Abstract:
A positioning device has a pneumatic motor for longitudinally translating an arm. Four bars are parallel with the arm and form three guideways along which stopping devices can be lockable in desired positions. The stopping devices have heads that are selectively activatable into positions to form abutments for a head of the arm in order to define stop positions for the arm when the arm is moved by the motor that stalls when the arm is stopped. A shock absorber provides for a gentle stopping of the arm and its distance of operation prior to a stop position varies with the distance of displacement of the arm.

Description:
This invention relates to a positioning device comprising a first and a second main part which are translatable relative to each other along a linear path by means of a motor and arrestable in preselected various relative positions. 
     Such positioning devices are highly demanded, e.g. for carrying out the automating of various machining operations such as the drilling of holes in a workpiece and the machining of threads in the holes. Usually, at first the workpiece must be clamped and then displaced to various positions and possibly also turned. Advantageously, the clamping and displacement can be carried out pneumatically and all the operations can be controlled by a pneumatic peforated-tape reader, e.g. a reader of the kind that is described in U.S. Pat. No. 3,745,311. It is important that the positioning is fast and very accurate and that it is possible to pre-select positions that are very close to each other. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a positioning device comprising a first and a second main part which are translatable relative to each other along a linear path, first and second guide means on said first main part and parallel with said linear path, a first stop device slidable along said first guide means and lockable in various positions thereto, a second stop device slidable along said second guide means and lockable in various positions thereto, said stop devices having stop members, said stop members having inactive positions for permitting free translation between said main parts and being selectively activatable into positions for engagement with a stop means on said main part so as to limit relative movement between the main parts in one direction, and a pressure fluid motor for effecting translatory movement between the main parts until it stalls out when an activated stop member of said stop devices and said stop means on said second member abut against each other to define a pre-selected relative position between said main parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a part of a positioning device; 
     FIGS. 2 and 3 are cross sections taken along lines 2--2 and 3--3, respectively, in FIG. 1; 
     FIG. 4 shows a part of FIG. 1 with some elements in another relative position; 
     FIG. 5 shows enlarged and in a longitudinal section a detail shown in FIG. 1; 
     FIG. 6 shows schematically a detail in FIG. 1; and 
     FIG. 7 shows schematically an alternative design of the detail shown in FIG. 5. 
    
    
     DETAILED DESCRIPTION 
     The positioning device shown in the figures comprises a stationary part that is mounted in a non-illustrated frame and generally designed by 11, and a movable part that is generally designed by 12. The movable part 12 comprises an arm in the form of a box girder 13 of square cross section, that is guided and beared in a stationary bearing box 14 by means of roller bearings 15 so that it is axially movable. The bearings 15 are not illustrated in detail. By means of a gear 17 meshing with a rack 18 on the box girder 13, a pneumatic motor 16 of the sliding vane type can displace the box girder axially in both directions. The right end of the box girder 13 is not shown and it is to be understood that a workpiece or the like which is to be positioned is affixed on the non-illustrated right end of the arm; either directly if only a linear positioning is desired or indirectly via a transverse positioning device that is carried by the arm in case an orthogonal positioning is desired. Alternatively, the part 11 that is named the stationary part can of course also be movably carried by a transverse linear positioning device of the same kind as the one illustrated. Often, a possibility of turning supplements the orthogonal positioning. 
     The stationary part 11 comprises a part that includes of four bars 19 (FIG. 3) that form three parallel guide ways for seven identical stopping devices 20-26. These stopping devices are lockable in desired axial positions along and between the bars 19 by means of screws 27 and yokes 28 as is best shown in FIG. 5 that shows a stopping device at a larger scale than the other Figures. A housing 30 of the stopping device forms a cylinder for a piston 31 which, when air is supplied to a pressure chamber 29 through a hose 32 and a hose fitting 33, is forced upwardly into an end position that is defined by two annular surfaces 34 and 35 that abut against each other. 
     Still referring to FIG. 5, a return spring 36 holds normally holds the piston 31 in its inactive position as shown in FIG. 5. The piston has a piston rod 37 and the outer end of the piston rod forms a head 38 that is a stopping element and has a flat stopping surface 39 and a transverse recess 40. In the flat surface 39, there is a hole 41 with a sealing ring 42 and a hose fitting 43. This fitting 43 is supplied with compressed air through a signal hose 44 that is supplied with compressed air at a low pressure through a non-illustrated restriction. When the hole 41 is closed off as will be described below, the pressure in the signal hose 44 will increase and indicate that the desired position is achieved. The piston rod 37 is guided by a pin 45 that slides in a groove 46 that will permit turning of the piston rod through a small angle of one or a few degrees. 
