Patent Publication Number: US-3877180-A

Title: Drive systems for a grinding wheel

Description:
. [22] Filed:  
 &#39; United States Patent 1 Brecker DRIVE SYSTEMS FOR A GRINDING WHEEL [75] Inventor: James N. Brecker, Pittsburgh, Pa.  
 [73] Assignee: Carnegie-Mellon University,  
 Pittsburgh, Pa.  
 Nov. 12, 1973 [21] Appl. No.: 414,651  
 [56] References Cited UNITED STATES PATENTS 4/1938 Johnson 51/1345 F 11/1960 Dunigan 5l/l65.92  
 Primary Examiner Harold D. Whitehead Attorney, Agent, or Firm-Buell, Blenko and Ziesenheim Apr. 15, 1975 [57] ABSTRACT A system for driving a grinding wheel and urging it against a work piece employs two hydraulic systems linked together. One system drives the grinding wheel and applies a torque to it while building a fluid pressure proportional to the torque. The second system includes a set (or reference) fluid pressure which urges the grinding wheel into the work. The two hydraulic systems are linked together in such a manner that when the pressure in the hydraulic system which drives the grinding wheel equalizes the set pressure in the hydraulic system which urges the grinding wheel against the work, the entire system is in equilibrium and maintains a constant torque at the grinding wheel. If excess pressure guilds up in the hydraulic system which drives the grinding wheel, it will counteract the set pressure in the second hydraulic system and cause the grinding wheel to back away from the work in order to maintain the constant torque.  
 6 Claims, 2 Drawing Figures DRIVE SYSTEMS FOR A GRINDING WHEEL This invention relates to a system for driving a grinding wheel and urging it against a work piece.  
  In the steel industry during the processing of steel billets and slabs, abrasive conditioning, or snagging, is used extensively to remove scale and other surface defects before the final processing of the steel. Most automatic conditioning machines have an AC motor V-belt drive and use an hydraulic or pneumatic cylinder to force the grinding wheel into the work with a constant force. Since wheel wear increases significantly as the wheel surface speed decreases, a mechanical transmission is used to increase the wheel RPM in several steps because wear reduces the wheel diameter. The metal removal rate varies by more than a factor of two due to cyclic wheel wear. This cyclic wear is avoided by providing a relatively constant tangential grinding force which gives a constant material removal rate and results in more consistent quality. A DC motor drive has been used to accomplish the necessary tangential grinding force. However, this is expensive and is so bulky that it is difficult to follow the contour of severely curved work pieces at constant power.  
  Applicants invention which employs an hydraulic system overcomes these problems and has many advantages. Wheel speed can be easily adjusted by changing the hydraulic pump displacement. The grinding wheel support can be made very rigid and surface contours can be accurately followed because of the small size and light weight of the hydraulic motor. The hydraulic drive is less expensive than the variable speed DC drive technique. The hydraulic pressure in the drive system can be used as a very responsive control signal to provide constant grinding power. The drive system of the invention offers the advantage of low cooling requirements at all power levels due to the constant flow circuitry as opposed to a constant pressure hydraulic circuitry.  
  The invention uses a hydrostatic transmission to drive the grinding wheel spindle and utilizes the transmission pressure to apply a correction signal to an hydraulic cylinder which urges the grinding wheel against the work in order to maintain a constant power operation or a constant torque.  
  An AC motor is used to drive a variable displacement hydraulic pump which in turn supplies fluid flow to an hydraulic motor. The variable displacement pump enables the wheel RPM to be increased as the wheel wears so that the wheels peripheral speed can be maintained constant for optimum wheel wear. When a grinding torque is applied to the wheel by the hydraulic motor, the supply pressure to the hydraulic motor increases proportionally. In operation, a fluid pressure (referred to as a set pressure) which is equivalent to the desired power level is introduced into a forcing side of the hydraulic cylinder which urges the grinding wheel against the work. The wheel is urged into the work until the transmission pressure (for rotating the wheel) increases to a level required to counteract the set pressure and thus reaches an equilibrium. This equilibrium position will change continuously to reflect changes in the workpiece geometry and material properties. A feedback circuit maintains a close force equilibrium on the wheel feed cylinder and thus maintains a constant motor torque and insures a constant power operation applied to the grinding wheel which is desirable to keep a constant. material removal rate.  
  I provide a system for driving a grinding wheel and urging it against a work piece which comprises a first hydraulic means driving the grinding wheel and applying a torque to the grinding wheel, the first hydraulic means developes a dynamic pressure in a fluid supply in the first hydraulic means which is used to transmit the torque to the grinding wheel; and a second hydraulic means urges the grinding wheel into the work and is fluid coupled to the first hydraulic means, the second hydraulic means is responsive to changes in the dynamic pressure of the fluid supply in the first hydraulic means and the pressure applied by the second hydraulic means in urging the wheel against the work varies according to the dynamic pressure in the fluid supply in the first hydraulic means.  
  Other details, objects and advantages of my invention will become apparent as the following description of the present preferred embodiment thereof proceeds.  
  In the accompanying drawing I have illustrated a present preferred embodiment of the invention in which:  
  FIG. 1 is a schematic showing the system of the invention illustrating the principles and a typical circuit; and  
  FIG. 2 is a detailed schematic of the safety and control valve circuits with the valves 12 and 13 shown in their normally inoperative position.  
