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UNDERSTANDING SOLENOIDS:DEVELOPMENT AND SUPPORT FOR BETTER SOLUTIONS
Our core competence is the joint development of solenoids solutions that focus precisely on your application-specific problem matrix. At the same time, they deliver cost-effective volume production for us and for yourselves. Our responsive development teams are made up of dedicated experts at the top of their fields, able to set new benchmarks for solenoids technology time and again.
On this page, we focus on the important things to know about solenoids. The aim being to give you an initial understanding of the topic, so that you are better able to evaluate the benefits of using this technology in your application.
Contact us to evaluate your specific requirements on a joint basis and to devise the optimum solution for your application.
This is what you gainAdvantages
solenoids
Electromagnetic systems compete with an immensely wide variety of actuator principles such as electric motors, piezo actuators or pneumatic systems. Solenoids can be characterised as having the following advantages:
- Short switching times and good dynamic properties
- Simple mechanical design
- Direct drive
- Good scope for integration in relation to design and interfaces
- Flexible in relation to ambient conditions (temperature range and protection classes)
- Simple electrical control
- Maintenance-free
A linear solenoid is a solenoid that can generate a linear movement by applying a force. For this, there are various forms of how types of movement can be performed.
SINGLE LINEAR SOLENOID PUSH-TYPE & PULL-TYPE:
In push mode, force is transmitted by a non-magnetic plunger.
In pull mode, force is transmitted by what is known as an armature.
REVERSIBLE LINEAR & SPREADING SOLENOID:
This illustration shows the reversal of movement and direction of force on each double coil system. This transmission facilitates alternating switch-overs.
Here, force is transmitted in the opposing direction by two simultaneous movements. This makes it possible to create a version that can push as well as pull.
A rotary solenoid is a solenoid that generates rotational movement in response to a torque input. Depending on static or dynamic requirements, different forms of build and mounting can be used.
Monostability refers to a design that has a stable position when not energised, for example with a return spring. In contrast to this, on a bistable design, the solenoid has two stable positions when not energised, typically achieved through the use of a permanent magnet.
All previously described forms of linear and rotary solenoid can be designed to be monostable as well as bistable, depending on requirements.
A hinged armature solenoid is a solenoid that generates a rotational movement in response to a force. One side of the moving part of the solenoid is in contact with the stationary solenoid system.
A holding solenoid is a solenoid that generates a holding force against what is known as an armature plate. A distinction is made here between a holding solenoid and a permanent holding solenoid.
HOLDING SOLENOID AND PERMANENT HOLDING SOLENOID:
The holding force is generated on the black armature plate by excitation of the coil.
While de-energised, this involves a permanent solenoid generating a holding force on the black armature plate that can be neutralised again by excitation of the coil.
With an oscillating solenoid, oscillating or linear movements are generated in a targeted manner. In this process, vibrations are used in a targeted manner for the conveying, provision, shaking or sorting of workpieces or other loose components. In a modified form, this principle is also applied in active haptics for motor vehicles.
Understanding important product properties
DEFINITION OF STROKE
- The stroke is the working range across which the armature can operate freely. External or internal forces position the armature in its initial stroke position. (at X mm, initial stroke position)
- After switching on the power supply the armature moves towards its final stroke position (at 0 mm, final position of stroke that limits movement mechanically).
STROKE EFFORT
- Surface A below the MAGNETIC FORCE STROKE CHARACTERISTIC CURVE is referred to as stroke effort.
- When using standard materials, the achievable stroke effort depends on the volume of the solenoid and the available electrical power.
MAGNETIC FORCE STROKE CHARACTERISTIC CURVE
- The geometric design of the iron circuit enables the distribution of stroke effort (and therefore the force characteristic curve) to be adapted to suit specific tasks.
- For an initial estimate, it can be said that the surface (stroke effort) remains constant.t.
Dynamic behaviour describes the electrical, magnetic and mechanical compensation processes arising during switch processes in response to energy transformations. The requirements on the dynamic behaviour of a solenoid can vary greatly depending on the application.
When designing a solenoid, a compromise needs to be made between the rapid increase in current (low inductivity) and a high level of acceleration force.
(source: VDE 0580)
U: Voltage
I: Current
s: Stroke
t: Time
A PROCESS OF INCREASING AND DECREASING TAPER IS DIVIDED INTO THE FOLLOWING INTERVALS OF TIME:
t1 Pull-in time
Time to completion of pull-in
t11 Response delay
Time from applying voltage to the start of armature movement. As current rises, the magnetic field builds up that generates magnetic force (electromagnetic energy conversion). The armature starts to move once the solenoid force and the restoring force are in balance.
t12 Stroke time
The time from the start of armature movement to the point when final stroke position is reached (electro-magneto-mechanical energy conversion). Intermittently, the coil current drops in response to a negative induction voltage that is prompted by a change in field and armature movement.
t2 Drop-off time
Time until complete drop-off. The field change due to a drop in current and armature movement generates a negative induction voltage.
t21 Drop-off delay
Time from when voltage is switched off to the start of release movement. As current drops, the magnetic field builds up, generating magnetic force. The release movement starts once restoring force and magnetic force are in balance.
t22 Release time
The time from the start of release movement until initial stroke position is reached.
t5 Switch-on time
Time with voltage applied.
