Method and system for controlling a compressor at a rock drilling apparatus and a rock drilling apparatus

1. Method for controlling a compressor at a rock drilling apparatus, said rock drilling apparatus including a power source for driving a first consumer at a rock drilling process, said first consumer being a compressor and said compressor being arranged to operate according to a first mode and according to a second mode, wherein, in said first mode, the work produced by the compressor is arranged to be controlled by a control device in communication with said compressor by controlling rotation speed of said compressor, and wherein, in said second mode, the work produced by the compressor is arranged to be controlled by controlling air flow at an inlet of the compressor, the method including:

determining a first parameter value representing a demand of work from said compressor,

controlling the compressor by the control device according to said first mode when said first parameter value representing a demand of work from said compressor exceeds a first demand, and

controlling the compressor by the control device according to said second mode when said first parameter value representing a demand of work from said compressor is lower than said first demand;

wherein said rock drilling apparatus includes at least a second consumer being driven by said power source, wherein the method further includes determining a lowest speed of said power source that is required for operation of said at least one second consumer, wherein control according to said second mode is performed when said first parameter value is below the work that the compressor delivers at said determined lowest speed of said power source, and

wherein control according to said first mode is performed when said first parameter value equals or exceeds the work that the compressor delivers at said determined lowest speed of said power source.

2. Method according to claim 1 , wherein said first parameter value represents a pressure or flow demand.

3. Method according to claim 1 , wherein said first parameter value represents a pressure or flow demand, where said flow demand is determined independent from a prevailing pressure in a flow circuit after the compressor.

4. Method according to claim 3 , wherein, when said pressure in the flow circuit after the compressor is lower than a first pressure, said flow demand is determined independent from said prevailing pressure in the flow circuit after the compressor.

5. Method according to claim 1 , wherein the method further includes changing said demand for work during operation.

6. Method according to claim 1 , wherein said rock drilling process includes at least the subprocesses flushing and at least one of percussion and rotation.

7. System for controlling a compressor at a rock drilling apparatus, said rock drilling apparatus including a power source for driving a first consumer at a rock drilling process, said first consumer being a compressor, said system including:

a control device for controlling said compressor according to a first mode and according to a second mode, wherein, in said first mode, the work produced by the compressor is arranged to be controlled by controlling rotation speed of said compressor, and wherein, in said second mode, the work produced by the compressor is arranged to be controlled by controlling air flow at an inlet of the compressor,

said control device controlling the compressor according to said first mode when a parameter value representing a demand of work from said compressor exceeds a first demand, and

said control device controlling the compressor according to said second mode when said parameter value representing a demand of work from said compressor is lower than said first demand,

said control device determining a lowest speed of said power source that is required for operation of said at least one second consumer arranged to be driven by said power source, and

said control device controlling the compressor according to said second mode when said parameter value is below the work that the compressor delivers at said determined lowest speed of said power source, and controlling the compressor according to said first mode when said parameter value equals or exceeds the work that the compressor delivers at said determined lowest speed of said power source.

8. System according to claim 7 , wherein said rock drilling apparatus includes at least a second consumer being driven by said power source.

9. System according to claim 7 , further including means for, when controlling according to said second mode, controlling the air flow at the compressor inlet.

10. System according to claim 7 , further including means for, when controlling according to said second mode, controlling the air flow at the compressor inlet by controlling an opening area of the compressor inlet towards the surroundings.

11. System according to claim 10 , wherein the pressure in the compressor inlet is arranged to be controlled by controlling the opening area of the compressor inlet towards the surroundings by an electrically controllable valve.

12. System according to claim 7 , further including means for, when controlling according to said first mode, controlling the rotation speed of said compressor by controlling rotation speed of said power source.

13. System according to claim 7 , further including means for controlling the compressor according to said first or second mode based on a first electrical control signal, wherein said first electrical control signal includes a representation of a requested work to be delivered by said compressor.

14. System according to claim 13 , wherein said control means for controlling the compressor consists of a control unit being arranged to deliver a second electrical control signal to control means for controlling said compressor inlet and/or speed of said power source.

15. System according to claim 13 , wherein determination of said first electrical control signal is arranged to be performed at least partially based on one or more from the group: a pressure in the flow circuit, present hole depth, a representation of the rotational speed of the tool, a representation of a percussion mechanism power, hole diameter, drill string diameter, nature of the rock.

16. System according to claim 7 , wherein said compressor consists of a compressor having fixed displacement.

17. Rock drilling apparatus, wherein said apparatus includes a system according to claim 7 .

18. System for controlling a compressor at a rock drilling apparatus, said rock drilling apparatus including a power source for driving a first consumer at a rock drilling process, said first consumer being a compressor, said system including:

a control device for controlling said compressor according to a first mode and according to a second mode, wherein, in said first mode, the work produced by the compressor is arranged to be controlled by controlling rotation speed of said compressor, and wherein, in said second mode, the work produced by the compressor is arranged to be controlled by controlling air flow at an inlet of the compressor,

said control device controlling the compressor according to said first mode when a parameter value representing a demand of work from said compressor exceeds a first demand, and

said control device controlling the compressor according to said second mode when said parameter value representing a demand of work from said compressor is lower than said first demand,

wherein said rock drilling apparatus includes at least one second consumer being driven by said power source; and

wherein said at least one second consumer being driven by said power source is dimensioned such that the power that can be delivered by said at least one second consumer is independent from the rotation speed of the power source for rotation speeds exceeding a rotation speed ωe_ober, where ωe_ober is a lower rotation speed than the speed ωe_max at which said compressor discharges maximal flow.

19. System according to claim 18 , wherein said deliverable power consists of a maximum required deliverable power of said at least one second consumer in said system.

20. System according to claim 18 , wherein said speed ωe_ober consists of a speed in the range 40-95% of said speed ωe_max at which said compressor discharges maximal flow.