Hall sensor movement detection device

Abstract: A piston rod (6) of a piston (4) and cylinder (8) device has an axial bore (22) through which a fixed non-ferromagnetic monitoring member (24) extends, and a detection insert (26) of ferromagnetic materially extending generally axially of the monitoring member. A magnetic circuit is created through a base of the cylinder, a sidewall, the piston and the detection insert, and movement of the piston is detected by a Hall sensor (34) which detects a change of flux in the magnetic circuit.

Description: The present invention is concerned with detecting the movement of a piston head and piston rod in a piston and cylinder device. Such a device according to the preamble of claim 1 is known from DE-A-3 907 944. There are many circumstances in which piston and cylinder devices, which may be pneumatically or hydraulically operated, are utilized to move parts in machines and in which it is desired to know the precise position of the piston head and piston rod in the cylinder. Various types of transducer have been proposed for monitoring such position, but frequently suffer from disadvantages, for example bulk, fragility or undue sensitivity to hostile environments. Glassware forming machines are particularly good examples of machines in which a hostile environment may affect transducers which are used to monitor the movement of parts. It is one of the objects of the present invention to provide an improved piston and cylinder device having means for monitoring the position of the piston and piston rod. The present invention provides a piston and cylinder device comprising a piston head mounted on a piston rod and movable in a cylinder the piston rod having an axial bore there through and a monitoring member fixed to a first end portion of the cylinder and extending through the axial bore towards the other end portion of the cylinder and in sealing relationship with the piston head characterized in that the monitoring member is made of non-ferromagnetic material and comprises a detection insert of ferromagnetic material, the detection insertion extending generally axially of the monitoring member and that a magnetic circuit incorporating a Hall sensor and a magnet is established through the detection insert, said first end portion of the cylinder, a wall portion of the cylinder and the piston head, such that movement of the piston alters the flux in the circuit and is thus detected by the Hall sensor. Preferably the detection insert comprises a surface which is inclined at a small angle to the surface of the monitoring member. Preferably the detection insert is of uniform cross section. One particular mechanism in a glass machine in which accurate monitoring of movement is particularly required is in the movement of a parison forming plunger at a blank station of a glassware forming machine. Movement of the plunger not only gives an indication of the formation of a parison at the station but can be used, for example, to control the amount of glass in a gob fed to the station for forming into a parison. The present invention also provides a plunger mechanism for the formation of parisons in a glassware forming machine comprising a piston and cylinder device as set out as above characterized in that the piston and piston rod are connected to the plunger and air for cooling the plunger and the mechanism is passed through an axial bore of the monitoring member. A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which Figure 1 shows a plunger mechanism of a glass container making machine, largely in cross section Figure 2 shows certain parts of Figure 1 on a larger scale. Figure 3 shows one portion of Figure 2 on an even larger scale. The illustrative plunger mechanism comprises a piston and cylinder device 2 comprising a piston head 4 mounted on a piston rod 6 and movable in a cylinder 8. A plunger 10 is mounted on the piston rod 6 and is moved in its operation by the piston and cylinder device 2. The cylinder 8 comprises a lower end cap 12 and is closed at its upper end by an end wall 14. A passage 16 through a wall portion of the cylinder 8 leads to a groove 18 in the end cap 12 through which compressed air may be provided to a lower end of the cylinder 8. A further passage 20 is provided in the end wall 14 through which air may be provided to an upper end of the cylinder 8. The piston rod 6 has an axial bore 22 extending through it and a monitoring member in the form of a tube 24 is secured in the cup 12 and positioned in the bore 22: cooling air may be supplied to the plunger 10 in the operation of the plunger mechanism through the tube 24. Sealing rings 25 secured between collars of magnetic material 27 act between the bore 22 in the piston head to prevent the passage of air between the tube 24 and the bore 22. A passage way 28 is provided in the end cap 12 through which cooling air may be provided to the tube 24. The tube 24 is made from non-magnetic material, preferably electrolytic chromium. Mounted in the wall of the tube 24 is a detection insert in the form of a strip 26 of magnetic material, preferably electrolytic nickel. The strip 26 is of uniform cross section, and extends generally axially in a wall portion of the tube 24 at a slight angle to the axis of the tube 24, so that at the lower end of the tube it is close to the outer surface of the tube 24, but an upper end of the strip 26, which extends beyond the end wall 14, the strip is spaced inwardly from the outer surface of the tube 24. Thus an outer surface 29 of the strip 26 is inclined at a small angle to the outer surface of the tube 24. A block 30 of ferro-magnetic material is secured in the end cap 12 in contact with a lower end of the strip 26. The end cap 12 is itself made of non-ferro magnetic material, e.g. chromium. A permanent magnet 32 is in contact with the block 30, and a Hall sensor 34 is positioned between the magnet 32 and a further block 36 of ferro magnetic material mounted in the cap 12 and in close contact with an end face 38 of the cylinder 8. The cylinder 8 itself is made of ferro magnetic material, e.g. steel. It can be seen that in the arrangement just described, a magnetic circuit is provided which extends from one end of the magnet 32, through the sensor 34, the block 36, the wall of the cylinder 8, the piston head 4 (which is also of ferro-magnetic material), the collars 27, a thin portion of the non-ferro magnetic wall of the tube 24, the strip 26 and the block 30. It can be seen that, as the piston 4 moves upwards in the cylinder 8, not only is the length of the magnetic circuit increased, but also the thickness of the non-magnetic material in the circuit between the collars 27 and the strip 26 increases. Thus the magnetic flux in the circuit produced by the magnet 32 will alter, and thus movement of the piston will produce an appropriate signal from the Hall sensor. Sensing of the movement of the piston can, as is known, be used to control penetration of the plunger into glass in a parison mould in the formation of a parison and also to monitor gob size. Compensation for temperature variations in the Hall sensor can be obtained by the use of a second Hall sensor not in the magnetic circuit, which is subject to the same temperature variation as the sensor in the circuit and is connected thereto in a bridge circuit. It will be realized that variations may be made of the illustrative device. In particular, the strip 26 may be replaced by a strip which tapers in thickness, being thicker at the bottom than the top, if even greater sensitivity is required. Further, if less sensitivity is acceptable, the strip 26 may be replaced by a strip of uniform thickness which has its longitudinal faces parallel to the wall of the tube 24.

