Abstract: The object of the present invention is to provide a nozzle gate opening and closing timing adjusting mechanism used for multiple gate injection molding machine.

Abstract: An injection control apparatus includes an injection member; a drive section for injection; an injection-speed detection processing section which detects injection speed; an injection-pressure detection processing section which detects injection pressure; and a drive control processing section which drives the drive section for injection on the basis of the injection speed and the injection pressure to thereby perform pressure control before start of charging of a molding material into a cavity, and speed control after the start of charging of the molding material into the cavity. Since the drive section is driven on the basis of the injection speed and the injection pressure such that pressure control is performed before start of charging of a molding material into a cavity, and speed control is performed thereafter, the pressure of the cavity after the molding material has entered the cavity becomes stable and uniform.

Abstract: Disclosed is an injection moulding machine, comprising an extruder for continuously producing a melt of a desiccant-filled polymer; at least one injection device fluidly connected with the extruder by a first conduit to receive melt and including an injection ram movable to a forward position for injection of melt into an injection mould and a rear position for introduction of melt into the injection device; characterized in that the injection moulding machine further comprises a sensor which allows determination of the viscosity or melt flow index of the desiccant-filled polymer. Further disclosed is a method of operating such a compounder-type injection moulding machine.

Abstract: An actuator for a hot runner has a piston and a valve pin holder threadably connected to the piston. The piston can be translated by fluid pressure and rotated by an electric motor. The valve pin holder is rotationally fixed, and therefore moves along the thread when the piston is rotated. A valve pin connected to the valve pin holder moves in response to fluid pressure and also in response to the electric motor rotating the piston.

Abstract: Thermoplastic polymers, rubbery polymeric components and reinforcing fillers are mixed and heated to a range of 380° F. to 440° F. The resulting mixture is then fed into a BANBURY mixer, with the resulting mixture fed into a diverter feeding two molds. The velocity of the piston of each mold being filled is controlled to thereby control the density of the molded product along its length (BANBURY is a registered trademark of Farrel Corporation). As each mold is filled, it is deposited in a cool water bath (50° F.–60° F.) while the next mold is being filled. The molds are sequentially transferred to an air cooling rack to complete the process. A texture, generally comprising indentations perpendicular to the longitudinal axis on the molded object, provides a frictional surface between the railway crosstie and the ballast beneath the crosstie.

Abstract: The invention is a pressure reducing valve for reducing the pressure supplied to a head tooling hydraulic positioning valve and a controller for bypassing the pressure reducing valve in a blow-molding machine. A pressure-reducing valve and electrical controller are used to regulate the pressure of a cylinder that controls the position of a head tooling pin and die assembly in a blow-molding machine. The invention reduces pressure during all time intervals except during a “parison formation” interval of the cycle. The invention is also a process for regulating the pressure of a cylinder that controls the position of a head tooling pin and die assembly in a blow-molding machine and for bypassing the pressure reducing valve in a blow-molding machine.

Abstract: A process for producing physically foamed injection molded articles is provided. The process involves feeding a propellant-free thermoplastic melt into a cavity followed by delivering a physical propellant directly into the cavity or directly into the melt flowing into the cavity. The pressure exerted on the propellant during the injection stage is greater than that exerted on the propellant during the holding phase.

Abstract: The invention provides an injection molding method comprising supplying a gas into a molten resin in a plasticizing cylinder and injecting the molten resin having the gas dissolved therein, wherein when the resin is being plasticized, a gas space with a predetermined gas pressure is formed within the plasticizing cylinder in a gas supply section and the pressure at the front end of the screw is adjusted to be at least equal to the gas pressure in the gas space and within a range where the gas space can be maintained within the plasticizing cylinder in the gas supply section. According to the invention, the necessary amount of gas can be dissolved in the molten resin with good reproducibility in a quantitative manner.

Abstract: Device and process for injection molding of molded parts made from plastic material having at least one cavity, which has means for injecting plastic melt into the cavity of an injection-molding die along a melt flow path and means for injecting a fluid into the still molten plastic material, wherein the means for injecting a fluid are designed in order to inject a liquid at preset pressure and preset quantity. Provision is made in that the means for injecting a liquid includes a first part element, which is arranged centrally and remote from the injection-molding die and supplies at least one injection-molding die, and includes at least one second part element, which is arranged in the immediate vicinity of the injection-molding die, and a third part element, which is arranged locally on the injection-molding die at least during injection of the liquid.

