A DRIVE SYSTEM FOR A BENDING MACHINE

Abstract: An improved bending machine with three or more rollers (1,2,3) which may be driven at different speeds and/or with differing torques has a control system unit (12) which receives signals indicative of the position and speed of rotation of one or more of its rollers and which is connected to means for adjusting the position and rotational speed of the or each roller so that commands can be given to vary these parameters. The torque on one or more of the rollers may also be measured and varied. The machine can thus be readily and accurately adjusted to produce bends of differing dimension in strip metal material.

Description: The present invention relates to apparatus for and a method of bending strip metal material such as 'I' section beams and 'U' section beams or other formed sections. In order to bend such sections it is conventional to provide three or more rolls which straddle and feed path of the material to be bent. The first roll normally has a fixed axis on one side of the path, the next or second along the path is on the other side, whilst the third roll is on the same side of the path as the first, the second and third rolls have axes which are adjustable with respect to the bending path. Other rolls may also be provided. The axes of the rollers are essentially parallel (or sometimes on an angle in order to generate a cone shape) to each other, and are arranged in approximately a triangular pattern so that a strip or sheet like workpiece passed between them is bent in to a curved shape. Such a bending machine will hereafter be referred to as a bending machine of the type described. A conventional roll bending machine is driven by a single motor and/or gearbox. One or more of the rollers may be driven directly or by shafts, gears, chains etc. and consequently all driven rollers rotate at the same speed or fixed ratio of speeds. One or more rollers may not be driven at all and allowed to freewheel. When bending thin section or large radius curves this does not present a problem but with small radii and thicker sections the different relative speeds of the outside and inside of the curve results in either slip, distortion of the section or overloading of the gearbox components. When bending large sections this problem is kept to a minimum by passing the workpiece backwards and forwards several times making progressive reduction in radii and permitting some slip on one or more of the rollers. If a small radii is attempted in a single pass of the workpiece, the internal forces induced in the workpiece will cause severe and unacceptable deformation. On the other hand, if one or more of the rollers is allowed to freewheel to eliminate slip, then the driven roller(s) will also slip and/or distort the section. The general object of the invention is to eliminate or substantially to eliminate these problems and to enable a bending machine to be readily adjusted accurately to produce bends of differing dimensions. US-A-. 4047411 describes a pyramid roll forming machine according to the preamble of claim 1 in which the vertical position of the upper roll is continuously controlled and the position of the ends of upper roll can be changed to skew the axis of the upper roll with respect to the axes of the lower rolls. The rate of movement of a part to be bent through the machine is sensed and the information is employed to control the rate of comparison between signals relating to the upper roll position and signals for changing that position to allow continuous compensation to be made for springback. A machine for bending strip metal material with three or more rollers arranged to act on the strip along a roller path so as to bend the strip in accordance with the invention, has, for at least one of the rollers, means for ascertaining the position of the roller and means for adjusting that position in a plane perpendicular to the axis of rotation of the roller, characterised in that means for measuring the speed of rotation of the said at least one roller and means for adjusting that speed, are provided, in that signals from the means for measuring the position and speed of the said at least one roller are fed to a control system unit which in turn is connected to the means for adjusting the position and speed of the said at least one roller so that commands may be given to vary these parameters and in that means for measuring the torque applied to one or more of the rollers, and means for adjusting that torque are provided. Preferably, a signal from the means for measuring the applied torque on the roller(s) is fed to a control system unit which in turn is connected to the means for adjusting the applied torque of the roller(s) so that a command may be given to vary this parameter. Suitably a single control system unit is provided. Thus complete control over each of the parameters is maintained and as we have discovered that it is these parameters which effect the proper bending of the arch to a determined radius, the apparatus may be readily adjusted for any desired arch within limits by giving the control unit the necessary instructions. For example, the section to be bent should be driven forward at a reasonable speed with sufficient torque force being applied through the rollers to achieve bending without the rollers slipping and to enable the desired internal force to be generated in the section. It will be appreciated that normally the rollers will be driven at different speeds and/or with differing torques. However with one control system unit on each motor it is possible to control either motor pressure or motor speed, but not both simultaneously. The rollers will normally be driven either by independent hydraulic, electrical or pneumatic motors or by or by variable speed drives. The invention will now be further described by way of example with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic view of a three roll bending machine of the type described showing an 'I' section beam being bent to form a colliery arch, Figure 2 is a side elevation of the apparatus shown in Figure 1, Figure 3 is a schematic view of the apparatus shown in Figures 1 and 2 illustrating the control system, and Figure 4 is an example of one particular embodiment of a bending machine incorporating the principles generally illustrated in Figure 3. Referring to Figure 1 a typical three roll arch bending machine of the type described is illustrated but the invention is in no way restricted to such a particular layout. Three rolls 1, 2 and 3 are located in a triangular position with an 'I' section beam 4 moved between the rolls in the direction of the arrow. The axes of the rolls are movable relative to each other so that they can be positioned to achieve the desired radius of curvature of the bent section. As can be seen from Figure 2 each of the three rolls is driven by a separate motor 5, 6 and 7 through gears 8. As each roll has its own drive motor the speed and torque applied to each roll may differ and the relevant speeds may be adjusted during bending of the 'I' section beam. As is illustrated in Figure 3 the position of each of the rolls 1, 2 and 3 is adjustable by means of a positioning actuator generally indicated at 10 in the direction both of the axis x and the axis y. The position of each roll at any one time can be measured by a measuring device generally indicated at 11. The speed of rotation of each roll can be adjusted by a rotation actuator (not shown) which in effect can adjust the speed of rotation of each roll through the drive motors 5, 6 and 7 and gearing 8. The instant speed of each roll is measured by a measuring device 11. Finally the torque applied to each roll is both adjustable and measurable. Signals from the measuring units 11 of both the position in the x and y directions, the rotational speed and the torque, is fed to a control unit 12. The control unit in accordance with instructions which it has received for some particular section and some particular desired radius then issues instructions for alterations to the position, speed and torque of each of the three rolls to adjustment means 13 so as to achieve the desired curvature. This control system continues to operate during the formation of the bend in the section. It will be appreciated that for example the torque applied to the various rolls may differ for example for one power unit, roll 3 could have two units of torque applied to it, roll 2 could have no torque applied and roll 1 could have minus one unit of torque. This would then give the effect of stretching the outer curved face of the section helping to prevent the tendency to crumple and help to prevent elongation of any holes which may be present in the web of the 'I' section along the central zone where deformation tends to occur. In the machine exemplified in Figure 4, the rolls are driven by hydraulic motors. Roll 1 is provided with a pressure measuring device 14 and a proportional valve pressure control 15 for control over the fluid pressure applied to the motor so that the torque may be varied. The position of the proportional valve is set by the control device 17 and the device 14 for measuring pressure is then linked to the device 15 also for controlling the position of the proportional valve. Similar controls are provided for the roll 2 but the roll 3 is provided with a hydraulic piston and cylinder device generally indicated at 10 designed to alter the position of roll 3 in both the x and y direction. This device is also linked to a position measuring device 16 giving signals to the control unit 17. A fluid pressure measuring device 14′ is also provided for the fluid flow to the hydraulic motor for roll 3 and the output from this measuring unit is fed to the control unit 17 rather than to the proportional valve pressure control as in the case with rolls 1 and 2. Indeed a proportional valve flow control unit 15′ is provided which receives instructions from the control unit 17 so that the speed of rotation of roll 3 may be adjusted. It will thus be appreciated that when control unit 17 issues instructions for alteration of the torques applied to rollers 1 and 2, the net torque may not be enough to ensure the movement of the section through the machine at the desired speed, in which case the actual rotation speed of roll 3 will drop. Roll 3 may be speed controlled in which case its control valve will increase oil flow to the motor driving roll 3 to correct the speed error; in so doing, the torque that it supplies will automatically increase, ensuring that the net torque supplied by rolls 1,2 and 3 is enough to achieve the correct bend at the correct speed. In this way the overall control system can compensate automatically for any process variations. A problem with bending machines of the type described is that on varying the velocity of the rollers, a high frequency gear-box resonance can be excited. This results in poor performance and machine wear. An advantage of providing a control system as shown in the drawings for such a bending machine is that the system can be arranged to increase 'roll-off' at high frequencies and thus minimise the effect of the gear-box resonance.

