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Cam timer
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Cam timer
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A 7 cam 7 contact cam timer

A cam timer[1] or drum sequencer is an electromechanical system for controlling a sequence of events automatically. It resembles a music box with movable pins, controlling electrical switches instead of musical notes.

Description

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An electric motor drives a shaft arranged with a series of cams or a drum studded with pegs along its surface. Associated with each cam is one or more switches. 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. Complex sequences of opening and closing switches can be made by the arrangement of the cams and switches. 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 determines which switch will activate along the length of the drum. Where the peg lies along the circular circumference of the drum determines at what point the peg will activate the switch in the drum's spin. The drum performs repetitive switching operations by controlling the timing and sequence of switches.

Most cam timers use a miniature mains synchronous motor to rotate the mechanism at an accurate constant speed. Occasionally, more complex timers with two motors are seen.

A drum sequencer is a reprogrammable electromechanical timing device that activates electric switches in repetitive sequences. These sequencers were primarily used in industrial applications to enable automated manufacturing processes.

Uses

[edit]

Industrial machines use Cam timers and drum sequencers to control repetitive sequencing operations. The cam followers often operated hydraulic valves. Cam timers in the industry were superseded by the introduction of programmable logic controllers (PLCs), which offer improved flexibility and more complicated control logic functions.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 machines, which drive the washing sequence according to a pre-programmed pattern. They are gradually being superseded by microprocessor-controlled systems, which have greater versatility and thus can more efficiently respond to various feedback.

Another example is the usage in electromechanical pinball machines, where the Cam timer is also known as a 'Score Motor.'

Methods used to increase control

[edit]

The most basic cam timer rotates continually, which is inconvenient when waiting 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 to heat up to a preset temperature). To achieve this, the cam motor is subjected to control by one of its switches. The timer 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 machine 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 for the method to heat to the nearest temperature below the one desired, then uses only the 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, 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 machines, 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

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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 in most applications, primarily to reduce costs and also to maximize product features.

Cam timers don't offer the greater flexibility that CPU-based controllers provide. In addition to 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. It also provides feedback on real-world failure rates and causes. All of these reduce manufacturing and business costs.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Cam timer

View on Grokipedia
from Grokipedia
A cam timer is an electromechanical device that employs a rotating cam mechanism, typically driven by a , to control the precise timing of on/off switching events for electrical circuits in systems. It operates by having cams mounted on a rotating shaft that activate or deactivate electrical contacts at predetermined positions during each cycle, which corresponds to one full revolution of the , enabling the repetition of a fixed of operations without requiring programming or software. Cam timers function through a combination of components including a drive motor, , adjustable cam discs for setting timing intervals, and contact mechanisms that interface with the cams to switch loads such as relays, motors, or valves. These devices support cycle times ranging from seconds to hours and can handle multiple channels (up to 30 or more) for synchronizing several actions, with options for AC or DC power inputs and mounting styles like or panel installation. In single-revolution mode, they can be configured to stop after one cycle via external controls, making them versatile for both continuous and intermittent operations. Widely applied in industrial and process control, cam timers are used for tasks such as sequencing cup dispensing in vending machines, controlling motors and valves in production lines, managing in greenhouses or street systems, and coordinating conveyor operations in factories. Their simplicity positions them as a cost-effective intermediary between basic and advanced programmable logic controllers (PLCs), particularly in environments requiring reliable, low-maintenance timing without digital interfaces. Key advantages include high timing accuracy (down to milliseconds in electronic variants), durability with minimal , ease of setup through physical cam adjustments, and long-term stability that avoids obsolescence issues common in software-dependent systems. Historically, cam timers represent an early form of sequential control in , predating PLCs and serving as a foundational for repeatable electromechanical programming in .

