Overview
SQUIGGLE micro motors are smaller, more power-efficient and more
precise than stepper motors for micro optical systems. Unlike MEMS
or voice coil actuators, they also provide long travel for zoom as
well as high precision for autofocus. TRACKER position sensors are
tiny, high-resolution magnetic encoders. Unlike optical encoders,
they do not require a light source or external zero reference
sensor.
By combining these technologies, New Scale has created designs
for uniquely small and precise motion modules. The reference design
for an optical zoom module (Figure 2) showcases the components integrated
for high-precision lens motion:
- Two SQL-RV SQUIGGLE motors.
- Two TRACKER NSE-5310 position sensors.
- Two moving lens holders.
- Rail assembly with a spring preload, providing zero backlash
for precise bi-directional repeatability.
- Motor control ASIC (external to the module).
Figure 2: Optical zoom module reference design
The reference design demonstrates precision optical zoom in the
thinnest
assembly possible (6.5 mm height) with SQUIGGLE motors. The length
of the reference design module is 23 mm; actual length would be
determined by the OEM's optics design and required stroke. The width
of the reference design module is 13 mm; actual width would be
determined by the OEM's optics and shutter.
The closed-loop motion module is driven by two NSD piezo motor drive ASICs,
each in a 1.8 x 1.8 x 0.6 mm BGA package.
Working demonstration modules (without imaging components) based
on this reference design are available to qualified OEMs. New Scale
works with each OEM to design modules specific to the OEM's needs,
and can provide prototype production services and ramp up to
large-scale manufacturing.
System description
A zoom camera system block diagram is shown in Figure 3. (The
gray-shaded blocks are not included in the reference design module.)
Figure 3: Zoom system block diagram
Imaging components
The reference design assumes that the OEM will select the imaging
components: an autofocus (AF) lens, an optical zoom (OZ) lens, a
CMOS image sensor and an image signal processor (ISP). A prism can
be used to "fold" the light path and enable the thinnest possible
assembly, especially for consumer devices.
New Scale provides the motion technology to maximize the performance
of high-end imaging components such as larger image sensors (5MP,
8MP and up) and precision lenses. Our precision motion technology
ensures that sharp, focused images are projected onto the sensor,
while respecting the low power budgets and miniaturization
requirements of system designers.
Lens holders and rail system
The lens holders slide along a three-point rail system designed for
smooth linear motion.
Micro motors
One SQUIGGLE micro motor is used to move each lens holder along the
rails. This robust piezoelectric motor provides high-precision
linear motion. In operation, the screw rotates freely against a
low-friction surface on the lens holder, held in contact by the
spring preload (Figure 4). The screw pushes the load in the
"forward" direction against the spring load. In the "reverse"
direction, the spring pushes the load as the motor screw retracts
and provides precision control of the motion, with zero backlash for
the most precise bi-directional repeatability.
Figure 4: SQUIGGLE motor pushes against the lens holder, with a
spring proving the preload for "forward" motion and the push force
for "reverse" motion along the rail.
The SQUIGGLE motor holds its position without drawing any power. Its
high speed enables users to quickly zoom and focus, further reducing
power use and providing excellent user experience.
Key features of the SQUIGGLE motor:
- Tiny ... 2.8 x 2.8 x 6 mm
- Lightweight ... 0.16 grams
- Fast ... 7 mm / sec
- Precise ... 0.5 μm resolution
- Low power use ... 0 mW to hold position, < 340 mW
moving
- Simple & robust ... no gears or lubrication
- Quiet, ultrasonic operation
Position sensors
The TRACKER NSE-5310 is a magnetic sensor array with 0.5 μm
resolution and integrated on-chip digital encoding. It delivers
absolute positioning in a 2 mm range. Unlike optical encoders or
stepper motors, it does not require a separate zero-reference
sensor.
In the reference design module the sensor is packaged using
chip-on-board packaging for the thinnest profile of 0.6 mm. In
high volume production quantity, it is available in an even
smaller, wafer-level chip-scale packaging as small as 2.5 x 3.9
x 0.6 mm package size. Including the magnet, the sensor can be
fit in a space less than 1.5 mm thick.
