FAQ:


Below you will find a list of the most ask questions. Please shoot us an email info [at] pcbmotor [dot] com if you are not able to the answer.

Control driver FAQ

What’s the maximum resolution of a PCBMotor?

The rotors on the High Resolution Twin Motor Kit are made of PCB and the code wheel is implemented in the copper layer with 200 lines/revolution.

By triggering on both leading and trailing edge of the light pulses, resolution can be increased to 400 and by using both channels in the position sensor’s edges resolution can be increased further to 800.

Interpolation and micropulsing significantly increases resolution.

Using a custom-designed encoder with an even higher pitch is of course also an option.
It’s possible to have a pitch as fine (and precise) as your optical switch and code wheel allows.

The finest resolution is achievable with a technique called micropulsing. Movement size can be as small as 1/2,500,000 of a revolution.
See What is micropulsing? above.

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What is micropulsing?

Micropulsing is a technique that makes it possible to rotate the motor in extremely small increments.

Power is applied to the motor as very short pulses. Using an unloaded rotor, increments as small as 1/2,500,000 of a revolution are possible.

Please note:
By nature these increments are not well-defined step sizes like those based on a code wheel and, therefore, increment size varies according to temperature and load. Calibration on the fly can, however, be implemented and increase precision which makes interpolation within an encoder unit possible.

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Other FAQ

What does the control driver do?

The driver is controlled via two input pins, one for turning power ON/OFF, and another for selecting direction CW/CCW. When turned ON, the control driver converts the motor supply voltage Vs of up to +5V into two square wave signals at around 45 kHz, shifted 90 degrees.

Two transformers step up the voltages to around 200Vrms before being applied to the motor. It is the phase shift that makes the waves on the stator wandering instead of standing.

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Why do I need frequency tracking?

The rotating force is achieved by exciting the piezo elements on the stator in a pattern that generates a traveling wave. This wave makes the rotor rotate.

To get the maximum wave amplitude, and thereby maximum torque, the stator has to vibrate at its mechanical resonance frequency. This is around 45 kHz, but varies with ambient temperature and self-heating.

Therefore a tracking system to track the mechanical resonance frequency on the fly is necessary.
The output stage of the driver is designed to have an electrical resonance frequency close to the mechanical resonance frequency of the motor in order to increase motor efficiency. The electrical resonance frequency is defined by circuit design. Because of a low Q it does not need to be adjusted over temperature to track the mechanical resonance frequency.

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Do I have to purchase the control driver from PCBMotor?

No. We’re happy to provide you with the full schematic, BOM and white papers enabling you to design and manufacture your own control driver. However, if you prefer we are also happy to do this for you.

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What supply voltage do the driver need?

The control driver is supplied with nominally +5V used for the driver circuitry and for the motor supply.

A voltage regulator can set the motor supply to anywhere between the +5V and 0V.

Maximum rotating speed and torque is achieved at +5V. Lowering the motor supply will lower the rotating speed (and torque). How low the motor supply can be set before the torque is unable to win over the static friction, and therefore not turn, depends on the actual application, but typically occurs at around 1V.
Lowering motor supply during ‘start & stop’ can make a ‘start/stop sweep softer

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Can several PCBMotors be controlled by the same driver?

Yes, one central driver can drive several motor positions by multiplexing.

These boards are examples of designs with several motors driven by same control driver. We have had customer design with more than 40 motors in one design.

The motors can be on same board or on different boards. To save space multiple motors can be distributed on two or more PCB layers.

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Can a PCBMotor, control driver and application circuit be mounted on the same PCB?

Yes. The PCBMotor, the control driver and your application circuit can be mounted on the same PCB if you want to.

See the images on Our design gallery

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Can I expect EMC issues wth the control driver and motor?

No, the control driver is working at fairly low frequencies (40kHz and 160kHz) and furthermore the stator is operating at resonance and therefore the content of higher harmonics will be low.