Fundamentals

Definition and Basic Principles

A cam timer is an electromechanical device designed to automate the sequential control of multiple events by mechanically actuating electrical switches at predetermined intervals. It typically employs a motor-driven shaft equipped with cams or a peg-studded rotating , where the physical profile of the cams or protrusions directly engages switches to open or close electrical circuits, thereby controlling elements such as motors, valves, solenoids, or relays in a repeating cycle. The fundamental operating principle relies on the continuous of the cam shaft or drum, driven by an , which translates angular motion into precise temporal actions through mechanical interaction. As the cams or drum lobes rotate, their raised sections or pegs depress or release switch actuators at specific angular positions, corresponding to time intervals determined by the rotation speed; this triggers electrical signals to initiate or terminate operations in a programmed . Synchronous motors are commonly used to ensure consistent rotational speed, independent of load variations, while integrated gearboxes reduce the motor's high speed to achieve the desired cycle duration, often ranging from seconds to hours for repetitive tasks. At its core, a cam timer functions as a physical analog to a , where the fixed cam profiles encode a deterministic sequence of states—each switch actuation representing a transition—governed solely by elapsed time rather than electronic logic or programming. This mechanical approach provides reliable, tamper-proof timing for applications requiring synchronized multi-step processes, such as industrial cycles.

Historical Development

The origins of cam timers trace back to 19th-century mechanical cams employed in looms and automata, where they facilitated precise sequential control of mechanical actions. In power looms, invented by in 1785 and widely adopted during the , cams converted rotary motion into linear movements to automate weaving patterns, marking an early form of programmed sequencing in machinery. Similarly, in automata such as Henri Maillardet's drawing automaton from the early 1800s, cams and levers orchestrated complex, timed motions to simulate human-like drawing and writing, demonstrating cams' role in repeatable event control. By the early , these mechanical principles evolved into electromechanical cam timers, integrating synchronous motors with cam-driven switches for automated electrical sequencing. A key milestone occurred in the 1930s and 1940s, when cam timers enabled industrial automation by providing timed control signals for repetitive processes, predating programmable logic controllers. In entertainment, machines from the 1930s onward incorporated score motors—electromechanical cam systems that stepped through scoring sequences via rotating cams actuating switches, powering the electromechanical era of arcade games until the 1970s. Concurrently, automatic washing machines, introduced in 1937 by Bendix, relied on cam timers to sequence wash cycles, filling, agitating, rinsing, and spinning through motor-driven cam contacts. Post-World War II, cam timers proliferated in consumer appliances as affordable synchronous motors, developed from early 20th-century clock technologies, became widely available for precise timing. , having acquired dishwasher technology in 1930, adopted cam timers in its 1950s models like the portable Mobile-Maid, automating full wash-to-dry cycles and contributing to the boom in household . This development drew influence from related relay-based sequencing systems in computing precursors, such as drum controllers that used rotating mechanisms with raised contacts to trigger operations in electromechanical calculators and early control devices.

Components and Mechanism

Key Components

The core of a cam timer is its drive motor, which provides the consistent rotational force necessary for sequencing operations. Typically, this is a operating at standard mains frequencies of 50/60 Hz, ensuring precise and repeatable speed without the need for feedback controls. These motors are often paired with reduction gearing, such as gear trains or modules offering ratios like 10:1, to extend cycle durations from as short as 3-6 seconds to over 24 hours per revolution, accommodating diverse timing requirements in industrial settings. Central to the timer's functionality are the cams or drum assembly, mounted on a rotating shaft to mechanically actuate connected devices at predetermined intervals. Cams are usually lobed discs made of durable plastic or metal, adjustable via screwdriver slots or ratchet locks to set the timing lobes' positions for on/off transitions. Alternatively, some designs employ a cylindrical with removable or adjustable pegs and studs inserted into grooves, allowing for straightforward reconfiguration of switch activation points without specialized tools. Up to 8-12 such cams or stations can be incorporated per timer, enabling multi-circuit control. The actuation of electrical circuits relies on switches positioned adjacent to the cams, which open or close in response to mechanical contact. Microswitches, often SPDT (single-pole double-throw) rated for 10-16A at 240V AC, are the standard for reliable, low-wear operation in modern units, providing snap-action responses for precise timing. In older or specialized designs, mercury-wetted contacts were used for their low resistance and arcing suppression, though they have largely been phased out due to environmental concerns. Enclosing the internal components, the serves to protect against , , and mechanical damage while facilitating integration into . Constructed from metal for robustness in industrial environments or impact-resistant for lighter applications, these casings often feature IP-rated seals and mounting brackets for panel, surface, or DIN-rail installation. Manual adjustment mechanisms, such as a supplied key or wrench for cam repositioning, are typically accessible via a or removable cover, allowing on-site programming without disassembly. Power supply integration ensures compatibility with control systems, with low-voltage wiring connecting the timer to external circuits. Common configurations support 24V for safety in automated setups or 120V AC for direct mains operation, using terminals or screw blocks for secure, low-resistance connections that minimize across multiple stations.