Abstract: A method of manufacturing a molded article from a settable mixture includes the steps of in-taking a plurality of components into a plurality of separate material discharge containers sized relative to each other to provide the required mix ratio of the settable mixture. The components contained in the material discharge containers are discharged to a mold tool through a mixing head that receives each of the components separately and thoroughly mixes them into the settable mixture. The settable mixture flows from the mixing head to fill the mold tool. The mold tool rotates about an axis during the filling step to evacuate air from the mold tool. Pressure of the settable mixture is monitored during the filling step and rate of discharge of the settable component is varied in response to changes in pressure of the settable mixture.

Abstract: A multi-cavity injection molding method and device, and a controller for sequentially injecting material into cavities in the injection molding device. The methods and devices are effective to reduce the clamping force needed to clamp multiple cavity molds.

Abstract: A pair of hoses connects directly from the feed pumps to the extruder without utilizing a PCV (pressure compensating valve). Each feed unit has automatic air pressure relief through a solenoid valve on top of the feed unit so that the unit does not stall at full static line pressure. When the dispense valve at the extruder is shut off, air pressure to the air motor is dumped. A pair of electric eyes is utilized—the first signals the pump (by providing pressurized air) to provide pressure while the second actually opens the extruder when the article to be coated comes into position. The first valve is located only a short distance ahead of the second valve so that the line pressure does not have a chance to exceed the dynamic pressure before the extruder opens.

Abstract: An injection molding system includes a manifold and a valve gated hot runner nozzle. The gating mechanism includes an actuated valve pin, where the mold gate orifice is open when the valve pin is in a first position to allow melt to flow there through. The mold gate orifice is closed when the valve pin is in a second position to prevent melt from flowing there through. A first flow control surface is disposed on said valve pin within the melt channel of the nozzle. The first flow control surface has a complementary geometry with that of the melt channel at a second flow control surface. The valve pin is raised and lowered to a lesser degree than that required to seat and unseat the valve pin head to constrict or release the flow of a melt stream in the melt channel.

Abstract: An apparatus comprising a die having at least one application slot. The slot is in fluid communication with a die cavity. An expansible chamber device is disposed within the die cavity and changes volume in response to changes in pressure within the expansible chamber device. Another aspect of the invention is a method of translating a liquid through a die. A coating die is provided. The die comprises at least one applicator slot in fluid communication with a die cavity. An expansible chamber device is disposed within the cavity. The expansible chamber device is actuated by changes in the fluid pressure within the expansible chamber device. The liquid is translated through the die and delivered from the application slot at intervals corresponding to actuation of the expansible chamber device. Another aspect of the invention is a method for forming a die. An apparatus comprising a die having at least one applicator slot in fluid communication with the die cavity is provided.

Abstract: An injection molding apparatus and method are provided in which the rate of material flow during an injection cycle is controlled. According to one preferred embodiment, an injection molding apparatus is provided that includes a manifold, at least one injection nozzle coupled to the manifold, an actuator, and a valve pin adapted to reciprocate through the manifold and the injection nozzle. The valve pin has a first end coupled to the actuator, a second end that closes the gate in a forward position, and a control surface intermediate said first and second ends for adjusting the rate of material flow during an injection cycle. Retracting the valve pin tends to decrease the rate of material flow during the injection cycle and displacing the valve pin toward the gate tends to increase the rate of material flow during the injection cycle.

Abstract: A system for generating a simulation of fluid flow in an injection molding process carried out by an injection molding machine having an injection unit for injecting the fluid into a manifold delivering the fluid to at least two injection ports leading to one or more cavities of one or more molds. The system comprises one or more programs containing a set of instructions that generate a calculated property, state, position or image of the fluid flowing into or through each cavity, the one or more programs using one or more variable inputs that are representative of one or more selected properties, characteristics or operating parameters of the machine or the fluid. The variable inputs include at least a first value indicative of a first fluid flow rate downstream of the injection unit leading to or through a first injection port and a second value indicative of a second fluid flow rate downstream of the injection unit leading to or through a second injection port.

