Direct torque control

This is an alternative to FOC and can provide a very fast response. The choice of a static drive, whether through a simple V7/control, field-oriented phasor control or direct torque control with open or closed-loop control and feedback schemes, would depend upon the size of the machine, the range of speed control (whether required to operate at very low speeds, 5% and below), the accuracy of speed control and the speed of correction (response time). The manufacturers of such drives will be the best guide for the most appropriate and economical drive for a particular application or process line. 

Flux (/, ) control Double-phasor (vector) or Direct torque control (single-phasor afield-oriented control (DTC)... 

These drives are normally open loop (sensor-less) without encoder. For higher regulation, it is better to adopt a two-phasor control, such as a field-oriented control (FOC) or a direct torque control (DTC) drive. 

To facilitate model verification, experiments have been performed under similar conditions. The milling equipment (Thomas Wiley Mill, Thomas Scientific, Swedesboro, NJ) used in this study is a variable speed, digitally controlled, direct drive mill that provides continuous variation of cutting speeds from 600 to lldOipm with constant torque maintained throughout the speed range. Parametric studies were conducted with lactose granules to study the effect of impeller wall tolerance and feed rate on particle size reduction. 

P. Lataire, White Paper on the New ABB Medium Voltage Drive System, Using IGCT Power Semiconductors and Direct Torque Control , EPE journal, Vol. 7, No. %, December 1998, pp. 40-45. 

Battery-Electric Equipment. This is mechanically simpler in design than engine-driven equipment. Typically, the high-torque dc electric-drive motor is coupled directly to the drive axle through a constant-mesh drive train. An electronic silicon-controlled rectifier (SCR) speed-control device regulates the motor s revolutions per minute through operator foot control. Direction is reversed electrically with a delay interlock to avoid reversing motor direction while in motion. 

Expansion anchors transfer tension loads to the hase material via friction between the expansion elements of the anchor and the wall of the hole. The magnitude of the friction resistance is directly proportional to the degree of expansion force developed by the anchor. Expansion forces are produced in response to the relative movement of sloping surfaces within the anchor mechanism. The maimer in which this relative movement is produced is important for distinguishing the anchor function in response to tension loads. The two most common mechanisms for producing expansion forces are represented by displacement-controlled and torque-controlled anchors ... 

Thyristors have been replacing saturable reactors they are small, efficient, and easily controlled by a wide variety of control systems. A modern crane control drive uses fixed secondary resistors and two sets of primaiy thyristors (one set for hoist, one for lower). With tachometer feedback for speed sensing, the control for the motor provides speed regulation and torque hmiting in both directions, all with static-devices. A wide variety of control systems is possible the control should be designed for the specific application. 

The use of hydraulic units to drive rubber processing machinery has enabled the elimination of cumbersome gear boxes and their respective couplings. The hydraulic drive unit is fitted directly to the end of the shaft to be driven. It can be controlled fully across the entire speed range and provides full torque from rest, even under heavy load, up to the maximum rotational speed demanded. Shock loads do not affect performance and it has the ability to stop immediately on demand, due to its low inertia, unlike conventional drive systems. The unit requires little maintenance. 

The shear-stress convention is a bit more complicated to explain. In a differential control volume, the shear stresses act as a couple that produces a torque on the volume. The sign of the torques defines the positive directions of the shear stresses. Assume a right-handed coordinate system, here defined by (z, r, 9). The shear-stress sign convention is related to ordering of the coordinate indexes as follows a positive shear xzr produces a torque in the direction, a positive xrg produces a torque in the z direction, and a positive x z produces a torque in the r direction. Note also, for example, that a positive xrz produces a torque in the negative 6 direction. 

Synchronous motors are made in speeds from 1800 (two-pole) to 150 rpm (48-pole). They operate at constant speed without slip, an important characteristic in some applications. Their efficiencies are 1-2.5% higher than that of induction motors, the higher value at the lower speeds. They are the obvious choice to drive large low speed reciprocating compressors requiring speeds below 600 rpm. They are not suitable when severe fluctuations in torque are encountered. Direct current excitation must be provided, and the costs of control equipment are higher than for the induction types. Consequently, synchronous motors are not used under 50 HP or so. 

Direct current motors are used for continuous operation at constant load when fine speed adjustment and high starting torque are needed. A wide range of speed control is possible. They have some process applications with centrifugal and plunger pumps, conveyors, hoists, etc. 

Options for connecting the motor drive to the shaft depend on the shaft orientation. A vertical-shaft cantilever design would prefer a belt drive to reduce the cost of manufacture of the support structure and to facilitate maintenance. A horizontal shaft has the additional option of direct coupling. Variable speed can be accomplished through a gearbox or preferably through variable frequency control on the motor. In addition to the power requirements discussed previously, the startup power to overcome the torque of the rotor must be considered. This startup power is related to the time required to reach the desired rotor speed. 

Relation (6.40) represents a dynamical mapping which is mediated by Hamilton s equations of motion in the upper state and ultimately by the forces —dV/dR and —dV/dr and the torque —dV/d y. The energy dependence is mainly determined by the slope dV/dR of the potential in the direction of the dissociation path while dV/dr and dV/d y control the vibrational and rotational state distribution of the fragment. 

Ultimately, the feed system is not only responsible for conveying powder to the rolls, but also aiding in an initial deaeration of the blend. Weggel7 found that the torque on the feed system screw(s) is directly related to the precompaction pressure. He concluded that by maintaining a constant back pressure, the resulting compact quality can be better controlled. 

Several publications have described the use of molybdenum disulphide pastes for the lubrication of screw threads. This is an application in which the paste assists assembly and subsequently acts as an anti-seize. The critical factors in screw or bolt assembly are the friction between male and female thread and between bolt-head and workpiece, and their effect on the relationship between assembly torque and bolt tension (clamping force). The stiffness and integrity of a bolted assembly are determined by the bolt tensions, but since it is impracticable to measure bolt tension directly, the required bolt tension is controlled by the torque applied to the bolt or nut. However, the relationship between assembly torque and bolt tension is determined by head friction and thread friction. If the friction is reduced, the required bolt tension will be obtained at a lower assembly torque. 

---