Operational Mechanics

A cam timer's operation commences with cycle initiation, wherein a synchronous activates to drive the cam shaft or at a constant, predetermined speed, often calibrated for one full revolution to correspond to a complete operational cycle. This motor, typically powered by AC voltage, engages through a reduction gearbox to ensure smooth and reliable rotation, preventing abrupt starts that could disrupt sequencing. During the actuation process, as the cam shaft rotates, the contoured lobes or protrusions on individual cams sequentially engage follower arms or levers linked to electrical switches. These engagements mechanically displace the switch contacts, closing or opening circuits to activate connected devices in a programmed order; for example, a lobe might depress a follower to close a switch and energize a after approximately 30 degrees of shaft . The precise positioning of lobes on the cams dictates the timing and duration of each switch state, allowing for complex sequences without electronic intervention. Timing precision in cam timers relies on the gearbox's gear ratios, which regulate the motor's high-speed output into slower, controlled dwells and transitions between actuations. For instance, in a 12-hour cycle configuration, a gearbox with appropriate reduction might enable 12 switches to trigger events at hourly intervals by apportioning the shaft's 360-degree rotation into equal 30-degree segments. This mechanical gearing ensures repeatability, with dwell periods determined by the angular extent of flat or low-profile sections on the cams where followers remain stationary. In single-revolution configurations, upon completing one revolution, an end-of-cycle cam or integrated notch interrupts the motor circuit via a dedicated switch, resetting the system to its initial state. In continuous mode, the sequence repeats indefinitely under power, or until manually halted or de-energized, maintaining operational continuity in repetitive tasks.

Applications

Industrial Applications

Cam timers play a crucial role in industrial automation, particularly for sequencing complex machinery in environments. In process industries, cam timers facilitate the sequencing of and pumps during batch operations, such as chemical mixing or , where cycles range from 3 seconds to 24 hours. These devices ensure accurate timing for ingredient addition, agitation, and discharge, minimizing waste and adhering to safety protocols in hazardous environments like chemical plants. A mechanical cam timer mechanism, for example, can automate multi-step control to regulate fluid flow in processing lines. A historical example of cam timer application appears in mid-20th century machines, where score utilized stacked cams to execute multi-step scoring sequences. These electromechanical assemblies rotated to trigger switches for adding points, running lights, and resetting mechanisms, demonstrating early precision timing in entertainment manufacturing. While effective for repetitive sequencing, cam timers in industrial settings are increasingly supplemented or replaced by programmable logic controllers (PLCs) for greater flexibility in modern .

