BioMetal is a thin fiber-like metal actuator (driving unit) which acts like a muscle.
Although soft and pliable like a nylon thread under normal conditions, it becomes stiff like a piano wire and sharply contracts when a current is fed through it.
If the passage of current is stopped, it will soften and extend to its original length.
It can be repeatedly moved any number of times.
The same effect can be obtained by heating it by hot air.
Actuators mainly used for extension and contraction are called artificial muscles to distinguish them from ordinary motors.
Artificial muscles are generally classified into two types: rubber-based (pneumatic pressure-driven) and chemicals-based (high polymer).
BioMetal is a metal-based artificial muscle made of a shape-memory alloy.
Its name is derived from the fact that it is a metal actuator which moves flexibly and smoothly like a living being.
BioMetal is a registered trademark of TOKI CORPORATION. It is incorporated nto two families of products: thread-like BioMetal Fiber (BMF series) and microcoil-like BioMetal Helix (BMX series)

BioMetal is not a mere shape-memory alloy wire but an artificial muscle made of a shape-memory alloy.
It is anisotropically structured so as to deliver its superb performance characteristics in the direction of extension/contraction.
The term anisotropy refers to the characteristic of a material for which a physical property varies with the direction.anisotropy Lumber and cloth are typical examples of anisotropic materials.anisotropy Living bodies are made mainly of anisotropic materials.

BMF (BioMetal Fiber) is a thin wire into which BioMetal is made for use in the direction of extension/contraction, and BMX (BioMetal Helix) is a thin coil/spring into which BioMetal is worked.
Although the kinetic distortion (the magnitude of movement or the variation in length) of BMF is as small as about 5% of its original length, it is possible to obtain a considerably great force from it.
BMX is not superior in terms of practical load (generated force).
With reference to the contracted state, however, a great kinetic distortion of 100% or more can be produced.

BioMetal Fiber, BMF series
(PDF 356KB)

BioMetal Helix, BMX series
(PDF 708KB)

The thinner the thickness of BioMetal, the higher do its durability, self-extension/contraction, and other performance characteristics tend to be.
Except for applications where a great force is required of a single wire, it is recommended to select a product thinner than BMF150 as an actuator which is to be repeatedly operated multiple times.
At present, BMF100, the standard product in the BMF series, offers the most excellent balance of performance, price, and quality.
The same is true of the BMX series.
It may be said that full advantage of BioMetal can be taken in such applications that only a relatively small magnitude of force is demanded of a thin wire.

Here, the term "kinetic distortion" means the difference between the length of BioMetal in the energized state and that in the non-energized state.
It is equal to the operation distortion or stroke of BioMetal used as an actuator.
The load may be regarded as the magnitude of the force produced by BioMetal for exertion on the outside.
The load (force) and kinetic distortion are closely associated with service life.
Even if repeatedly operated, BioMetal is kept highly stable in structure, involving practically no change in movement or performance, as far as it is within proper ranges of load and kinetic distortion.
The proper range of load is referred to as the practical load, and the proper range of kinetic distortion as the practical kinetic distortion.
MioMetal can be activated more than 100 thousands times as far as it is used within these ranges.
Further, it can be repeatedly used several thousands of millions of times, depending on the conditions.
Reference: Practical service range.

The service life of BioMetal is defined as the number of times it can be utilized as an actuator.
It has a track record of making more than three thousands of millions of reciprocating motions within the appropriate ranges of load and kinetic distortion.
It would never be overheated when used within these ranges.
BMF100, for example, has been activated 0.42 billion times for performance testing at a load of 80.0 gf and at a kinetic distortion of 2.5%, and the test still remains continued.
If BioMetal is continuously used to the limit of kinetic distortion, it may be overheated even under proper load conditions, resulting in a loss of life.
It is the most basic in the use of BioMetal to turn off current before it contracts completely.
When it is to be repeatedly used, it should be operated in an appropriate range, referring to the practical service range diagram.

It is thermal energy that drives BioMetal directly.
When a current is fed through it, it is activated by Joule heat generated in it by the current.
The greater the current, the quicker does it move. After the passage of current is stopped, it cools and returns to its original length.
The speed of motion is determined by the cooling rate.
The thinner BioMetal contracts more quickly under the same conditions. When BMF100 is repeatedly heated and cooled so that its length varies to 3% of its total length, it makes three reciprocating motions per second.

BioMetal can produce a stress of about 500 MPa unless it is used repeatedly. This is equivalent to a force of about 400 gf for BMF100 which is 0.1 mm in diameter.

