Abstract:
The impulse drive mechanism has a drive pawl which is periodically retracted sufficiently to engage a tooth at maximum tooth spacing to advance the sequence control cam a maximum step. If a lesser step is desired (can be used) the ratchet tooth spacing is decreased and the masking device which incorporates a follower engaging the cam on the inside of the ratchet is moved into position to prevent engagement of the pawl with a tooth at greater spacing. The cam drum can be advanced in small angular increments when only tolling time and the angular increment can be increased to accomodate sequential switching during the advance step if required.

Description:
BACKGROUND OF THE INVENTION 
     Process timers such as used on clothes washing machines generally have a sequence control cam (drum or disc) which is rotated one revolution (360°) and has various cams for sequencing the program function switches. During some steps of the drum various switches are actually sequenced relative to each other and this has generally kept the angular step to 6-71/2° which means a total of 60 or 50 steps per revolution. As the program content increases there is need for more steps . . . a need which runs counter to the need for steps large enough to provide sequencing during the step. Some steps do nothing more than take time and can in theory be appreciably smaller but there has been no way to accommodate appreciable variation in step size. Some variation while maintaining accuracy was shown in my U.S. Pat. No. 3,395,585 which could vary between 6° and 8°. An arrangement for stretching an interval by requiring the pawl to drive a mask out of the way to reach the ratchet is shown in U.S. Pat. No.  3,306,118 but accuracy of the steps was not as good as in my patent. 
     SUMMARY OF THE INVENTION 
     The principal object of this invention is to provide sequence timer having an impulse step drive mechanism providing angular steps of various size matched to the sequence needs and sensing the size of the step the cam is to make. With this invention steps of 21/2°-71/2° are readily provided. The drive pawl is periodically impulsed to engage a ratchet tooth 71/2° from the prior tooth. If a lesser step is to be taken a mask is moved into position to prevent the pawl from engaging any but the next tooth which can be only 21/2° from the prior tooth. Movement of the mask is controlled by a cam on the inside of the ratchet and having 3 diameters for positioning the mask. In one position the mask limits pawl engagement with a tooth to 21/2°, the middle position allows engagement with a tooth between 4° and 5° from the prior tooth, and the third position allows for tooth spacing of 51/2° to 71/2°. This invention is compatible with the drive in my U.S. Pat. No. 3,395,585 and therefore has the step accuracy of that construction which has proven to be outstanding. And that construction with its control of the ratchet position at the end of the step enhances the ability of the present invention to control small steps accurately. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partly schematic plan view showing the arrangement of the parts with the step-limiting mask in position to limit the step to 21/2°. 
     FIG. 2 is similar to FIG. 1 but the mask is retracted and a full step can be taken. 
     FIG. 3 is a detail showing another mask position limiting the step to the intermediate range; and 
     FIG. 4 shows the parts of FIG. 1 with the impulse pawl retracted ready to deliver the step impulse. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Ratchet wheel 10 is carried at one end of timer cam bank 12 which is provided with a plurality of cams each of which is adapted to actuate one or more switches in a sequence determined by the rotational position of the cam bank. The cam bank is mounted for rotation about the axis of the cam bank with hub 14 projecting into a cooperating aperture in the timer end plate 16. Lever 18 is journaled on the hub for movement about the same axis and projects to one side for actuation by cam 20 which is rotatable with shaft 22 driven by motor 24. Spring 26 is coiled around hub 14 and has one end anchored against a fixed abutment 28 while the other end bears against the upstanding tab 30 on the lever to urge the lever against the contour or face of drive cam 20. Drive lever 18 carries a pin 32 on which drive pawl 34 is mounted. As the drive cam rotates in a counterclockwise direction, the lever is moved in a clockwise direction about its pivot point to a maximum position and then the follower 50 drops down the slightly inclined or non-radial face 36 to deliver an impulse of power to the timer cam bank 12 by reason of engagement of the drive pawl with the ratchet. 
     Fixed pin 38 on the end plate 16 supports spacer 40 and pivotally mounted stop pawl 42. Stop pawl 42 has an upstanding tab 44 which serves as an anchor point for tension spring 46, the other end of which is anchored on the upstanding tab 48 carried by the drive pawl 34. This biases both pawls into engagement with the ratchet teeth. 
