Machines with Shaft Drive

With shaft machines, information about the shaft position for each single weft insertion is read from an input-output media (punched card, software) directly before weft insertion (Fig. 4.17). In this procedure, the pick repeat is theoretically unlimited. A change in the type of weave pattern may be realized easily with an exchange of the data media. 

Double-lift dobbies insert two wefts per machine revolution. During the first half of the weft insertion, the position of the shafts for the following shed is read in. Double-lift dobbies work according to the Hattersley principle as reverse motion dobbies or with rotational motion. 

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This shedding principle is characterized by a direct, rigid connection of the shafts and the primary drive shaft. The motion sequence is repeated with every revolution of the drive shaft. Eccentric drives allow very high weft insertion frequencies. Their disadvantages are a small pick repeat and the large effort necessary when changing products. Machines with eccentric drives are mostly used in mass production. 

When geared winders are preferred for economic reasons, and this applies generally to machines with drives of less than ISOOkW in magnitude, proprietary, self-contained gearboxes with shafts running in roller bearings are now supplied. (See Figure 25.)... 

Repeated twisting of the spindle s tube or the solid shaft used in jackshafts results in a reduction in the flexible drive s stiffness. When this occurs, the drive loses some of its ability to absorb torsional transients. As a result, damage may result to the driven unit. Unfortunately, the limits of single-channel, frequency-domain data acquisition prevents accurate measurement of this failure mode. Most of the abnormal vibration that results from fatigue occurs in the relatively brief time interval associated with startup, when radical speed changes occur, or during shutdown of the machine-train. As a result, this type of data acquisition and analysis cannot adequately capture these... 

Figure 16.33 shows a schematic of a simple gas turbine. The machine is essentially a rotary compressor mounted on the same shaft as a turbine. Air enters the compressor where it is compressed before entering a combustion chamber. Here the combustion of fuel increases its temperature. The mixture of air and combustion gases is expanded in the turbine. The input of energy to the combustion chamber allows enough power to be developed in the turbine to both drive the compressor and provide useful power. The performance of the machine is specified in terms of the power output, airflow rate through the machine, efficiency of conversion of heat to power and the temperature of the exhaust. Gas turbines are normally used only for relatively large-scale applications, and will be dealt with in more detail in Chapter 23. 

Figure 274(a) depicts the drive system which was already part of the earliest machines (see Figure 225). More recent machines, instead of powering shaft (3) by transmission belts, apply a motor (5) with a torque-limiting clutch, a gear reducer (4), and a flexible coupling to drive gear shaft (3) mounted in or on the roller press frame. The gear on shaft (3) transmits torque to the coupled gears (2) on the roll shafts between two roller bodies (1).

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