6.1 (martensite low-temperature phase) to 8 (austenite high-temperature phase) cal/mol℃.

If the load is within the proper range, BioMetal undergoes no significant changes in performance even if it is heated to about 200℃.

No problem would arise as far as it is used at a temperature lower than the heat resistance of plastic (100℃).

The force generated by BioMetal is proportional to its cross-sectional area. Even with the same machine, its area varies proportionately with the square of its length, and its weight and volume with the cube of its length. While the force produced by a magnetic actuator such as a motor is proportionate to the cube of its length, the one generated by BioMetal is proportional to the square of its length.
It can therefore be said that BioMetal is an actuator suitable for micromachines.
One other outstanding feature of BioMetal is its ability to produce a great force even at the start of movement.
When using a solenoid (electromagnet) which can produce only a small magnitude of force at the start of movement, for instance, it is necessary to select a large-size one.
With BioMetal, however, it is possible to construct a compact and lightweight actuator because it can produce a great force even at the start of movement.

The products to which BioMetal has been most widely applied are unlocking devices.
They include small door unlocking devices for refrigerator-type vending machines for use in hotels and unlocking systems for security-related equipment.
Having the advantages of being able to produce a great force even at the start of movement, requiring only a small space for installation, generating no noise, and being capable of being driven by small current at low voltage, BioMetal is considered suitable for such applications as unlocking devices.
Further, ultra-compact air valves employing BioMetal as their actuator have been used as pressure reducing valves for high-precision sphygmomanometers. These applications are put on view in our homepage video library.

The ends of BioMetal can be secured with screws and washers, with crimp contacts, or with sleeves. When using crimp contacts, note the following points. If the tightening or end part of the crimp is too sharp, BioMetal will tend to break easily.
Although appearing flexible, BioMetal becomes brittle when subjected to excessive deformation. Measures should therefore be taken to prevent its ends from being subjected to abrupt deformation (stress concentration would otherwise result).

No part of such a wire can be reused.

It would not contact to its original length. It would not delivery its expected performance.

If it is forcibly deformed it may be destroyed or degrade in performance. To avoid such situations, the maximum allowable load has been set for the BioMetal products.
It is 30-40 gf for BMX150 and 100 gf for BMF100. The maximum allowable load for BMF or BMX is nearly proportional to the square of its diameter.
If BioMetal is energized when it is restrained, it may be destroyed by the force produced by itself. Reference:Practical service area for BMF.

BioMetal is a fiber-like artificial muscle tailored to move in the direction of extension/contraction.
It is not fit for shape-memory applications. Use shape-memory alloy wires for such purposes.

When BioMetal Fiber is to be bent by a pulley through an angle of 90° or more, it is desirable that the diameter of the pulley be at least 40 times greater than the wire diameter. For BMF100, for example, a pulley having a groove diameter of 4 mm is necessary.
If this condition is met, the wire will not become prone to bending even if it is repeatedly activated.
When the angle of turn is wider the condition may be weakened.
The same is true of round rods. When the surface of the round rod is slippery, however, the wire may rupture there.
If the material of the round rod is iron or glass-containing heat-resistant plastic, the wire tend to break easily.
When using a metal round rod, it is recommended to select one made of brass. Polyimide is an ideal resin material.
Polycarbonate or polyacetal may be used if measures have been taken to prevent overheat. Polyacetal, which is a low-friction material, is suited for pulleys.
BMF cannot be bent to an acute angle when in use. It would be broken if an attempt is made to forcibly bend it to an acute angle.

BioMetal is not heated to above 80℃ when used under proper conditions. Under inappropriate conditions, however, its temperature may rise to above 80℃, causing it to cut in a low-melting point resin which is in direct contact with it.

Yes. However, the BMX-pulley contact area does not contract easily because it is not heated easily.
Attention should also be given to the degree of slipperiness.

BioMetal can be very minutely controlled by using feedback from positional sensors in driving it through energization.
In principle, as with functional materials such as piezoelectric devices and bimetals, it has a resolution of the order of interatomic shift.
Ultra-compact servo actuators have already been built as a trial. However, BioMetal, which is basically a temperature-activated material, has the disadvantage of being susceptible to the flow of air.
In addition, it is inferior to electromagnetic actuators in terms of fast-response characteristics because of its slight temperature hysteresis.

