Abstract: Method for controlling the processing and output feeding of plastic melt by extrusion, by means of an extrusion plant including a process unit (1) for processing the plastic material, a pump (3) for feeding the plastic melt to a die (4) or the like, and a screen pack assembly positioned between the process unit (1) and the pump (3). In the process unit (1) the melt is imparted a constant level of kinetics of extrusion, and the plastic melt pressure (P2) between the screen pack assembly (2) and the pump (3) is kept above a predetermined level. As a measure of the level of kinetics of extrusion, the pressure (P1) of the melt between the process unit (1) and the screen pack assembly (2), is used, preferably in combination with the melt pressure (P2) after the screen pack assembly (2).

Abstract: An apparatus for monitoring the curing of a fiber reinforced composite plastic which is cured at temperatures of the order of 350.degree. C. and an ultrasonic transducer assembly useful in the apparatus. The transducer assembly comprises a lithium niobate piezoelectric element having anisotropic coefficients of thermal expansion which is mounted on a metal base of the transducer assembly by means of a layer of structured copper. The structured copper is thermo-compression diffusion bonded to the lithium niobate element and to the metal base, and is compliant in a transverse direction to compensate for differential thermal expansions while affording good electrical and thermal conductivity and good acoustic coupling between the lithium niobate element and metal base.

Abstract: A process and apparatus for marking an article made of foam material whenever during its manufacturing process some irregularity has occurred. As a consequence of having ascertained an irregularity in some operational parameter, after the introduction of the reactive mixture in the inner cavity of the lower shell of the mould and as long as the mould is still open, to a part of the inner cavity of the upper shell of the mould is applied a mark formed by a dyestuff resistant to the processing conditions, physically and chemically compatible with the formed article and capable of adhering thereto when, during its expansion, the article reaches to contact the marked part of the inner cavity of the upper shell of the mould. The marking operation can take place automatically by action of an equipment comprising an ejector arranged for spraying towards the internal cavity of the upper shell of the open mould the dyestuff intended to form the mark.

Abstract: An apparatus for forming an egg roll. A sheet of dough is placed on a conveyor belt, with a corner of the dough pointed in the direction of movement of the belt. An egg roll filling is placed on the dough with the filling extending transversely to the direction of movement of the conveyor belt. The leading corner of the dough is reversely folded over and around the upper surface of the filling by a deflector. The dough is creased along its length of movement on both sides immediately outwardly of the ends of the egg roll by O-ring belts guided about pulleys. The opposite corners of the dough, which extend transversely to the direction of movement of the conveyor belt, are folded about the creases inwardly over the filling and the opposite corners of the dough are pressed downwardly toward each other by belts which gradually bend from a horizontal support surface to an inwardly inclined belt surface. The corners of the dough are pressed to their final positions by disks.

Abstract: Control apparatus for an injection molding machine having a sensor provided for the injection molding machine for producing a signal representing the quality of the molded product or a molding condition of the injection molding machine, a set value memory device in which a permissible range of the signal is set, a judging member for judging as to whether the signal lies in the permissible range, a production lot data memory device containing control data for the injection molding machine with respect to a lot now being produced, and a destination table showing a destination of the data corresponding to a result of judgment of the judging member, a controller for controlling the injection molding machine in accordance with the control data stored in the production lot memory device, and another memory device for storing a plurality of sets of the production lot data regarding various lots or production conditions, and a storing device for determining a destination of the production lot data based on the result

Abstract: A method and apparatus for the manufacture of a diaphragm from a fabric-containing sheet (material). The fabric-containing sheet produced by an extrusion molding machine in a width which is a multiple of the diameter of diaphragms to be manufactured is continuously fed in fixed pitches to a press vulcanizing device and an punching device, to permit automation of the manufacture of diaphragms and an appreciable reduction in the number of steps. This method, thus, improves the yield of materials used, permits down sizing of the production equipment, and reduces the motive power consumption.

Abstract: Forming an optical fiber so as to have a relatively constant bend loss characteristic includes apparatus for continuously bending the optical fiber downstream from a preform from which it is drawn and continuously detecting light withdrawn from the fiber at the bend so created to determine the fiber bend loss characteristic, the fiber bend loss characteristic being maintained constant by using feedback control to vary a drawing speed of the fiber and hence a diameter of a core of the fiber.

