Interlock (engineering)
Encyclopedia
Interlocking is a method of preventing undesired states in a state machine
, which in a general sense can include any electrical, electronic, or mechanical device or system.
In most applications an interlock is a device used to help prevent a machine from harming its operator or damaging itself by stopping the machine when tripped. Household microwave oven
s are equipped with interlock switches which disable the magnetron if the door is opened. Similarly household washing machine
s will interrupt the spin cycle when the lid is open. Interlocks also serve as important safety devices in industrial settings, where they protect employees from devices such as robots
, presses, and hammers. While interlocks can be something as sophisticated as curtains of infrared
beams and photodetector
s, they are often just switch
es.
is a method of ensuring safety in industrial environments by forcing the operator through a predetermined sequence using a defined selection of keys, locks and switches.
It is called “Trapped Key” as it works by releasing and trapping keys in a predetermined sequence. After the control or power has been isolated, a key is released that can be used to grant access to individual or multiple doors.
For example, to prevent access to the inside of an electric kiln
, a trapped key system may be used to interlock a disconnecting switch and the kiln door. While the switch is turned on, the key is held by the interlock attached to the disconnecting switch. To open the kiln door, the switch is first opened, which releases the key. The key can then be used to unlock the kiln door. While the key is removed from the switch interlock, a plunger from the interlock mechanically prevents the switch from closing. Power cannot be re-applied to the kiln until the kiln door is locked, releasing the key, and the key is then returned to the disconnecting switch interlock. A similar two-part interlock system can be used anywhere it is necessary to ensure the energy supply to a machine is interrupted before the machine is entered for adjustment or maintenance.
an interlock is hardware that stalls the pipeline (inserts bubbles) when a hazard
is detected until the hazard is cleared. One example of a hazard is if a software program
loads
data from the system bus
and calls for use of that data in the following cycle in a system in which loads take multiple cycles (a load-to-use hazard).
that prevents release of the firing pin unless the chamber is properly closed.
In the operation of a device such as a press or cutter that is hand fed or the workpiece hand removed, the use of two buttons to actuate the device, one for each hand, greatly reduces the possibility of operation endangering the operator. No such system is fool-proof, and such systems are often augmented by the use of cable–pulled gloves worn by the operator; these are retracted away from the danger area by the stroke of the machine. A major problem in engineering operator safety is the tendency of operators to ignore safety precautions or even outright disabling forced interlocks due to work pressure and other factors. Therefore such safeties require and perhaps must facilitate operator cooperation.
Finite state machine
A finite-state machine or finite-state automaton , or simply a state machine, is a mathematical model used to design computer programs and digital logic circuits. It is conceived as an abstract machine that can be in one of a finite number of states...
, which in a general sense can include any electrical, electronic, or mechanical device or system.
In most applications an interlock is a device used to help prevent a machine from harming its operator or damaging itself by stopping the machine when tripped. Household microwave oven
Microwave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
s are equipped with interlock switches which disable the magnetron if the door is opened. Similarly household washing machine
Washing machine
A washing machine is a machine designed to wash laundry, such as clothing, towels and sheets...
s will interrupt the spin cycle when the lid is open. Interlocks also serve as important safety devices in industrial settings, where they protect employees from devices such as robots
Industrial robot
An industrial robot is defined by ISO as an automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes...
, presses, and hammers. While interlocks can be something as sophisticated as curtains of infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
beams and photodetector
Photodetector
Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...
s, they are often just switch
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
es.
Trapped key interlocking
Trapped key interlockingTrapped key interlocking
Trapped key interlocking utilizes locks and keys for sequential control of equipment and machinery to ensure safe operation. A simple system might consist of two locks and a single key. Normally inserting the key into a lock would enable a power supply, thus in this simple system only one power...
is a method of ensuring safety in industrial environments by forcing the operator through a predetermined sequence using a defined selection of keys, locks and switches.
It is called “Trapped Key” as it works by releasing and trapping keys in a predetermined sequence. After the control or power has been isolated, a key is released that can be used to grant access to individual or multiple doors.
For example, to prevent access to the inside of an electric kiln
Kiln
A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...
, a trapped key system may be used to interlock a disconnecting switch and the kiln door. While the switch is turned on, the key is held by the interlock attached to the disconnecting switch. To open the kiln door, the switch is first opened, which releases the key. The key can then be used to unlock the kiln door. While the key is removed from the switch interlock, a plunger from the interlock mechanically prevents the switch from closing. Power cannot be re-applied to the kiln until the kiln door is locked, releasing the key, and the key is then returned to the disconnecting switch interlock. A similar two-part interlock system can be used anywhere it is necessary to ensure the energy supply to a machine is interrupted before the machine is entered for adjustment or maintenance.
Microprocessors
In microprocessor architectureCPU design
CPU design is the design engineering task of creating a central processing unit , a component of computer hardware. It is a subfield of electronics engineering and computer engineering.- Overview :CPU design focuses on these areas:...
an interlock is hardware that stalls the pipeline (inserts bubbles) when a hazard
Hazard (computer architecture)
Hazards are problems with the instruction pipeline in central processing unit microarchitectures that potentially result in incorrect computation...
is detected until the hazard is cleared. One example of a hazard is if a software program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
loads
Load (computing)
In UNIX computing, the system load is a measure of the amount of work that a computer system performs. The load average represents the average system load over a period of time...
data from the system bus
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
and calls for use of that data in the following cycle in a system in which loads take multiple cycles (a load-to-use hazard).
Mechanical
Interlocks may be strictly mechanical, as in the internal safety of a firearmFirearm
A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...
that prevents release of the firing pin unless the chamber is properly closed.
In the operation of a device such as a press or cutter that is hand fed or the workpiece hand removed, the use of two buttons to actuate the device, one for each hand, greatly reduces the possibility of operation endangering the operator. No such system is fool-proof, and such systems are often augmented by the use of cable–pulled gloves worn by the operator; these are retracted away from the danger area by the stroke of the machine. A major problem in engineering operator safety is the tendency of operators to ignore safety precautions or even outright disabling forced interlocks due to work pressure and other factors. Therefore such safeties require and perhaps must facilitate operator cooperation.
See also
- Poka-yokePoka-yoke' is a Japanese term that means "fail-safing" or "mistake-proofing". A poka-yoke is any mechanism in a lean manufacturing process that helps an equipment operator avoid mistakes . Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they...
- Fail-safeFail-safeA fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel....
- Breath alcohol ignition interlock deviceBreath alcohol ignition interlock deviceAn ignition interlock device or breath alcohol ignition interlock device is a mechanism, like a breathalyzer, installed to a motor vehicle's dashboard...
- Safety instrumented systemSafety instrumented systemA Safety Instrumented System is a form of process control usually implemented in industrial processes, such as those of a factory or an oil refinery. The SIS performs specified functions to achieve or maintain a safe state of the process when unacceptable or dangerous process conditions are detected...