Patent Publication Number: US-2023138486-A1

Title: Apparatus for clamping workpieces on machine tools

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus for clamping workpieces on machine tools. 
     BACKGROUND ART 
     As is well known, in the large-scale production of mechanical workpieces that require machining on the machine tool, the use of systems with a high level of automation is widespread wherein an anthropomorphic robot brings the workpieces to be machined to a machine tool, where special apparatuses of the hydraulic type, take over the workpiece and clamp it in position to allow the machining thereof. 
     When the machining process is completed, the aforementioned means release the machined workpiece, which is moved away once again by means of the robot. 
     The clamping apparatuses must be capable of exerting even very high clamping forces on the workpiece being machined. 
     This need is particularly felt, e.g., in the automotive sector, wherein the continuous need to optimize the production cycles has led to the use of tools that operate at very high speeds, unloading very strong forces and vibrations on the workpiece that must be offset by the fastening systems. 
     Still in the automotive sector, moreover, the use of particularly light materials such as aluminum is becoming more and more widespread but, during machining, they are not able to ensure the same resistance as materials such as e.g. cast iron and steel. 
     It is therefore necessary that the clamping apparatuses, in addition to exerting a very high force, rest on the workpiece at predetermined points, with a great precision and in a repeatable manner every time a new workpiece to be machined is mounted on the machine tool; otherwise, in fact, the high force exerted by the clamping apparatus may cause the deformation of the workpieces, which compromises the quality of the machining and the risk of obtaining workpieces that are out of tolerance. 
     In such automated systems, the level of operational reliability of the individual components, including the apparatuses for clamping the workpieces, is usually very high. 
     Nevertheless, it sometimes happens that the mechanical workpieces to be machined are not placed correctly and precisely, so the clamping apparatuses fail to clamp the workpiece perfectly (or do so but in the wrong position), thus risking to jeopardize the entire machining process and to damage the workpiece and/or the machining tools and/or the clamping apparatuses. 
     Similar problems can also occur when unloading the workpiece at the end of the machining process; in fact, if the clamping apparatuses do not completely and correctly release the machined workpiece, in fact, the workpiece movement robot picks (or tries to pick) a workpiece which is not perfectly released, with the risk of seriously damaging the workpiece and/or the clamping apparatuses and/or the robot itself. 
     In this context, it is important to underline that, in highly automated systems, any malfunction that causes the stoppage of the processing can easily turn into a lack of production or, even worse, into a damage of the systems, and into a consequent economic damage of non-negligible entity. 
     DESCRIPTION OF THE INVENTION 
     The main aim of the present invention is to devise an apparatus for clamping workpieces on machine tools which allows preventing machining operations from being performed on workpieces that are not properly placed and clamped on the machine tool. 
     A further object of the present invention is to devise an apparatus for clamping workpieces on machine tools which allows preventing the machined workpieces from unloading that are not perfectly and properly released. 
     Last but not least, the object of the present invention is to devise an apparatus for clamping workpieces on machine tools with high reliability and precision of operation. 
     Still another object of the present invention is to devise an apparatus for clamping workpieces on machine tools which allows avoiding unwanted malfunctions and damage to the workpiece being machined and/or to the tools of the machine tool and/or to the workpiece movement robot and/or to the clamping apparatus thereof. 
     Another object of the present invention is to devise an apparatus for clamping workpieces on machine tools which allows overcoming the aforementioned drawbacks of the prior art within the scope of a simple, rational, easy, effective to use and affordable solution. 
     The objects set out above are achieved by the present apparatus for clamping workpieces on machine tools having the characteristics of claim  1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the present invention will become more evident from the description of some preferred, but not exclusive, embodiments of an apparatus for clamping workpieces on machine tools, illustrated by way of an indicative, yet non-limiting example, in the accompanying tables of drawings wherein: 
         FIG.  1    is an axonometric view of a first embodiment of the apparatus according to the invention; 
         FIG.  2    is an exploded view of the apparatus in  FIG.  1   ; 
         FIG.  3    is a cross-sectional view of the apparatus in  FIG.  1    in the clamping position; 
         FIG.  4    is a cross-sectional view of the apparatus in  FIG.  1    in an intermediate transient position; 
         FIG.  5    is a cross-sectional view of the apparatus in  FIG.  1    in the release position; 
         FIG.  6    is a cross-sectional view of a second embodiment of the apparatus according to the invention; 
         FIG.  7    is an exploded view of a third embodiment of the apparatus according to the invention. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     With particular reference to the embodiment shown in  FIGS.  1  to  5   , reference numeral  1  globally indicates an apparatus for clamping workpieces on machine tools. 
