Abstract:
A protection device for controlling the motion of a pneumatic actuator, having at least one elongated cylinder provided with a piston, dividing the cylinder into a first chamber and a second chamber, an actuating pressure supply line connectable to at least one of the first and second chambers, a control unit for controlling the motion of the piston relatively to the cylinder, and a motion sensor adapted to sense a piston feature related to the piston motion and co-operating with the control unit. According to the invention, the control unit limits the motion of the piston as soon as signal from the sensor indicates that an excessive value of the piston motion has been established.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a protection device for controlling the motion of a pneumatic actuator, according to the preamble of claim 1. 
     Known pneumatic devices used in milking systems for milking an animal, e.g. a cow, suffers from disadvantages in that they do not include any satisfactory additional overload protection against kicks or other not desirable movements of the animal, furthermore they do not include any parallel protection function preventing a fast movement of the actuator in case of a malfunction of the control means comprising servo-pneumatic positioning elements. The known pneumatic devices suffers furthermore from disadvantages in that the protection function is performed in a not sufficiently quick manner. A milking system of this kind is described in for example EP-A-0 360 354. 
     It is, accordingly, an object of the present invention to overcome the problem of the known devices. 
     A further object of the invention is to provide a protection for the control of a pneumatic actuator comprising a piston against external accidental influence on the piston movement 
     SUMMARY OF THE INVENTION 
     This has been solved by a protection device as initially defined, which is characterized in that said control means limits the motion of said piston as soon as signalling from said sensor means indicates that an excessive value of said piston motion has been established. 
     Hereby is prevented that a fast movement of the piston relatively to the cylinder arises in case of a malfunction or if an animal or a person runs into a robot arm with operating said. 
     Preferably, a valve means controlled by said control means being connectable to said first and second chambers, and adapted to open a connection between said first and second chambers. Hereby an equalisation of pressure between the first and second chambers is achieved. The piston relatively to the cylinder is therefor flexible due to an external influence. 
     Suitably, said sensor means comprises a position sensor adapted to sense the position or the relative position per unit of time of said piston in relation to said cylinder, and that said control means is adapted to control said valve means to open in response to a signaling from said position sensor indicating that the value of the position change per unit of time is higher than a predetermined value. Hereby a value of the velocity of said actuator is determined A signal from the control means is given if the value of the motion is exceeded and an equalization of pressure between the first and second chambers is achieved. 
     Preferably, said sensor means comprises a differential pressure transductor adapted to sense the pressure difference between said first and second chambers, and that said control means is adapted to control said valve means to open in response to a signalling from said transductor indicating that the value of the pressure difference is higher than an estimated pressure composed by a model dependent on the actual control situation of said piston. Hereby an equalization of pressure between said first and second chambers is achieved. 
     Suitably, said model is derived by means of a Kalmar filter. Hereby is achieved a state, which not will be exceeded 
     Preferably, said control means is divided into at least one separate control unit controlling the motion of said piston and at least one protective pressure control unit controlling the pressure difference between said first and second chambers, that the signal from said differential pressure tansductor is fed to said protective pressure control unit, that said valve means is controlled by said protective pressure control unit when the pressure difference value sensed by said transductor is higher than an estimated value in dependence on the actual control situation of the piston Hereby an equalization of the pressure between said first and second chambers is achieved even if a malfunction of the control means or the servo valve arises in a situation where an animal or a person runs into the robot arm. 
     Suitably, for each of said control unit and said protective pressure control unit, the differential pressure is compared with an estimated pressure, which is computed from a model derived by means of the Kalmar filter, and the control signal to said valve means. Hereby either a malfunction in the SW or in the HW do have an effect on the protection function 
     Preferably, a valve means is associated with said control means, said valve means being connectable to said actuating pressure supply line and to at least one of said first and second chambers, a first valve means is connectable between said valve means and said first chamber, and a second valve means is connectable between said valve means and said second chamber, and a control valve means, connectable to said supply line and associated with said control means, being adapted to control said first and second valve means, and wherein said first and second valve means are in position for normal operation of the device in response to said sensor means, by said excessive value of said piston motion said valve means operates to equalize the pressure between said chambers. Hereby, when a malfunction or an external influence on the actuator arises, the first and second chambers are disconnected from the pressure source, without shutting down the supply line. 
     Suitably, a first pressure supply line is connectable between said first chamber and said valve means, a second pressure supply line is connectable between said second chamber and said valve means. Hereby the pneumatic pressure may have an effect on the piston relatively to the cylinder in at least one direction. 
