Active Control of Machine Tool Chatter for a Boring Bar: Experimental Results

A study of cutting process stability of a boring bar with active dynamic absorber

Analysis of BTA deep hole drilling bar on Liquid-Solid Coupled Vibration model, there are vortex and unstability on bending deformation of the rotating boring drilling bar induced by cutting fluid force. At first, the rotating fluid force inside the boring bar was expressed linear physical form, and it’s stiffness and damping coefficients were derived by the unsteady reynolds dynamic equation of the fluid. Then establish conditions including eddy and mechanical mechanism of the boring bar by cutting fluid force. The results of analysis show that the solution on coupled vibration model are more accurate than the other vibration model. Coriolis effect is the main reason for eddy or unstability of the deep hole boring bar induced by cutting fluid internal the drilling bar’s wall. Some rules are also derived with which cutting parameters can be selected reasonably, which is coincide with the parameters used in heavy machine building industry.

In this paper, a low power mechanism with power block management is proposed to reduce the power consumption in DSP chips. Because the digital signal processing (DSP) chips use many functional units in the data-path to achieve parallel processing, the unnecessary functional units are also executed simultaneously, and they dissipate the power. In the paper, we classify the types of instruction sets based on their data flow in the DSP to generate the control signals which active the necessary units in their data-path. The mechanism is called power block management (PBM). We employ particular guarded circuits in the different situations to avoid the actions of unnecessary functional units so as to reduce the power dissipation. The experimental results show that the power consumption can be saved about 14% at the cost of less than 2.7% area increment.

Chatter in machining processes is one of the most important factors limiting production rates. In order to suppress machine tool chatter during orthogonal cutting processes, a real time active chatter controller is designed and implemented that is able to adapt to the continuously changing machining parameters. An electro-hydraulic servo system is used to control the movement of the cutting tool. The cutting force, workpiece acceleration, and tool displacement are measured in real time. The transfer function of the workpiece is estimated by using the cutting force and the acceleration of the workpiece. All the digital signal acquisition and processing tasks are performed by a digital signal processor (MicroStar DAP3200a/415). The digital controller is designed such that the servo/actuator dynamics is adjusted to match the workpiece dynamics to suppress chatter. To make the controller adaptive to the changing dynamics of the workpiece, a recursive least square technique is used to identify the workpiece dynamics in real time. The estimated workpiece dynamics parameters are then used in the digital controller to calculate a new servo output, thus controlling the tool movement. Simulations show that chatter can be suppressed successfully by using this method. Experiments agree well with simulations.

Vibration in internal turning is a problem in the manufacturing industry. A digital adaptive controller for the active control of boring bar vibration may not be a suficient solution to the problem. The inherent delay in a digital adaptive controller delays control authority and may result in tool failure when the load applied by the workpiece on the tool changes abruptly, e.g. in the engagement phase of the cutting edge. A robust analog controller, based on a lead-lag compensator, with simple adjustable gain and phase, suitable for the industry application, has been developed. Also, the basic principle of an active boring bar with embedded actuator is addressed. The performance and robustness of the developed controller has been investigated and compared with an adaptive digital controller based on the feedback filtered-x algorithm. In addition, this paper takes into account those variations in boring bar dynamics which are likely to occur in industry; for example, when the boring bars is clamped in a lathe. Both the analog and the digital controller manage to reduce the boring bar vibration level by up to approximately 50 dB.

Some machining processes, such as boring, have been historically limited by excessive bar vibration, often resulting in poor surface finish and reduced tool life. A unique boring bar system has been developed to suppress bar vibration, or chatter, during machining using active control technology. Metal cutting test programs have shown proven, repeatable performance on hard-to-cut, aircraft industry high-temperature nickel alloys as well as more easily cut carbon steels. Critical bar length-to-diameter (L/D) ratios, depths-of-cuts, feed rates and cutting speeds far exceed those attainable from the best available passively-damped boring bars. This industry-ready system consists of three principle subsystems: active clamp, instrumented bar, and control electronics. The active clamp is a lathe-mountable body capable of supporting bars of varying sizes and articulating them in orthogonal directions from the base of the bar shank. The instrumented bar consists of a steel shank, standard insert head and imbedded accelerometers. Wire harnesses from both the bar and clamp connect to control electronics comprised of highly-efficient switched- capacitor amplifiers that drive the piezoelectric actuators, sensor signal conditioning, a PC-based program manager and two 32-bit floating-point DSPs. The program manager code runs on the host PC and distributes system identification and control functions to the two DSPs. All real-time signal processing is based on the principles of adaptive filter minimization. For the described system, cutting performance has extended existing chatter thresholds (cutting parameter combinations) for nickel alloys by as much as 400% while maintaining precision surface finish on the machined part. Bar L/D ratios as high as 11 have enabled deep boring operations on nickel workpieces that otherwise could not be performed free of chatter.