Domestic and Consumer Applications

Cam timers have been integral to the of laundry appliances, particularly in older washing machines where they orchestrate pre-programmed cycles such as filling, washing, rinsing, and spinning. In models like those from in the 1950s, an electromechanical cam timer uses a small motor to rotate cams that activate switches, precisely timing water intake via valves, agitation through the motor, drainage, and high-speed spinning to extract moisture. This mechanical sequencing ensured reliable operation without electronic components, allowing users to select cycles via a dial that advanced the timer through fixed stages. In dishwashers, cam timers provide control over chemical dispensing and management, with adjustable cams enabling customization for optimal cleaning. For instance, in commercial-grade consumer models like the CMA UC65e, the timer assembly features dedicated cams for and rinse-aid pumps: the cam, adjustable by rotating its halves, initiates dispensing at the start of the wash cycle, while the rinse-aid cam times injection during the final rinse to prevent spotting based on . These adjustments, often set by chemical suppliers, also influence levels for effective without over-dosing. Clothes dryers from the mid-20th century similarly employed cam timers to sequence application and tumbling for efficient . The timer's motor drives connected to cams that open and close circuits, controlling the and rotation in stages—such as initial high- tumbling followed by cool-down periods to minimize fabric damage. This setup allowed for selectable cycles like "normal dry" or "delicate," with the cam mechanism ensuring the process halted automatically after a set duration. Older kitchen appliances utilized cam-based mechanical timers for basic operational sequencing. These electromechanical devices, common before the , rotated cams to switch elements on and off, integrating with manual dials for user-set durations in standalone timers or built-in controls. In consumer entertainment and vending devices, cam timers facilitated electromechanical sequencing for interactive experiences. Early arcade games and coin-operated vending machines, such as kiddie rides from the mid-20th century, relied on cam timers to control payout mechanisms and play durations, where inserted coins activated a motor-driven cam that timed lights, sounds, and mechanical actions before resetting. This approach provided reliable, tamper-resistant automation in public settings.

Advanced Features

Methods to Enhance Control

To enhance the control flexibility of basic cam timers, which typically operate on fixed sequences driven by a constant-speed motor, several mechanical and electromechanical modifications have been developed. These allow integration of external conditions, such as or load states, to pause or adjust the timing cycle without altering the core cam design. For instance, motor speed control can be achieved by incorporating or switches that temporarily halt the rotation until a specific condition is met, effectively varying the overall cycle duration. Stop-and-wait mechanisms further refine this by employing auxiliary cams or levers that disengage the drive train until an external signal, like a temperature reaching equilibrium, reactivates the motor. These auxiliary components, often in the form of pivoted arms or catch systems on the timer shaft, allow the cam timer to synchronize with process variables; for example, in equipment, a microswitch connected to a booster heater halts cam advancement if rinse water is below 180°F (82°C), ensuring compliance with sanitation standards before proceeding. This approach mimics conditional pausing in sequences, where the timer remains in a holding position—such as during a soak phase—until the sensor feedback confirms readiness. Fast-forward capability introduces user or diagnostic overrides to accelerate cycles, bypassing unnecessary steps for testing or abbreviated operation. This is commonly realized through manual override mechanisms, such as a rotatable dial or knob directly advancing the , or alternate gearing sets that increase motor-to-cam ratio for quicker revolutions. In automatic timers, a selector knob permits manual rotation to skip to later phases like spin, reducing full-cycle time from hours to minutes when needed, while preserving sequential integrity for normal use. Such features rely on slip clutches or detents to prevent backlash during override. Feedback loops in cam timers extend control by adding simple state-detection switches that enable rudimentary conditional logic, allowing the sequence to based on detected conditions rather than strict time-based progression. Additional microswitches, positioned along the cam path or externally, monitor variables like fill levels or , feeding back to interrupt or redirect the motor path via circuits.