Claims: A piston and cylinder device comprising a piston head (4) mounted on a piston rod (6) and movable in a cylinder (8) the piston rod having an axial bore (22) there through and a monitoring member (24) fixed to a first end portion (12) of the cylinder and extending through the axial bore towards the other end portion of the cylinder and in sealing relationship with the piston head characterized in that the monitoring member (24) is made of non-ferromagnetic material and comprises a detection insert (26) of ferromagnetic material, the detection insert (26) extending generally axially of the monitoring member (24) and that a magnetic circuit incorporating a Hall sensor and a magnet is established through the detection insert (26), said first end portion (12) of the cylinder, a wall portion of the cylinder and the piston head (4), such that movement of the piston head (4) alters the flux in the circuit and is thus detected by the Hall sensor. A piston and cylinder device according to claim 1 characterized in that the detection insert (26) comprises a surface which is inclined at a small angle to the surface of the monitoring member (24). A piston and cylinder device according to claim 2 characterized in that the detection insert (26) is of uniform cross section. A plunger mechanism for the formation of parison in a glassware forming machine comprising a piston and cylinder device according to one of claims 1, 2 and 3 characterized in that the piston and piston rod are connected to the plunger and air for cooling the plunger and the mechanism is passed through an axial bore of the monitoring member.

Inventors: KELLER RENE, KELLER, RENE, Keller, René
Applicants: EMHART GLASS MACH INVEST, EMHART GLASS MACHINERY INVESTMENTS INC.
Application year: 1992
Main classification: F15B15
IPC codes: G01B7, F15B15