1. Field of the Invention
The present invention generally relates to electronically operated exit devices in which an electrical signal causes the exit device to retract the latch bolt.
2. Description of Related Art
An “exit device” is a lock mechanism installed on the inside of an exit door that swings outward. The exit device is designed to allow exit without prior knowledge of how the lock operates, whenever a horizontal force is applied to a pushbar or push rail actuator. The term “push rail” will be used herein to refer to all types of exit device actuators, including pushbars and paddles.
The horizontal pressure required to open the door may be applied to the push rail by anyone who understands how the door operates. However, the design of an exit device is such that the required opening pressure is automatically applied to the push rail as the result of contact between the push rail door actuator and people in a crowd during an emergency.
Exit devices are typically required by fire or building codes and are used in public buildings where many people may be gathered, to reliably allow rapid, safe and easy egress in case of emergency. Exit devices ensure that an exit door is free to operate from the inside of the locked area, yet they allow the exit door to remain locked to prevent unauthorized entry from the outside.
Electronically operated exit devices are often used in access control applications where they are activated by a card reader or keypad from the outside to allow access through a door that also serves as an exit door from the interior space. When the exit device is latched, the exit door cannot be opened from the outside, but it can easily be opened by pressure on the push rail or pushbar of the exit device from the inside. Other applications for electronic exit devices include operation in conjunction with power door operators, allowing the latch to retract in a timed sequence with the door operator and in facilities that are locked and unlocked on a timed schedule, such as a school. The electrical control for the exit device may be integrated into a fire detection system.
The simplest conventional electronically operated exit devices only retract the latch bolt and do not move the push rail when electrically operated. Because the push rail actuator is in the same position when the latch bolt is electrically retracted (door unlocked) and when the latch bolt is extended (door locked) the position of the push rail actuator cannot be used as a visual indication of the locked or unlocked status of the door. It is difficult to tell whether the door is locked or unlocked without actually opening the door.
Designs that retract only the latch bolt have a related problem in high traffic applications, such as a school. In these installations, when the latch bolt is electrically retracted, the push rail will still move each time it is pressed to exit through the door. The door may be opened many times during the day while the latch bolt is electrically retracted, and the constant motion of the push rail actuator and the mechanical actuator elements produces unnecessary wear on those components.
Another problem resides in prior art designs that use a solenoid to retract the latch bolt. A solenoid requires a relatively high in-rush current to reliably retract the latch bolt and overcome initial friction. Because the exit device is mounted on a movable exit door, this relatively high level of current must pass through a hinge or other flexible electrical connection designed to carry that level of current. Such electrical hinges are significantly more expensive than hinges that carry lower power as needed to power card readers, sensors and other low power and low voltage devices found on exit doors. Moreover, the power supply required to meet the high in-rush current requirements of these designs is relatively expensive.
Still another problem with high power solenoid retraction designs is that the solenoid produces significant noise when it is actuated. This noise is objectionable in many settings, such as hospitals and libraries.
Another known design for an electrically operated exit device uses a motor and a cam to electrically retract the push rail. The motor drives the cam, which pulls back the push rail and retracts the latch bolt. A switch detects when the push rail reaches the fully retracted position and turns off the motor drive. A low power solenoid magnetically holds an armature mounted on the push rail to keep the push rail in the fully retracted position until power is removed and the push rail is released.
In this design, the motor does not shut off until the push rail is fully retracted, as sensed by the switch. When the exit device drives other components, such as vertical rods, binding in the additional components can prevent the motor from moving the push rail to the fully retracted position. This produces a continuous drive to the motor, which can ultimately burn it out, break other components or burn out the control circuitry for the motor.
The design described above requires numerous components, including the motor and the holding solenoid. It would be desirable to reduce the number of components to reduce cost.
Another problem with existing electronic exit device designs is that they are mechanically difficult to adjust for correct operation. It would be desirable to be able to electrically adjust the distance the latch bolt moves to allow adjustment during installation and to adjust for wear during the life of the product.
Still another difficulty with conventional electronic exit device designs relates to controlling the time delay before the exit device releases the latch bolt and relatches after it has been electrically unlatched. In some cases, this time delay control is found in a separate external electrical control system, which simply supplies power to open the exit device and removes it to relatch. These separate external electrical control systems add expense.
In other cases the time to relatch is controlled by an integrated time delayed solenoid in the exit device. Changing the time delay requires changing the solenoid, which is difficult and expensive. Moreover, designs that use an integrated time delay are often incompatible with separate external electrical control systems. It would be desirable to have a system with an integrated electrical control of the time to relatch that is compatible with existing external electrical control systems.