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A cam timer or drum sequencer is an
electromechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems ...
system for controlling a sequence of events automatically. It resembles a
music box A music box (American English) or musical box (British English) is an automatic musical instrument in a box that produces musical notes by using a set of pins placed on a revolving cylinder or disc to pluck the tuned teeth (or ''lamellae'' ...
with movable pins, controlling electrical switches instead of musical notes.


Description

An
electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
drives a shaft on which is arranged a series of
cam Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...
s or a drum studded with pegs along its surface. Associated with each cam is one or more
switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
es. The motor rotates at a fixed speed, and the camshaft is driven through a speed reducing gearbox at a convenient slow speed. Indentations or protrusions on the cams operate the switches at different times. By arrangement of the cams and switches, complex sequences of opening and closing switches can be made. The switches then operate different elements of the controlled system - for example motors, valves, etc. A programmer may change or rearrange (reprogram) peg or cam positions. Much like the pegs in a music box cylinder activate the notes, in a drum sequencer, as the drum of the sequencer spins, the pegs run across switches activating machine processes. The placement of the pegs along the length of the cylinder determine which switch along the length of the drum it will activate. Where the peg lies along the circular circumference of the drum determines at what point in the spin of the drum the peg will activate the switch. By controlling the timing and sequence of switches, the drum performs repetitive switching operations. Most cam timers use a miniature mains
synchronous motor A synchronous electric motor is an AC electric motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Syn ...
to rotate the mechanism at an accurate constant speed. Occasionally more complex timers with two motors are seen. A drum sequencer is a re-programmable electromechanical timing device used to activate electric switches in repetitive sequences. Primarily, these sequencers were used in industrial applications to enable automated manufacturing processes.


Uses

Cam timers and drum sequencers were primarily used with industrial machines to control repetitive sequencing operations. The cam followers often operated hydraulic valves. Cam timers in industry were superseded with the introduction of programmable logic controllers (PLCs), which offer improved flexibility and more complicated control logic functions. In consumer products like washing machines, they were replaced with ASICs or microcontrollers. The most common use for cam timers is in automatic
washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...
s, where they are used to drive the washing sequence according to a pre-programmed pattern. They are gradually being superseded by
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...
-controlled systems, which have greater versatility, and thus can more easily respond to various feedback. Another example is the usage in electromechanical
pinball Pinball games are a family of games in which a ball is propelled into a specially designed table where it bounces off various obstacles, scoring points either en route or when it comes to rest. Historically the board was studded with nails call ...
machines, where the Cam timer is also known as a 'Score Motor'


Methods used to increase control

The most basic type of cam timer rotates continually, which is not suitable when needing to wait for events that occur at variable times. With washing machine cam timers, it is necessary to wait a variable amount of time (for example waiting for a tank of
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
to heat up to a preset temperature). To achieve this, the cam
motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
subjects itself to control by one of its
switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
es. The
timer A timer is a specialized type of clock used for measuring specific time intervals. Timers can be categorized into two main types. The word "timer" is usually reserved for devices that counts down from a specified time interval, while devices th ...
sequence switches the cam motor off, and the motor is started again by the signal from the thermostat when the required temperature is reached. Usually washing machines thermostats have fewer fixed temperature detection points than the number of wash temperatures used. For intermediate temperatures, the cam mechanism uses the stop and wait method to heat to the nearest temp below the one desired, then uses only fixed timing of the heating element to increase the water to the desired temperature. Some cam timers also have a fast forward mode, where applying power to a point on the controller causes rapid advance of the mechanism. This is often seen on washing machine controllers. Rapid advance can be achieved by moving of gearing, which may be triggered by various means. Using feedback and external time delay and other sensory circuits, it is possible to build an electromechanical state machine using a cam timer. These are common in
washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...
s, where the cam timer runs in phases, but also stops and waits for external signals such as a fill level sensor, or a water heating temperature sensor.


Replacement with electronic controllers

While still fairly popular, cam timers are mechanical and hence subject to wear and reliability problems. Their reliability record remains good, but there is always some failure rate with mechanical switch contacts. Electronic controllers have largely replaced cam timers for most applications, primarily to reduce costs, and also to maximize product features. Cam timers don't have the greater degree of flexibility that CPU-based controllers provide. As well as offering more wash program variations, a CPU based washing machine controller can respond to malfunctions, automatically initiate test cycles, reducing manufacturing costs, and provide fault codes in the field, again reducing repair costs, and providing feedback on real world failure rates and causes. All of these reduce manufacture and business costs.


See also

* Clock * Drum machine (electronic musical instrument) *
Timer A timer is a specialized type of clock used for measuring specific time intervals. Timers can be categorized into two main types. The word "timer" is usually reserved for devices that counts down from a specified time interval, while devices th ...
*
Player Piano A player piano (also known as a pianola) is a self-playing piano containing a pneumatic or electro-mechanical mechanism, that operates the piano action via programmed music recorded on perforated paper or metallic rolls, with more modern im ...
(with a looped tape) * :Mechanical musical instruments – contains automatic playing musical instruments using pinned cylinders, etc. *
Pinball Pinball games are a family of games in which a ball is propelled into a specially designed table where it bounces off various obstacles, scoring points either en route or when it comes to rest. Historically the board was studded with nails call ...


External links


Drum Sequencer
{{DEFAULTSORT:Cam Timer Electrical components Control devices Mechanisms (engineering)