Abstract: In an injection molding machine having upstream and downstream channels communicating with each other for delivering fluid material to one or more mold cavities, apparatus for controlling delivery of the melt material from the channels to the one or more mold cavities, each channel having an axis, the downstream channel having an axis intersecting a gate of a cavity of a mold, the upstream channel having an axis not intersecting the gate and being associated with an upstream actuator interconnected to an upstream melt flow controller disposed at a selected location within the upstream channel, the apparatus comprising a sensor for sensing a selected condition of the melt material at a position downstream of the upstream melt flow controller; an actuator controller interconnected to the upstream actuator, the actuator controller comprising a computer interconnected to a sensor for receiving a signal representative of the selected condition sensed by the sensor, the computer including an algorithm utilizing a v

Abstract: Method of making a proximity probe including providing a preform having an interior cavity accessible by an opened rearward end; coupling a coil to the preform proximate a forward most end of the preform for defining an assembly; locating a single support pin through the rearward end such that the support pin extends within the interior cavity while having an end emanating from the rearward end; cantilevering the emanating end between an upper and a lower mold plate defining a mold cavity for supporting the assembly; injecting moldable material into the mold cavity for molding an encapsulation of material over the assembly for defining an encapsulated probe tip, allowing the encapsulated probe tip to cure; removing the encapsulated probe tip from the mold cavity; removing the support pin from the assembly, and coupling a cable to the encapsulated probe tip for forming the proximity probe.

Abstract: In an injection molding machine, an apparatus for controlling delivery of a fluid material to mold cavities of selectively variable size, shape, volume or configuration, the apparatus comprising a modular mold mounting mechanism having mounting apertures for receiving first and second molds having first and second mold cavities of different size, shape, volume or configuration, the mounting apertures being adapted for ready insertion and ready removal of the first and second molds; a manifold into which fluid material is injected, the manifold having first and second fluid delivery channels through which the fluid material is injected, one channel having an exit aperture communicating with a gate to the cavity of one mold, the other channel having an exit aperture communicating with a gate to the cavity of the other mold; each channel being associated with a drive mechanism which is interconnected to and controls operation of a fluid flow controller which varies flow of the fluid material through an associate

Abstract: An injection molding apparatus, system and method are provided in which the rate of material flow during the injection cycle is controlled. According to one preferred embodiment, a method of open-mold purging is provided in an injection molding system including a manifold to receive material injected from an injection molding machine. The method includes the steps of selecting a target purge pressure; injecting material from the injection molding machine into the manifold; and controlling the purge pressure to substantially track the target purge pressure, wherein the purge pressure is controllable independently from the injection molding machine pressure.

Abstract: The invention provides an injection molding method comprising supplying a gas into a molten resin in a plasticizing cylinder and injecting the molten resin having the gas dissolved therein, wherein when the resin is being plasticized, a gas space with a predetermined gas pressure is formed within the plasticizing cylinder in a gas supply section and the pressure at the front end of the screw is adjusted to be at least equal to the gas pressure in the gas space and within a range where the gas space can be maintained within the plasticizing cylinder in the gas supply section. According to the invention, the necessary amount of gas can be dissolved in the molten resin with good reproducibility in a quantitative manner.

Abstract: An injection molding apparatus and method are provided in which the rate of material flow during an injection cycle is controlled. According to one preferred embodiment, an injection molding apparatus is provided that includes a manifold, at least one injection nozzle coupled to the manifold, an actuator, and a valve pin adapted to reciprocate through the manifold and the injection nozzle. The valve pin has a first end coupled to the actuator, a second end that closes the gate in a forward position, and a control surface intermediate said first and second ends for adjusting the rate of material flow during an injection cycle. Retracting the valve pin tends to decrease the rate of material flow during the injection cycle and displacing the valve pin toward the gate tends to increase the rate of material flow during the injection cycle.

Abstract: A system for injection moulding of large plastics components in a single shot comprises an extruder and an accumulator fed from the extruder The accumulator leads into the mould (14) via a mould valve (12) opive, when closed, to close the mould cavity substantially at the mould surface and also to close an outlet (20a) from the accumulator. The valve passage of the mould valve is of relatively large cross-section, typically several centimetres or more which facilitates injection at relatively low pressures and also facilitates passage of stones and other particulate matter which may be present if the extrudate is composed of post-consumer recycled plastics.