COMPARISON OF FAST AND POWERFUL SOLENOIDS OF THE SAME SIZE:
THE SWITCHING TIME OF A SOLENOID IS INFLUENCED BY:
- The type of control
- Speed of increase in current, speed at which the magnetic field and coil data build up
- Moved masses
- Level of the mechanical restoring and opposing forces
- Magnetic circuit as such (influencing of characteristic curve, measures to reduce the eddy current)
With the help of modern FEM calculations, dynamic behaviour can be designed accurately for any given application.
CONTROL OF SOLENOIDS
Control affects the force, switching time, noise generation and self-heating. Conversely, the inductive properties of the solenoid also have an effect on control and can lead to malfunctions or damage to electrical components that can however be avoided through the use of specific circuitry.
Without exception, the following can be assumed: The higher the current, the higher the magnetic force. This causal relationship is limited by the self-heating of the solenoid (see thermal behaviour of solenoids).
Different forces affect acceleration which in turn affects the switching time of solenoids. However, this does not only depend on the control, but is also affected by dynamic properties (see dynamic behaviour of solenoids).
Accordingly, with a selected control signal, coupled to design measures, noise generation can be reduced.
THE FOLLOWING SECTION SHOWCASES THE TWO FUNDAMENTAL TYPES OF CONTROL:
Control with constant voltage
Whenever the solenoid is being controlled at a constant voltage (U), the current (I) rises to a maximum value of Imax. The electrical load heats the coil, causing the current to drop to a value of Ihot after completion of the thermal compensation processes. The same applies to magnetic force (F).
Control with constant current
If the solenoid is operated at a constant current (I) a voltage peak occurs initially. Then voltage (U) drops to Ucold. This electric load heats the coil causing voltage to rise gradually to Uhot.
Although current control has the advantage of force (F) being independent of thermal factors, the costs compared to voltage control tend to be higher.
To match the choice of materials and stroke effort of a solenoid perfectly to suit application-specific conditions, it is important to pay attention to certain key parameters.
As well as self-heating of the solenoid, ambient conditions are of decisive importance. Which maximum and minimum ambient temperatures can arise? Are there other heat sources in the immediate vicinity? Can heat be dissipated by air cooling or by appropriate attachments or does heat build up because of the enclosure around the solenoid system?
In conjunction with the type of electrical control (see Electrical Control), the worst case scenario can be defined. This is the configuration in which the solenoid receives the lowest supply of power while being at the same time exposed to the highest temperatures. Under these conditions, the solenoid must be able to perform its function without, in extreme cases, overheating at minimum temperature and maximum power supply (exceeding the class of insulating material) or without exceeding the permitted level of input current.
The following section lists the most relevant operating modes for solenoids. In all cases, it is possible to distinguish here between three operating modes. The key thing is that the shorter the relative duty cycle, the higher the maximum possible power consumption which also applies to the achievable stroke effort of a solenoid.
Uninterrupted operation [UO] S1 = 100% DC
The solenoid can be operated continuously at the specified rating. The maximum temperature (stabilised temperature) that arises then does not exceed the permitted insulation class of these materials.
Short-time operation [SO] S2
The duty cycle is so short that the stabilised temperature is not reached and the zero-current intermissions become so long that the solenoid can cool down to reference temperature.
Intermittent operation [IO] S3
The duty cycle and the zero-current intermission alternate on a regular or an irregular basis with the intermissions short enough to prevent the solenoid from cooling down to the ambient temperature.
PV = Power dissipation
б = Temperature
t = Time
The operating mode is defined primarily by the relative duty cycle.
Duty cycle
This is the time span during which the solenoid is switched on.
Pulse width
This is the time span between switching off and then switching the solenoid back on.
Period
This is the sum of duty cycle and zero-current intermission.
The IP protection category classifies the protection of a product against foreign bodies, physical contact and water.
Generally speaking, distinctions between solenoids are made on the basis of the protection category of the device and the protection category of the electrical connection.
The design of a product can be influenced significantly by the IP protection class because other components such as sealing rings or moulding of the entire system may be required.
IP XY
X = Protection against foreign bodies / physical contact
Y = Protection against the ingress of water
Documentation for further reference/sources:
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INTERIOR PRODUCTS
Gruner HMI solutions are an incredibly important interface between man and machine. Whether in the form of haptic actuators, noise-damped interlocking solenoids or permanent solenoids: With Gruner you sense what it means to be in contact with the future.
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For a vast range of instruments: Our active haptic solutions are in a class of their own. In displays, touchpads, light outputs, switches on steering wheels or gear selector levers, we provide appropriate solutions that deliver perfect feedback.