Abstract: Disclosed are processes and apparatus utilizing, choke means at least partially providing restriction to passage of material and measurement of magnitude of force(s) exterted on said choke means by passage of material, to provide: (1) an indication of characteristics of the material, and/or; (2) control of said passage of material and/or control or processes or apparatus associated with said passage of material in response to the magnitude of the measured force(s).

Abstract: An extrusion apparatus includes a housing having parallel top and bottom surfaces and a converging portion and a cooperating diamond-shaped flow bar for aligning fibers during extrusion of a meat dough. The flow bar is disposed in the housing such that trailing faces of the flow bar are parallel to the converging faces of the apparatus and the leading faces of the flow bar converge with the parallel faces of the housing and are spaced therefrom a distance to effect fiber alignment. The flow bar is rotatably mounted within the housing to control and vary the extent of fiber alignment as desired. A discharge nozzle is provided having a constricted portion tapering longitudinally and transversely toward the center of the nozzle to ensure fiber alignment throughout the width of the extruded dough. The extruder is able to effect substantial fiber alignment across a wide extrudate such that when cut into individual pieces, each piece will have a substantial portion of fibers uniformly aligned.

Abstract: An automatic control for an extruder has a temperature sensor which monitors the exit temperature of the extrudate and several pressure transducers which monitor the pressure within the extruder to control the cooking of the mash inside the extruder to ensure production of high quality extrudate. The controller monitors and controls the temperature and moisture content of the mash in the extruder by controlling the input of various ingredients and also the cooling or heating of the mash near the exit of the extruder through a heat exchanger.

Abstract: A method and apparatus for machining dough that takes into account the different flow regimes exhibited by the dough during processing. As in conventional systems, the apparatus includes a hopper for extruding dough in a sheet and pairs of powered rollers for sizing the sheet. A computer controls the system. Mass flow rate is made constant throughout the system by establishing a master flow rate based upon predetermined criteria related to the product being produced, and the computer monitors the weight of the extruded sheet to maintain a constant input to the powered rollers. The flow rate is varied to remain constant by comparing the input to output, as measured by the sheet thickness at the cutter station. The gage rollers are controlled by setting a nominal roller speed, trimmed according to the tension present in the sheet upstream of the gage roll, as reflected in the position of a loop in the dough sheet between the gage roll and the pair of rolls immediately upstream of same.

Abstract: In apparatus for measuring injection speed of a die cast machine, there are provided a pulse generator responsive to a movement of an injection plunger for producing a pulse signal, a detector for detecting a width of the pulse signal to produce pulse width data, a memory device successively storing the pulse width data between commencement and termination of injection, and an arithmetic operation circuit for calculating an average speed in a predetermined high speed section of a stroke of the injection plunger based on pulse width data stored in the memory device.

Abstract: A toggle-type die-fastening apparatus has a movable platen that carries one mold part and is supported by and guided along a plurality of tie bars whose one ends are fixed to a fixed platen on which another mold part is mounted. The other ends of the tie bars are supported by a toggle support, and a toggle mechanism is disposed between the toggle support and the movable platen for pressing the mold part carried by the movable platen against the mold part mounted on the fixed platen. A die-fastening force adjusting nut is threaded onto the end portion of each tie bar that is closer to the toggle support so as to bear the reaction of the die-fastening force generated by the toggle mechanism. An adjusting cylinder is formed in this portion, and it is connected to a hydraulic circuit so that the pressure within each of the cylinders is controlled by a pressure adjusting valve in such a manner as to correspond to a die-fastening force set by a setting device.

Abstract: A hot press device has a pair of hot press rollers for heating and pressing a treatment object therebetween while rotating, and pairs of delivery rollers are arranged before and after the pair of hot press rollers. The treatment object passes back and forth through the pair of hot press rollers, and a controller controls the delivery rollers so that the circumferential speeds of the respective delivery rollers located downstream in the forward or reverse passing direction of the treatment object can be increased.

Abstract: A vibrating type concrete pipe making machine, in which very high frequencies of vibration and large inputs may be attained without excessive wear on the mold or shortened bearing life. It also includes lubricant and coolant systems which are combined into a single system.

Abstract: A method and apparatus for controlling back pressure in an injection molding machine. Forward and backward movements of an injection plunger are converted into rotational motion and the turning force and back pressure of the injection plunger during the step of charging material are controlled. An electric motor serves for carrying out back pressure control and a torque limiting control function is performed to limit the output torque of the motor according to the magnitude of a set value of back pressure.

