Self-centering timing disk hub and method of mounting the same

The invention relates to a self-centering timing disk hub with a timing disk support surface and a tubular hub sleeve, wherein the end of the hub sleeve can be pushed onto a motor shaft so as to provide in the hub sleeve a contact surface between the inner wall surface of the hub sleeve and the motor shaft. The outer wall surface of the hub sleeve has an at least approximately conical form, wherein the cone angle opens from the sleeve end to the timing disk support surface. The hub sleeve is slotted at least in the region of the motor shaft and a clamping element is movably arranged on the outer wall surface at the sleeve end. The invention also relates to a method for mounting a self-centering timing disk hub on a shaft, in particular a motor shaft of an encoder.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a self-centering timing disk hub with a
 timing disk support surface (1a) and a tubular hub sleeve (1b) and to a
 method for mounting the same on a motor shaft.
 2. Description of the Related Art
 Self-centering timing disks of the afore described type are known from DE
 196 41 929 A1 (RUHLATEC Industrieprodukte GmbH). The timing disk hub
 described therein is installed in an encoder which is connected with a
 motor by a simple rotational motion.
 Sufficient clearance should be provided for centering the timing disk hub
 on the motor shaft during installation. For this reason, the end of the
 timing disk hub facing the motor has a pilot bore for aligning the
 vertical axes of the shaft and the timing disk. With current
 state-of-the-art devices, a distortion tended to occur when the shaft is
 inserted into the timing disk hub, since the hub which is pushed onto the
 finish-machined shaft, has a reduced diameter. A housing surface exerts an
 axial pressure on the timing disk support surface, thereby moving the
 timing disk support surface and the timing disk hub connected thereto into
 the proper position for a centered placement in the encoder housing.
 Such timing disks are used in an increasing number of applications and
 produced in large quantities. The stringent requirements on the surface
 quality of the motor shaft and the timing disk hub as well as the tight
 manufacturing tolerances create a cost pressure in mass production. It is
 also difficult to maintain the required tolerances in production. A slight
 displacement of the timing disk relative to the motor shaft can adversely
 affect the operation of, for example, servo motors. Manufacturing
 tolerances can have a significant effect due to the large forces applied
 during the pressing process.
 SUMMARY OF THE INVENTION
 It is therefore an object of the present invention to provide a
 self-centering timing disk hub which can be placed, and adjusted without
 pre-tension and secured on a motor shaft. It should be possible to install
 the timing disk hub installation in mass production, while maintaining the
 accuracy required for encoders.
 According to the invention, a self-centering timing disk hub with a timing
 disk support surface and a tubular hub sleeve is provided. The sleeve end
 is being pushed onto a motor shaft with a contact surface being produced
 in the hub sleeve between the inner wall surface of the hub sleeve and the
 motor shaft. The outer wall surface of the hub sleeve is at least
 partially formed in the shape of a cone. The cone angle opens from the
 sleeve end to the timing disk support surface. The hub sleeve is slotted
 at least in the region of the motor shaft. A clamping element is movably
 arranged on the outer wall surface of the sleeve end. Further the cone
 angle is in the range of 10-15.degree. and the length of the at least one
 slot in the hub sleeve is in the range of 0.5-0.8of the contact surface
 length between the hub sleeve and the motor shaft. The hub sleeve includes
 a stop face which defines the rest position of the clamping element, with
 the stop face located on the outer wall surface in a region of the open
 end of the slot. Further, the clamping element includes a clamping ring
 and may be manufactured of an elastic plastic material.
 The at least one slot in the hub sleeve has a width of about 1-2 mm. In the
 first third of the hub sleeve, viewed from the side of the motor shaft, a
 locking face defining the tensioning position of the clamping element is
 machined circumferentially on the outer wall surface of the hub sleeve.
 The locking face has a protruding lip, disposed on the outer circumference
 of the hub sleeve. On the sleeve end on the side of the motor shaft, the
 inner wall surface of the hub sleeve has a conical enlargement. The
 conical enlargement on the inner wall surface of the hub sleeve extends
 from the end face over a range of 20% of the length of the hub sleeve.
 Preferably there are at least 4 slots within the hub sleeve of
 axis-parallel extension equally distributed on the circumference.
 In addition, a method for mounting a self-centering timing disk hub on a
 shaft, in particular, a motor shaft of an encoder, is provided. The timing
 disk hub includes a timing disk support surface and a tubular hub sleeve,
 with the sleeve end of the hub sleeve oriented towards the motor shaft and
 the end of the timing disk hub facing the motor shaft is slotted with a
 clamping ring being pushed onto the slotted end. The clamping ring is then
 moved from a tension-relieved position into a tensioned position after the
 timing disk hub is shifted onto the motor shaft.
 It has been observed that a timing disk hub formed according to the
 invention can be pushed onto the motor shaft and clamped at the time of
 installation, without displacing the timing disk axis radially or
 angularly relative to the motor shaft axis. Since during installation this
 does not produce a press-fit, only a relatively small force is required.
