Patent GB-1439651-A (GB)
Title: Pneumatic needle positioner
IPC: D05B69/12
Filed: 1973-06-06
Abstract: 1439651 Valves; clutch control; clutch-brake combinations FARAH MFG CO Inc 6 June 1973 [19 June 1972] 27078/73 Headings F2L and F2V [Also in Division D1] A pneumatically operated clutch brake device for stopping a sewing machine with the needle in a particular position comprises a power output member 60, a member 90 connected to the drive shaft 26 and movable between the members 60, 86, by means including first and second chambers 138, 140, pneumatic pressure in the first 138, engaging member 90 with the flywheel 60 while pressure in the second chamber 140 engages member 90 with the braking surface 83, pneumatic pressure being supplied to the second chamber at a pressure which varies with the speed at which the shaft is driven. The chambers 138, 140 are disposed each side of a piston and rolling diaphragm arrangement 132, 134 connected by pivoted arms (118, Fig. 3, not shown) engaging a bearing 104 engaged with the shaft 26 and its member 90. Pressure is supplied to the clutch chamber 138 and is bled off by valve 160, the bleed pressure increasing as the pedal operated lever 38 is rotated clockwise to increase the pressure of spring 168 on valve 160. When the pedal is released pressure in the clutch chamber is sufficient to lightly engaged members 60, 90 to slowly rotate shaft 26. Pressure supplied to brake chamber 140 is bled off (see Fig. 5) by a transducer 180 on shaft 26 comprising a valve stated to produce a pressure varying with shaft speed. As the pedal is depressed pressure in 138 rises to increase the driven speed until counterbalanced by pressure in chamber 140. At maximum pedal depression screw 206 on the lever 38 opens valve 188 to exhaust brake chamber 140 to secure full clutch engagement and full shaft speed. When the pedal is released lever 28 closes bleed 212 and valve 188 and reduces the bias on valve 160. The system thus reverts to the slow rotation state until air flow through a notch 218 in the periphery of disc 218 on the sewing machine arm shaft (Figs. 6 and 7, not shown) permits air to pass to an amplification valve 220 which then pressurizes the brake chamber 140 to stop the drive with the needle at chosen position. In an alternative arrangement, (Fig. 11, not shown), the valve 220 is coupled to the system in a manner which obviates the double N.R. Valve 183 and which reduces air loss through transducer 180. Valves.-The transducer 180 comprises two diametrically opposed hollow transducer stems 190 with exhaust ports 192 at their outer ends. Weights 194 slidably mounted on the stems, are counterboard at their outer ends and are held in place by stem heads 198. As the shaft rotates the sleeves are stated to move outward to vary the opening 204, decrease the bleed and thereby increase the system pressure. The second device comprises a disc 216, with an edge notch 218. The periphery of the disc blocks flow between two conduits (208, 214, Fig. 6, not shown) except when the needle shaft carrying the disc is in a required angular position, where the notch 218 permits flow through a conduit 242 (Fig. 2) to the third device, a plate valve 230, where the cylinder 238 moves the plate 234 rightwards to allow air from the supply port 248 to pass through plate port 252b to port 246 to apply a brake. It is stated that when the plate is in an intermediate position where ports 248, 252b are not directly connected to either port 244, 246 (Fig. 10, not shown) air may leak from port 249 along the plate faces to provide air bearing support for the plate.