     Preferably, a main valve means is associated with said control means and is connectable to at least one of said first and second chambers and to said actuating supply line. Hereby is achieved that the pressure generation into said device at least can be restrained 
     Suitably, said robot arm comprises at least one pneumatic actuator for controlling the motion of said robot arm. Hereby is achieved a controllable motion of said robot arm. 
     Preferably, said robot arm is connected to a robot arm suspension means, which is furthermore hingedly connected to a support means, and said robot arm suspension means being arranged to said support means about an substantially horizontal axis, and at least one of said pneumatic actuators is arranged between said robot arm suspension means and said support means, for allowing said robot suspension means to perform a substantially pendulum movement about said substantially horizontal axis. Hereby is achieved that the arm has good access to e.g. teats and that the risk is less for dirt, such as manure, to hamper the movement of mechanical parts, as the connection between the robot arm suspension means and the support means is arranged at a level substantially above said animal. 
     Suitably, at least one of said pneumatic actuator is arranged between said robot arm and said support means, for actively moving said robot am in a substantially vertical plane. Hereby is achieved a controllable pendulum movement. 
     Preferably, said robot arm is pivotally connected to said robot arm suspension means, for allowing said robot arm to perform a pivotal movement in relation to said robot arm suspension means. Hereby is achieved a movability of the robot arm in addition to said pendulum movement. 
     Suitably, at least one of said pneumatic actuators is arranged between said robot arm and said robot arm suspension means, for actively moving said robot arm in a substantially sideward direction. Hereby is achieved a controllable pivotal movement. 
     Preferably, said robot arm suspension means comprises a pivot means having a bar movable about a substantially horizontal axis, said bar being provided with a first connection member for said robot arm and a second connection member for said at least one of said pneumatic actuators, each of said first and second connection members being provided with a hinge movable about a substantially vertical axis. Hereby a joint for the pivotal movement is achieved. 
    
    
     DRAWING SUMMARY 
     The invention will now be described more closely by examples with reference to the accompanying drawings, in which 
     FIG. 1 illustrates the protection device according to a first embodiment of the invention, wherein a control means provided with a memory function opens a servo valve in response to a position sensor. 
     FIG. 2 illustrates the protection device according to a second embodiment of the invention, wherein the control means provided with a memory function opens an on/off valve in response to a differential pressure transductor and/or the position sensor. 
     FIG. 3 illustrates the protection device according to a third embodiment of the invention, wherein either the differential pressure tansductor separately feed a signal to a protective pressure control unit for controlling an on/off valve or the control means controls the servo valve in response to the position sensor. 
     FIG. 4 illustrates the device according to a fourth embodiment of the invention, wherein the control means controls a first and a second check valve means by a control valve means. 
     FIG. 5 illustrates an apparatus for performing an animal related operation arranged with the control devices  2   a ,  2   b ,  2   c.   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1 a pneumatic device  2  comprises a pneumatic cylinder  6  provided with a piston  4  connected to a piston rod  8 . 
     A first pressure line  10  is connected to a first chamber  5   a  of a cylinder  6  and to a servo valve  20 . A second pressure line  12  is connected to a second chamber  5   b  of the cylinder  6  and to the servo valve  20 . The servo valve  20  may be a 5/3 proportional flow control valve, and is controlled by a control unit  22  controlling the valve  20 . The valve  20  operates to control the movement of the piston  4  inside the cylinder  6 . 
     The servo valve  20  is connected to a pressure source  16  by a supply line  14  via a main valve  18 . 
     A position sensor  23  is adapted to the cylinder  6  for sensing the position of the piston  4 . The position sensor  23  is connected to a control means  22 , which furthermore is connected to the servo valve  20  and to the main valve  18 . The output of the sensor  23  is fed to a control unit  22 , which for example can be an ordinary kind of computer and which controls the operation of the pneumatic devise  2 . It is possible to have the position sensor  23  to indicate the speed of the piston  4 , i.e. the position per unit of time. However, it is also possible to have the position as an output and provide the speed indication by the sampling rate. 
     The position sensor  23  may be a linear potentiometer inside or outside the cylinder  6  or a linear inductive contactless sensor. Also may at least one optical incremental encoder, rotary potentiometer or rotary incremental encoder, adapted on a robot arm which will be further described bellow in connection with FIG. 5, be used. 
     FIG. 2 shows an example of a second embodiment of the invention, in which parts denoted with a reference sign correspond to parts of the first embodiment with the same reference sign. 
     The protection device according to the second embodiment thus includes a differential pressure transductor  30 , which is provided in a first connection line  31  between the two chambers  5   a  and  5   b,  and in practice connects the first pressure supply line  10  and the second supply pressure line  12 . 
