High demands are made of the lifting units which control the plurality of heddle frames in a weaving machine. Aside from the simple stepping devices, dobbies of the Hattersley system or lately rotational dobbies, for example U.S. Pat. No. 3,180,366, are primarily used for forming the shed. In the first case, the rectilinear movement of the heddle frames is caused by draw or push knives which move rectilinearly back and forth, which knives are suspended patternlike on controlled draw or holding hooks. The drive in rotational dobbies, on the other hand, occurs directly through a rotating drive shaft, on which through the motion of an eccentric a connecting rod is sequentially cyclically directly driven through the necessary back and forth movement. This facilitates the attainment of a higher speed, however, has the disadvantage that the actual control functions lead to problems.
For all stepping devices and dobbies there exists the condition that the dimension of the power-transmitting parts must lie within the width of the individual heddle frames, namely, within a space or pitch of 12 mm. In addition, it is important, for a general use of the two types of dobbies, that they can be controlled by an identical pattern card.
In the Hattersley dobbies, the controlled lifting members, for example draw hooks, are organized relatively spaciously in two separate planes in a double amount per heddle frame, for even and uneven picks. They are, during the control operation, at all times at the same point, which makes the control substantially easier. It is thereby not important which position the heddle frame is in.
The machine elements lie in rotational dobbies, due to the pitch, partially nested in one another, partially side-by-side. The actual coupling member, which must be sequentially controlled, in most cases a wedge, a pawl or a locking element, is embedded into or housed in an eccentric disk and becomes coupled or received in a groove in the drive shaft. This coupling member lies low or high, at two points which are offset at 180.degree., at the moment of the control, depending on the position of the heddle frame. That is, the coupling member must be controllable at each of these two points. The control signal which originates from a nonperforated or a perforated location on the pattern card must thereby be transmitted onto the wedge in relationship to the momentary heddle frame position. In other words: when the heddle frame is in the lower-shed position, a nonperforated location effects a "no engagement of the wedge", however, if the heddle frame is in the upper shed, the same nonperforated location means "effect an engagement of the wedge". In the first case, the heddle frame remains low and in the second case it will move down during the following half rotation of the shaft. The same law with reversed signs is valid for a perforated location in the card. This means, that one and the same reading of the pattern card, for example, a perforated location, a nonperforated location or a cam, result in a different control function, namely, a coupling or an uncoupling of the control member to or from the drive shaft.
German Pat. No. 1 410 724 illustrates a solution in which the control signal which originates at the card is acknowledged by a position indicator for indicating the heddle frame position or is changed in value. Such devices are very expensive and susceptible to breakdown.
The purpose of the invention is to provide a mechanism for transmitting the common control signals of different values in relationship to the position of the heddle frame onto the coupling part and without the help of a member which feeds back the heddle frame position.
This is achieved inventively with a dobby of the type mentioned above by movably securing a control member on the eccentric disk. The control member is operatively connected to the coupling wedge and has at least two control stops, which are in the base position of the shaft, in the region of at least one pressure finger of the control mechanism.
The new control member, which is associated with the eccentric disk and is movably connected to same, is moved directly in dependency of the momentary heddle frame position by the control elements so that the corresponding coupling and uncoupling occurs. The principal movement caused by the eccentric disk remains the same for the heddle frames. All elements are arranged within a spacing corresponding to the width of the individual heddle frames. The pattern card can be read with conventional means.