Surgical drape

1. A surgical drape for covering at least a portion of a surgical robot arm, the arm comprising at least one drive assembly interface element for transferring drive between the arm and an instrument engageable with the arm, the drape comprising:

an interface portion locatable between the arm and the instrument when the instrument is engaged with the arm, the interface portion comprising a drive transfer element engageable with the drive assembly interface element, a first drive transfer element portion disposed to one side of the drape, the first drive transfer element being engageable with the drive assembly interface element, a second drive transfer element portion disposed to another side of the drape, the second drive transfer element portion being engageable with an instrument interface element; and

a bulk portion encompassing the interface portion;

the interface portion and the bulk portion being adjacent one another, the interface portion comprising a material or configuration having a lower modulus than that of the bulk portion in at least one direction, so as to permit repeatable movement of a portion of the interface portion relative to the bulk portion.

2. A surgical drape according to claim 1 , in which the interface portion comprises a movable portion, the movable portion being movable relative to the bulk portion.

3. A surgical drape according to claim 1 , in which the bulk portion wholly encompasses the interface portion.

4. A surgical drape according to claim 1 , in which the material of the interface portion is at least one of a woven and a resilient material.

5. A surgical drape according to claim 1 , in which the interface portion comprises an unconstrained portion of the drape.

6. A surgical drape according to claim 1 , in which the interface portion comprises a ruckle control portion configured to at least partially control tension in the material of the drape.

7. A surgical drape according to claim 6 , in which the ruckle control portion comprises the movable portion.

8. A surgical drape according to claim 6 , in which the ruckle control portion comprises a concertina section, the concertina section being configurable between an expanded state and a contracted state.

9. A surgical drape according to claim 8 , in which the concertina section is biased towards one of the expanded state and the contracted state.

10. A surgical drape according to claim 6 , in which the ruckle control portion comprises a reel for at least one of winding on and unwinding material of the movable portion.

11. A surgical drape according to claim 10 , in which the reel is at least one of biased and drivable in a rotary direction.

12. A surgical drape according to claim 6 , in which the ruckle control portion comprises a strengthened portion, the strengthened portion being configured to permit a preferential deformation of the interface portion under action of a force.

13. A surgical drape according to claim 12 , in which the strengthened portion forms at least part of a periphery of a non-strengthened portion.

14. A surgical drape according to claim 6 , in which the drape is configured to engage with a plurality of drive assembly interface elements, and the drape comprises a ruckle control portion corresponding to each of the plurality of drive assembly interface elements.

15. A surgical drape according to claim 1 , in which the movable portion comprises a first drape portion and a second drape portion, the first drape portion and the second drape portion being releasably engageable with one another along a joining line such that a gap between the first drape portion and the second drape portion is movable along the joining line.

16. A surgical drape according to claim 1 , in which the drape comprises a sensor for sensing at least one of tension in the drape and force on the drape.

17. A surgical system comprising a surgical drape according to claim 1 , a control unit and a sensor; the sensor being configured to sense at least one of tension in the drape and force on the drape and to transmit a signal to the control unit, and the control unit being configured to determine at least one of the tension in the drape and the force on the drape in dependence on the signal.