RGB ENGINEERING

INSTALLATION EXAMPLES: LANDIS TRAVELING CARRIAGE ROLL GRINDER

COMPUTERIZED CROWNER RETROFIT SYSTEM

The standard older style Landis Type 30 traveling carriage roll grinder includes a mechanical cam type crowning device for grinding sinusoidal shapes on the roll bodies.  The crown cam is driven via a take-off shaft from the traverse gearbox, through a change gear interface as shown in the photo at the right.  The output or "driven" change gear connects to the cam actuator assembly (shown on the left) by means of a horizontal crossover shaft passing under the carriage step.  A right angle anti-backlash double worm unit meshes with the worm gear that is integral with the cam shaft assembly.  Therefore, as the carriage traverses along the bed, the cam rotates.  The "cam" is really not a cam in the true sense, but rather an eccentric which is offset a specific amount from the true center of rotation.  A cam follower vertical slide member imparts this crowning motion to the grinding wheel through the tilting subbase cambering system.  This consists of a simple trunnion pivot arrangement, with support points at the two front pivots, and the center mounted lever arm extending out the rear over the cam follower lift point.  Mechanical superposition of the crown input with the normal handwheel slide infeed is achieved with this system.  The normal wheel infeed occurs between the camber base (subbase) and the upper slide member (wheelslide).  For this vintage Landis design, compression springs mounted between the carriage and the tilting subbase relieve a portion of the load on the cam.  For this particular retrofit application, which was part of a total machine rebuild by Metal Manufacturing Company, since many of the necessary cam drive parts were missing from the candidate Landis grinder, it was decided to replace the complete cam mechanism with a new Servo Linear Actuator (SLA).  The photo on the left shows the stripped down carriage and subbase before the crowner retrofit.  One of the compression springs is shown, removed from its mounting location, for clarity.    

The mechanical system as described above has the advantage of simplistic operation, but is limited to the development of pure sinusoidal crown shapes only.  The FFG/FFP/SLA crowner retrofit addresses this issue, by utilizing a ball screw actuator for controlling the crown axis in conjunction with the basic elements of the proven trunnion tilt infeed system (SLA), which engages the subbase at a point slightly inboard of the old cam follower slide.  The ball screw actuator is designed for positive action due to the constant gravity preload effect and minimized backlash of the mechanical assembly.  This SLA is combined it with a state of the art computer system (FFG) and customized software (FFP) for producing any desired roll shape.  The DC servo motor operates through a harmonic drive reducer and timing belt reduction to rotate the ball screw and actuate the existing subbase.  The photos below show the crowner SLA assembly on the rebuilt Landis grinder after the conversion.

Carriage position is monitored using a multi-turn absolute encoder, coupled to a spur gear that engages a new rack bolted on the side of the back bed.  This feeds a digital display output on the computer as well as producing the signals for the “x” axis of the crown profile.

With this setup, the wheel infeed can be controlled very accurately with the servo motor.  There are no adjustments required as there were with the mechanical cam system.  Wheel “infeed” and “outfeed” is determined by the direction of motor rotation.  This has the additional advantage of always maintaining a positive gravity preload, since the cam never goes through TDC where the reaction forces change direction.

The command signals are produced by the FFG, which is located in a floor mounted enclosure.  An IBM compatible industrially rated computer, serially connected to the PLC, interfaces through an A/D board and other peripheral devices to provide the outputs to the SLA.  The FFG receives 16 bit digital inputs from the absolute encoder, and produces digital profiles from the FFP software.  The outputs go through a 15 bit D/A, then into analog summing circuits to command the servo motor for y-axis positioning.

To minimize backlash and lost motion, a LVDT is mounted on the back of the subbase to measure the crowning action directly, taking into account the magnification effect due to the pivot ratio.  This then forms the linear feedback to complete the positioning servo loop.

In addition to the normal functions of computerized crowning, bed correction, and the automatic trip switch feature, this order also includes the precision infeed and handwheel options.