Abstract: In an injection molding apparatus using a motor as a driving source, the injection speed and the injection pressure are controlled via a speed sensor, a pressure sensor and a closed loop control system, to provide higher accuracy and better operability during switching of the apparatus from an injection speed control phase to an injection pressure control phase and thereafter to a back pressure control phase.

Abstract: A method of injection molding thermoplastic material from an injection molding machine including a slidable screw into a mold whose optimum pattern of the injection rate has been determined on and is known for another injection molding machine. The method includes transferring the defined optimum characteristic values for a first injection molding machine onto a second injection molding machine. The known optimum injection flow rate pattern (V.sub.A) of a previously used first injection molding machine is introduced manually and/or by means of data carriers into a control device of a second injection molding machine to be used. The second injection molding machine is operated with any compatible injection flow rate pattern (V.sub.b), with the resulting injection time (t.sub.Eb) being adjusted to that of the first injection molding machine by means of a multiplicative change of the injection flow rate pattern. Forming an adjustment factor K.sub.V =V.sub.b /V.sub.

Abstract: A numerical control method and an apparatus therefor, in which a mold opening operation or an eject operation is performed during a metering operation so that the injection-molding cycle time is shortened. When a cooling period terminates or mold opening is completed during the metering operation, a programmable machine controller for sequentially controlling an injection-molding machine delivers information specifying a clamp axis or an eject axis, the displacement, moving speed, and moving direction of the axis, and a step feed command to a numerical control unit for controlling servomotors for axes of the injection-molding machine, through a common RAM. Pulse distribution for the clamp axis or the eject axis, based on this information, and pulse distribution for a screw rotating axis are alternately executed by a numerical control unit, which responds to the step feed command.

Abstract: A switching control method which can smoothly effect transfer from a pressure holding step to a metering and kneading step in an injection-molding machine employing a servomotor as an injection shaft driving source for axially driving a screw. At completion of the pressure holding step, follow-up of an error register of a servo circuit driving the injection shaft servomotor is effected so as to bring an error amount accumulated within the error register to zero (steps S6 to S8). A value of torque limit acting on the servomotor is then switched from a set value for pressure holding to a set value for metering and kneading (step S11). Further, the follow-up of the error register is again executed over a predetermined period of time from the time of execution of the switching of the torque limit (step S13). Subsequently, transfer is effected to the metering and kneading step (step S14).

Abstract: A tube container molding apparatus in which a cylindrical tube is inserted into a split mold in its closed state so that the end section of the tube comes into contact with a cavity face of the split mold. A core is then advanced to fit into the tube from its rear end, and finally a resin melt is introduced into the cavity formed by the cavity face of the split mold and the end face of the core.When the resin melt is injected into the cavity, a tube holding piece pushes the tube against the core to prevent the tube from being drawn out of the cavity.Midway during the advance of the core into the tube, the tube is held by the tube holding piece and the further advance of the tube is made together with the core. Thus, the forward end section of the tube is bent inward to a prescribed width.

Abstract: A method for controlling an injection molding machine involving the steps of: detecting, by a screw position detector, a position of a screw of the injection molding machine immediately before the start of injection, to produce a detecting signal; comparing the detecting value with a predetermined value for a plasticizing/measurement position set in a metering position setter, to calculate any deviation therebetween; and adding/substracting the deviation to or from predetermined values representative of switching-over positions set in switching-over position setters, thereby keeping constant an actual screw stroke from the plasticizing/measurement position to the switching-over position for every shot of the injection molding machine.

Abstract: Apparatus for preparing and dispensing thermoplastic resin has a conveyor with a chamber provided with heating elements, a conveyor screw mounted in the chamber and connected to a drive motor, a resin inlet and a resin outlet. To ensure the intended continuous dispensing of the resin even during intermittent operation, a control device is provided having inputs connected to a resin pressure sensor, a conveyor speed of rotation sensor and a resin temperature sensor. Intended values for the conveyor speed, resin pressure and resin temperature are supplied to the control device, which regulates the pressure during interruption of the dispensing of the resin and effects a speed regulation or a pressure regulation with a superimposed speed regulation during dispensing of the resin. For plasticizing of the resin, which is supplied in solid, preferably granular form, and since the conveyor geometry is designed to produce minimum friction, external heating by the heating elements is required.

