Determined how to mesh geartrains in 2501 card reader

CONTINUOUSLY RUNNING SHAFTS AND SOLENOID CLUTCHES

The IBM 2501 Card Reader has a motor that is spinning continuously while the device is ready for card moving and reading operations. A number of drive belts connect different shafts both side to side and front to back in the machine to provide energy to various rollers and other devices.

The card stacker where cards are ejected after reading is connected to one of these shafts and via a cam converts the motion to side to side movement of the bottom of the stacker. This helps move each newly ejected card to the left where it can fit closely against all the cards that were previously ejected. 

Rollers to move cards from the pre-read station through the read station and push them up into the stacker also run continuously. Most of these rollers have a spring loaded roller on the other side such that the cards will be moved.  Any card entering between a pair of rollers will be grabbed and moved leftward. 

At the rightmost side of the machine in the pre-read station, however, the first roller does not have a counterpart permanently pressing on it. Thus the card will not be moved from the pre-read station until a feed solenoid moves the counterpart roller down to pinch against the card. When pressed down, this roller starts the card moving until it enters the next pair of rollers where the pair are pressed together to keep the card moving. 

The input hopper for cards yet to be read has pairs of rollers turning just inside the opening into the reader. As long as the cards sit stacked in the hopper they are not yet touching the rollers so they will not move. A set of 'picker knives' move front to back when activated by a hopper solenoid. These have a lip that is less than the thickness of a punched card, so they only push on the bottommost card. The entry into the reader has a 'throat' that is adjusted to be less then two cards in thickness, thus ensuring that one and only one card enters per movement of the picker knives. 

A row of 12 photocells sit inside the card path so that they will sense light coming through punched holes in each column as it is moved past. Cards sit in the hopper with the face of the card down and the left side (column 1) of the card to the left in the hopper. 

READING CARD IN PRE-READ STATION

Activating the feed solenoid pinches the card in pre-read so the continuously turning rollers propel it leftward into the next set of rollers. The card moves under the photocell station where each of the 80 columns can be sensed in turn, then moved up into the stacker. 

Simultaneous with feeding a card to read it, the hopper solenoid is activated to feed in the next card from the hopper into the pre-read station where it can wait for the subsequent read request. 

FEEDING CARDS FROM HOPPER TO PRE-READ STATION

Firing the hopper solenoid will cause the picker knives to push a card into the throat, where the rollers will push the card to the rear so that it stops in the pre-read station. When the machine is initially empty, a feed cycle must be taken to put the first card in pre-read before the card reader becomes ready for operations. This is done by pushing the Start button. 

Every read operation (feed solenoid) also activates the hopper solenoid so that as long as there are cards left in the hopper it will have one ready in pre-read at all times. When the hopper becomes empty, there is still a card sitting in the pre-read station from the prior picker knife activation. The card reader will drop out of ready condition at this point, allowing the operator to add more cards to the hopper if desired. When new cards are in the hopper, pressing Start will turn on ready, read the card in pre-read and pull in a new one from the hopper. 

However, when there are no more cards to be put in the hopper, the reader has not yet read the last one since it is sitting in pre-read. Pressing the Start button without adding any cards to the hopper will turn the reader back to ready where another read request can be processed to read that final card. A special condition is raised so that the 1130 software can tell this was the 'last card' being read. 

KNOWING WHEN TO SAMPLE THE PHOTOCELLS FOR THE 80 CARD COLUMNS

The rollers pulling cards through from pre-read to the stacker move continuously, as does an 'emitter station' in the machine. When the leading edge of the card enters under the photocells, the logic detects that at least one row (actually all 12) is dark. It records pulses on the emitter station, spaced one card column apart as the emitter station rotates. 

Thus each pulse identifies the location of columns 0, 1, 2 . . . 80, 81 and then the trailing edge of the card. After the card exits the read station, the emitter station is erased to be ready for the next incoming card. Because the pulses are placed exactly as the card first enters the photocells, we have a precise start position for the card. Because the emitter station rotates in synchronization with the rollers moving the card along, the pulses mark off the location of columns very accurately. 

TIMING CB PULSES SYNCHRONIZE CARD MOVEMENTS AND SOLENOID ACTIVATIONS

A rotating disk with a permanent magnet glued on it spins continuously as the reader motor runs. It has three coils placed around the perimeter so that the magnet will generate a pulse from each in turn at specific points in the rotation of the disk. These are called CB, for circuit breaker, which is an IBM term for a circuit that is turned on or off based on motion of a cam or other mechanism. 

The three CB pulses control when the solenoids are activated, when the emitter station pulses are recorded and thus relate to the movement of cards through the machine.

The solenoids are activated at CB3 time and released at the start of CB1. Cards entering from the hopper will slide rearwards into the pre-read station near the end of a cycle. A photocell to detect whether a card was feed into pre-read is activated at around 211 degrees, we after any card moving out of the pre-read has passed fully through the photocells. 

A card being read (by activating the feed solenoid) will have its leading edge enter the photocell station around 15 degrees, as it moves rightwards, meanwhile the card from the hopper is moving rearwards at the same time. The trailing edge of the card clears the photocell station around 165 degrees, thus the entire card is out of the pre-read station sometime prior to that. The incoming card from the hopper is about halfway into the pre-read station (based on the location of the photocell that senses it) at 211 degrees and will be at rest and ready for feeding before CB3 at 335 degrees. 

This is a ballet of simultaneous card movement that must be managed lest the incoming card from the hopper jams into the card moving through the photocells. The activate time of the solenoids runs from CB3 of one rotation to CB1 of the next, which starts the movement of both cards. Thus most of the synchronization is purely done by using the CB pulses to control solenoid firing.

However, the card that comes in from the hopper is fed through the throat by the picker knives. The solenoid to release them is fired based on the CB pulses, but the physical back and forth movement is driven by a cam that is also rotating continuously along with the timing disk. If the knife moves early the card might crash into the card leaving the pre-read station. If it moves late, the card might not be fully at rest in the pre-read station when the feed solenoid is activated to start the card through the photocell station. 

A gear on the timing disk meshes with other gears that turn the picker knife cams. Thus, the relative position of the cam to the timing disk is important to ensure that we time the picker knife movement properly. 

The Field Engineering Maintenance Manual would contain the instructions for setting the gears in time with each other, but that manual is not available to me nor available online. Fortunately, there is a blurb in the Theory of Operations manual that tells me how to synchronize these.

MY PROCEDURE

I will disconnect the new white gear from the gears on the right, then rotate the motor so that the permanent magnet pole (red arrow below) will be positioned at the CB3 coil (green arrow below) when the disk and new white gear is reinstalled. Then I will turn the existing gears so the cam is in the position show in the diagram above. Meshing the new white gear to the existing gears in this orientation will give me the relative timing necessary for proper operation.