotates control knob 54 from the inspection mode 
position to the dead bolt mode position. With the "Z-Bar" latch assembly 
folded and locked together, and with latch 60 engaged with latch plate 30, 
the security system acts as a dead bolt, preventing the door from opening. 
III. Second Embodiment of the Latch Plate 
FIGS. 10 through 15 illustrate a second embodiment 90 of the latch plate 
system of the "Z-Bar" security system. In this embodiment of the 
invention, a latch-securing mechanism 92 is inserted into latch plate 
cylinder 32' for the purpose of securing the latch within the cylinder. 
Latch-securing mechanism 92 comprises tube 94, top cap 96, and bottom cap 
98. 
Tube 94 fits inside latch plate cylinder 32', as indicated by FIG. 10. Tube 
94 has a T-shaped aperture 100 through which latch 60 passes after 
entering latch plate 30'. Top cap 96 fits over the top of tube 94. FIG. 11 
shows handle 102, secured to top cap 96, that the user can turn to rotate 
tube 94. Bottom cap 98 is secured to the bottom of tube 94 and serves to 
mount and maintain tube 94 within latch plate cylinder 32'. Unlike top cap 
96, bottom cap 98 does not have a handle, as illustrated in FIG. 14. 
FIG. 15 illustrates how the latch-securing mechanism operates. Latch 60 
enters latch plate 30' at aperture 34' (FIG. 10), then passes through 
aperture 100 of tube 94. The user turns handle 102 of top cap 96, thereby 
rotating tube 94, and securing the ends of cross-piece 64 of the latch 
member behind the portions 120 of the rotated sleeve 92. The crossbar of 
latch 60 is held within latch plate cylinder 32', and cannot be pried out 
of latch plate 30' until the user turns handle 102 back to its original 
position. 
Concerning dimensions, it is desirable that the bolt or latch member be of 
considerable strength, and it is preferably made of steel, at least 1/8 
inch thick, and preferably 3/16 inch thick. It is 11/4 inch wide at the 
end, about 5/8 inch wide along its length, and about three inches long. 
These dimensions are given by way of example and not of limitation. 
With the rotating cylinder actuated in the latch plate assembly to the 
locked position, the security is equal to and probably greater than that 
provided by conventional dead bolts, as the bolt or latch member of the 
present invention cannot be directly withdrawn from the latch plate. 
In conclusion, it is to be understood that the foregoing detailed 
description and the accompanying drawings relate to preferred embodiments 
of the invention. Various changes and modifications may be made without 
departing from the spirit and scope of the invention. Thus, by way of 
example and not of limitation, the supplemental locking arrangements in 
the latch plate may be implemented by a sliding member instead of a 
rotating cylinder, and the locking end of the latch member may be 
bifurcated with inwardly directed end portions instead of outwardly 
projected end portions. In addition, instead of a locking member 66 on the 
control knob shaft, the three portions of the Z-Bar assembly may be locked 
together by a separate mechanical locking mechanism. Accordingly, the 
present invention is not limited to the specific embodiments shown in the 
drawings and described in the detailed description.