Abstract: An apparatus for controlling the transportation of cured tires on a tire feed path including a device for supplying a white tire which can be discriminated positively from the cured tires on the tire feed path, a device for placing cured tires on the tire feed path in such an order that the white tire is followed by the cured tires, a photoelectric sensor for detecting the white tire on the tire feed path to generate a reference signal, a memory circuit for storing tire identification signals by means of which the tires have been cured by curing machines, a circuit for reading the tire identification signals out of the memory circuit under the control of the reference signal, and a device for selectively transporting respective cured tires into predetermined paths in accordance with the read out tire identification signals.

Abstract: A molding system including a mold and a molding machine has been adapted to monitor the position of first and second mold surfaces that move relative to each other to form a mold cavity. The system includes a source of gas under pressure and an orifice on a first molding system surface to direct a flow of pressurized gas from the first molding system surface. A monitoring system monitors the condition of the gas remote from the first molding system surface to indicate the spacing between the first molding system surface and an adjacent second molding system surface as the first and second molding system surfaces move with respect to each other.

Abstract: A method and an apparatus for injection control for an injection-molding machine, adapted to perform injection control by means of a servomotor controlled by a numerical control unit, in which the injection control is completed by performing pulse distribution to the servomotor, up to a hold pressure end position, and a follow-up operation when injection-speed control and hold pressure control for individually predetermined times are finished, in order that the injection-speed control and the hold pressure control can be executed in a time-based manner.

Abstract: A suckback method and apparatus is capable of positively effecting a suckback operation in an injection molding machine using a servomotor as an injection axis drive source for axially driving a screw. When the screw reaches a metering completion position, screw rotation is stopped and a follow-up operation for an error register is carried out so that an error amount accumulated in the error register becomes equal to zero (steps S1, S4, S5). Then, a torque limit for the servomotor and for application of back pressure is released (step S8), and the screw is driven backwardly by the servomotor by a predetermined suckback amount (step 11).

Abstract: In a method of controlling a charging speed of an injection molding machine, a molten resin is charged by accumulating the same in a space in a heated barrel and in front of a screw by rotating the screw, the screw is moved rearward by a back pressure produced by the accumulated resin, the screw retracting speed is detected, the detected retracting speed is compared with a reference speed, and the back pressure acting upon the screw is controlled such that the difference between the screw retracting speed and the reference speed will become zero.

Abstract: In an injection molding machine combined with a peripheral apparatus, control units capable of interchanging signals are provided for the molding machine and the peripheral apparatus. Each control unit comprises a memory device storing set molding data applied with numbers or identifications. When the control unit of the molding machine sends the set data number or identification to the control unit of the peripheral apparatus to read out from the memory devices, the set molding data are formed when the numbers or identifications coincide with each other.

Abstract: An article extracting means which is mounted on a carriage means which in turn is slidably mounted on the side of an article forming machine having two members movable relative to one another to form an article between them. A pivoted extractor arm in mounted on the carriage means to pivot in a vertical plane toward and away from the forming machine. An upper portion of the extractor arm carries an independently pivoted arm which may move in the same vertical plane as the extractor arm between at least two 180 degree opposed positions related to positioning gripping members carried thereby between an article gripping and an article release positions. The gripping members feature a construction wherein opposing jaw members are moved in a parallel direction toward and away from one another. One jaw member is actuated in a linear direction which via a rack and pinion arrangement cause the other jaw to move in parallel, but opposing direction.

Abstract: An apparatus wherein there is provided a source of fiber forming material, with said fiber forming material being pumped into a die having a plurality of spinnerets about its periphery. The die is rotated at a predetermined adjustable speed, whereby the liquid is expelled from the die so as to form fibers. It is preferred that the fiber forming material be cooled as it is leaving the holes in the spinnerets during drawdown. The fibers may be used to produce fabrics, fibrous tow and yarn through appropriate take-up systems. The pumping system provides a pumping action whereby a volumetric quantity of liquid is forced into the rotational system independent of viscosity or the back pressure generated by the spinnerets and the manifold system of the spinning head, thus creating positive displacement feeding. Positive displacement feeding may be accomplished by the extruder alone or with an additional pump of the type generally employed for this purpose.