Claims: A machine for bending strip metal material with three or more rollers arranged to act on the strip along a roller path so as to bend the strip having for at least one of the rollers, means for ascertaining the position of the roller and means for adjusting that position in a plane perpendicular to the axis of rotation of the roller, characterised in that means (11) for measuring the speed of rotation of the said at least one roller and means (13) for adjusting that speed are provided, in that signals from the means (16,11) for measuring the position and speed of the said at least one roller are fed to a control system unit (17) which in turn is connected to the means (10,13) for adjusting the position and speed of the said at least one roller that commands may be given to vary these parameters and in that means (14) for measuring the torque applied to one or more of the rollers, and means (13) for adjusting that torque are provided. A machine as claimed in Claim 1 wherein a signal from the means (14) for measuring the applied torque on the roller(s) (1,2,3) is fed to a control system unit (17) which in turn is connected to the means (13) for adjusting the applied torque of the roller(s) (1,2,3) so that a command may be given to vary this parameter. A machine as claimed in Claim 2 wherein a single control system unit (17) is provided to receive the signals from the means (16, 11, 14) for measuring the position, speed and applied torque of the roller(s). A machine as claimed in Claim 3 wherein the single control system unit is connected to the means (10, 13) for adjusting the position, speed and applied torque of the roller(s) so that commands may be given to vary these parameters. A machine as claimed in any preceding claims wherein means are provided to drive the roller (s) (1, 2, 3) at different speeds and/or with differing torques. A machine as claimed in any preceding claim wherein the roller (s) (1, 2, 3) are driven either by independent hydraulic, electrical or pneumatic motors (5, 6, 7) or by variable speed drives. A machine as claimed in any preceding claim wherein the means (13) for adjusting either the speed and/or applied torque of the roller (s) (1, 2, 3) comprises a proportional valve control unit (15, 15'). A machine as claimed in any preceding claim wherein the means for measuring the speed and/or torque applied to the roller (s) (1, 2, 3) comprises a pressure measuring device (14).

Inventors: MASON, BENJAMIN
Applicants: CALEDONIAN MINING COMPANY LIMITED
Application year: 1987
Main classification: B21D7
IPC codes: B21D7