FIELD OF THE INVENTION 
     This invention concerns a support device for pneumatic prehensile members, such as suction cups, connectable to a suction system to control the action. 
     STATE OF THE TECHNIQUE 
     In some sectors pneumatic prehensile members are already used, in particular in the form of suction cups, to pick up parts, items and loads, etc., to be moved by means of manipulators, robots or the like and having a surface the suction cups can grip. The suction cups can be used individually or together with others depending on the dimensions and/or weight of the part or item to be moved, assembled on a support frame, each by means of a support device, and connected to a vacuum device. They are drawn near a surface of the part or item to be picked up, making them rest against and then tightly adhere to it by using a suction device. 
     According to the known technique, a supporting device for the suction cups designed for the abovementioned use comprises a fixed support body and a mobile tubular rod, guided axially in said body and susceptible to axial movements opposed by a return spring. One end of the tubular rod is connected to, and supports, a suction cup, whereas its opposite end is linked, directly or indirectly, to a tube in communication with the vacuum device. 
     The return spring however is positioned in the support body to operate so as: 
     to normally maintain the rod in an advanced position, in which it extends beyond the end of the support body on the side of the vacuum device, when the latter is idle, 
     to allow the tubular rod carry out varying lengths of backward strokes, so as to adapt, from time to time, the position of the vacuum device to the surface it has to adhere to, and 
     to then return the tubular rod to the forward, starting, position when the vacuum device is idle and at a distance from said surface. 
     In this embodiment of the invention the supporting device is relatively simple, but not without on drawback. 
     In fact, given the presence of a spring between the support body and the mobile rod, the latter, when moved fully forward it finds itself guided in said body only for a limited stretch, contiguous to the spring. So the rod is in an uncertain guide condition and such as not to exclude its torsion under force or due to the stress on the part of the suction ducts, a stress that can give rise to the rod sticking when moving back and therefore to malfunctions of the device itself. 
     OBJECTIVES AND SUMMARY OF THE INVENTION 
     The objective of this invention is to efficiently avoid the abovementioned drawback of the known technique. 
     Correspondingly, another objective of the invention is to propose a support device for the pneumatic prehensile members, in particular suction cups, in which the mobile rod is guided and slides more correctly in the body in each of the positions it undertakes and consequently is not subject to torsion and producing the self-defeating effect of sticking. 
     A further objective is to be able to make use of a support device for suction cups which is efficient and reliable under all working conditions, and furthermore which is simple, not cumbersome and particularly light in weight, all aspects that become mainly important in the pick-up system with a multiplicity of suction cups on a same support frame. 
     Said objectives are reached with a support device for prehensile members such as suction cups according to the introduction of claim  1  and where between the tubular rod and the distal end of the support body are inserted guide means for preventing the torsion/rotation of the rod during its longitudinal movements starting from the position in which it emerges most out of said body. 
     Advantageously the guide means include elements that help in the sliding of the rod of the support body, besides acting as an anti-torsion means in particular when the rod is in an advanced position. 
     Furthermore these rotation means are radialy stressed and kept in the operating position by flexible preloading means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will however be illustrated in greater detail in the continuation of the present description made in reference to the attached indicative and not limiting drawings, in which: 
         FIG. 1  shows a blowup view of the components of the support device; 
         FIGS. 2 and 3  show, respectively, a view in perspective and section plane of the assembled device; 
         FIG. 4  shows a side view of the device with the rod in the forward position; 
         FIG. 5  shows a partial section of the device in direction of arrows A-A in  FIG. 4 ; 
         FIG. 6  shows a cross section of the device in direction of arrows B-B in  FIG. 5 ; and 
         FIG. 7  shows a side view of the device with the rod in the retracted position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown, the device proposed herein basically comprises a support body, a mobile rod  12 , a return spring  13  and guide and anti-torsion means  14  for the mobile rod. 
     The support body has an end or rear, and a distal end, or front, and it forms an axial guide hole  15 . This hole has a basically constant diameter for all the length of the body starting from the distal end, except for a part which is tapered  16 , that is with a smaller diameter, on nearing the proximal end of the body. Furthermore, the axial guide hole  15  and its tapered part  16  form between them an annular striking surface  17 — FIG. 2 . 