  Referring to FIG. 1, an electric motor 1 is used to drive a variable displacement hydraulic pump 3 which in turn is coupled to an hydraulic motor 4 by a high pressure line 5 and a return line 6. The hydraulic motor 4 applies a torque to the grinding wheel or grinding wheel spindle 2. An hydraulic fluid reservoir 7 is coupled to a heat exchanger 8 which is coupled to a 10 micron filter which in turn is coupled to the hydraulic pump 3. An electric motor 17 drives in hydraulic pump 11 through a relief valve 16 to a safety valve 12. Safety valve 12 is also coupled to the high pressure line 5 from the hydraulic pump 3. Interposed in this coupling to the safety valve 12 is a low limit switch 15 which senses a pressure above psi. Safety valve 12 is coupled to a wheel positioning valve 13 which has one output coupled to the forced side of a piston and cylinder arrangement 10. The other output of valve 12 (see FIG. 2) is coupled to the opposite end of the force side of the cylinder 10. The piston is coupled mechanically to an arm about a pivot point. Whenever the cylinder is raised, the grinding wheel 2 is urged down on a work piece not shown.  
  The operation of the system shown schematically in FIG. 1 is as follows. A constant flow of fluid from the hydraulic pump 3 (driven by electric motor 1) drives the hydraulic motor 4 at a constant speed (allowing for speed drops in the electric motor). Pressure in the motor supply line 5 changes in response to the demands on the motor 4. The hydraulic motor 4 applies a torque to the grinding wheel 2. At the same time, hydraulic pump 11 driven by motor 17 applies a set pressure (or reference pressure) through the valve box 12 and 13 to the bottom of the cylinder 10 which urges the piston of that cylinder to raise and thereby urge the grinding wheel against the work. A line couples the top end of the cylinder 10 through valve box 12 and 13 to the high pressure line 5. This fluid pressure at the top of cylinder 10 opposes the set pressure applied at the bottom of the cylinder 10 from the pump ,11. When a torque is applied to the wheel 2 and a given depth of material is removed from the work by the grinding wheel 2, this produces a motor supply pressure in line equivalent to the set pressure developed by pump 11 coupled to the bottom of the cylinder 10. This equilibrium position (manifested in cylinder will change continuously to reflect changes in work piece geometry and material properties. The feedback circuit from the high pressure line 5 to cylinder 10 will maintain a force equilibrium on the wheel feed cylinder 10 and thus maintain a constant motor torque on the wheel which is what is desired.  
  FIG. 2 shows the schematic details of the safety valve 12 and wheel positioning valve 13, which are shown in FIG. 2 in the normally inoperative position with their solenoids not activated. The valves are operated by solenoids and the spools of the valves are spring biased. The springs are shown on the left side of each of the valves. The solenoids are shown on the right side of each of the two valves as the extended small square portion. The P is connected to the relief valve 16 which is connected to the pump 11. The P is connected through the limit switch 15 which is connected to the high pressure coupling 5. The check valve 18 is coupled to the return of the hydraulic pump 11.  
  Releasing a solenoid in valve 12 disconnects the high pressure from line 5 to the top of the cylinder 10 and the set pressure or reference pressure developed from the hydraulic pump 11 shown in FIG. 1 is connected to the top of the cylinder 10 thereby keeping the wheel 2 away from the work. The limit pressure switch 15 works in conjunction with the solenoid in safety valve 12. The purpose of switch 15 is to remove the grinding wheel 2 away from the work in the event that the high pressure line 5 should fail or in the event the high pressure falls below the pump operating limit.  
  In starting the system, the electric motor 1 is turned on, the solenoid in valve 12 will then move the spool in the valve to the left thereby reversing the outputs coming from 12 of P and P However, this will still not move the wheel 2 toward the work until a manual switch which is not shown, moves the solenoid and the spool in the positioning valve 13 to the left, thereby placing the P at the bottom of the cylinder 10 and the P at the top end of the cylinder 10 as shown in FIG. 1, and urging the grinder against the work.  
 I claim:  
 1. A system for driving a grinding wheel and urging it against a work piece which comprises:  
 a. a first hydraulic means driving the grinding wheel and applying a torque to the grinding wheel, the first hydraulic means developes a dynamic pressure in fluid supply in the first hydraulic means which is used to transmit the torque to the grinding wheel; and a second hydraulic means urges the grinding wheel into the work and is fluid coupled to the first hydraulic means, the second hydraulic means is continuously responsive to changes in the dynamic pressure of the fluid supply in the first hydraulic means and the pressure applied by the second by draulic means, in urging the wheel against the work, continuously varies according to the dynamic pressure in the fluid supply in the first hydraulic means.  
  2. A system as recited in claim 1 wherein the second hydraulic means includes a third hydraulic means supplying a set fluid pressure to the grinding wheel to urge it against the work, the grinding wheel is urged against the work until the dynamic pressure in the fluid supply in the first hydraulic means counteracts the set pressure and reaches an equilibrium while the grinding wheel is removing material from the work thereby maintaining a constant torque at the grinding wheel.  
  3. A system as recited in claim 2 wherein the second hydraulic means includes an hydraulic piston and cylinder in which the cylinder is coupled to the grinding wheel and urges the grinding wheel into and away from the work, the set pressure in the fluid from the third hydraulic means is coupled to a forcing end of the cylinder and the fluid pressure from the first hydraulic means is coupled to an end opposite the forcing end.  
  4. A system as recited in claim 3 wherein the first hydraulic means includes:  
 a. an electric motor;  
 b. an hydraulic pump coupled to the electric motor;  
 and  
 c. an hydraulic motor with a fluid coupling to the hydraulic pump, the hydraulic motor is coupled to the grinding wheel.  
  5. A system as recited in claim 4 which includes a fourth means coupling the fluid coupling between the hydraulic pump and the hydraulic motor to the cylinder at the end opposite the forcing end.  
 6. A system as recited in claim 5 wherein the fourth means includes a safety valve and a positioning valve. i=