Supplying build material

1. An apparatus for supplying build material to a three-dimensional printing system, comprising:

a build material supply module having a first side to adjoin a build material support platform in the printing system, the supply module structured such that, when installed in the printing system, a top of the first side of the supply module is above the platform;

and wherein

the supply module includes only one vane, the vane rotatable around and extending away from an axis in only one direction, and the vane rotatable from:

a pre-feed position below the top of the first side of the supply module to hold a portion of build material above the top of the first side of the supply module and a measured dose of build material below the top of the first side of supply module; to

a horizontal feed position level with the top of the first side of the supply module to hold the measured dose of build material above the top of the first side of the supply module.

2. The apparatus of claim 1 , further comprising a build material spreader to spread build material from the supply module over the platform and wherein the build material spreader is movable across the supply module in a first direction with the vane in the pre-feed position to push the portion of build material above the top of the supply module into the supply module, thereby leaving the measured dose of build material on the vane between the top of the first side of the supply module and the vane.

3. The apparatus of claim 2 , wherein the build material spreader is movable across the vane in a second direction opposite to the first direction with the vane in the feed position to spread the measured dose of build material over the platform.

4. The apparatus of claim 1 , further comprising a build material delivery system to deposit build material from a build material store to the build material supply module.

5. The apparatus of claim 4 , wherein the supply module includes a spreading mechanism to distribute deposited build material within the supply module and wherein the spreading mechanism comprises a reciprocating member that can reciprocate along a base of the supply module.

6. An apparatus for supplying build material to a three-dimensional printing system, comprising:

a build material supply module;

a build material delivery system to deposit build material from a build material store to the build material supply module;

a spreading mechanism to distribute deposited build material within the supply module;

a vane rotatable in a first direction to move a quantity of build material in the supply module above a top of the supply module; and

a protrusion along a length of one side of the supply module, and wherein the vane is movable in a second direction opposite to the first direction to compress a quantity of build material between the vane and the protrusion, the apparatus further comprising a measurement module to determine an angle of the vane when the vane compresses the build material against the protrusion, the angle indicative of a quantity of build material within the supply module.

7. A 3D printing system comprising:

a platform to support layers of build material during printing, the platform movable vertically to control a height of each layer of build material spread over the platform;

a supply module to receive build material from a build material store, the supply module positioned next to the platform such that, during printing, a top of the first side of the supply module is above the platform the supply module including a rotatable blade;

a build material spreader to spread build material from the supply module over the platform; and

a controller to:

control the deposition of build material in the supply module from the build material store;

control the blade to rotate from:

a pre-feed position below the top of the first side of the supply module to hold a first portion of build material above the top of the first side of the supply module and a second portion of build material below the top of the first side of supply module; to

a horizontal feed position level with the top of the first side of the supply module to hold the second portion of build material above the top of the first side of the supply module; and

control the build material spreader to move:

across the supply module in a first direction with the blade in the pre-feed position to push the first portion of build material into the supply module and leaving the second portion of build material on the blade between the top of the first side of the supply module and the blade; and

across the supply module in a second direction opposite to the first direction with the blade in the feed position to spread the second portion of build material over the platform.

8. The 3D printing system of claim 7 , wherein the controller controls the blade to reciprocate as build material is deposited in the supply module to assist in the distribution of build material along the length of the supply module.

9. The 3D printing system of claim 8 , wherein the supply module further comprises a protrusion along a length of a second side of the supply module opposite the first side, and wherein the controller is to control the blade to compress a portion of build material against the protrusion and to determine from an angle of the blade a quantity of build material in the supply module.

10. The apparatus of claim 7 , wherein the blade is only one blade rotatable around and extending away from an axis in only one direction.

11. The apparatus of claim 10 , comprising a spreader to distribute build material within the supply module and wherein the controller is to control the spreader to distribute build material along a length of the supply module.