Figure 2: Drive electronics are provided on a PCB
or as a chip set for OEMs to mount on their own PCB. Alternatively,
the drive electronics can be integrated into the module housing.
Background and applications
Board cameras are used for compact imaging systems in security,
medical and industrial applications. They typically consist of a CCD
or CMOS sensor mounted on a small printed circuit board, with a
fixed lens mounted over the sensor.
The addition of autofocus to the board camera provides
significant benefits in high-performance applications with a minimum
sized package. By allowing greater variation in the distance from
the camera to the object being imaged, autofocus improves imaging
speed and throughput and can dramatically improve ease of use for
macro imaging as well as wide field imaging applications. Image
quality and system accuracy is also enhanced. Examples include:
- Face and fingerprint recognition. With autofocus, the system
can obtain an accurate match with less time and effort on the
part of the user.
- Machine vision systems. Autofocus allows greater variation
in the type or alignment of object scanned. In endoscopic
imaging, it speeds readings by reducing the amount of time
required to align the endoscope.
- Barcode scanning. Autofocus allows faster reading of
barcodes and 2D symbols with less accurate alignment.
- Medical imaging. Adding autofocus to surgical,
ophthalmological and dental imaging equipment speeds readings
and improves image quality.
Advantages over other auto focus modules
Miniature auto focus modules available today are generally
targeted at high-volume consumer applications such as cell phones,
and are not customizable for low- to mid-volume applications. New
Scale's auto focus module is customizable and offers the further
advantage of higher resolution over open-loop stepper modules.
Other technologies include liquid lenses. New Scale advantages over
liquid lenses include:
- Easier integration
- Greater flexibility in lens selection
- Lower cost
- Configurable product platform vs. unique custom design for
each camera
Customizable module description
New Scale's customizable modules provide a plug-and-play
motorized focus solution that can be adapted to fit almost any image
sensor PCB and lens using parametric computer design tools. The
platform offers flexibility to accommodate specific board mounting
needs, lens travel (macro to infinity), lens thread and motion
control. This enables OEMs to create high-performance board camera
solutions in less time and at lower cost.
Each module incorporates a piezoelectric SQUIGGLE micro motor and
a magnetic TRACKER position sensor with a moving lens holder in a
robust polymer housing (Figure 3). The customer defines the PCB
mechanical mounting interface, dimensions of the threaded lens
assembly, and the macro and infinity image plane locations. Housing
dimensions are approximately 20 x 20 x 22 mm depending on OEM
specifications.
Figure 3: Customizable auto focus module design
platform.
System description
A block diagram for an auto focus module in a board camera system
is shown in Figure 4. The auto focus module mounts on the OEM's
camera PCB, over the image sensor. The SQUIGGLE motor moves the lens
barrel. The TRACKER position sensor detects the movement of a
multi-pole magnetic strip attached to the lens barrel, and provides
the direct digital position information to the OEM's system
processor. The NSD motor controller ASIC accepts commands from the
processor, also via I2C interface, and drives the motor. The system
can operate on standard 3.3 V battery power.
Additional detail about the components follows.
Micro motor
A patented SQUIGGLE micro motor provides high-precision linear
motion, with no gears and no need for lubrication. It holds its
position without drawing any power. Its high speed enables rapid
focus, further reducing power use and improving the user experience.
This robust piezoelectric device offers quiet, ultrasonic operation.
It is smaller, more power-efficient and more precise than stepper
motors.
Position sensors
The TRACKER NSE-5310 is a magnetic sensor array with integrated
on-chip digital encoding. The sensor measures the spatially-varying
magnetic field produced by a moving magnetic strip mounted on the
lens holder. It provides direct digital output of the absolute
linear position within a 2 mm range.
The TRACKER does not require a light source or a separate
zero-reference sensor. There is no need to hunt for zero position on
power-up, resulting in lower power use and less wait time to capture
images. Standard I2C protocol enables simple integration into the
system processor.
Motor driver ASIC
An NSD piezo motor driver ASIC is powered by a single 3 V battery. Like the TRACKER, the motor driver ASIC uses
a standard I2C interface for integration with the system processor.
It creates pairs of phase-shifted square waves to drive the motor.
On-chip registers store driver instructions. A power-down mode
provides for minimal power consumption in stand-by.
The drive electronics are provided on a separate circuit board
that accepts USB, analog and I2C motion commands as shown in Figure
2. Alternatively, New Scale can integrate the electronics into the
module housing, or provide the chip set for direct
integration on the board camera. The motor driver ASIC is available
in a 4 x 4 mm 16-pin QFN package or in chip scale packaging as small
as 1.8 x 1.8 mm (4-by-4 ball grid array).
Figure 4: Simplified block diagram of the
customizable auto focus module design platform.
Typical performance
|
Customizable auto focus module typical performance |
| Size |
20 x 20 x 22 mm (depending on customer specs) |
| Auto focus stroke |
up to 6 mm |
| Velocity |
7 mm/s |
| Lens thread |
M6 to M12 |
| Position resolution |
0.5 micrometers |
| Position repeatability |
2 micrometers |
| Step and settle time |
< 20 ms for 30 micrometer step |
| Encoder type |
Hall sensor array with on-chip digital encoder (TRACKER
NSE-5310) |
| Actuator type |
Ultrasonic linear motor (piezoelectric SQUIGGLE motor) |
| Mechanical limits |
Included |
| Zero reference sensors |
None required |
| Driver IC |
NSD |
| Standard commands |
Move to target, move step |
| Motion interface |
Digital: USB (using Windows GUI or I2C) Analog: 0 to
3.3 V |
Learn more
Additional information and detailed specifications for the
SQL-1.8 SQUIGGLE micro motors.
Additional information detailed specifications for
TRACKER position sensors.
This autofocus module is a customizable
platform to meet unique OEM optical and system needs. Fill out our
specification worksheet to request a proposal,
or email sales@newscalestech.com.
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