Simple Torque Control Method for Hybrid Stepper Motors Implemented in FPGA

Stepper motors are employed in a wide range of consumer and industrial applications. Their use is simple: a digital device generates pulse-bursts and a direction bit towards a power driver that produces the 2-phase currents feeding the motor windings. Despite its simplicity, this open-loop approach fails if the torque load exceeds the motor capacity, so the motor and driver should be oversized at the expense of efficiency and cost. Field-Oriented closed-loop Control (FOC) solves the problem, and the recent availability of low cost electronics devices like Digital Signal Processors, Field Programmable Gate Arrays (FPGA), or even Microcontrollers with dedicated peripherals, fostered the investigation and implementation of several variants of the FOC method. In this paper, a simple and economic FOC torque control method for hybrid stepper motors is presented. The load angle is corrected accordingly to the actual shaft position through pulse-bursts and direction commands issued towards a commercial stepper driver, which manages the 2-phase winding currents. Thanks to the FPGA implementation, the control loop updates the electrical position every 50 μs only, thus allowing a load angle accuracy of −1/100 rad for a rotor velocity up to 750 rev/min, as shown in the reported experiments

Data-Adaptive Coherent Demodulator for High Dynamics Pulse-Wave Ultrasound Applications

Pulse-Wave Doppler (PWD) ultrasound has been applied to the detection of blood flow for a long time; recently the same method was also proven effective in the monitoring of industrial fluids and suspensions flowing in pipes. In a PWD investigation, bursts of ultrasounds at 0.5⁻10 MHz are periodically transmitted in the medium under test. The received signal is amplified, sampled at tens of MHz, and digitally processed in a Field Programmable Gate Array (FPGA). First processing step is a coherent demodulation. Unfortunately, the weak echoes reflected from the fluid particles are received together with the echoes from the high-reflective pipe walls, whose amplitude can be 30⁻40 dB higher. This represents a challenge for the input dynamics of the system and the demodulator, which should clearly detect the weak fluid signal while not saturating at the pipe wall components. In this paper, a numerical demodulator architecture is presented capable of auto-tuning its internal dynamics to adapt to the feature of the actual input signal. The proposed demodulator is integrated into a system for the detection of the velocity profile of fluids flowing in pipes. Simulations and experiments with the system connected to a flow-rig show that the data-adaptive demodulator produces a noise reduction of at least of 20 dB with respect to different approaches, and recovers a correct velocity profile even when the input data are sampled at 8 bits only instead of the typical 12⁻16 bits

In-Vivo Comparison of Multiline Transmission and Diverging Wave Imaging for High Frame Rate Speckle Tracking Echocardiography

High frame rate (HFR) speckle tracking echocardiography (STE) assesses myocardial function by quantifying motion and deformation at high temporal resolution. Among the proposed HFR techniques, Multi-Line Transmission (MLT) and Diverging Wave (DW) imaging have been used in this context both being characterized by specific advantages and disadvantages. Therefore, in this paper, we directly contrast both approaches in an in-vivo setting while operating at the same frame rate. First, images were recorded at baseline (resting condition) from healthy volunteers and patients. Next, additional acquisitions during stress echocardiography were performed on volunteers. Each scan was contoured and processed by a previously proposed 2D HFR STE algorithm based on cross-correlation. Then, strain curves and their end-systolic (ES) values were extracted for all myocardial segments for further statistical analysis. The baseline acquisitions did not reveal differences in estimated strain between the acquisition modes (p>0.35); myocardial segments (p>0.3) nor an interaction between imaging mode and depth (p>0.87). Similarly, during stress testing, no difference (p=0.7) was observed for the two scan sequences, stress levels nor an interaction sequence-stress level (p=0.94). Overall, our findings show that MLT and DW compounding give comparable HFR STE strain values and that the choice for using one method or the other may thus rather be based on other factors, e.g. system requirements or computational cost.status: accepte

Requirements and Hardware Limitations of High-Frame-Rate 3-D Ultrasound Imaging Systems

The spread of high frame rate and 3-D imaging techniques has raised pressing requirements for ultrasound systems. In particular, the processing power and data transfer rate requirements may be so demanding to hinder the real-time (RT) implementation of such techniques. This paper first analyzes the general requirements involved in RT ultrasound systems. Then, it identifies the main bottlenecks in the receiving section of a specific RT scanner, the ULA-OP 256, which is one of the most powerful available open scanners and may therefore be assumed as a reference. This case study has evidenced that the “star” topology, used to digitally interconnect the system’s boards, may easily saturate the data transfer bandwidth, thus impacting the achievable frame/volume rates in RT. The architecture of the digital scanner was exploited to tackle the bottlenecks by enabling a new “ring“ communication topology. Experimental 2-D and 3-D high-frame-rate imaging tests were conducted to evaluate the frame rates achievable with both interconnection modalities. It is shown that the ring topology enables up to 4400 frames/s and 510 volumes/s, with mean increments of +230% (up to +620%) compared to the star topology

Requirements and Hardware Limitations of High-Frame-Rate 3-D Ultrasound Imaging Systems

The spread of high frame rate and 3-D imaging techniques has raised pressing requirements for ultrasound systems. In particular, the processing power and data transfer rate requirements may be so demanding to hinder the real-time (RT) implementation of such techniques. This paper first analyzes the general requirements involved in RT ultrasound systems. Then, it identifies the main bottlenecks in the receiving section of a specific RT scanner, the ULA-OP 256, which is one of the most powerful available open scanners and may therefore be assumed as a reference. This case study has evidenced that the “star” topology, used to digitally interconnect the system’s boards, may easily saturate the data transfer bandwidth, thus impacting the achievable frame/volume rates in RT. The architecture of the digital scanner was exploited to tackle the bottlenecks by enabling a new “ring“ communication topology. Experimental 2-D and 3-D high-frame-rate imaging tests were conducted to evaluate the frame rates achievable with both interconnection modalities. It is shown that the ring topology enables up to 4400 frames/s and 510 volumes/s, with mean increments of +230% (up to +620%) compared to the star topology

Flow-VizTM –A fully integrated and commercial in-line fluid characterization system for industrial applications

The enhanced tube viscometer concept aiming to derive information on the flow behavior of industrial fluids using the UVP+PD methodology, i.e. Ultrasound Velocity Profiling (UVP) with Pressure Difference (PD) is older than 30 years [1]. Despite this, no in-line fluids characterization instrument based on Doppler velocimetry has been made commercially available meeting industrial requirements [2]. In this work we present an embedded in-line fluids characterization system, “Flow-VizTM”, specifically designed for the in-line velocity profile measurements and rheological assessment of opaque, non-Newtonian industrial fluids. The Flow-VizTM, system is the result of the work of several research groups that have systematically improved this concept for a period of more than 14 years to ensure that the system can be used in industry for a quantitative analysis of the rheological properties of real industrial fluids, [2-5]. New improved and extended UVP+PD electronics, based on former work [6-8] have been developed. In industrial processes it is an absolute requirement to measure non-invasively through stainless steel pipes. Despite this, no such transducer technology has been made available as an off-the-shelf product [2,5]. To overcome this limitation, new non-invasive sensor technology has been developed, optimized and validated for SS316L stainless steel process pipes of different diameters and wall thicknesses [2,5]. The instrument has been validated to meet industrial requirements for many different applications and to deliver accurate real-time data, such as instantaneous velocity profiles and rheology of opaque industrial fluids [2-4, 7-8]. The Flow-VizTM system is already installed in industry, e.g. for chocolate and grouting applications