Patent GB-1202795-A (GB)
Title: Milking pulsator
IPC: A01J5/14
Filed: 1968-03-15
Abstract: 1,202,795. Milking machines. MACEWANS MACHINERY Ltd. and N. C. CURTIS. 15 March, 1968 [16 March, 1967], No. 12695/68. Heading A1M. [Also in Divisions G4, H2 and H3] The pulsator solenoids of a milking machine are operated in sequence by a ring of bistable circuit stages switched "on" and "off" by pulses under control of the stages of the ring. As described eight pulsator solenoids are controlled by a ring of eight bistable stages 64, (Fig. 8) switched by "on' and "off" pulses applied to the bistable circuits in parallel from a generator 65. The stages are initially "off" and through a lead 12 each when "off" inhibits the "on" pulse input of the succeeding stage and when "on" inhibits the "off" pulse input. Operating the bush button switch 2 switches the first stage "on' allowing the next "on" pulse to switch the second circuit "on" and in this manner the successive circuits are switched "on" in sequence. "Off" pulses, which occur simultaneously or in delayed relation to the "on" pulses, pass to the bistable circuits by a duty cycle setting gate. If (as described) a 50 per cent "on" cycle is required, the gate is opened and latched "on" the fourth stage going on. Thus, as the first stage is preceeded by a stage that is "off" (the eighth stage), the next "off" pulse switches the first stage "off". Accordingly a pattern of four adjacent stages "on" and four "off" is stepped round the ring. Alternatively on/off ratios are obtainable in steps by opening the duty cycle setting gate from another stage of the ring, so that a different number of "on" stages circulates. Intermediate values are obtained by varying the delay between "on" and "off" pulses and by interchanging "on" and "off" pulses so that either precedes the other. All circuits may be switched "on" together to provide "in line washing" and the system comprises a "releaser" circuit. The bistable stages (Fig.1) each comprise a complementary bistable circuit 3, 5, an output amplifier 6 feeding the pulsator 1, an "on' pulse input transistor 8 and an "off" pulse input 17. When the circuit is first switched on a pulse through diode 14 has switched the stages to an "off" state. Each stage has an input inhibit lead 12 coupled to the output lead 11 of the preceeding stage so that when the preceeding stage is off diode 10 is backbiased and "on" pulses applied to 7 are ineffective. Operation of the first stage is initiated by pushing a button (2) to provide through resistor 14 a potential to switch the bistable circuit to its "on" state. This energizes the pulsator solenoid and removes the inhibit voltage from output line 11 so that the next "on" pulse at line 7 of the succeeding circuit switches that stage "on". In this manner the stages are switched "on" in sequence". The "off" pulses at 17 are effective only when the preceding stage is "off", due to the voltage applied by it in the "off" state, as described above, the "off" pulse line is initially blocked by the duty cycle gate until a selected stage is switched "on". All stages may be switched on together by applying appropriate bias to a common line 20. This provides the "in line washing" facility. The duty cycle setting gate (Fig. 2) comprises a further bistable circuit 25, 26 switched through diode 29 by a selected stage in the ring. The output of the bistable circuit controls a gate transistor 27 which shorts to earth the "off pulse path 28, 17 to the main bistable stages until the selected stage is first reached. The "on" and "off" pulse generator (Fig. 3) comprises an adjustable frequency multivibrator 32, 33 feeding a monostable circuit 30, 41 through an inverter 39 which in turn feeds a further monostable circuit 36, 37. As illustrated in Fig. 4 (not shown) the trailing edge of the relatively narrow pulses from the multivibrator produce relatively wide pulses from the monostable circuit 40, 41 and monostable multivibrator 36, 37 produces from 'the trailing edge of the pulses a further pulse train similar to that from the multivibrator but delayed by an amount corresponding to the adjustable width of the pulses from the monostable circuit 40, 41. The delay may be adjusted only over a region of about 60 per cent of the interval between pulses and in order to cover the remaining part of the interval the function of the multivibrator pulses and delayed pulses are interchanged so that the delayed pulse is used as the "on" pulse and the multivibrator pulse as the "off" pulse. The releaser circuit (Fig. 5, not shown) comprises a variable frequency multivibrator feeding a transistor controlling the releaser solenoid. The power supply (Figs. 6 and 7, not shown) includes a mains rectifier, a transistor voltage stabiliser (53, 54) and also a standby battery coupled to the supply terminals through isolating diodes.