We’ve done some preliminary EMC-testing with the present layout of the driver. Customers have done the necessary optimization including additional decoupling and shielding to pass a standard EMC test.

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Are there any options if I need a smaller control driver footprint?

Yes. The transformers we use in our control drivers can handle the power requirements for our full motor range.

When dealing with the smaller versions of PCBMotors, there is room for optimization of the transformer size. This requires careful redesign, as the transformers – apart from stepping up the voltage – also act as inductors that, together with the piezo capacitance, comprise a resonance circuit.

The frequency of this electrical circuit needs to match the mechanical resonance frequency of the stator for maximum motor performance.
If you want to follow this path for optimization please contact PCBMotor for more technical information.

Another option is to consider designing an ASIC integrating some of the control driver components into one IC. NRE for this will of course depend on the technology chosen, project complexity, timeframe and so on.7

If space around the motor is an issue, a third option could be to split up the driver placing only transformers and FET’s close to the motor, and placing the rest in a less constrained area. With this cut, the interface cable only transfers low current/low voltage signals.

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What’s the lifetime of a PCBMotor?

The lifetime is related to the wear of the friction tape.

A lifetime test over 666 hours has shown no indication of performance degradation or wear of friction tape. A lot of friction tape remained intact at the end of the test, indicating an expected lifetime of 1000 hours or more.

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What is the cost of a control driver for larger volumes?

The most expensive components in the driver are the transformers.

In large volumes >100ku the transformer price will be app. 0.80 EUR each – each driver needs two transformers. The price is not negotiated, so it might be possible to drive the cost down even further. The remaining components for the driver will be at a price level of approximately 0.8 EUR.

The estimated total component prices per driver will be approximately 2.50 EUR for volumes above 100Ku. This is based upon the present design for the driver components, and there is no NRE needed to achieve this price.

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What is the step size of a PCBMotor?

A PCBMotor has no inherent, mechanically-defined step size. It will rotate with a constant speed of around 1 revolution per sec is requiredond as long as power is applied.

To establish stepping functionality a positioning system is required. See Positioning system FAQs below.

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How much weight can a PCBMotor hold?

The rotors are preloaded by springs pressing them against the stator ensuring stable contact between piezos and rotor. The spring force is set for optimum motor performance.

A load of 100-200 grams on the rotor or the axle will have little or no effect on performance. Heavier objects should be mounted directly onto the axle which needs to be supported by the customer’s mechanical design so that only rotational forces are applied to the rotors through the springs.

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How quickly can a PCBMotor start and stop?

With no load on the rotor the start/stop time is less than 1 ms. With load on rotors the start and stop time will of course increase.

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Is power required to hold the motor in position?

No, the rotors are preloaded by springs pressing them against the piezo elements. This results in a holding torque whether the power is on or off.
The holding torque is about 2-3x the stall torque.

Being able to turn motor power off when not rotating can, in some applications, prove to be a very important power saving feature.

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Can I damage the motor if I turn the rotor by hand?

No, you will be able to turn the rotor without damaging anything. If the positioning system power is still ‘On’, the positioning system will keep track of its position.

This can be used in, for example, a sound mixing console allowing a PCBMotor-operated control to be set to a specific setting and adjusted manually to a new setting which is then stored.

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Why is friction tape needed?

It is the friction between piezo elements and rotor that translates the traveling wave on stator into a rotational force on rotor.

To ensure sufficient friction a friction tape is mounted on rotor. We’ve had good experience and results using H-old: GL.96.glass fiber enforced adhesive tape with an alu layer.

Apart from ensuring the required friction properties, the tape also prevents acoustical noise.

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What applications are best suited for this technology?

  • Medico
    • Microscope focus
    • Dosing equipment
  • Instrumentation
    • Dashboard pointers
    • Positioning
    • Laboratory equipment
  • Telecom
    • Filter tuning
  • Audio and video
    • Audio mixing equipment
  • Factory automation and robotics
    • Industrial machinery and equipment
  • Aerospace and aviation
  • Automotive/Marine
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Does PCBMotor build the motors?