Abstract: An automated system is provided for selectively separating resin pellets having a gel count below a specified maximum from pellets having a gel count above the specified maximum, while the pellets are flowing in a pneumatic conveyor. The separation is based on an essentially continuous measurement in which a laser beam is utilized to detect the number of gels in a film made from pellets withdrawn as a sample stream from the main pellet stream. In response to the gel count measurement, a control signal is established that is utilized to manipulate a diverter valve located in the pneumatic conveyor, which diverts pastic pellet flow between a preferred storage means storing pellets having a low gel count and a secondary storage means for storing pellets having a higher gel count.

Abstract: An apparatus for checking or controlling cross-linking in products made of elastomeric material which is the object of the present invention, comprises a mold of a fixed volume provided with at least one pressure sensor able to detect pressure variations in the mould during cross-linking in order to obtain data referring to the progress of the cross-linking in the case of laboratory applications, while, should the apparatus be used in manufacturing, it can provide an automatic control of the duration of the various stages of the manufacturing cycle by means of microprocessor controlled equipment to which such sensors are connected.

Abstract: An injection molding machine includes a machine bed having a support face and a vertical side wall; a mold closing unit mounted on the support face; an injection molding unit mounted on the support face; a computer; a data display device spaced from the computer accessible by operating personnel in a service location laterally adjacent the machine; and a vertical slide panel mounted on the vertical wall. The vertical slide panel and the vertical wall constitute a partition separating a service zone from a danger zone. A vertical carrier column is supported adjacent the carrier block of the injection molding unit on the vertical wall of the machine bed; and a protective door is supported by the vertical carrier column and is arranged for displacement in a travelling path parallel to the injection axis. The protective door is arranged for shielding a frontal side of the injection molding unit.

Abstract: An apparatus for distributing and metering a granular and sticky mass, in particular a mass to be moulded into biscuits. The apparatus comprises a main conveyor device comprising juxtaposed parallel screws of alternate pitch and direction of rotation, which are sub-divided into groups of at least one pair of screws, a main motor and main transmission means comprising one clutch per group of screws, hoppers which are juxtaposed below the downstream end of the main conveyor device in a ratio of one hopper per group of screws and, beneath each hopper, a distribution column comprising an inlet, a holding chamber and an outlet, the said inlet being provided with a device for measuring the level of filling which is electronically connected to a control device for controlling the clutch of the said group of screws.

Abstract: A rotational molding machine having an oven enclosed by a pivotable top clam shell cover, front entry doors for interior oven access, and a spider arm and drive spindle which is supported by bearing members on opposite walls of the oven for removable mounting thereon.

Abstract: The present invention is directed to the continuous production of microcellular plastic web material having integral unmodified laminar skin. In accordance with the invention a web of plastic material impregnated with an inert gas is delivered continuously to a degassing device in which the degree to which gas diffuses out of the surfaces of the web can be selectively and continuously controlled, whereupon the web enters a foaming station where it is reheated to induce foaming. The temperature of the reheated web and the duration of the foaming process prior to quenching are also selectively controllable to produce the desired web characteristics.

Abstract: In a pelletizing operation in which a synthetic thermoplastic polymeric material is reduced to particulate form, automatic startup of the flow of cooling fluid to the cutting chamber associated with the pelletizing operation is provided so as to insure that the flow of the cooling fluid is started at the time required.

Abstract: Topology body apparatus having an extrusion head for extruding a settable plastic material, a mounting arm on which the extrusion head is mounted, a carriage bar on which the mounting arm is mounted, a base, extrusion head drive means for driving the extrusion head relative to the carriage bar, carriage drive means for driving the carriage bar relative to the base, and control means for controlling the extrusion head, the extrusion head drive means and the carriage drive means, separately and independently from one another, to procure three axes of movement of the extrusion head to progressively extrude and deposit portions of a three-dimensional solid body having a predetermined topography.

Abstract: According to the invention, the dipolar orientation of an object made of material adapted to present piezoelectric properties is obtained by exposing at least one of the faces of the object to a jet of charged microparticles in order to create therein a sufficient electrical field to obtain the said orientation, and in a variant of the invention, a direct polarization is carried out by displacing a film in front of at least one generator of charged microparticles, this invention applying in particular to the production of film in a piezoelectric polymer or copolymer.

