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PCB-Mounted Motors

18 March 2013

By mounting actuator components directly onto a PCB and integrating everything on the board, PCB motors can reduce application size and even eliminate the need for gears. Andy Pye looks at one of the innovators in this field

Traditional motive power design methods use PCBs motor controllers with a physical motor located in the vicinity. Thinking out of the box, Danish technology company PCBMotor builds flat, yet highly accurate piezoelectric motors, directly onto the PCB itself.

There are numerous precision motion control applications that could utilise this technology, spanning the laser and optics, camera, medico, telecom, aviation/aerospace, as well as the robotics and instrumentation industries.

Piezoceramics were actually invented during World War II. Their most interesting characteristic is that they act as a transducer, transforming electrical energy into mechanical energy – expanding in one dimension and contracting in another.

The PCBMotor system consists of the following: PCB mounted with patented piezoceramic components which act as the stator/resonator; Application- specific rotor mounted on top of the stator; Driver, sensor and motor built as a very compact unit with the electronics placed on a separate PCB.

PCBMotors use the travelling wave principle to create the motion in the stator. The motor is driven by resonance from the mechanical system. The driver generates a two- phase voltage that matches the resonance frequency in the stator (mechanical system). The resonance is determined by the stiffness of the PCB material, the motor’s diameter, the thickness of the PCB, and the size and location of the piezo components mounted onto the PCB.

The stator, made from the PCB itself, holds the actuators (piezo components) and electrical connecting circuit. The PCB can also hold the driver.

The application rotor, pressed onto the surface of the stator, delivers the mechanical output. A travelling wave is generated over the stator surface, acting as a flexible ring to produce elliptical motion on the rotor interface. The elliptical motion of the contact surface propels the rotor and the connected drive-shaft.

The PCB used for a PCBMotor is made of standard FR4 material and can be a single or multiple layers, depending on requirements.

COMPLEX PROCESS
On the surface it might seem like designing a stator is simple. In fact, it’s actually a very complex process with many parameters that need to be taken into consideration to achieve the best resonance frequency: materials, physical dimensions, size, thickness, ring width, piezo component placement, bridge length, shape and form.

The High Resolution Twin Motor Kit is a rapid prototyping tool which promises electronic application designers resolution precision, greater design flexibility and full holding torque even in power-off mode. The new twin- motor kit is controlled by a single driver circuit, which saves space and is cheaper to produce.

With a device that manages 2.6 million steps per revolution, PCBMotor has set a new performance record in printed circuit board (PCB) motors. With its latest controller prototype, short micro-pulses were used to drive the motor. The controller is powered from the USB port and handles a wide range of settings for the motor such as pulse length and interval, drive voltage, and the number of micro-pulses and digital steps. Operating in open-loop mode it also has on-board memory (EEPROM) for storing the drive settings.

When in position, the PCBMotor and driver can be completely powered down, removing all mechanical and electrical interference (noise). "The inherent holding torque of the motor is sufficient to stop and hold its position when the power is turned off – unlike a stepper motor. And this is very important for high-precision applications sensitive to even the smallest movement or vibration,” explains Henrik Stæhr-Olsen, CEO of PCBMotor.
 
COMPARISON TABLE

DC & Stepper Motors
  • Conventional electromagnetic motor using built-in step motor functionality for position control (open- loop motion control)
  • Innovative piezoelectric motor technology for slackless movement in application (closed-loop only with position sensor)
  • Require more application ‘real estate’
  • Can’t be integrated on-board
  • Require additional parts and mechanisms
  • Have a higher bill of materials
  • Aren’t conducive to thin, light applications
  • Are constant power devices
  • Lose torque with increasing resolution
PCB Motors
  • Offer compact design possibilities
  • Integrate motors & drivers onto PCB
  • Do not require clutches, gears & brakes
  • Result in lower Bill of Materials
  • Will lower application height
  • Only utilize power in operation-mode
  • Maintain full holding torque in power-off
  • Are more energy efficient
  • Offer more accurate angular positioning
 
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