 Instead, the hub and the shaft slide relative to each other during
 installation and are changed to each thereafter only.
 Other objects and features of the present invention will become apparent
 from the following detailed description considered in conjunction with the
 accompanying drawings. It is to be understood, however, that the drawings
 are intended solely for purposes of illustration and not as a definition
 of the limits of the invention, for which reference should be made to the
 appended claims.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
 FIG. 1 shows a cross-sectional view of a timing disk hub according to the
 invention with a timing disk support surface 1a and a tubular hub sleeve
 1b. As seen from FIG. 1, the outer wall surface of the hub sleeve 1b has a
 conical form, with the cone angle opening from the sleeve end E to the
 timing disk support surface 1a. Slots 1d are formed in the hub sleeve
 which extend into the contact region with the motor shaft W (FIG. 2).
 A stop face 1c which reliably secures a clamping element S in the rest
 position before installation, is formed at the end of the hub sleeve 1b.
 The clamping element S preferably includes a clamping ring 2 which in its
 rest position is not pre-tensioned, but is placed loosely on the outer
 wall surface of the sleeve end.
 FIG. 2 shows a timing disk hub according to the invention after
 installation on the motor shaft W. As seen in FIG. 2, the clamping ring 2
 has moved to a tensioning position on the conical outer wall surface of
 the hub sleeve 1b. The clamping ring 2 is retained in the displaced
 position (tensioning position) on a locking face 3 to provide in this
 position a non-slip, force-transmitting connection between the motor shaft
 and the timing disk hub.
 FIG. 3 schematically illustrates the installation process. After the timing
 disk hub 1b is pushed onto a motor shaft W, the clamping ring 2 is moved
 from its forward position onto the cone, thereby clamping the motor shaft
 W. Since the shaft is made of plastic--preferably of the type ABS--a small
 tensioning force is sufficient to reliably secure the timing disk on the
 motor shaft W. This situation is illustrated in FIG. 4 which shows a front
 view, as viewed from the side of the motor shaft.
 The width of the slots is preferably greater than the wall thickness of the
 tubular timing disk hub. A relatively elastic body which can be placed in
 intimate contact with the shaft W by applying only a small external
 pressure, is formed by providing at least four slots which are distributed
 uniformly over the tubular circumference of the timing hub. FIG. 4
 indicates the displacement of the clamping ring from the rest position
 (lightly shaded area H) into the tensioning position (dark area D).
 According to a preferred embodiment, the clamping ring can be made of
 rubber. The clamping forces act on the motor shaft radially in the
 direction of the arrows.
 In both positions, the clamping ring should be held securely on the timing
 disk hub. As seen from the enlarged section A of FIG. 5, the lip 1c safely
 retains the clamping ring in the rest position on the hub. A conical
 enlargement 1c is provided at the output end E of the timing disk hub of
 the invention, with the conical enlargement serving as a catch bore for
 the motor shaft.
 A cross-sectional view through an encoder before installation is
 illustrated in FIG. 6 to serve as a comparison with a conventional timing
 disk and to explain the installation. A base plate 4 of an encoder housing
 11 which is flange-mounted against the motor side, is shown.
 A timing disk 10 is arranged on the hub 9. A locking ring 14 prevents the
 timing disk 10 from falling out before installation. A centering surface
 17, which cooperates with the guide surface of the housing 16 for
 automatically centering the hub 9, is formed on one end of the hub 9. A
 sensor unit 8 with a terminal strip 13 is arranged next to the centering
 surface 17. A conventional encoder unit can also be used with the present
 invention if the timing disk hub 9 is exchanged for a timing disk hub
 constructed according to the invention.
 It has been experimentally observed that the timing disk axis can be
 exactly aligned with the motor shaft axis using the installation method of
 the invention. Only a small force is required for the installation, so
 that no bending stress should be transmitted to the timing disk. The
 design of the locking positions for the safety ring guarantees a permanent
 attachment of the timing disk on the timing disk hub. Experiments with
 different materials have further demonstrated that timing disks produced
 according to the invention fit snugly on the motor shaft even if the
 surface quality of the motor shaft is degraded. As a result, the
 manufacturing costs can be reduced even further without affecting the
 manufacturing quality.
 Thus, while there have been shown and described and pointed out fundamental
 novel features of the invention as applied to a preferred embodiment
 thereof, it will be understood that various omissions and substitutions
 and changes in the form and details of the devices illustrated, and in
 their operation, may be made by those skilled in the art without departing
 from the spirit of the invention. For example, it is expressly intended
 that all combinations of those elements and/or method steps which perform
 substantially the same function in substantially the same way to achieve
 the same results are within the scope of the invention. Substitutions of
 elements from one described embodiment to another are also fully intended
 and contemplated. It is also to be understood that the drawings are not
 necessarily drawn to scale but that they are merely conceptual in nature.
 It is the intention, therefore, to be limited only as indicated by the
 scope of the claims appended hereto.