In the process of manufacturing steel billet the molten steel is continuously poured from a tundish car and formed into a strip by passing between a series of pairs of rollers. The spacing between the individual rollers of a roller pair is adjusted to give the correct thickness of billet. As the steel cools from the outside surfaces towards the centre, the last section of steel to cool is in the middle of the strip. In order to eliminate the crystalline cooling defect the strip is squeezed under pressure at the correct point of cooling. This point of cooling is not predictable in the process as it varies along the strip dependent on the speed of the strip through the series of pairs of rollers and the pressure on the strip created by the head of steel

in the tundish car. The known technology is not capable of determining the point to squeeze the strip and it is therefore necessary to inspect the steel after the process is complete and thereafter strip is sorted into good or bad sections.

It is an object of the present invention to provide a system which overcomes the deficiencies in the prior art arrangements.

Accordingly, in the present invention there is provided a control system for an actuator device, the system comprising a first means for generating a first signal representative of the load exerted by the actuator device, a second means for generating a second signal representative of the extent of actuation of said actuation device and a control circuit for receiving said first and second signals and controlling the position and load exerted by said actuator device and controlling the extent of actuation by the actuation device.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:- Fig 1 is a diagrammatic representation of one embodiment of a control system of the present invention; and Fig 2 is a view of the system of Fig 1 applied to a plurality of actuators.

Referring to the drawings, a control system for an actuator 10 is generally designated by the reference numeral 1. The actuator 10 is an electrical mechanical linear actuator that consists of a planetary roller screw, driven by an electric motor 101 through a reduction gearbox. The roller screw converts rotary motion to linear movement. As the screw rotates a nut engages the screw extending or retracting a ram 103 that is attached to the nut.

The roller screw consists of a multi-start screw with an involute thread form and a number of planetary rollers with annular grooves that engage with the screw. The rolling action of this arrangement results in a high efficiency mechanism while the line contact and hardened and ground construction achieves a high dynamic load carrying capacity together with almost no axial play. A suitable actuator is commercially available under the Trade Mark SPIRACON The ram 103 (through arm 104, illustrated schematically) exerts a load on and effects vertical positional movement to a roller 21 which forms the lower one of a pair of rollers 20, the upper roller 22 being fixed. In a steel manufacturing process, steel strip 2 passes between the rollers 21 and 22 of the pair of rollers 20.

The roller pair 20 is provided with a load sensor 11 which generates a first signal representative of the load exerted on the roller pair 20 which acts on the steel 2 during the rolling process. This first,

load signal is passed to a control interface 15 through a load monitor 111.

The roller pair 20 is also provided with a position sensor 12 which generates a second signal representative of the extension of the ram 103 of the actuator 10 relative to a datum point. This second, position signal is passed to the control interface 15 via a position monitor 112.

Whilst the load sensor 11 and position sensor 12 have been described as being provided on the roller pair 20, they may be fixed directly on the actuator 10 or associated with the roller pair 20 and actuator 10 such as to give the appropriate load and position signals.

The control interface 15 is programmed on receipt of the load and position signals to produce a control signal and feed the control signal to the motor 101 on the actuator 10 to vary the load and position to the desired values.

Referring now to Fig 2 of the drawings, one example of the invention is in the application to a steel manufacturing process when the molten steel is formed into a strip 102 by being passed between a series of pairs of rollers 120-190. The position and load applied to these rollers is determined by a respective actuator 220-290 which determine the point in the strip process to apply the correct load to the rollers. This is achieved through a

programmable control unit 116 which receives input data from a control interface 115 which in turn receives position and load signals from each of the actuators 220-290 via load and position monitors 211,212 in a manner analogous to that described above.

By using the programmable control 116 to combine and manipulate the signal received from the interface 115 the correct position and load for each individual actuator 220-290 can be applied to the steel through the length of the rolling process. In this way, the thickness of the strip being rolled can be defined progressively through a multitude of roller positions in the rolling process. Whilst only ten actuators 101-105 have been illustrated, it should be appreciated that any many actuators as required in a particular process may be employed.

The system is also provided with an operator interface 117 which allows input of desired control values and, if required, separate manual control of the system.

Accordingly, the control system of the invention can be implemented during the rolling process to apply the correct loading to eliminate the crystalline cooling defect referred to above.

The system is arranged to sense the difference in steel condition by measuring the pre-determined required loading relative to position thickness of

the strip and conclude automatically the correct point to apply the loading to eliminate the crystalline cooling defect.

In addition, the system of the invention is arranged to recognise when a defect in the steel is travelling through the rolling process. A defect in the steel occurs occasionally and is normally in the form of a hard over thick section. The system will sense the over thick section and retract the rollers to ensure that no damage occurs to the rolling equipment. The system verifies the defect has passed and automatically resumes the normal rolling process.

The system of the invention is thus capable of positioning very high loads with extreme accuracy and sensing the load condition at the ram allowing the in process condition of the steel to be concluded resulting in an automated determination of the soft squeeze point in the steel process.

The control system of the invention can be used with any linear actuator and has application not only in the steel manufacturing process but in all applications employing jacking systems and linear actuation systems.

Modifications and improvements can be incorporated without departing from the scope of the invention.