variable-speed drive[′ver·ē·ə·bəl ¦spēd ′drīv]
a separate or built-in unit of a machine for the smooth alteration of the gear ratio. The drive consists of one or several infinitely variable transmissions and devices that ensure their operation. The basic characteristic of the variable-speed drive is the range of regulation—that is, a ratio of the largest gear ratio to the smallest (usually 3-6; less frequently 10-12).
Variable-speed drives provide optimal speed conditions of a machine under various operating conditions. For example, on a machine tool the best cutting speed for the various parts of a blank can be maintained when processing a rotating surface of varying radius. On subway escalators, variable-speed drives serve to closely match the speeds of the handrails and the stairs. These drives are used on machine tools, machines, and mechanisms of the textile, paper, and chemical industries, and in transportation. A widespread construction is a V-belt variable-speed drive with a built-in electric motor. The use of such drives as infinitely variable speed regulators (with programmed control when necessary) is rising significantly in connection with the possibility of using them for the automation of the control of production processes.
N. IA. NIBERG and A. A. PARKHOMENKO