BioMetal can be regarded as being an electric resistance. Any of AC, DC, and pulse current may be used for driving it.
It is advisable that current be used as a guide for heating.
The necessary current varies with the operating conditions and the type (thickness) of BioMetal.
For concrete numerical data, see the catalogs for BMX and BMF.

Since BioMetal is driven by controlling the amount of heat produced in the resistor, in principle, it can be controlled by changing the current fed through it or the voltage applied to it.
PWM (pulse width modulation) is a frequently used method for such control.
Reference: Pulse width modulation.

When it is expected that BioMetal will be actuated 100 thousands times or more, it is customary to stop or suppress heating before it completely recovers its shape within the proper ranges of load and kinetic distortion.
Avoid energizing it in such a way that there may occur more than 4.5% contraction as kinetic distortion.
When it is to be slowly contracted by a standard current, the ON condition may be maintained for a duration of 1 to 2 seconds because it does not tend to overheat easily.
In the event of abrupt current changes, it is necessary to securely stop heating before it completes contraction.
For products which is required to repeatedly actuate 100 thousands times or more, it is advisable to take appropriate measures to prevent overheat.
Even for a mono-stable type actuator, its position and force can be safely maintained after heating by employing the method of feeding a small holding current after passing a large accelerating current through it for a short period of time.

The presently available BioMetal products are not insulated. When they are used in parallel, care should therefore be exercised so that they may not come into contact with each other. There is no high-performance insulator that can follow the movement of BioMetal which will be deformed to a very large extent. Even if an insulator can follow the motion of Biometal it would interfere with the actuation of Biometal because it is required to have a high capability of deformation.
Under present circumstances, BioMetal coated with silicone rubber gives relatively satisfactory results. Since the voltage applied is low, insulation is secured even if the coat is considerably thin.
Silicone oil-coated BMF contained in a silicone rubber tube moves relatively smoothly because of the slipperiness between the BMF and the inner surface of the tube.
BioMetal can move most freely when it is not coated with anything.
For BMX, insulation can be achieved by applying a thin coat of silicone rubber only to the surfaces of the wires in the stretched condition so that enough space is secured between them.
The method of moving the wire in a sufficiently insulated cylinder is relatively effective for both BMX and BMF.

As shown in its catalog, basically, BioMetal is not suited for high-speed repetitive movement.
It would be difficult to repeatedly move it at high speed like electromagnetic and piezoeletric actuators. A full-stroke movement in the direction of contraction can be achieved within a millisecond by feeding a large current through it.
The rate of elongation during cooling, however, depends on its heat capacity and heat conductivity.
It is therefore considered that a thin, short product might allow high-speed repetitive movement. Roughly speaking, the response speed at the time of cooling is inversely proportional to the diameter of the wire.
High-speed repetitive movement can be achieved by reducing the operation distortion. For example, in our company's accelerated aging test with BMF, the operation distortion which is originally equal to 5% of the original length is reduced to about 2% of it by the use of displacement sensors to achieve reciprocating motion.
For BMF100, a repetitive movement at a frequency of about 3 Hz has been realized even in the air.
Since the operation distortion of BioMetal is by far greater than that of piezoelectric devices, care should be exercised to avoid the occurrence of an overload condition due to inertia.

An important point to consider in using multiple BMFs in bundle is to ensure that they are cooled uniformly.
Uniform cooling would not be achieved merely by tying them together in bundle.
The BMFs near the center of the bundle resist cooling so that they are delayed in extending and receive most of the force produced.
The bundle of wires are uniformly cooled when the number of wires is as small as two or three.
Excellent coordination may be achieved by running in the product after tying.
Conditions would change for the better when it is used in oil or water.
Higher performance can be obtained by arranging the wires in parallel through the use of pulleys, keeping them separated from one another, rather than by tying them together in bundle.
In our company's butterfly robot "Papillon," the force produced is doubled by bending a single BMF in the center to form a loop.
With this method, the product can offer excellent performance even from the standpoint of practical use. For applications requiring a force that cannot be obtained without tying a number of BMFs together in bundle, it is advisable to use another type of actuator such as a motor.

We appreciate your linking to us! Use our site within the bounds of good judgment. The photos, technical information, and movie data available on our site can be freely cited or used, provided that the name of our company (TOKI CORPORATION or BioMetal) and the names of other rightful claimants are stated explicitly.
No approval from them are required.
If possible, please contact and let us know.
Most of the ideas and descriptions on the actuators and their related electrical and mechanical devices put on view on our site are protected by the Patent Law and the Copyright Law.
They should not be copied or used for commercialization without permission.