Patent GB-958412-A (GB)
Title: Positioning mechanism
IPC: G11B5/55
Filed: 1961-04-20
Abstract: 958,412. Data storage; magnetic recording &c. heads, supporting. SPERRY RAND CORPORATION. April 20,1961 [April 20, 1960], No. 14339/6f. Headings G4C and G5R. An arrangement for positioning a read/record head opposite a track of a magnetic drum, provides for coarse and fine head positioning. As described, a data storage system comprises ten drum units each unit including two magnetic storage drums together with the circuitry shown in Fig. 2. Each drum has 2,000 tracks which are addressed by two decimal digits in combination with one vigesimal digit, all digits being expressed in binary coded form and the least significant (vigesimal) digit address lines being coupled to a gate 48 while the other address lines are coupled to a gate 50. The heads for the two drums, which are in juxtaposed relationship with their axes parallel are mounted in a carriage 70 driven by a motor 82 controlled by a servo network 62 supplied with a signal from the carriage motor to indicate the carriage position and with signals representing the desired position. In operation a control circuit (not shown) selects the required drum unit and individual drum thereof. The required address number is supplied via the gates 48, 50 to registers 52, 54, the register 54 being connected to relay tree switching circuit 60 to translate the input to decimal signals supplied to potentiometers in the servo network 62. The carriage 70 carries a pawl 72 co-operating with a rack 68. If a new address differs from an old address only in the units digit, a comparator 84 is arranged to avoid use of the servo system 62. If the higher address digits differ, a flip-flop 88 is set to energize a relay 100 whose contact 102 changes over so that a temporary voltage V F  is effective to drive the carriage 70 forward to raise the pawl 72. When the voltage V F  terminates, the output of the servo 62 is connected to cause the motor 82 to drive the carriage until the servo error signal becomes zero, the pawl 72 then being dropped electrically under the control of a solenoid 75. The flip-flop 88 is now reset and the relay 100 deenergized to connect the motor 82 to a source V R  which is effective to drive the pawl 72 firmly against the perpendicular face of a tooth on the rack 68. Fine positioning is obtained in response to the number stored in the register 52, which is effective to cause a lever adder 66 (Fig. 4, not shown; fully described in Specification 910,636) to position the rack 68 in accordance with the vigesimal digit. "Trim" heads are arranged in advance of the main heads and when writing is to take place are adapted to erase narrow bands on either side of the track to remove possible unwanted data which may be present due to slight misalignment. Initial start. A speed sensing element 118,120 is utilized on each drum 115, 117 and when actuated these elements trigger a timer 126 which gives another minute for full speed to be attained. The ten individual drum units start sequentially to avoid heavy current surges as determined by the successive closing of the speed sensors 118, 120 in the various drum units. When the timer 126 actuates its relay, a differentiator 132 produces a pulse to actuate the carriage motor 82 which, since a relay R y  is de-energized and its contact R y -2 in the position shown, is controlled by the servo network 62 to drive the carriage 70 to a "landing strip track" (fully described in Specification 958,411). A landing strip switch SW-1 closes and the relay Ry is energized to enable the servo network to respond to an input address on change over of contact R y -3 thereby lowering the heads which when in "flying" position, i.e. supported relative to the drums by an air cushioning effect, change over a flying head switch SW-1 and normal positioning now proceeds. Manual Switches. Operation of a clear switch SW-1 resets the registers 52, 54 and causes the carriage 70 to move to track location 0000 and remain there with the heads flying. Opening a raise heads switch 142 releases the relay R y  thereby causing the heads to be raised. Errors and failures. Means are provided as described in Specification 910,637 for raising the heads when repeated or long contacts of the heads with the drums occur. If the carriage 70 is driven to either end of the rack 68, crash switches SW-1, 2 are operated to cut the power to the motor 82 and raise the heads. Means not described are provided for parity checking all data read from the drums. Preceding each sector of data on the drums is a six decimal digit address which specifies the number of the drum unit and the track address and these addresses are checked before a reading or writing operation takes place.