     The apparatus  1 , in particular, is intended to clamp a workpiece P after it has been placed on a worktop L of a machine tool M and before mechanical machining has started. 
     Preferably, the machine tool M is of the highly automated type, wherein an anthropomorphic robot is dedicated to load the workpieces P to be machined and unload the machined workpieces P. 
     It should be noted that the machine tool M is provided with a plurality of apparatuses  1 , which are arranged at adequate positions and in appropriate amounts based on the shape of the workpiece P and on the type of mechanical machining that is to be performed. 
     In the figures and in the remainder of the present disclosure, reference will be made for simplicity&#39; s sake to a single apparatus  1 , unless otherwise indicated. The apparatus  1  comprises at least one basic frame  2  that is fixable to the machine tool M, e.g. to its worktop L, to its bedplate or to any other part thereof. 
     The apparatus  1  comprises at least one clamping unit  3  associated with the basic frame  2  in a movable manner between a release position and a clamping position of the workpiece P, passing through a plurality of intermediate transient positions. 
     Conveniently, the clamping unit  3  comprises:
         at least one bracket element  4  hinged to a movable portion  5  around a first hinging axis A and adapted to come into contact with the workpiece P in the clamping position;   at least one hinging linkage  6 ,  7  hinged to the basic frame  2  around a second hinging axis B and hinged to the bracket element  4  around a third hinging axis C.       

     Advantageously, the hinging axes A, B, C are substantially parallel to each other. 
     By virtue of the shape of the clamping unit  3 , in actual facts, in the release position the bracket element  4  is placed in an almost vertical position, which leaves free access to the worktop L for the positioning and the removal of the workpiece P; in the clamping position, on the other hand, the bracket element  4  is positioned in a substantially horizontal position and overhanging on the worktop, so as to clamp the workpiece P between the bracket element  4  and the worktop L. 
     The hinging between the bracket element  4  and the movable portion  5  around the first hinging axis A is defined by a series of first holes  8 , formed on the bracket element  4  and on the movable portion  5 , and by a first pin  9 , inserted into the first holes  8  aligned with each other. 
     For example, the hinging linkage  6 ,  7  comprises a first connecting rod  6  and a second connecting rod  7 , both hinged around the second and third hinging axes B, C. 
     Conveniently, the connecting rods  6 ,  7  are arranged on symmetrically opposite sides of both the bracket element  4  and of a hinging portion  10  of the basic frame  2 . 
     The hinging between the connecting rods  6 ,  7  and the basic frame  2  around the second hinging axis B is defined by a series of second holes  11 , formed on the connecting rods  6 ,  7  and on the hinging portion  10 , and by a second pin  12 , inserted into the second holes  11  aligned with each other. 
     The hinging between the connecting rods  6 ,  7  and the bracket element  4  around the third hinging axis C, on the other hand, is defined by a series of third holes  13 , formed on the connecting rods  6 ,  7  and on the bracket element  4 , and by a third pin  14 , inserted into the third holes  13  aligned with each other. 
     The apparatus  1  comprises at least one sensing channel  15  formed on at least one of either the basic frame  2  or the clamping unit  3 . 
     The sensing channel  15  can be supplied with pressurized air and can be connected to a sensing sensor  16  which is adapted to sense the pressure of the pressurized air. 
     More in detail, the sensing channel  15  is connected to a first pneumatic circuit  17  adapted to supply the pressurized air. 
     The first pneumatic circuit  17  is provided with the sensing sensor  16  (such as a pressure switch), by means of which the air pressure inside the sensing channel  15  can be known. 
     The sensing channel  15  is hermetically sealed when the clamping unit  3  is in the clamping position and is open outwards at least when the clamping unit  3  is in the intermediate transient positions. 
     Therefore, when the clamping unit  3  is in the clamping position, the air supplied under pressure into the sensing channel  15  remains trapped in the sensing channel itself and its pressure tends to increase; in the intermediate transient positions, however, the air is allowed to vent outwards and its pressure tends to decrease. 
