1. Field of the Invention
The present invention relates to machining devices that machine a workpiece.
2. Description of the Related Art
Among machining devices that grind a workpiece of a cylindrical object such as a workpiece to be used as an inner ring or an outer ring of a rolling bearing, a machining device is known which uses a two-roll, one-shoe spindle mechanism as one type of spindle mechanism that rotates a workpiece when grinding of the workpiece is carried out (see, e.g., Japanese Patent Application Publication No. 2014-240094 (JP 2014-240094 A)). As shown in FIG. 10, the two-roll, one-shoe spindle mechanism has an upper roll 91 that contacts a workpiece W from above, a lower roll 92 that contacts the workpiece W from below, and a shoe 93 that prevents the workpiece W from falling off.
The use of such a two-roll, one-shoe spindle mechanism is advantageous in that a workpiece can be loaded relatively quickly and idle time during operation can be reduced (the net operation rate can be improved). However, the two-roll, one-shoe spindle mechanism has the following disadvantages. In the two-roll, one-shoe spindle mechanism, components of the spindle mechanism such as the rolls are frequently required to be replaced or adjusted in position when the bearing number (specifications) of workpieces is changed. This work is complicated and increases the operation stop time of the machining device for changeover. As a result, the operation rate of the machining device is reduced, which results in reduction in productivity.
A machining device (grinding machine) described in JP 2014-240094 A includes a position adjustment mechanism and an angle adjustment mechanism as a configuration that carries out changeover between workpieces. The position adjustment mechanism changes the positions in the up-down direction of the upper and lower rolls. The angle adjustment mechanism changes the tilt angles of the central axes of the upper and lower rolls with respect to the horizontal direction.
In order to change the bearing number of workpieces (changeover), the position adjustment mechanism can adjust the positions of the upper and lower rolls 91, 92 and the angle adjustment mechanism can adjust the angle of the upper roll 91 by using a master workpiece. However, these adjustments need be made every time the bearing number is changed. In the case of machining many kinds of workpieces with different bearing numbers in small quantities, the operation of the machining device is stopped every time changeover is carried out, which may significantly reduce the operation rate of the machining device. Depending on the machining device, adjustment of a stopper for an upper frame (not shown) that is integral with the upper roll 91, adjustment of the position of a proximity switch for the rolls, etc. are required in addition to the above adjustments. This further increases the operation stop time.