Abstract: In the proposed method of molding toothbrushes, a mold with relatively movable mold parts (14, 16) defining at least one molding cavity (20) corresponding in shape to a toothbrush body is used. One of the mold parts (16) has a brush head defining cavity portion with a plurality of holes (24) for partial penetration into the cavity portion of a like number of fiber tufts. Plasticized molding material is injected under pressure into the cavity (20). Pressure within the cavity is sensed during the injecting step. The injection is stopped when the pressure within the cavity exceeds a predetermined pressure value, thereby avoiding any leakage of molding material through the holes (24).

Abstract: An injection assembly for an injection moulding machine, comprising a screw (2) mounted in a plasticising cylinder and an injection piston (8) which moves the screw (2) in the longitudinal direction and which is mounted in an injection cylinder, wherein there is provided a supply conduit for the injection cylinder having a control valve (13) which can be shut off and there is provided an additional conduit (14) which bypasses the control valve (13) and in which are arranged a device (17) for reducing the amount of the pressure fluid flowing to the injection cylinder (7) and possibly a device (16) for reducing the pressure.

Abstract: According to this invention, there is provided a molding method and apparatus which increase the gas permeation speed in obtaining a foamed resin molded product by letting a gas permeate a molten resin material.

Abstract: The present invention is directed to feeding steam, which is let out of a stream outlet, into the conditioning stage of an installation for boiling extrusion of products. In the installation according to the invention, a connecting line is provided from the aforementioned steam outlet to a predetermined point on the conditioning stage.

Abstract: A process and apparatus for fabricating a colorful three-dimensional object in accordance with a computer aided design (CAD) image of the object.

Abstract: An injection molding method and apparatus in which an injection molding metal mold having a valve gate 7 mechanically opening and closing a gate facing an injection molding cavity is used, and the timing of closing the valve gate is set with reference to a melted resin pressure in the injection molding cavity during a holding pressure step in a molding process. The molding method and apparatus result in high accuracy molded products by utilizing a valve gate system in the injection molding of thin products, and also result in molded products having less variations among cavities even in the case where a plurality of products are molded at the same time.

Abstract: A method of injection molding for use with an injection molding machine includes: a) generating pressurized gas and pressurized moisture within molten plastic as plastic pellets are plasticized in the injection molding machine, the pressurized gas and the pressurized moisture having a total pressure defining an internal counterpressure within the molten plastic; (b) pressuring air within a cavity of a mold in the injection molding machine to an air pressure level which is substantially equal to the internal counterpressure in order to counterbalance the internal counterpressure as the molten plastic is injected into the cavity, thus providing a substantially pressure balanced molding environment for the plastic; and (c) maintaining the air pressure level in the cavity substantially constant as the molten plastic is injected into the cavity.

Abstract: A supply of pressurized gas is separated into a first quantity of pressurized gas at a first temperature and a second quantity of pressurized gas at a second lower temperature. The first and second quantities of gas are injected into molten plastic in an injection mold in a predetermined sequence to form a hollow molded plastic article. A controller independently controls the pressure and time of delivery of the first and second quantities of pressurized gas supplied to the mold. A third quantity of extremely lower temperature gas may also be supplied to the mold in a timed sequence with the first and second quantities of gas. A variable pressure regulator receives stored pressure signals from the controller and establishes the pressures of the first, second and the optional third quantities of gas independent of each other.

Abstract: A method of granulating synthetic resin by extrusion and an apparatus thereof by which a large quantity of pellets can be effectively produced is provided. A plurality of sets of granulating sections are connected with an end of an extruder in parallel. The plurality of sets of granulating sections are simultaneously and independently operated for granulation in a normal operation. When one of the sets of granulating sections is stopped, the other set may still operate for granulation.

Abstract: A method of injection molding for use with an injection molding machine (10) includes: (a) generating pressurized gas and pressurized moisture within molten plastic as plastic pellets are plasticized in the injection molding machine (10), the pressurized gas and the pressurized moisture having a total pressure defining an internal counterpressure within the molten plastic; (b) pressuring air within a cavity (30) of a mold (22) in the injection molding machine (10) to an air pressure level which is substantially equal to the internal counterpressure in order to counterbalance the internal counterpressure as the molten plastic is injected into the cavity (30), thus providing a substantially pressure balanced molding environment for the plastic; and (c) maintaining the air pressure level in the cavity (30) substantially constant as the molten plastic is injected into the cavity (30).