     Conveniently, the sensing channel  15  is formed on the basic frame  2  and the hinging linkage  6 ,  7  is shaped so as to open and close the sensing channel  15  based on the position of the hinging linkage  6 ,  7 . 
     More specifically, the sensing channel  15  emerges on a first surface  18  of the basic frame  2  which, e.g., is formed on the hinging portion  10 . 
     The first connecting rod  6  rests in rotation on the first surface  18  and comprises a first venting recess  19 . 
     With the first connecting rod  6  are associated first preloading means  20 ,  21  adapted to keep the first connecting rod  6  in sealed contact on the first surface  18  and to keep the sensing channel  15  normally closed. 
     The first preloading means  20 ,  21  consist, e.g., of a set of cup springs  20  and washers  21  mounted on the second pin  12  and on the third pin  14  and operating so as to push the connecting rods  6 ,  7  against the hinging portion  10  and against the bracket element  4 . 
     This way, on the one hand, it is ensured that the existing clearances between the basic frame  2 , the connecting rods  6 ,  7  and the bracket element  4  are reset, so as to achieve a more stable and precise assembly operation, and on the other hand the sealed closure of the sensing channel  15  is achieved even without the presence of rubber seals or other soft material. 
     The opening of the sensing channel  15 , in actual facts, only takes place when the first venting recess  19  overlaps at least partly the sensing channel  15  which occurs, as mentioned, when the clamping unit  3  moves to the intermediate transient positions. 
     As described and shown, the sensing channel  15  is formed on the basic frame  2  and the hinging linkage  6 ,  7  is shaped so as to open and close the sensing channel  15 ; alternative embodiments cannot however be ruled out wherein the sensing channel  15  is differently arranged and its opening and closure are achieved by means of components other than the hinging linkage  6 ,  7 . 
     For the movement of the clamping unit between the release position and the clamping position, the apparatus  1  comprises at least one hydraulic actuator  22 ,  23 , provided with a fixed portion  24 , associated with the basic frame  2 , and a movable portion  5 , connected to the clamping unit  3 . 
     The movable portion  5  of the hydraulic actuator  22 ,  23  conveniently coincides with the movable portion to which the bracket element  4  is hinged around the first hinging axis A. 
     For example, the hydraulic actuator  22 ,  23  comprises a cylinder  22 , defining the fixed portion  24 , and a stem  23 , which is provided with a plunger  25 , comes out of the cylinder  22  and defines the movable portion  5 . 
     The cylinder  22  of the hydraulic actuator  22 ,  23  is formed in a single body piece with the basic frame  2 . 
     Inside the cylinder, the hydraulic actuator  22 ,  23  comprises at least a first chamber  26  which can be supplied with a first pressurized hydraulic fluid to displace the clamping unit  3  from the release position to the clamping position. Within the present disclosure, by hydraulic fluid is meant any fluid in the liquid state (and therefore ideally incompressible) used as a carrier for the transport of energy in a hydraulic circuit; preferably the hydraulic fluid consists of a traditional synthetic oil but alternative embodiments cannot however be ruled out wherein it may be mineral oil, vegetable oil, water or the like. 
     The first chamber  26  operates on one side of the plunger  25 . 
     The first chamber  26  is connectable to a first sensing device  27  for sensing the pressure of the first pressurized hydraulic fluid. 
     More in detail, the first chamber  26  is connected to a first duct  28 , formed in the cylinder of the hydraulic actuator  22 ,  23 , in turn connected to a first hydraulic circuit  29  adapted to supply the first hydraulic fluid. 
     The first hydraulic circuit  29  is provided with the first sensing device  27  (e.g., a pressure switch), by means of which the pressure of the first pressurized hydraulic fluid inside the first chamber  26  can be known. 
     The first sensing device  27  and the sensing sensor  16  are connectable to a control system adapted to authorize the machining of the workpiece P when the pressure of the first hydraulic fluid under pressure in the first chamber  26  and the pressure of the air in the sensing channel  15  are simultaneously higher than their respective threshold values. 
     The control system, not shown in the figures, consists, e.g., of a control unit (electronic, hydraulic or a combination of both) that manages the operation of the machine tool M. 
     In actual facts, in order to consent to the start of the mechanical machining on the workpiece P, the control system carries out a double check:
         it checks whether the first chamber  26  is pressurized, i.e., it is supplied with the first pressurized hydraulic fluid; and   it checks whether the sensing channel  15  is pressurized, i.e. it is closed and air cannot vent outwards.       

