Drive system

Older motor drive systems generally consist of a DC brush motor, a power conversion unit (PCU), and operator controls. A frequent problem with the motor itself Is worn brushes these should be replaced at regular Intervals as recommended by the manufacturer. In troubleshooting an extruder drive, one should follow the procedure recommended by the manufacturer of the drive. A typical troubleshooting guide for a DC motor is shown in Table 11.2. 

Motor will not start Low armature voltage Make sure motor is connected to proper voltage 

Motor runs too slow Low armature voltage Check for resistance in armature circuit 

Motor runs too fast High armature voltage Reduce armature voltage 

Brush chatter Incorrect brush pressure Measure and correct 

In previous Lessons, we showed the path taken through the injection molding machine by the plastics material/melt, on its way to becoming a molded article. We have shown, that this requires the machine to execute many different movements, sueh as  

Two types of drive are employed for these movements one is of the hydraulic and the other one of the eleetrie kind. It is usual for both to be employed in a machine. 

It has been shown with the example of the hydraulic clamping unit, how hydraulic modules are employed to execute the mold movements. 

To drive the hydrauhe elements, the hydrauhc oil pressurizes these elements. A pmnp, fed with hydrauhe oil from a storage tank, is employed for that purpose. 

Of course, the individual eomponents of the hydrauhe system must be intercoimected by flexible hoses as weh as fixed pipelines. 

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Acetal resins are also used extensively in transportation, especially automotive. Handles and internal components (gears, gear racks, cables) for window lifts and other similar devices are examples. Most of the appHcations which do not involve painting or plating are below the window line. Many common consumer items are manufactured essentially entirely from acetal resin (eg, disposable lighters) or have critical components molded from acetal resin (eg, hubs and platforms for videocassettes). The properties that make acetal resins useful in industrial appHcations make them useful for internal components, especially mechanical drive systems, of many household appHances. 

One successful total artificial heart is ABIOMED s electric TAH. This artificial heart consists of two seamless blood pumps which assume the roles of the natural heart s two ventricles (Fig. 7). The pumps and valves are fabricated from a polyurethane, Angioflex. Small enough to fit the majority of the adult population, the heart s principal components are implanted in the cavity left by the removal of the diseased natural heart. A modest sized battery pack carried by the patient suppHes power to the drive system. Miniaturized electronics control the artificial heart which mns as smoothly and quietly as the natural heart. Once implanted, the total artificial heart performs the critical function of pumping blood to the entire body (6). 

Pneumatic and hydrauHc drive systems have also been used, although not widely. 

In the large tied houses or big independent pubs the installation of the so-called beer drive system, ie, beer suppHed by tankers to relatively big cellar tanks combined with sophisticated beer dispensing systems, has been used successfully. The beer drive system might be seen as an alternative to the pub breweries or something which happened prior to the pub brewery period. 

Backstops. A backstop is a device that permits rotation of the pulley in the forward direction but automatically prevents rotation in the opposite direction. A backstop should be installed at the headshaft of an inclined belt to prevent the belt from moving in reverse if the power to the motor is intermpted or if there is a failure in the mechanical drive system. 

The weight of material in the buckets on the loaded side of an elevator chain causes the elevator to momentarily mn backwards if, during operation, the power is intermpted or there is a failure in the driving system. Because this could be a ha2ard to operating personnel, as well as damage to the elevator, a backstop, similar to that described for a belt conveyor, should be used. 

Hydraulic-drive samplers are also available, but cost factors tend to be substantially greater than electromechanical units. Recent use of hydraiilic-drive systems has diminished with the availability of increased strength and durabihty electric-motor linear-drive units capable of reliable operation in high-capacity applications. 

The great flexibility of dc motors both through inherent design charac teristics and through the way in which they are operated makes them ideally suited to adjustable-speed drives, particularly regulated drive systems. 

A modification of this basic drive system uses solid-state rectifiers and thyristors to convert the wound-rotor, variable-frequency slip power first to direct current and then to hne-frequency power (60 Hz in the United States). This in turn is fed back to the power system as useful energy. 

NEMA/1CS7.1/1995 Safety standards for construction and guide for selection, installation and operation of adjustable speed drive systems ... 