Algebraic Reconstruction Technique (ART) is an age-old method used for solving the problem of three-dimensional (3-D) reconstruction from projections in electron microscopy and radiology. In medical applications, direct 3-D reconstruction is at the forefront of investigation. The simultaneous iterative reconstruction technique (SIRT) is an ART-type algorithm with the potential of generating in a few iterations tomographic images of a quality comparable to that of convolution backprojection (CBP) methods. Pixel-based reconstruction (PBR) is similar to SIRT reconstruction, and it has been shown that PBR algorithms give better quality pictures compared to those produced by SIRT algorithms. In this work, we propose a few modifications to the PBR algorithms. The modified algorithms are shown to give better quality pictures compared to PBR algorithms. The PBR algorithm and the modified PBR algorithms are highly compute intensive, Not many attempts have been made to reconstruct objects in the true 3-D sense because of the high computational overhead. In this study, we have developed parallel two-dimensional (2-D) and 3-D reconstruction algorithms based on modified PBR. We attempt to solve the two problems encountered by the PBR and modified PBR algorithms, i.e., the long computational time and the large memory requirements, by parallelizing the algorithm on a multiprocessor system. We investigate the possible task and data partitioning schemes by exploiting the potential parallelism in the PBR algorithm subject to minimizing the memory requirement. We have implemented an extended hypercube (EH) architecture for the high-speed execution of the 3-D reconstruction algorithm using the commercially available fast floating point digital signal processor (DSP) chips as the processing elements (PEs) and dual-port random access memories (DPR) as channels between the PEs. We discuss and compare the performances of the PBR algorithm on an IBM 6000 RISC workstation, on a Silicon Graphics Indigo 2 workstation, and on an EH system. The results show that an EH(3,1) using DSP chips as PEs executes the modified PBR algorithm about 100 times faster than an LBM 6000 RISC workstation. We have executed the algorithms on a 4-node IBM SP2 parallel computer. The results show that execution time of the algorithm on an EH(3,1) is better than that of a 4-node IBM SP2 system. The speed-up of an EH(3,1) system with eight PEs and one network controller is approximately 7.85.

In this paper, we present a design of modem and vocoder digital signal processor (DSP) chips for CDMA mobile station. The modem chip integrates CDMA reverse link modulator, CDMA forward link demodulator and Viterbi decoder. This chip contains 89,000 gates and 29 kbit RAMS, and the chip size is 10 mm x 10.1 mm which is fabricated using a 0.8 μm 2 metal CMOS technology. To carry out the system-level simulation, models of the base station modulator, the fading channel, the automatic gain control loop, and the microcontroller were developed and interfaced with a gate-level description of the modem application specific integrated circuit (ASIC). The Modem chip is now successfully working in the real CDMA mobile station on its first fab-out. A new DSP architecture was designed to implement the Qualcomm code exited linear prediction (QCELP) vocoder algorithm in an efficient way. The 16 bit vocoder DSP chip has an architecture which supports direct and immediate addressing modes in one instruction cycle, combined with a RISC-type instruction set. This turns out to be effective for the implementation of vocoder algorithm in terms of performance and power consumption. The implementation of QCELP algorithm in our DSP requires only 28 million instruction per second (MIPS) of computation and 290 mW of power consumption. The DSP chip contains 32,000 gates, 32k (2k x 16 bit) RAM, and 240k (10kx24 bit) ROM. The die size is 8.7 mmx8.3 mm and the chip is fabricated using 0.8 μm CMOS technology.