Variations and Types

Cam timers, also known as drum sequencers in certain configurations, utilize a rotating cylindrical fitted with pegs or cams to actuate switches at predetermined intervals, enabling easy reprogramming by repositioning the pegs for adjustments. This design was prevalent in early industrial control systems where flexibility in event sequencing was required without complex wiring. Disc cam timers feature multiple lobed discs mounted on a common shaft, allowing for compact arrangements that support high-precision timing across several output stations, typically up to eight. These discs are often adjustable via ratchet locks on a hexagonal , facilitating precise control of multiple load circuits in applications demanding synchronized operations. For instance, models like the Rotalink PN63 series employ such disc configurations to manage 2 to 5 valves with cycle times ranging from 4 to 20 minutes. Pneumatic variants of cam timers incorporate air-driven motors, rendering them intrinsically safe for use in hazardous environments such as chemical plants, where electrical sparks pose risks. These timers operate on pressure between 25 and 100 psi, avoiding ignition hazards while maintaining reliable sequencing; examples include the Rotalink HSMP2 and GMG types, which support cycle durations from 1 minute to 16 hours and are enclosed in molded housings with centrifugal governors for consistent performance. Modular cam timers, such as the Eagle Signal TM series, consist of modules that assemble in a single orientation via keyed designs, enabling customization of cycle lengths from minutes to hours by stacking appropriate time modules. Each module contributes a specific timing increment, with the overall assembly driving cams to control repeat cycles, as seen in configurations supporting up to 4 or more output cams for industrial repeat operations.

Evolution and Replacement

Advantages and Disadvantages

Cam timers exhibit several advantages, particularly in environments requiring consistent, repetitive operations. Their simple mechanical construction, consisting of rotating cams that actuate switches, ensures high reliability for fixed sequences without dependence on electronic components or power supply fluctuations. This design eliminates software vulnerabilities, such as bugs or cyber threats, making them suitable for critical applications where electronic failures could disrupt processes. In low-variation settings like household appliances, cam timers demonstrate a long lifespan, often exceeding 10 years with proper use, due to their robust build and minimal part count. Additionally, they are cost-effective to manufacture and maintain, especially when compared to early electronic timers that required more complex circuitry and were prone to higher production costs. These timers deliver precise, repeatable timing for predetermined cycles, avoiding calibration drift common in some older electronic systems affected by temperature or aging components. Despite these strengths, cam timers possess notable disadvantages that limit their applicability in modern contexts. Their flexibility is inherently restricted, as modifying timing sequences necessitates physical reconfiguration of the cams, which is labor-intensive and error-prone compared to programmable alternatives. Over time, mechanical wear on the cams, followers, and associated switches can cause inaccuracies or outright failures, particularly under frequent use. For applications demanding complex sequences with numerous switching events, cam timers tend to become relatively bulky due to the need for additional cam shafts and switches, increasing overall size and installation challenges. Furthermore, they are sensitive to environmental factors like , , and , which can accelerate wear, jam mechanisms, or degrade timing accuracy.

Shift to Electronic Alternatives

The transition from cam timers to electronic alternatives began gaining momentum in the industrial sector during the 1970s, primarily through the adoption of programmable logic controllers (PLCs), which were developed to replace hardwired relay systems, drum sequencers, and mechanical timers like cam timers. This shift addressed the limitations of mechanical devices in adapting to frequent production changes, as seen in early applications by in 1968, where PLCs were sought to simplify rewiring for automotive assembly lines. By the , the move extended to consumer goods, with microcontrollers enabling more precise and flexible control in appliances. Key drivers for this replacement included the reprogrammability of electronic systems, which allowed for easy modifications without physical alterations, unlike cam timers that required manual reconfiguration of mechanical components. Electronic alternatives also provided built-in diagnostics for fault detection, greater compactness to save space in control panels, and reduced wear from , leading to lower long-term maintenance costs compared to the and degradation inherent in cam mechanisms. These advantages made particularly appealing in environments demanding and reliability, such as and household . In industrial settings, cam timers used for sequencing operations were largely supplanted by PLCs, which offered scalable logic execution for complex processes without the need for custom mechanical builds. For consumer applications, washing machines transitioned from electromechanical cam-based cycle controls to microcontroller-driven systems by the early 1980s. Application-specific integrated circuits () further refined this in later designs, enabling dedicated control logic tailored to appliance cycles. Despite the widespread adoption of electronic controls, cam timers persist in certain legacy systems where mechanical simplicity and proven reliability outweigh the need for advanced features, such as in some safety circuits that employ retiring cam protection timers to ensure safe door operations between landings. These applications highlight the enduring value of cam timers in scenarios prioritizing minimal electronic dependency and robustness against power fluctuations.

References

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