     A valve  36  is arranged in a second connection line  33 . The second pressure line  33  connect the first pressure line  10  and the second pressure line  12 , and connect the two chambers  5   a  and  5   b  with each other. 
     Furthermore, the valve  36  and the transductor  30  are connected to the control unit  22 . 
     The valve  36  may be an on/off valve. 
     FIG. 3 shows an example of a third embodiment of the invention, in which parts denoted with a reference sign correspond to parts of the second embodiment with the same reference sign. 
     The protection device according to the second embodiment comprises a protective pressure control unit  37  associated with the valve  36  and the differential pressure transductor  30 . 
     Furthermore, the valve  36  and the transductor  30  are preferably connected to the protective pressure control unit  37  separate from the control unit  22 . The protective pressure control unit  37  could then be of a more simple kind than the control unit  22  and for example be a simple electronic circuit. However, it is also possible that the a protective pressure control unit  37  is a part of the control unit  22 . 
     This arrangement implies that a parallel protection system is arranged, functioning parallelly with the embodiments described in FIGS. 1 and 2. The protection action is performed in a very quick response compared with known protection devises. 
     FIG. 4 shows an example of a fourth embodiment of the invention, in which parts denoted with a reference sign correspond to parts of the first embodiment with the same reference sign. 
     The protection device according to the fourth embodiment thus includes a control valve  24 , a first valve means  28  and a second valve means  29 . The control valve  24  is connected to the supply line  14 . A third connection line  26  is connected to a fourth connection line  27  and to the control valve  24 . The fourth connection line  27  connects the first valve means  28  and the second valve means  29 . 
     The first valve means  28  and second valve means  29  shown in the figure are check valves, but said valves may of course be valves constructed to open the connection between the first supply pressure line  10  and the second supply pressure line  12 , with that the chambers  5   a  and  5   b  would have an open connection to each other through the connection line  27 . 
     This embodiment may also comprise a differential pressure transductor and a valve means as are arranged in the earlier described embodiments. 
     A positive effect of this arrangement is that the actuator pressure supply line  14  never has to be shut down. 
     As shown in FIG. 5, which illustrates an embodiment of a milking machine in which the control devices  2   a,    2   b,    2   c  described above is inserted, a robot arm  38  is connected to a robot arm suspension means  40 . The robot arm suspension means  40  is hingedly connected to a support means  42  and is arranged to said support means  42  about a horizontal axis (X-X). 
     The support means  42  is connected to a railing  50  of an animal stall  60 . 
     The robot arm  38  is pivotally connected to the robot arm suspension means  40 . 
     A first pneumatic actuator  3   a  is arranged between the robot arm suspension means  40  and the support means  42 . 
     A second pneumatic actuator  3   b  is arranged between the robot arm  38  and said support means  42 . 
     A third pneumatic actuator  3   c  is arranged between the robot arm  38  and the robot arm suspension means  40 . 
     Furthermore, the robot arm  38  is connected to the suspension means  40  via a pivot means  44 , including a tubular member  47 , movable about a pair of hinge members  46   a,    46   b,  the tubular member  47  forming a substantially horizontal axis A-A, and furthermore via said third pneumatic actuator  3   c  connected to the tubular member  47  of the pivot means  44 . 
     The first, second and third pneumatic actuator  3   a,    3   b,    3   c  could be connected to a common control means (not shown) or separately to its own special control means  22 ,  37  (not shown). 
     OPERATION 
     Of course it is very important that service personnel inside the robot area or an animal to be milked do not run the risk of a hit with the robot arm. If the risk of an abnormal motion of the robot arm for any reason come into existence, the invention prevent such an undesired motion by the described protection device. 
     Thereby either the service personnel or the animal get a hit from the robot arm in case of a malfunction. 
     An animal to be milked, such as a cow, wish undoubtedly to evacuate the milking robot if a malfunction arises. The safety function according to the invention could be connected to a release function and a grid opening function. 
     Subsequently, the grid of the milking robot will be opened if an abnormal movement of the cow arises. 
     The safety function according to the invention could furthermore be associated with an alarm function if a malfunction come into existence or if a risk of an abnormal motion of the robot arm for any reason come into existence. 
     The arrangement according to the invention implies two parallel protection systems, of which at least one first control system is included in the software and at least one second differential pressure control system is included in the hardware, i.e. respectively the control unit system and the protective pressure control unit system. 
     This implies that if one protection system would be out of order and at this very moment an accidental movement of the piston arises, the other protection system still would correct this fact. 
     By means of the arrangement with the differential pressure transductor the action is performed in a very quick response compared with known protection devises. 
     Even though the invention was developed for milking machines the device according to the invention has a number of other applications where pneumatically controlled pistons are involved.