Abstract: An extruding apparatus for intermittently supplying a predetermined quantity of highly viscoelastic material, e.g. food material. The apparatus has a hopper having a supply pump, a supply pipe having one end connected to the pump and the other end to an extrusion valve, and an accumulator (constant pressure device) mounted to the extrusion valve for maintaining the pressure of the food material in the extrusion valve at a predetermined constant pressure.

Abstract: A method of injection molding for use with an injection molding machine includes: (a) generating pressurized gas and pressurized moisture within molten plastic as plastic pellets are plasticized in the injection molding machine, the pressurized gas and the pressurized moisture having a total pressure defining an internal counterpressure within the molten plastic; (b) pressuring air within a cavity of a mold in the injection molding machine to an air pressure level which is substantially equal to the internal counterpressure in order to counterbalance the internal counterpressure as the molten plastic is injected into the cavity, thus providing a substantially pressure balanced molding environment for the plastic; and (c) maintaining the air pressure level in the cavity substantially constant as the molten plastic is injected into the cavity.

Abstract: An apparatus for pelletizing a polymer melt, in which the polymer melt to be pelletized is divided in a housing of a pelletizing device into at least two part-streams, which are deflected and fed to at least two die plates which are spatially separate from one another and are heatable, whereupon the polymer melt streams are transformed into pellets by the cutting devices downstream of the die plates and are post-treated by means of a cooling medium.

Abstract: It is proposed that a pressure control device and/or pressure regulating device (8) be used for a fluid medium, in particular air or gas, preferably nitrogen, which is to be supplied to an injection mold in addition to the molten plastic, this pressure control device and/or pressure regulating device (8) being provided as a stationary, but preferably as a mobile unit between a pressure generator/pressure accumulator (7) and an injection system associated with the injection mold (3), e.g., in a nozzle head or add-on building block.

Abstract: An adaptive controller is provided for controlling the transition, in an injection molding apparatus, from the injection stage to the packing stage. The controller operates by controlling the velocity of the ram during the injection stage, and controlling the ram pressure during the packing stage. The controller anticipates the transition from the injection stage to the packing stage by monitoring the ratio of pressure to velocity. The divergence of this ratio forecasts the onset of the packing stage. At this time, a pressure relief valve is preset in anticipation of the packing stage, to prevent a pressure spike during the transition period. The flow control valve is held constant during the transition.

Abstract: Disclosed herein is a molding apparatus comprising a mold member at least partially defining a mold cavity including a vent, a valve comprising a valve housing including a bore having a central portion with first and second axially opposite ends, a first end portion communicating with the first end of the central portion and with the vent, and a second end portion communicating with the second end of the central portion, a vent discharge port, and a flushing discharge port, and a conduit including an inlet port communicating with the first end portion of the bore, an outlet port communicating with the second end portion of the bore, and a valve member located in the bore and being operably moveable between a venting position wherein the vent communicates with the conduit inlet port, wherein the conduit outlet port communicates with the vent discharge port, wherein communication between the flushing medium outlet port and the conduit inlet port is blocked, and wherein communication between the conduit outlet p

Abstract: A machine for producing extruded products of polymers that are cross-linked by adding at least one additive in a polymerization reaction. A feed hopper for plastic granules is coupled to a mixing container which is formed with side ports to admit the desired additives. Mixing is accomplished in a mixing container and the mixed ingredients are fed to an extruder.

Abstract: For the extrusion of a calibrated profile of a thermoplastic polymer onto articles, the polymer, which is melted in an extruder (17), is fed, via a heated pressure hose (22), to an extruder head guided by a robot (5) and, by means of said extruder head, extruded and deposited on the article. At the end of each extrusion operation, the material flow to the extruder head is maintained and, by means of a change-over valve within the extruder head, redirected into an outlet orifice provided in the vicinity of the die orifice until the commencement of the subsequent extrusion operation. The redirected material flow emerges from a pipe connector (29) which is arranged on the extruder head and is coupled to a coupling piece (33). The material collected in this manner may be pelletized and fed back to the feed hopper (16) of the extruder (17).

Abstract: An injection molding apparatus particularly usable for low pressure structural foam molding with improved control device for providing adjustment and controlling relative positioning between the injection molding apparatus and the mold. A novel device is included for adjusting the nozzle body with respect to the injection molding apparatus and for adjusting the nozzle rod with respect to the nozzle body. An improved device is also included for facilitating adjustment of injection stroke length and of the position of the nozzle body as well as automatic adjustment of positioning of limit switches responsive to indicate the extremes of movement during the cyclical injection stroke. Automatic and manual devices are also included for maintaining alignment between the nozzle rod and the nozzle body extending therearound.

