Tag Archives: TI

SLI: Sensing Without Touching

MEMS is revolutionizing technology, causing microminiaturization and increasing the precision of conventional solutions. Ubiquitous MEMS applications are emerging as the next most promising frontier by removing the need for touch in structured light illumination or SLI.

DLPs or digital light processors from Texas Instruments contain millions of mirrors. TI is pioneering SLI that works by projecting moving stripes of light onto objects. It then measures the deformities in the reflected patterns by reconstructing their 3-D shapes using algorithms. The biggest customers so far are OEMs that manufacture touch-free fingerprint scanners.

These scanners are different from the traditional, as they do not require the traditional ink-blotter protocol. Therefore, SLI is revolutionizing biometric, facial, dental and medical scanning by opening up a whole new frontier in DLP applications. That includes the entire range from scientific instrumentation to industrial inspection systems.

So far, TI already has OEM development kits with DLPs and algorithm libraries. These can recognize 3D shapes, contours, surfaces, discontinuities and roughness. Operating on light sources ranging from near-infrared to ultra-violet, they enable accurate, fast and non-contact 3D scanning and recognition systems.

With its new DLP LightCarrier development platform, TI will be using nearly half a million micro-mirrors for illuminating simultaneously almost anything with structured light. That will allow almost instant recognition and characterization of 3D objects without touching them.

For example, TI uses FlashScan3D in DLP technology to capture far greater detail of fingerprints with higher accuracy than any other SLI solution can. That helps in cutting down on the possibilities of technician error and fraud. Moreover, the new DLP LightCrafter can scan faster and store data internally as against on a separate storage device such as a laptop. Therefore, it helps in building even smaller and more portable SLI applications.

YoungOptics Inc. of Taiwan origin manufactures the DLP LightCrafter as a plug-n-play module for TI. YoungOptics also manufactures TI’s DLP Optical Engine for OEMs that make projection televisions. LightCrafter, along with TI’s DLP 0.3 WVGA chipset, is ready to be used by OEMs for research and development. However, it can serve as the main subsystem in their finished end-user products as well.

Along with the DLP chip that contains exactly 415,872 micro-mirrors is an ASIC or Application-Specific Integrated Circuit acting as a second custom controller. There is also a DVP or a DaVinci digital video processor with its own 128MB NAND flash memory for storing patterns, a configurable IO trigger for integrating cameras, sensors and other peripherals needed for SLI.

Users can optionally add an FPGA, thereby speeding up the SLI patterns that LightCrafter displays, making them faster up to 4,000 per second. Finally, LightCrafter is capable of generating 20 lumens of light as it has an integrated light-emitting diode array for generating red, blue and green light.

OEMs can also use embedded Linux for developing their software to run the DaVinci DVP in the LightCrafter. That makes it an evaluation module compact enough for integrating projected light for scientific, medical and industrial applications, creating faster development cycles for end equipment needing high-speed pattern display with a small form factor, intelligent and lower cost.

Why are Inductance-to-Digital Converters Useful?

Inductive sensing is bringing a revolution in the technical world. Inductive sensing offers capabilities for measuring position, motion and or composition of a conductive or metal target, with a contact-less, magnet-free sensing technology. In addition, inductive sensing can help to detect twist, compression or extension of a spring.

Now, LDC or Inductance-to-Digital converters from Texas Instruments, such as the LDC1614, is helping to utilize springs and coils as inductive sensors that can deliver better reliability, improved performance and increased flexibility when compared with existing sensing solutions. In addition, inductive sensing offers solutions at lower system costs and with lower power consumption.

Users of LDC technology can expect several advantages –

Higher resolution: 24-bit inductance values and 16-bit resonance impedance offers sub-micron resolutions in position sensing.

Better reliability: sensing is contact-less and therefore, immune to non-conductive contaminants such as dust and dirt.

Increased flexibility: The sensor can be located away from the electronics and in areas that do not have space for PCBs.

Low system power: LDC consumes less than 9mW during standard operations and less than 2mW when in standby mode.

Lower system costs: As no magnets are required for both the sensors and the targets, the entire system can be significantly low-cost.