The development and initial evaluation of a prototype boring bar feature active vibration control for increased chatter immunity is described. The significance of active damping both normal and tangential to the workpiece surface is evaluated, indicating the need for two axis control to ensure adequate performance over expected variations in tool mounting procedures. The prototype tool features a commercially available boring bar modified to accommodate four PZT stack actuators for two axis bending control. Measured closed-loop dynamics are combined with a computer model of the boring process to simulate increased metal removal rate and improved workpiece surface finish through application of feedback control.

The authors present a VLSI multiprocessor architecture for 2-D digital signal processing. This multiprocessor architecture uses a specially designed high-performance DSP (digital signal processor) as a node in a real-time system. The DSP architecture is based on a computational primitive developed by algorithm decomposition techniques and is used for the real-time implementation of 2-D DLSI (discrete linear shift-invariant) systems. As an example, the authors designed a prototype single-chip DSP chip using 1.25- mu m double-metal CMOS technology to operate with a 40-MHz system clock. This multiprocessor system has a simple interconnection network and a simple control scheme. Each processor in this multiprocessor system operates asynchronously, thus providing very efficient operation. This VLSI architecture also has the advantage that the complexity and number of computations per input do not increase as the size of the input data is increased. Thus, very large 2-D data can be processed in near real time. >

A computing structure for control applications in which there is a natural hierarchical structure (allowing algorithms devoted to simple tasks to be placed at the lowest level and complex tasks at the higher levels) is described. The architecture consists of a high-level general-purpose computer (host) and up to eight digital signal processors (DSPs) that can be interfaced with the controlled plant(s). The high-level computer is either a work station or an advanced personal computer with sufficient memory space (RAM and mass memory), equipped with peripherals for implementation of a user-friendly interface, and with the ability to communicate with other computers, perhaps in a local network. The synchronization and the real-time communications between the host and a DSP are implemented by the two memory banks alternatively switched between the host and the DSP. A complete transparency and a minimum overhead result for the tasks running on the DSP.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We describe a digital technique for measuring the spectral density of resistance fluctuations with simultaneous background subtraction. The technique implements either of two equivalent ac bridge techniques that rely on extremely good orthogonality between the two channels of a dual-phase lock-in amplifier. We use a digital signal processor (DSP) chip and a personal computer in place of both the lock-in amplifier and spectrum analyzer. The digital system can measure sample 1/f noise that is 100 times smaller than the experimental background noise; this performance equals or surpasses that of any analog system. The system is low cost, very flexible, and can function as a stand-alone digital lock-in amplifier or low-frequency spectrum analyzer.

In this paper, noise spectroscopy has been reported earlier as an efficient tool for enhancing the selectivity of biosensors and the analysis was carried out by desktop spectrum analyzer. There were no reports, however, on the efficacy of this method in complex mixture. We have performed here for the first time, noise spectroscopy analysis on complex mixture of food toxin samples and observed that the first cut-off frequencies are indicative of the fact whether the solution has only specific antigen, mixture of specific and nonspecific antigen or no specific antigen at all. To realize a portable immunosensor, we have developed an electronic interface using digital signal processor (DSP) chip of Microchip Technology which has the embedded Fast Fourier Transform (FFT) algorithm for computation of noise spectrum. The entire system has been successfully demonstrated to detect 0.1 fg/ml aflatoxin B1 (AfB1) from a complex mixture with as high as 1000ng/ml non-specific toxins.

Design of power monitoring system for new energy grid-connected operation based on LoRa and 4G technology

In order to obtain excellent varied speed performance of welding robot, the predictive model of motor drive system was established. On the basis of the analysis of the permanent magnet synchronous motor drive system, generalized predictive control method was adopted to control the rotor speed and position of the rotor. Because of the input and output constraint of the system, convex quadratic problem was proposed, and then an active set algorithm was adopted to deal with these constrained input and output. At last, the performance of this method is demonstrated by a real-time implementation using a digital signal processor (DSP) chip on a permanent-magnet synchronous motor with sinusoidal flux distribution. Theoretic analysis and experiments verify the validity and feasibility of this approach.