Frameless motors

are extending the popularity of frameless motors into more registration-oriented operations such as paper converting and printing. Construction of frameless ac motors, electrically, is no different than conventional permanent-magnet and induction motors. The frameless designs can be controlled by the same drives as those used to control frame-type motors. Mechanically, however, frameless motors are a horse of a different color.

  They are delivered as individual com- ponents  a rotor, stator and feedback assembly, which are installed as an integral part of a machine,Frameless motors typically have continuous torque ratings from 100 lb-in. to 10,000 lb-in. and speeds from 300 to 20,000 rpm.

Advantages include:
 • Increased rigidity (stiffness).

  Overall machine stiffness is dependent on the cumulative stiffness of all mechanical elements between the motor rotor and load. These typically include belts, pulleys, gear sets or gearboxes, and couplings. In many applications, these can be eliminated by direct coupling. Moreover, shaft stiffness is a function of the cube of the shaft diameter. On frameless motors, the shaft diameter can be approximately three times greater than that of a conventional motor, thus giving 27 times more stiffness.

 • Versatile motor cooling methods.
  Among them, fluid cooling enables a compact motor to deliver high power.
 • Shafting options. Units can incorporate  a shaftless rotor with a bore through it or with a hollow shaft. This design offers machine builders the freedom to configure a variety of shafting options. For example, material or process fluids can pass directly through a hollow shaft.
 • Tailored bearing structure. Machine builders can tailor bearing structures to the precise needs of each machine. High-speed applications, such as spindles, can use a structure that minimizes bearing heat. Lowspeed applications, such as rotary tables, can be designed to handle large radial or axial loads.
 • Compact design. Frameless motors
  can be one-seventh the volume of conventional framed motors with the same power rating,