Abstract: The present invention discloses a method for determining the level of contamination in electrical cable insulation. This is achieved by extruding the cable insulation about the conductor and simultaneously producing a thin ribbon of the insulation which is then screened via a laser beam for contaminants.

Abstract: A screw extruder comprises a barrel including a section that is supported for rotation about the longitudinal axis of the barrel. A screw extends and is supported for rotation in the barrel; and, in use, rotation of the screw rotates and advances plastic material through the barrel. Rotation of the screw also causes the rotatable barrel section to rotate, and a brake is connected to that rotatable section to maintain the rotational speed of the rotatable section less than the rotational speed of the extruder screw. The rotational speed of the screw relative to the rotatable barrel section controls the relative rates at which plastic is mixed, heated, and pressurized in the barrel.

Abstract: A control method for a granulating apparatus of the type in which a binder liquid is added to powder material having high moisture absorbing properties while fluidizing the powder material thereby producing granules or granular material of a desired particle size. In this control method, the moisture content of powder material to be granulated is continuously detected with a high degree of accuracy by a moisture content detector and in accordance with the detected value the rotation speed of a binder feed pump or the like is adjusted through a moisture content regulator thus varying for example the rate of addition of the binder and thereby controlling the moisture content of the powder material.

Abstract: An injection molding apparatus for automatically presetting parameters of injection conditions by performing trial injection. A time (T0) and an injection quantity (C0) are obtained (step 124), wherein a drive current (I2) of a servo motor (M2) for performing trial injection reaches a drive current (i0, step 123) corresponding to a maximum injection pressure. Parameters (A, B, D) of the injection conditions stored in a memory, are read out in accordance with the detected time (T0) and the detected injection quantity (C0) to automatically set the injection conditions (step 131).

Abstract: A coil section for being excited by a primary ac signal and producing a secondary output signal is provided on the open end side of a bag-cylinder main body. A material consisting of such substance and having such configuration that bring about reluctance change of a magnetic circuit passing through the coil section in accordance with displacement of a piston rod of the bag-cylinder is provided in a predetermined pattern about the piston rod. In a detection circuit, position detection data representing the position of the piston rod is obtained in response to the secondary output signal from the coil section. In a position establishing circuit, stop position data representing a desired position at which the piston rod should be stopped is established depending upon the diameter of a tire to be vulcanized.

Abstract: A method and apparatus for regulating the drive of dosaging devices for the controlled feeding of plastic particles, color concentrates and additives into a supply hopper of a screw extruder for producing a mixed plastic product of determined coloration, comprising periodically measuring the coloration of the mixed product at an outlet of the extruder by a spectrometer connected to a measurement probe, comparing the measured coloration of the mixed product with the coloration of the desired product, and adjusting the supply of the plastic product, concentrates and additives, as necessary, so that the measured coloration of the product at the outlet of the extruder is the same as the coloration of the desired product.

Abstract: Means for polarizing ferroelectric materials up to a predetermined polarization level include the application of an electric field E to these materials. According to this method the ferroelectric material is subjected to an alternating electric field E, the frequency of which ranges from about 0.001 to 1 Hz, and which is made to increase gradually and in a cyclic way between 0.+-.E.sub.N, E.sub.N being slightly in excess of the coercive force E.sub.C of said material. Simultaneously, the intensity i of the current traversing the material (2) is measured as a function of the applied field (E) using a unit of visualization, until a stable curve i=f(E) is attained. The invention is particularly suitable for obtaining a stable polarization of ferroelectric polymers, copolymers, crystals, and polycrystals, with the objective of using the piezoelectric and/or pyroelectric properties of these materials.

Abstract: The thickness of the barrier layer in coextruded multilayer, thermoformable resinous sheet material is controlled by transverse color monitoring during coextrusion of the sheet.

Abstract: In an extrusion process, desired product quality parameters are maintained very accurately by manipulating the rotational speed of the screw associated with the extrusion process so as to maintain a desired ratio of feed rate to drag flow in the extrusion process and by manipulating the feed rate of the material to the extrusion process so as to maintain a desired energy input per unit of the material being processed.

Abstract: A clamp mechanism for selectively locking and unlocking a first member in a first position relative to a second member comprises a linkage system connecting the first and second members and drive means for articulating the linkage system for moving the first member relative to the second member. A fluid link is provided for locking the first member in position relative to the second member wherein the fluid link is actuated upon sensing the first member approaching the first position.