Yes. PCBMotor can design and manufacture an entire PCBMotor solution – comprising stator, driver and positioning system – all designed specifically for your application.

See our Steps to Success and how we can accelerate your product’s time-to-marke

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Can I build a PCBMotor on my own?

Yes. PCBMotor can provide you with training and help you to design and build your own PCBMotors.

We can also provide schematic for the control driver (free of charge), which you then can build on your own. See our Steps to Success.

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Does PCBMotor deliver the rotor?

No, the rotor is a part of the individual customer’s application and, therefore, not part of our delivery.

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Why is the stator connected to the board via only a few bridges?

The piezos generate the vibrations, a traveling wave, on the stator which makes the rotor turn. The stator needs to be able to vibrate freely for this traveling wave to exist.

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What’s in it for me/the customer?

You can improve your market position by offering your customers state of the art technology/applications AND save them money at the same time.

Offer your customers faster, smaller and cheaper motors.

That’s because of the innovative design of the PCBMotor:

  • Mounted directly on the PCB – the motor and all electronics (driver) are integrated into the PCB itself, using less materials and space
  • Multiple motors on one card – unbelievable design flexibility
  • Flat with no gears or connections – makes it more robust
  • Fast start/stop – increases accuracy
  • Optional position sensor
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What’s in it for PCBMotor?

Our technology is patented. We, obviously, want to spread the use of this new technology and will earn our investment by being the sole supplier of piezo components used in PCBMotors.

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What are the advantages of a PCBMotor compared to a stepper motor?

By driving the integration of the motor (including electronics) into the PCB itself, we’re facilitating the design of smaller, cheaper and faster applications.

  • PCBMotor uses less space and material.
  • Electronics (driver) and mechanics (motor) are mounted directly on the PCB – so it’s totally flat and without gears and connections.
  • PCB enables more design flexibility – multiple motors can be mounted on one board.
  • PCBMotor is a non-magnetic device.
  • PCBMotor can generate more power and torque at a lower speed (without gears) than an electric motor of comparable size.
  • PCBMotor has faster start/stop than electrical motors – giving more accuracy to the application.

We’ve actually a written a white paper highlighting the main differences between PCBMotor technology and Stepper motors. Sign up for free and discover:

  • Major differences between stepper motors and PCBMotors
  • Top 5 Pains electronic movement designers & engineers have
  • Top 5 Gains you can achieve by employing a PCBMotor
  • Motor performance results: Lifetime; Torque-Speed-Power; Torque Precision Correlation
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Do I need a positioning system?

If you want to rotate the motor to a specified position the answer is yes, you do.

A positioning system is needed to keep track of position and turn the power off when it’s in position. Such a system is implemented on our High Resolution Twin Motor Kit.

If you’re not interested in the exact position but want to rotate, for example, a focusing lens until the camera software indicates when it’s in focus, you will not need a positioning system.

In some applications a combination of these principles can be used to decrease system response time. The positioning system can, for example, bring the focus into range, and then use microstepping to find the exact focal point.

 

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What does a positioning system look like?

The basic elements are a:

1. Code wheel on the rotor. The rotors on our demo PCBMotors are made from standard PCB material – the code wheel pattern is an etched Cu-layer. Code wheel
2. Optical reflective switch that sends light towards the code wheel and senses reflected light pulses. The demo kits use the reflective optical switch QRE1113GR. Sensor/ Optical switch
3. Software that converts sensor output into actual position and controls the driver. .

The actual implementation will depend on the requirements of specific application.

Absolute positioning can be achieved by adding an index track to the code wheel and letting the software count the increments to calculate the position. Alternatively a multi-track code wheel can be used for absolute position reading in any position.

If the application requires absolute positioning over more than one revolution other application dependent measures are required. If the motor is, for example, pulling a filter tuning spindle, an absolute reference position could be when the spindle is moved to its end-stop position. The end-stop position must mechanically be well defined.

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