Rotary Motor Mount

The DOVER Motion 23 frame motor mount is made of aluminum, and (among other things) mounts a motor to a DOVER positioning table.

We feel that the careful attention to detail and continuous design improvement in our motor mount exemplifies the quality and consideration that go into our entire product line. Key features of the motor mount include integral motor and limit/encoder connectors, built-in encoder and index signal capabilities, and positive motor alignment.

Our standard 23 frame stepping motors are custom manufactured with the motor leads exiting the motor face, and terminated in a locking, strain-relieved DE-9 connector. When bolted to the motor mount, the leads perform a 180 degree bend within the mount, and the connector is secured with two #4-40 jackscrews. This is superior to conventional motor wiring, which requires offset lead cutting, soldering the main cable, heat shrinking the solder joints, sliding back the insulation jacket, etc. Such cable assemblies, common among competitive designs, are permanently wired to the motor, have no strain-relief, and are prone to wire chaffing and shorts. With our motor mount connector, the cable is easily detachable, with an electrical shield terminated at the motor case, a secure strain-relief, and a metal connector hood with locking jackscrews for a positive interconnection that remains save during point-to-point, constant velocity, or interpolated motion. The motor connector is a male (pin type); this choice of connector polarities assures that the cable coming from the motor drive electronics has socket contacts, and hence cannot short out on exposed metal surfaces.

On the other side of the motor mount, an internal surface-mount PC board combines the limit switch and (if optionally selected) the encoder signals and brings these out on the limit/encoder connector. As with the motor connector, a secure interconnection is provided via this DE-9 connector with its locking jackscrews. The limit/encoder connector is of opposite polarity (socket contacts) to the motor connector, preventing inadvertent misconnection.

The motor mount also has an internal chamber for a flexible shaft coupling, which connects the motor drive shaft to the leadscrew shaft. Access slots at the top and bottom of the motor mount allow two-sided access to the clamp screws, which secure the helical coupling. Since the coupling diameter (1.00″) is less than the clearance hole which accepts the motor mounting boss, the coupling can be removed along with the motor, should service be necessary. The torsional stiffness of our most widely used coupling is 100 N-m/rad (0.07 oz-in/arc-sec); higher stiffness couplings are optionally available.

DOVER has developed 2000 or 4000 count per revolution optical encoders, which can be mounted within the motor mount. This option consists of a modular read head, which mounts to the stage body, and a 500 or 1000 line/revolution code disk, which mounts to the leadscrew shaft via an aluminum hub. The encoder is powered through the limit/encoder connector, resides entirely within the motor mount, and outputs A and B channel position information on pins 6 and 7 of this connector. Mounting the encoder on the table side of the flexible coupling provides more accurate positional tracking, and its location within the motor mount keeps the encoder safely out of harm’s way. An index on the 2000 count per revolution encoder provides a convenient signal once for each motor revolution. This can improve the accuracy of an end-of-travel limit sensor used as a “home” reference position (among other things). The standard DOVER rotary encoder and internal PC board provided differential outputs. When a linear encoder is specified, the output signals are wired to our standard limit/encoder PC board, and are present on the same pins of the DE-9 connector as with our rotary encoder.

In applications where DOVER positioning stages are shipped without motors, a slot is machined in the motor mount to allow the user to dress the leads forward to a connector. This technique is recommended over direct cabling to the motor, since it allows the use of separate cables, and provides a locking, strain-relieved connection.