The power from the motor shaft to the driven shaft can be transmitted in many ways, depending upon the power and load application. In this chapter we deal with the most common types of driving systems, their influence on the starting characteristics of the motor and their effect on bearings. 

For critical loads and belt drives particularly, the user is advised to seek the opinion of the motor manufacturer to determine the mechanical suitability of the motor selected, its shaft and the DE bearing for the load to be transmitted, according to the drive system being adopted. The following are some important parameters that may help to determine... 

Electric drive systems have been tried as a means of achieving propulsion without harmful emissions. Currently, most battery-operated vehicles use... 

Wright, J., A Practical Solution to Transient Torsional Vibration in Synchronous Motor Drive Systems, American Society of Mechanical Engineers, Pub. 75-DE-15. 

These AC drive systems require the inverters to operate with either low-slip induction motors or reluctance-type synchronous-induction motors.. Such systems are u.sed where DC commutator motors are not acceptable. Examples of such applications are motor operations in hazardous atmospheres and high motor velocities. 

The inverter drive system that uses a current-controlled rectifier and parallel-capacitor commutation operates to both improve reliability and reduce cost. Such systems are built commercially for the ranges from 20 to 500 hp for the typical 20 1 constant-torque speed range. 

Most prime movers rotate at a higher speed than the operational driven equipment. Therefore, speed reduction is necessary for most belt drive systems. The speed ratio i between the prime mover drive shaft and the drive shaft is... 

Using the data contained in the API specifications for V belting, the following steps can be used to find V-belt drive system dimensions. 

Where maintenance service is infrequent, a counterweighted, spring-loaded, or automatic idler adjustment is best suited to promote long chain life. Manually adjusted idlers, if not periodically checked for proper chain tensioning, may become a destructive source in the drive system. 

There are various types of drive systems employed throughout the elevator industry, and the following are the most commonly used ... 

Elevators of this type are of a configuration similar to the geared drive systems mentioned above. The difference lies in the increase in the physical size of the drive as the required operating torque of a gearless d.c. motor is produced at a fraction of the rpm of a geared a.c. motor. 

Drive system machinery, pulley mechanisms and control panels ... 

Unlike gear sets, there can be two distinctive tooth-mesh frequencies for a chain-drive system. Since the drive and driven sprockets do not directly mesh, the meshing frequency generated by each sprocket is visible in the vibration profile. 

The process envelope must define the full range of operating conditions that will be expected of the belt-drive system. For example, will the drive operate continuously in one direction or will it be subjected to start/stops or direction reversals Will the drive system be subjected to radical speed changes or be used for braking the driven unit Such factors are important in that they help define the full range of load dynamics that the belt system must accommodate. From this data, the appropriate service factor that... 

Few belt-drive systems use a single belt for power transmission. The number of belts is determined by the horsepower requirements of the machine train. Determination of these requirements must be based on the full operating range of the system. Rapid speed changes, direction reversal, and other operating practices have a direct impact on the requirements of the belt system. Therefore, the selection process should be based on the most demanding operating conditions. 

A thorough inspection of the belt-drive system components (i.e., belt and pulleys) should be performed prior to installing new or replacement belts and pulleys. However, before conducting any inspection or maintenance, always determine, understand, and follow all plant safety rules. 

Before carrying out any inspections or maintenance procedures on belt drives, make sure they are not in operation. Equipment operators should electrically isolate the drive system and lock-out and tag the machine that is to undergo maintenance. Once this precaution has been taken, the belts and pulleys can be removed from the machine for inspection, cleaning, and repair. 

Excessive belt whip Excessive belt whip is usually more common on long-center applications (applications where the distance between the two pulley shafts is great). Pulsating loads in the drive system can produce this... 

For uniform and stable extrusion it is important to check periodically the drive system, the take-up device, and other equipment, and compare it to its original performance. If variations are excessive, all kinds of problems will develop in the extruded product. An elaborate process-control system can help, but it is best to improve stability in all facets of the extrusion line. Some examples of instabilities and problem areas include... 

There are several techniques available for SFA to drive a sample along the normal direction and to position it to a specified site. A common feature of these techniques is to employ a multi-stage driving system of increasing sensitivity. The apparatus developed by Israelachivili s team, for example, uses a two-stage screw as the coarse and medium control, which gives positioning accuracy of 1 /rm and 1 nm. 

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