     As cam 20 rotates in a counterclockwise direction the follower 50 is moved downwardly to pull the drive pawl rearwardly to &#34;take a bite&#34; on the next tooth. During this retracting motion of the drive pawl, the stop pawl prevents movement of the ratchet and cam bank by reason of its engagement with the ratchet wheel 10. When the follower drops off lobe 52 of drive cam 20, it rapidly comes down the inclined face 36 until the drive pawl, which has now picked up and is driving a ratchet tooth, comes into contact with the end of spacer 40 which now determines the exact end position of the step. This is slightly beyond the position which would be determined by the operating face of the stop pawl 42 to insure that the stop pawl drops into place. Since both the spacer and the stop pawl are located by the same pivot the difference in length between the spacer and the stop pawl will determine this stop pawl gap and this gap is kept within small tolerances resulting in a more accurate drive. Since both pawls operate on the same tooth, no allowance for tooth-to-tooth error is required and the stop pawl gap can be reduced with increased capacity for accurate sequencing of switches actuated by the cam bank. 
     The construction described to this point is essentially that of my U.S. Pat. No. 3,395,585 and has unique features which enhance the present invention. 
     The spacer 40 is pivoted on pivot 38 (in my U.S. Pat. No. 3,395,585 patent the spacer did not need to pivot) and the stop (limiting) face 54 is curved with pivot 38 as its center to provide an operative stop in any position of the spacer. The spacer also has a laterally projecting portion 56 fixed thereon and formed to project beyond the end of the ratchet to project inside the cam bank and ratchet. The inner part of portion 56 has a mask 58 and a cam follower 60 which rides on the surface of control cam 62 molded on the inside of ratchet 10. Spring 64 tensioned between tab 66 on spacer 40 and fixed tab 68 biases the spacer counter clockwise to hold the follower on the control cam. Cam 62 has a contour having three active surfaces and three different radii R 1 , R 2  and R 3 . When follower 60 is on radius R 1  mask 58 is in its maximum masking position and the drive pawl can only reach and engage a tooth 21/2° from the tooth last engaged. This  21/2° spacing is the minimum I utilize. It will be noted that I have provided for three spacings of the teeth, the first being 21/2°, the second being for 4°, 41/2°, 5° and the third embracing steps of 51/2° to 71/2°. The 21/2° step is used where nothing much happens at that step and the only purpose is to use up time. The mask allows the tip of the drive pawl to drop only into notch M 1  and it can only engage the next tooth at 21/2° when the follower 60 is on radius R 1 . If the follower is on radius R 2  the drive pawl can now engage a tooth at 4°, 41/2° or 5° from the tooth last engaged since a tooth so positioned will be accessible by reason of cut-out M 2 . The pawl is actually retracted somewhat more than 71/2° in preparation for a step but mask surface M 3  will prevent engagement of the pawl with a tooth anywhere from 51/2° to 71/2° from the last engaged tooth with the follower on R 2 . With the follower on R 3  the mask is fully retracted and the pawl can engage a tooth as much as 71/2° from the last engaged tooth. 
     When the pawl drives a tooth 51/2° to 71/2° there is ample travel for proper sequencing of switches during the step. A simple switching operation may only require 4° to 5° steps and, as noted, simply tolling time can be confined to 21/2° step. Therefore, while the indexing mechanism can (and does) deliver a uniform actuating stroke for a 71/2° step the mask functions to limit the step, when desired, to lesser stops. In the prior art the step size was basically uniform and sized to that necessary for proper sequencing of the switches. With the present design simpler switching can be done in fewer degrees and non-switching can be done in still fewer degrees. The cumulative total of degrees so saved can now be used to provide added functions or cycles. This then adds to the versatility or utility of the timer. 
     As shown, the timing cams are on the outside of the drum type cam bank but this invention is of equal utility in connecting with a disc type (face cam) timing cam. The drawings illustrate various tooth spacings and the relationship of the control cam contour to the teeth. In some instances it is not necessary to actuate the mask even though a small step is to be taken. For example, after a given step is taken one could provide for the next step at 21/2° (or 4°, 41/2° or 5°) followed by a step of 71/2° and not require masking simply because only one tooth (the one at 21/2°, 4°, 41/2° or 5°) can lie in the stroke (71/2°) of the drive pawl. Put another way the next tooth space--21/2°--plus the next at 71/2° will be 10° placing the 2nd tooth to be actuated out of reach of the drive pawl . . . therefore no masking is required.