     If both of these circumstances occur at the same time, then the control system senses that the clamping unit is correctly arranged in the clamping position and consents to the tools of the machine tool M to carry out the machining operations; such a circumstance is shown in  FIG.  3   . 
       FIG.  4   , on the other hand, shows a situation wherein the workpiece P has been placed on the machine tool M in a wrong position, and the bracket element  4  fails to reach the clamping position because it gets in contact with the workpiece P when the clamping unit  3  is still in one of the intermediate transient positions. Under this circumstance, the first hydraulic fluid in the first chamber  26  is pressurized and the first sensing device  27  senses this pressure; the first venting recess  19 , on the other hand, is however at least partly overlapped to the sensing channel  15 , the pressurized air vents outwards and the sensing sensor  16  senses that the pressure in the sensing channel  15  is not higher than the threshold value. Under this circumstance, therefore, the control system learns that the clamping unit  3  has not reached the clamping position and does not authorize the start of the mechanical machining operations. 
     The lack of authorization safeguards the workpiece P and the machine tool M by preventing operations that are potentially dangerous for their integrity from being carried out. 
     In response to the lack of authorization, protocols aimed at restoring normal working conditions may be activated, such as e.g. the repositioning of the workpiece P and/or the intervention of an operator. 
     In the embodiment shown in  FIGS.  1 - 5   , the hydraulic actuator is of the double acting type and comprises at least a second chamber  30  which can be supplied with a second pressurized hydraulic fluid to displace the clamping unit  3  from the clamping position to the release position. 
     Preferably, the second hydraulic fluid is identical to the first hydraulic fluid used as a carrier to set the first chamber  26  under pressure; in other words, the same hydraulic fluid may be pumped into the first chamber  26  and into the second chamber  30  as required. 
     Alternative embodiments wherein two different hydraulic fluids are used cannot, however, be ruled out. 
     The second chamber  30  operates on one side of the plunger  25  opposite the first chamber  26 . 
     The second chamber  30  is connectable to a second sensing device  31  of the pressure of the second pressurized hydraulic fluid. 
     More in detail, the second chamber  30  is connected to a second duct  32 , formed in the cylinder of the hydraulic actuator  22 ,  23 , in turn connected to a second hydraulic circuit  33  adapted to supply the second hydraulic fluid. 
     The second hydraulic circuit  33  is provided with the second sensing device  31  (such as e.g. a pressure switch) by means of which the pressure of the second pressurized hydraulic fluid inside the second chamber  30  can be known. 
     Advantageously, the sensing channel  15  is hermetically closed when the clamping unit is in the release position, and the second sensing device  31  and the sensing sensor  16  are connectable to a control system adapted to authorize the picking of the workpiece P from the machine tool M when the pressure of the second hydraulic fluid in the second chamber  30  and the pressure of air in the sensing channel  15  are simultaneously higher than their respective threshold values. 
     The control system intended to authorize the picking of the workpiece P may conveniently coincide with the control system intended to authorize the machining of the workpiece P and consist, e.g., of the control unit that manages the operation of the machine tool M. 
     In actual facts, in order to consent to the picking of the workpiece P, after the machining operations have been completed, the control system carries out a double check:
         it checks whether the second chamber  30  is pressurized, i.e., it is supplied with the second pressurized hydraulic fluid; and   it checks whether the sensing channel  15  is pressurized, i.e. it is closed and air cannot vent outwards.       

     If both these circumstances occur at the same time, then the control system senses that the clamping unit is correctly arranged in the release position and allows the movement robot of the workpiece P to pick it from the machine tool M; such a circumstance is shown in  FIG.  5   . 
     The apparatus  1 , as described and shown in  FIGS.  1  to  5   , has several workpieces in contact with the pressurized hydraulic fluid and, therefore, special seals are arranged at various points of the apparatus  1  which, for simplicity of representation, have been commonly identified with reference numeral  34 . 
       FIG.  6    shows a second embodiment of the present invention wherein the apparatus  1  is identical to the embodiment of  FIGS.  1  to  5    except for the fact that the hydraulic actuator  22 ,  23  is of the single acting type and comprises at least one springback element  35  to displace the clamping unit  3  from the clamping position to the release position. 
