Position detector for workpiece-machining apparatus

In combination with

• a workpiece having a face;
• and
• a support having a surface adapted to engage the workpiece face;
• a workpiece-position detector comprising:
• an element at the surface formed with a passage having a mouth open generally at the surface and blockable by the face of the workpiece, the element including
• a block formed with the passage and
• a plug formed with a central throughgoing passage and having a small-diameter stem fitting snugly in the passage and a large-diameter head projecting from the block and forming part of the surface;
• a flexible hose connected to the passage of the element;
• a feed line connected to the hose;
• pump means connected to the feed line for supplying a gas under pressure to the hose, whereby the gas exits from the passage mouth when same is not blocked;
• a restriction in the feed line;
• a pressure sensor in the feed line downstream of the restriction producing an output corresponding to pressure in the conduit, whereby when the mouth is blocked the pressure at the sensor is relatively high and when not blocked it is relatively low;
• and
• control means connected to the pressure sensor for taking action when the pressure sensor detects the relatively low pressure.

In combination with

• a workpiece having a face;
• and
• a support having a surface adapted to engage the workpiece face;
• a workpiece-position detector comprising:
• an element at the surface formed with a passage having a mouth open generally at the surface and blockable by the face of the workpiece, the element being formed with a part-spherical seat and including a part-spherical body having a body face and engaged in the seat, the body being movable between a blocking position with the body face parallel to the surface and blocking flow out of the passage and a vent position with the body face nonparallel to the surface and permitting flow out of the passage;
• a flexible hose connected to the passage of the element;
• a feed line connected to the hose;
• pump means connected to the feed line for supplying a gas under pressure to the hose, whereby the gas exits from the passage mouth when same is not blocked;
• a restriction in the feed line;
• a pressure sensor in the feed line downstream of the restriction producing an output corresponding to pressure in the conduit, whereby when the mouth is blocked the pressure at the sensor is relatively high and when not blocked it is relatively low;
• and
• control means connected to the pressure sensor for taking action when the pressure sensor detects the relatively low pressure.