Solenoids for automatic dispensing systems in kiosks and smart ticket machines

Solenoids for automatic dispensing systems are the actuators that release product, open compartments and lock doors in self-service kiosks, smart lockers and vending terminals. They convert an electrical signal from the controller into linear motion or a holding force, within milliseconds and without any user intervention.

In this type of equipment, the solenoid is one of the few components that moves in every transaction. That is why its selection determines much of the machine’s reliability. An undersized force or a miscalculated duty cycle leads to compartments that fail to open, jammed product and maintenance call-outs.

What a solenoid does inside a kiosk or automated locker

A self-service terminal usually has three distinct electromagnetic functions, and each one requires a different type of device.

• Product release and ejection

A linear solenoid moves a plunger when it is energised. That movement actuates a flap, releases a product from a channel or pushes a card towards the exit slot. It can work in pull or push mode and, if it includes a return spring, it goes back to its initial position when the power is cut.

It is the usual solution in ticket, card and receipt dispensers, and in gravity-fed dispensing mechanisms.

• Compartment locking

An electromagnetic lock keeps each compartment door closed until the system validates the operation (code, QR, payment or identification). A parcel locker can have dozens of locks managed by a single controller, each one assigned to a cell.

Here the critical parameter is not just force. What happens if the power supply is cut also matters, which we cover further below.

• Holding doors and covers

Electromagnetic holding magnets retain a metal door or cover through attraction force, with no parts in sliding contact. They are used on service doors, restocking panels and technical access covers, where firm and silent holding is required.

Technical requirements in high-use terminals

A kiosk in a station or a locker in a shopping centre can accumulate hundreds of operations a day. These are the parameters worth checking on the datasheet before choosing a model.

Duty cycle and coil temperature

The duty cycle (ED %) indicates what percentage of the time the coil can remain energised without exceeding its maximum temperature. A solenoid sized for short pulses can overheat if the software keeps it energised longer than planned, for example when a door is left open.

It is advisable to define the real usage profile: the duration of each pulse, the frequency of operations and the internal temperature of the equipment. In kiosks with a screen and electronics, that temperature is usually higher than the ambient temperature.

Force across the full stroke

The force of a linear solenoid is not constant: it increases as the plunger approaches the end of its stroke. The figure that matters is the force available at the point where the mechanism offers the most resistance, which is usually the start of the movement.

As a reference, our ECM Series covers strokes from 3 to 12 mm and forces from 0.02 to 32 N, a suitable range for compact release and interlocking mechanisms.

Behaviour during a power failure

In lockers and dispensers holding valuable contents, this is the design decision with the greatest consequences.

Bistable locks only draw power during the change of state. In a locker with many cells powered by battery or solar energy, this difference can determine the sizing of the entire installation.

Mounting space and protection rating

Self-service terminals have very compact internal layouts. The solenoid format (circular, square or open-frame) and its fixing method must be defined together with the mechanical design, not afterwards.

The IP protection rating, defined in IEC 60529, indicates the enclosure’s resistance to the ingress of dust and water. For indoor equipment, IP40 is usually sufficient. For lockers installed outdoors or in semi-covered areas, this point should be reviewed in more detail. We explain it in our article on IP ratings in solenoids.

Real applications in self-service equipment

• Parcel lockers and smart luggage lockers

Each cell incorporates a lock that releases when the user enters their code. The usual set-up is a fail-secure lock, which protects the contents during a power failure, combined with a sensor or contact that confirms to the system that the door has been closed again.

• Ticket kiosks and card dispensers

A linear solenoid actuates the mechanism that separates and ejects the ticket or card. Here, repeatable movement and a stable response time are the priority, because the system coordinates the actuator with rollers, readers and passage sensors.

• Product dispensers and retail pick-up points

In dispensers for higher-value products or at click & collect points, the solenoid combines two functions: releasing the product and blocking access to the rest of the inventory. This is a typical case where a custom design simplifies the equipment’s mechanics.

• Terminals with restricted technical access

Service doors on kiosks and payment terminals are usually protected with electromagnetic locks or holding magnets managed by the controller itself, which allows every opening to be logged.

How to choose the right solenoid for each mechanism

The table is a starting point. The final choice depends on the force required at the critical point of the stroke, the available voltage, the duty cycle and the real mounting space. You can browse the full range of electromagnetic safety locks and magnetic and electromagnetic holding magnets.

When a custom solenoid makes sense

Catalogue models cover most cases. A specific development makes sense when any of these situations arise:

• The available space does not accommodate the standard format.
• A specific force or stroke is required at a given supply voltage.
• The equipment combines release and locking in a single device.
• Production volume justifies optimising cost, fixing and wiring.

At NAFSA we have been designing and manufacturing solenoids since 1996, and we work under a quality management system certified to ISO 9001:2015. In our custom manufacturing projects, we start from the equipment manufacturer’s requirements, develop prototypes and carry out functional tests before moving to series production.

Benefits of a correctly sized solenoid in self-service equipment

Selecting the right actuator from the design stage has a direct effect on the terminal’s operation and maintenance:

• Fewer service incidents. A force and duty cycle matched to real use prevent compartments that fail to open, product jams and maintenance visits.
• Fast, repeatable response. The solenoid actuates within milliseconds of the controller’s signal, which is key when it is coordinated with readers, rollers and sensors.
• Security defined by design. Choosing between fail-secure, fail-safe or bistable sets in advance how the equipment behaves during a power failure.
• Reduced consumption. Bistable locks only draw power during the change of state, which simplifies sizing in battery- or solar-powered lockers.
• Holding without friction wear. Electromagnetic holding magnets retain doors and covers with no sliding parts and silently.
• Access traceability. Because they are managed from the controller, every service door opening can be logged.

In kiosks, lockers and automatic dispensers, the solenoid is a small component with a direct impact on equipment availability. Most failures that appear once the equipment is in service can be avoided by properly defining four things: the function (release, lock or hold), behaviour without power, the real duty cycle and the mounting space.

Frequently asked questions

What type of solenoid is used in a smart locker?

Normally one electromagnetic lock per cell. The most common choice is a fail-secure model, which keeps the door locked if the power is cut, to protect the contents of the compartment.

What is the difference between a fail-safe and a fail-secure lock?

A fail-safe lock unlocks when it loses power, while a fail-secure lock remains locked. The first is used where access or evacuation must be guaranteed, and the second where the priority is protecting the contents.

When should a bistable lock be used?

When the equipment runs on battery or needs to reduce consumption. A bistable lock only draws power during the change of state and holds its position without current.

What is the duty cycle of a solenoid?

It is the percentage of time the coil can remain energised without exceeding its maximum temperature. If real use exceeds the specified duty cycle, the coil heats up, loses force and its service life is shortened.

What IP rating does a solenoid need for a kiosk?

For indoor equipment, IP40 is usually sufficient, as it protects against solid particles. For outdoor lockers or semi-covered areas, the protection of the equipment enclosure should be assessed and, if necessary, that of the solenoid itself.

Can solenoids be custom-made for a specific dispenser?

Yes. When the format, force or voltage does not fit a standard model, we develop the solenoid from the manufacturer’s specifications, with a prototype phase and testing before series production.