In the zoom module reference design, a magnetic strip with
alternate north-south poles is mounted on the lens holder and
positioned above the sensor (Figure 5). A Hall sensor array on
the TRACKER NSE-5310 chip measures the spatially-varying
magnetic field produced by the moving magnetic strip. An
integrated digital encoder on the chip provides direct digital
output of the absolute linear position within a 2 mm pole pair
on the magnet.
Figure 5: TRACKER NSE-5310 position senor
provides closed-loop feedback of lens holder position with 0.5 μm
resolution. A magnetic encoder is smaller than optical encoders and
needs no light source.
By counting pole pair crossings and storing
this information in flash memory, a system processor can determine
absolute position along the length of the magnet.
The absolute magnitude of the magnetic field
intensity is used to detect the end of the magnetic strip and serves
as a built-in zero reference. Standard I2C protocol
enables simple integration into the system processor.
Key features of the TRACKER NSE-5310 position sensor:
NSD-2101 motor driver
Two NSD-2101 piezo motor driver ASICs are powered by a single 3 V
battery. Like the TRACKER, the NSD-2101 uses a standard I2C interface for
integration with the system processor.
The NSD-2101 uses patented full-bridge switching technology to
create the ultrasonic motor drive frequency. The IC also has
patent-pending smart drive features built in that optimize motor
performance while minimizing power consumption over a broad range of
operating and environmental conditions. A power-down mode provides for minimal
power consumption in stand-by.
For the demonstration module, the NSD-2101 ICs are integrated into New
Scale's MC-3300-RV motor controller (Figure 6). This control board has
convenient connectors for the SQUIGGLE motors and TRACKER position
sensors. It connects to a PC via USB connector.
Figure 6: Above: Two NSD-2010 motor drive ASICs
in the
MC-3300-RV development platform.
Below: New Scale Pathway software for motor and
sensor evaluation and system development.
New Scale Pathway Software provides an easy to use, "point and
click" user interface for easy evaluation of the demonstration
module. Scripts for focus and zoom demonstration are included. A
powerful script generator allows users to create and run their own
scripts to evaluate module performance and for embedded system
development.
Advantages over other zoom modules
The zoom system using SQUIGGLE motors and TRACKER position
sensors offers the distinct advantages of smaller size, higher
precision and lower power use compared to zoom systems that employ
stepper motors.
The very low height profile (6.5 mm) is of particular benefit in
many micro camera applications.
The combination of SQUGGLE motor with the spring preload creates
precision motion with zero backlash.
When using a stepper motor, error can accumulate through the
motor, lead screw and coupling to lens holder. With the TRACKER the
lens is directly measured by the encoder for greater precision.
Typical performance
Table 1 shows the performance of New Scale's demonstration
modules based on the zoom reference design. Please refer to our
product data sheets for additional specifications on SQUIGGLE motors
and TRACKER position sensors.
|
Table 1: optical zoom module reference design performance |
| Size |
6.5 X 13 X 23 mm |
| Auto focus stroke |
4 mm (customizable up to 30 mm) |
| Optical zoom stroke |
4 mm customizable up to 30 mm) |
| Position resolution |
0.5 microns |
| SQUIGGLE motors |
Two SQL-RV-1.8-6 |
| TRACKER position sensors |
TWO NSE-5310 in chip-on-board packaging |
| Driver IC |
TWO NSD-2101 in 1.8 x 1.8 x 0.6 mm BGA
package |
| Zero reference sensors |
none required |
| Audible noise |
< 35 dB (in housing) |
| Operating temperature |
-30°C to +70°C |
| Storage temperature |
-40°C to +80°C |
| Lifetime |
> 300,000 cycles |
For more information
This design
demonstrates a customizable platform to meet unique OEM optical and
system needs. Our custom engineering group works with OEM designers
to create miniature modules for focus, zoom and other motion to suit your application. Contact New Scale
at +1 (585) 924-4450 or email
sales@newscaletech.com.
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