     Externally, the support body can be cylindrical, at least partially threaded and provided with means—not shown—such as nuts or ring nuts, for fixing it to an arm or a support frame and with movements carried out by a manipulator, robot or some other means. 
     As an alternative, said body can be smooth on the outside and be provided with clamps or the like for fixing it when operating on an arm or movable frame. 
     The movable cylindrical-tubular rod  12  has an axial through passage  18  and has a longer length than that of the support body. The rod  12  is housed and is longitudinally movable in the axial bore  15 ,  16  of said support body. In more detail, it has a first portion  19  of its length with an external diameter larger than the second remaining portion  20 . The diameter of the axial bore of said first portion  19  corresponds to the diameter of the axial bore  15  of the support body and that of the second portion  20  to the diameter of the tapered part  16  of said axial bore contiguous to the proximal end of the body. The first portion  19  and the second portion  20  of the rod  12  between them form an annular step  21 — FIGS. 2 and 5 . 
     The rod  12  is housed in the support body so that its first portion  19 , with a larger diameter, emerges from the front of the distal end and its second portion  20 , with a smaller diameter; emerges from the proximal end of the body. The first portion  19  of the rod is provided with a terminal head  22  to which a gripper device is connectable, such as a vacuum device—not shown. To the second portion  20  of the rod is fixed a nipple or terminal connector  23  which is connectable to a suction duct—not shown—controlled by a diffusion group. 
     The return spring  13  is assembled inside the support body between the latter and the second smaller diameter portion  20  of the rod, and it is held axially and compressible between the annular striking surface  17  on the side of the support body and the annular step  21  on the side of the rod  12 . 
     The movable rod  12  is guided and moveable in the body of the support body between two end positions: one advanced, limited by the resting of the nipple  23  against the proximal end of the support body, and one retracted, limited by the resting of the head  22  of the rod against the distal end of the support body”— FIG. 7 . 
     The guide and anti-torsion means  14  are placed between the distal end of the support body and the first portion  19  of the moveable rod  12 . They are made up of longitudinal guide grooves  24  provided along the first portion  19  of the moveable rod, in guide devices, preferably rolling, such as balls  25 , housed in radial bores  26  at the distal end of the body and engaging in said grooves, and in a collar  27  holding some balls, positioned around said distal end of the support body on a level with a depressed part  28  of said body. Preferably, the collar is such as not to increase the radial dimensions of the support body, and made of a basically flexible material, for example nylon, and, on the inside it is provided with radial dentils  29  facing towards and resting against the balls to make sure they couple with a certain preload with the guide grooves  24 . 
     All together, the return spring  13  acts so as to maintain and return the rod  12  into the forward position, in which its first portion  19  emerges out of the distal end of the fixed body of the support body, remaining however always partially fitted into the axial bore  15  so that the guide balls  25  always remain coupled to the respective guide grooves  24 — FIG. 5 . 
     The rod of the support body moves back towards the retracted position, compressing the spring  13  in different ways, depending on the position of the surface on which the gripper device, that is the vacuum device, finds itself from time to time resting on and engaged to. Then, when it is resting on the surface of the item or load to be moved, the vacuum device is activated by the application of the rod, from behind, by a suction of the supporting device. Subsequently, as soon as the suction stops the vacuum device moves away from the surface it was adhered to and with the removal of the device from said surface, the rod, stressed by the return spring  13 , moves back into the advanced position. 
     During all its movements from any other position the rod however remains guided axially and centred in the fixed body tank to the guide means without any substantial possibility of torsion.
A support device for pneumatic prehensile members, in particular suction cups, for picking up and moving the parts, items and the like. It includes a fixed support body (support body) a tubular rod ( 12) moving axially in the body, and a return spring ( 13) between the body and rod. Between the tubular rod ( 12) and a distal end of the fixed support body (support body) are interposed some guide elements ( 14) provided to prevent torsion/rotation of the rod during its longitudinal movements in and with respect to the fixed body.