     The springback element  35  consists, e.g., of a helical spring operating on the plunger  25  on the opposite side with respect to the first chamber  26 . 
     In this embodiment, the apparatus  1  is provided with the first chamber  26 , which is connected to the first sensing device  27 , but is not provided with the second chamber  30  and with the second sensing device  31 . 
     By means of the apparatus  1  in  FIG.  6   , therefore, it is not possible to identify with certainty the achievement of the release position by means of the clamping unit  3  as is the case in the embodiment of  FIGS.  1  to  5   , but it is still possible to identify with certainty the achievement of the clamping position and the start of the mechanical machining operations when it is checked that the pressure of the first hydraulic fluid in the first chamber  26  and the air pressure in the sensing channel  15  are simultaneously higher than their respective threshold values. 
     A third embodiment of the invention is shown in  FIG.  7   , wherein the hydraulic actuator  22 ,  23  is still of the single acting type and is provided with the springback element  35  that allows the clamping unit  3  to be displaced from the clamping position to the release position. 
     Unlike the embodiment in  FIG.  6   , however, the apparatus  1  comprises at least one auxiliary channel  36  located on at least one of either the basic frame  2  or the clamping unit  3 . 
     The auxiliary channel  36  can be supplied with pressurized air and can be connected to an auxiliary sensor  37  adapted to sense the pressure of the pressurized air. 
     More in detail, the auxiliary channel  36  is connected to a second pneumatic circuit  38  adapted to supply air under pressure. 
     The second pneumatic circuit  38  is provided with the auxiliary sensor  37  (such as e.g. a pressure switch), by means of which the air pressure inside the auxiliary channel  36  can be known. 
     The auxiliary channel  36  is hermetically sealed when the clamping unit  3  is in the release position and is open outwards at least when the clamping unit  3  is in the intermediate transient positions. 
     Therefore, when the clamping unit  3  is in the release position, the air supplied under pressure into the auxiliary channel  36  remains trapped in the sensing channel itself and its pressure tends to increase; in the intermediate transient positions, however, the air is allowed to vent outwards and its pressure tends to decrease. 
     Conveniently, the auxiliary channel  36  is formed on the basic frame  2  and the hinging linkage  6 ,  7  is shaped to open and close the auxiliary channel  36  based on the position of the hinging linkage  6 ,  7 . 
     In more detail, the auxiliary channel  36  emerges on a second surface  39  of the basic frame  2  which is formed on the hinging portion  10 , on the opposite sides with respect to the first surface  18 . 
     The second connecting rod  7  rests in rotation on the second surface  39  and comprises a second venting recess  40 . 
     Second preloading means are associated with the second connecting rod  7  and are adapted to keep the second connecting rod  7  in sealed contact on the second surface  39  and to keep the auxiliary channel  36  normally closed. 
     The second preloading means usefully coincide with the first preloading means  20 ,  21 . 
     The cup springs  20  and the washers  21 , in fact, operate so as to push both the connecting rods  6 ,  7  against the hinging portion  10  and against the bracket element  4 . 
     The opening of the auxiliary channel  36 , in actual facts, takes place only when the second venting recess  40  overlaps at least partly the auxiliary channel  36 , which occurs, as mentioned above, when the clamping unit  3  moves to the intermediate transient positions. 
     In the embodiment shown in  FIG.  7   , the first sensing device  27  and the auxiliary sensor  37  are connectable to a control system adapted to authorize the picking of the workpiece P from the machine tool M when the pressure of the first hydraulic fluid in the first chamber  26  is lower than a respective threshold value and, at the same time, the pressure of the air in the auxiliary channel  36  is higher than a respective threshold value. 
     Again, the control system intended to authorize the picking of the workpiece P in the embodiment in  FIG.  7    may conveniently coincide with the control system intended to authorize the machining of the workpiece P and may consist, for example, of the control unit that manages the operation of the machine tool M. 
     In actual facts, in order to consent to the picking of the workpiece P after the mechanical machining operations have been completed, the control system carries out a double check:
         it checks whether the first chamber  26  is not pressurized, i.e., not supplied with the first pressurized hydraulic fluid; and   it checks whether the auxiliary channel  36  is pressurized, i.e., closed and air cannot vent outwards.       

     If both these circumstances occur at the same time, then the control system senses that the clamping unit  3  is correctly arranged in the release position and allows the movement robot of the workpiece P to pick it from the machine tool M.