Limitless possibilities: Permits endless possibilities for innovative and creative system design, such as with conductive ink and pressed foil.

Inductive sensing applications can range from simple push buttons, on/off switches and knobs to high-speed motor controllers, turbine flow meters and high-resolution heart rate monitors. The versatility of the LDC1614 allows it to be used in several markets including medical, industrial, computing, mobile devices, consumer electronics, white goods and automotive industries.

LDC1614, from Texas Instruments, is a series of inductance-to-digital converters comprising four devices. They offer two or four matched channels along with 12-bit or 28-bit resolution. Available in a compact 4x4mm package, users can configure these LDCs easily via an I2C interface. These converters offer precise position and motion sensing almost independent of the environment.

Inductive sensing involves low-cost, high-reliability inductors as sensors. Use of LDC converters enables the sensors to be located remotely from the PCB containing the IC. As the LDC1614 can integrate up to four channels, designers can distribute sensors throughout the system, while centralizing the electronics on a few PCBs. Since the channels are well matched, users can perform ratio metric and differential measurements. That allows easy compensation for aging and environmental conditions, such as those caused by mechanical drift, humidity and temperature.

The 28-bit resolution allows detection of submicron level changes in distance measurements. With the LDC converters supporting a frequency range varying from 1KHz to 10MHz, users can employ a large variety of inductors as sensors. As the converters require powering by a 3.3VDC supply, the power consumption is only about 6.9mW during standard operation and about 0.12mW when in shutdown mode.

TI offers its LDC1614 in QFN-16 packages and in the cheaper WSON-12 packages for both the 12-bit and the 28-bit devices. LDCs applications can be extremely wide-ranging and seemingly endless, covering fields as diverse as automotive, medical, consumer electronics, white goods and other industries.

Efficient Control of Motors at Low Speeds

When a motor is operating at high electrical frequency or high mechanical speed, the back EMF signal generated by the rotating rotor presents an efficient feedback technique for a sensor less motor control.

However, generation of the back EMF requires a minimum frequency and that makes it difficult to control motors running at low speeds. The process of continuously estimating the rotor flux angle at zero and very low speeds, together with stably moving between low-speed and high-speed estimators helps to improve the effectiveness of starting the motor under load without using sensors.

TI or Texas Instruments’ InstaSPIN-FOC software called FAST helps to make this estimation at very low speeds, sometimes below 1Hz. Although the initial rotor flux angle is unknown, FAST estimates this using sensor less techniques. Until it has measured enough back EMF, this estimate remains unpredictable and the estimated angle is incorrect.

However, FAST feeds the control system applicable to the motor and induces motor movement. Enough back EMF is generated with only a small amount of rotor movement and the algorithm can then converge on a reasonable estimate for the angle very quickly. This allows a controlled high-torque drive at low-speeds with excellent operation. Although the start-up performance may not be consistent, this method can start the motor with enough torque for rotor movement.

With increase in the starting load, the torque requirement goes up. The amount of torque the system can generate depends on the current through the motor and the alignment angle between the magnetic fields of the stator and the rotor. For ensuring generation of enough current, the speed controller must necessarily have a maximum output larger than the rated current required to generate the necessary torque.

For example, a motor starting under full load may require 4A of current to produce the necessary torque to move. This requires setting the speed controller’s maximum current output to 6A. When started, the motor will draw a current of 6A in its first electrical cycle for moving the rotor. With FAST providing a valid angle within this first cycle, the control system will quickly regulate the current usage to the required level of 4A.

However, even when there is a stable feedback angle, the rotor may not necessarily align itself properly for generating the maximum torque. In reality, you are simply sweeping the stator field and waiting until the rotor field locks on and synchronizes. If the stator field is not oriented properly, the motor may fail to generate enough torque or even produce torque in the opposite direction. Control systems can improve this situation only by starting with a better starting angle.

The simplest way to control the initial alignment is to inject a DC current in a field-oriented control system. This defines the orientation of the rotor flux. A large enough DC current injected will move the rotor and the load to a known angle. Even though the forced angle is still emulated, the orientation will be proper for correct starting and the rotor will be in the best position for produce torque. The DC current injection may be done manually or programmed through FAST.