SERVO OPERATED SPRAY MACHINE AND METHOD FOR OPERATING

Abstract

A method of operating a plurality of machines. Each of the machines uses a servo motor and a motor drive coupled to the servo motor, and the motor drive incorporates a regenerative braking system. The method comprises synchronising the servo motors in order to achieve overlap of the acceleration phases of some machines with the deceleration phases of other machines and providing electrical power from the regenerative braking systems of machines in a deceleration phase to machines in an acceleration phase. A controller for a machine implementing the method, and a system comprising such a controller and a plurality of machines are also disclosed.

Claims

1. A method of operating a plurality of machines each of which uses a servo motor and a motor speed controller coupled to the servo motor, the motor speed controller incorporating a regenerative braking system, the method comprising synchronising the servo motors in order to achieve overlap of the acceleration phases of some machines with the deceleration phases of other machines and providing electrical power from the regenerative braking systems of machines in a deceleration phase to machines in an acceleration phase.

2. A method according to claim 1, wherein each machine is a can internal spray machine.

3. A method according to claim 2, wherein the can internal spray machines each comprise an indexing mechanism, the indexing mechanism comprising the servo motor.

4. A method according to claim 1, wherein the step of synchronising the servo motors comprises synchronising the servo motors in order to achieve optimal overlap between acceleration and deceleration phases of the machines and thereby achieve substantially maximum energy transfer from decelerating to accelerating machines.

5. A controller configured to operate a plurality of machines each of which uses a servo motor and a motor speed controller coupled to the servo motor, the motor speed controller incorporating a regenerative braking system, with electrical power being redistributed between machines, the controller being configured to synchronise the servo motors to achieve overlap of the acceleration phases of some machines with the deceleration phases of other machines.

6. A controller according to claim 5, wherein the machines are can internal spray machines.

7. A controller according to claim 6, wherein the can internal spray machines each comprise an indexing mechanism, the indexing mechanism comprising the servo motor.

8. A controller according to claim 5, the controller being either a central controller or controller distributed across the machines.

9. A system comprising a controller according to claim 5, and a plurality of machines each of which comprises a servo motor and a motor speed controller coupled to the servo motor, the motor speed controller incorporating a regenerative braking system, wherein the controller is configured to operate the machines.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is shows an exemplary servo operated spray machine;

[0014] FIG. 2 shows acceleration profiles of each of a bank of servo operated spray machines according to an embodiment;

[0015] FIG. 3 shows a typical velocity and energy profile for a servo operated spray machine;

[0016] FIG. 4 is a flowchart of a method according to an embodiment; and

[0017] FIG. 5 is a schematic diagram of system according to an embodiment.

DETAILED DESCRIPTION

[0018] Within a can manufacturing plant, there is a significant desire to reduce power usage, both to save costs and to be more environmentally friendly. Spray machines incorporating a servo motor (servo operated spray machines) will typically undergo up to 420 acceleration and deceleration cycles a minute. When servo motors decelerate, an electrical current is generated. In known servo operated spray machines, this current is directed through a braking resistor and allowed to dissipate as heat. There are commercially available regenerative braking systems which convert the current generated by deceleration into usable power which can be used by other devices or stored for later use. However, power storage will generally involve losses, and requires further components to be provided, significantly reducing the potential savings from regenerating braking, and so these systems have not been considered for spray machines.

[0019] Spray machines are typically placed in banks, generally containing seven to ten spray machines, each of which operates independently. A new way of operating such a bank of spray machines is proposed herein to allow a bank of machines to make better use of power generated from regenerative braking. It is recognised that there is no need for the spray machines to operate in synchronisation with one another. It is therefore proposed to control the bank of machines in such a way that when one machine (A) in the bank is in a decelerating phase, another machine (B) in the bank is in an accelerating phase, and therefore the electricity generated by the machine (A) can be used to reduce the external mains electricity required to operate machine (B). Applying this to all of the machines in a bank of seven to ten machines would allow such an overlap to occur for most of the acceleration phases of the machines, significantly reducing power consumption.

[0020] FIG. 2 illustrates a possible synchronisation scheme for seven machines running at 420 stops per minute, with each machine having a cycle labelled 1 to 7. 420 stops per minute gives a total cycle time of 1/7 of a second, approx. 143 ms, which means that each machine has a 100 ms dwell, a 21 ms acceleration phase, and a 21 ms deceleration phase. The acceleration phase is shown as +1 on each graph, the deceleration phase as 1, and the dwell as 0. As can be seen from the graphs, the acceleration and deceleration phases can be matched up so that each acceleration phase corresponds to the deceleration phase of the previous machine, i.e. the acceleration phase of machine 2 occurs simultaneously with the deceleration phase of machine 1. The synchronisation is not perfect, there is a short period at T=0 where both machines 1 and 7 are accelerating, and only machine 6 is decelerating, but it can be appreciated that there is always an accelerating machine to use the energy generated by a decelerating machine. This ensures that as much energy as possible is moved back into the system without the need for storage.

[0021] FIG. 2 relates to an idealised situation where each machine is operating at the same constant rate, the acceleration and deceleration phases are equal, and there is no period of constant velocity between the acceleration and deceleration phases. This may not be the case, the machines may operate at different rates, and the rate of each machine may change over time, e.g. due to changes in the rates of other machines in the production line. The acceleration and deceleration phases may be varied, provided the minimum dwell time and required stops per minute are achieved, and the motion of the cans is sufficient to move them into the required position. Typically, each machine in the bank will run at the same rate (though this rate may change frequently).

[0022] A typical velocity profile is shown in FIG. 3, with the red line representing velocity and the yellow line representing the power input/output of the servo motor. As will be appreciated, the power input during acceleration and output during deceleration are very similar. The required synchronisation may be achieved, for example, by starting the machines out of phase with each other, so that each machine begins its acceleration phase as the previous machine begins its deceleration phase.

[0023] The spray machines are typically fed power via a DC voltage bus, with one bus for each spray machine. To enable power to be transferred between the machines easily, it is proposed that all of the spray machines in a bank be connected to the same DC voltage bus, and that the regenerative braking systems feed power into this bus during the deceleration phase.

[0024] While the above description relates to the example of servo operated can internal spray machines, the skilled person will appreciate that a similar principle can be applied to other machines which operate with an acceleration phase and a deceleration phase. A flowchart for the generic method is shown in FIG. 4. The machines use a servo motor and a motor speed controller coupled to the servo motor, the motor speed controller incorporating a regenerative braking system, and the servo motors are synchronised in order to achieve overlap of the acceleration phases of some of the machines with the deceleration phases of the other machines S101. Electrical power is provided from the regenerative braking systems of machines in a deceleration phase to machines in an acceleration phase S102.

[0025] The servo motors may be synchronised in order to maximise total overlap between acceleration and deceleration phases of the machines. Of course, this method only applies where there are multiple machines present. This allows the savings of regenerative braking to be maximised, as there are no losses relating to the need to store the energy between a deceleration phase and an acceleration phase.

[0026] FIG. 5 is a schematic diagram of system 100. The system comprises a controller 200 and a plurality of spray machines 300, 301, 30X. Each machine comprises a servo motor 31 and a motor speed controller 32 coupled to the servo motor, the motor speed controller incorporating a regenerative braking system 33 (shown in machine 300), and the machines are connected in order to allow power to be redistributed between the machines.

[0027] The controller may be a single unit, which is connected to each machine, as shown in FIG. 5. Alternatively, the controller may be implemented as a distributed unit, with processors in each of the machines cooperating in order to act as the controller.

[0028] Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.