Abstract: An hydraulic control circuit for an injection molding machine feedback-controls the operations of an injection cylinder by connecting an hydraulic source and an oil tank to a hydraulic actuator through a plurality of servo valves. The plurality of servo valves, such as four-port servo valves, are connected in parallel and a servo valve control function unit is used which controls the servo valves preferentially to the feedback control to permit series or parallel control of the servo valves. Thus, even when the specifications of an injection molding machine require a larger size and higher speed, the size of the injection molding machine is prevented from increasing, the cost is decreased, the response speed and the stability are remarkably improved, and fine control is realized over a wide control range.

Abstract: A method and an apparatus for applying afterpressure on injection molding compounds, particularly PET compounds in an injection molding machine including an injection mold and a screw connected to the injection mold through supply ducts. The injection molding material is conducted to the mold cavity by the screw in order to fill the injection mold. After the filling procedure has been concluded, the material flow is cutoff in the vicinity of the screw opening. During the phase of material shrinkage, the loss of volume is compensated by additionally conveying material present in the supply duct between the screw and the mold cavity. After cooling of the injection molding material, the continuous material flow of injection molding material into the mold cavity is separated from the material flow in the supply duct.

Abstract: Upstream of a distributor at which flow from an actuator is fed to the shaping orifices for the production of plastic extrusions and downstream of the extruder producing the stream of plastified plastic, a rotary adapter having a displacement body subdividing its cross section into asymmetrical partial cross sections is provided so that, upon deviation of a property of the extrusions from a desired value, the adapter can be rotated to compensate.

Abstract: A non-return valve (10) primarily for use with an injection molding machine utilizes a frame (12) which surrounds a first bore (34) and a second bore (32). The second bore (32) is accessed by inlets (30). Outlet passages (40) are located downstream of said inlet (30) and connect second bore (32) with an accumulation area (6). A piston (60) is dimensioned to slidably fit within the first bore (34) and extend into the second bore (32). In a downstream position, the piston (60) allows positive flow of material from the inlet (30) to the outlet (40). In an upstream position, the piston (60) positively blocks flow of material from the inlet (30) to the outlet (40). The piston (60) can be forced to its upstream position at the beginning of the injection step or can be preclosed by eliminating rearward movement prior to injection.

Abstract: A method of injection molding for use with an injection molding machine includes: (a) generating pressurized gas and pressurized moisture within molten plastic as plastic pellets are plasticized in the injection molding machine, the pressurized gas and the pressurized moisture having a total pressure defining an internal counterpressure within the molten plastic; (b) pressuring air within a cavity of a mold in the injection molding machine to an air pressure level which is substantially equal to the internal counterpressure in order to counterbalance the internal counterpressure as the molten plastic is injected into the cavity, thus providing a substantially pressure balanced molding environment for the plastic; and (c) maintaining the air pressure level in the cavity substantially constant as the molten plastic is injected into the cavity.

Abstract: A parison molding method and its apparatus in which at least two kinds of materials are used, and the layer formation and dispersion are uniform in the weld part and in the circumferential direction. In the parison molding method and its apparatus, molten resin at a weld part within a parison head is discharged out of the parison head by way of a flow control valve.

Abstract: An installation is provided which has a press-through surface containing openings (13) and pressure elements (14) for pressing goods through the openings (13). According to the invention, the size of the openings (13) is variable in the installation. Preferably, this is effected in that opposite edges of the openings (13) are movable with respect to one another counter to the action of restoring elements (19). In this context the size of the openings (13) can be determined by the pressure exerted by the pressure elements (14). Preferably the press-through surface (12) is made up of segments (17), which delimit the openings (13).

Abstract: An electro-mechanical-hydraulic drive mechanism (10) for moving a lead (11) relative to a support (12) includes an electric motor-driven element (14) and a hydraulic reaction element (15). The two elements are arranged mechanically in series between the lead and the support. The motor-driven element may be operated independently of the reaction element to move the lead relative to the support when the reaction element is held at a fixed displacement. The two elements may be operated cooperatively to move the load when the motor-driven element is operated at a controlled velocity to pressurize the reaction element, and the reaction element is operated by controlling its pressure.