     As seen in FIGS. 1 and 4, at the outer end of the box girder 13 there is a head or frame 47 with two fixed stopping surfaces 48,49. When any one of the stopping devices 20,21,22 that are located to the left of the stopping surface 48 are in their activated positions, i.e. in the extended position that is shown by the stopping device 20 in FIG. 1, the stopping surface 39 (designated on FIG. 5) of this stopping device will be in position to abut against a respective part of the surface 48 which is thus common to the stopping devices 20,21,22 that are carried by parallel guideways. In the same way, the stopping surface 49 is common to the stopping devices 23,24,25,26 to the right thereof. In FIG. 4, the stopping device 23 is shown activated, i.e. with its piston rod 37 extended and its stopping surface 39 in position for abutment against the stopping surface 49. 
     Two yokes 50,51 are suspended in the frame 47 on the outer end of the box girder 13 to swing on two transverse shafts 68,69, as shown in FIGS. 1 and 4. Between the yoke 51 and an arm 52 affixed on the yoke 50, a damping jack 53 is pivotally coupled. The damping jack 53 is schematically shown in FIG. 6 and it includes a spring 54, a one-way restrictor 55 and an oil reservoir 56. The one-way restrictor 55 comprises a one-way valve 57 and two adjustable restrictions 58,59. By means of the spring 54 the damping jack 53 braces the yokes 50,51 outwardly into their mechanically defined end positions against the frame 47 as shown in FIG. 1. When the arm 13 moves to the right in FIG. 1, a transverse plate 60 on the yoke 51 will abut against the recess 40 in the stopping device 23 that is activated, i.e. has its head 38 extended. As a result the yoke 51 swings inwardly towards the yoke 50 and the damping jack 53 is compressed. The damping force is controlled by the adjustable restriction 59 in the one-way restrictor 55. The stop position is defined by the contact between the flat stopping surface 39 of stopping device 23 and a respective part of the flat stopping surface 49 on the frame 47 as shown in FIG. 4 and causes the air motor 16 to stall at its full output torque. By means of the recess 40 in the stopping head 38, this head 38 is held in its extended position also if the pressure chamber 29 of the stopping device 23 (FIG. 5) is vented. The stopping head 38 is limitedly turnable as previously described with reference to FIG. 5 so that the flat stopping surfaces 39 and 49 will always have surface contact and the annular sealing 42 on the stopping head will always seal against the surface 49. Thus, the stopping heads have three functions, namely a) to be abutments for the respective damping yokes 50 and 51, b) to define the stopping positions of the arm 30 by means of their flat surfaces 39 that cooperate with respective parts of the surface 48 and 49, respectively, and c) to indicate the reached positions by means of the sealing rings 48 and the valving action thereof. 
     The three stopping devices 23,24,25 can be adjusted to define stopping positions that are as close to each other as permitted by the tolerances since these three stopping devices are displacable and activatable completely independently of each other. A plurality of stopping devices facing in the same direction can be slidable along the same guideways as examplified by the stopping devices 23 and 26. 
     The three stopping devices 20,21,22 to the left of the frame 47 act in the same way together with the stopping surface 48 and the yoke 50 in order to define the stop position of the arm 12 when the latter moves to the left in FIG. 1, and therefore, this is not described in detail. Since the damping jack 53 is coupled between the yokes 50,51 and the yoke 50 has a transverse plate 61 that corresponds to the transverse plate 60 of the yoke 51, the damping jack will dampen the yoke 50 in the same way as it damps the yoke 51. The restriction 58 in the one-way restrictor 55 (FIG. 6) results in that the spring 54 will need for example 0.2 seconds to brace apart the yokes 50,51 from their compressed condition. During a short movement of the arm 13, for instance from the position defined by the stopping device 20 to the position defined by the stopping device 23 in the positions these stopping devices take up in FIG. 1, the spring 54 will not have time to brace the yokes 50,51 apart into their resting positions in which they are shown in FIG. 1, and as a result, the damping distance will be shorter than normally. This is advantageous since in this case the arm 13 will not reach its normal speed. Since the damping jack 53 is common to all the stopping devices 20-26 in both directions, the damping distance and thereby the damping time will vary together with the speed of movement. If, instead, there would be a complete damping distance also after short displacements of the arm and the low speeds in connection therewith, the damping time would be longer than normal after short displacement. 
     An alternative embodiment of a stopping device is shown in FIG. 7. Instead of being extended by means of a piston, the head 38 is swingably mounted and can be swung up and swung down by means of a double-acting jack 62 that is coupled to the joint between two links 63,64 to provide a toggle action. FIG. 7 is only schematical and three attachements 65,66,67 are part of the housing of the stopping device that is slidable along two the bars 19 in the same way as in the previously described embodiment. An advantage of the embodiment according to FIG. 7 is that the head 38 can be moved from its active position to its inactive position, i.e. be swung down while the air motor 16 maintains its output torque.