Abstract:
A clamping device includes an expansible polymer that is disposed in a polymer chamber ( 14 ). A heat transfer conduit ( 22 ) transports heat transfer fluid and brings it into thermal conductivity with the polymer. By cooling or heating the polymer as needed, the polymer expands and contracts as it melts and freezes, respectively. The volume change of the polymer is used to advance a piston ( 16 ). The piston is used to engage upon a surface, e.g., clamp a machine part. In this manner, the surface is disposed between the actuated piston ( 16 ) and an immobile plate, causing the surface to become rigidly held in position. When the piston ( 16 ) contacts the surface, pressure builds in the polymer chamber( 14 ), which translates into clamping force on the surface.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the mechanical clamping arts. It finds particular application in conjunction with securing assembly parts in a factory or mill setting and will be described with particular reference thereto. It will be appreciated, however, that the invention is also applicable to other settings and is not limited to the aforementioned application. 
     Mechanical clamps have a very wide range of applications in the manufacturing industry. Generally, application of clamping devices can be divided into three main classes. First, clamps are used to secure parts that are being worked upon, such as machined, formed, stamped, etc. Second, clamps are used to clamp various machine parts into a locked position within a manufacturing tool. Third, clamps are used to position machine tool components for operations they are meant to perform. Some examples of these devices that are generally known as clamps are machine vises, fixture clamps, lathe chucks, tool holders, drill feed units, electrical discharge machining (EDM) electrode feed units, weld wire feed units, and others. 
     One method of clamping which can be generically applied to any of the aforementioned devices is mechanical clamping. These devices include screw clamps, over center cam devices, and wedges. They are manually applied with levers or tools such as socket wrenches or air guns. The manual opening and closing of these clamps creates direct labor and extra mill downtime. Additionally, such workers are at risk for repetitive task related injuries. 
     Hydraulic systems are frequently used to operate clamps. Hydraulic systems have the benefits of being remotely operated, and having very high clamping pressures. However, hydraulic systems have a relatively high failure rate. Leaks, damaged o-rings, fittings, and hoses create situations of long down-times and high repair costs. Leaking hydraulic fluid can be hazardous to those who come into contact with it, making clean-up necessary, and dangerous if not handled properly. Oil leaks from hydraulic systems can contaminate cutting fluids, causing potential health problems when the fluids are vaporized by cutting blades. Moreover, hydraulic systems experience wear when torn down and built up, such as when arranging a shop to machine different goods. If a machine shop changes its output product often, the hardware degrades more quickly. 
     In hydraulic systems, the supply hoses are at pressure when the system is actuated. These stresses on the hoses often cause them to warp and bend in unwanted directions. In an automated mill, such a situation can present a catastrophic problem. If a hose becomes warped such that it gets in the path of an automated mill part, the automated part can tear the hydraulic hose causing loss of clamping force and leakage of hydraulic fluid. Both results present dangerous situations to mill workers. 
     Pneumatic devices are also known in the art as an option for operating clamps. Pneumatic systems are beneficial because production is not halted to repair minor leaks. Typically, pneumatic systems run in shops constantly hiss, and spit, indicative of damaged o-rings and minor leaks. However, pneumatic systems also have their share of setbacks. Noise levels generated by pneumatic systems often exceed OSHA limits. Typical pneumatic systems are low pressure systems not suitable for machining. Pneumatic clamps, as a result can have a compressibility that is undesirable. Moreover, pneumatic systems can release oil-laden air, which is a potential health risk. 
     Electric motors are also known, but are relatively poor for generating a static, clamping force. They are relatively massive, require extensive electronic packages, and are costly to operate. 
     The present invention provides a new and improved method and apparatus which overcomes the above-referenced problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a mechanical actuating system is provided. A housing defines a polymer chamber, piston ports, and thermal medium ports. A volume of polymer is contained within the polymer chamber. A fluid passage extends between the ports. Pistons are disposed in the piston ports. Heat transfer fluid flows through the passage. 
     In accordance with another aspect of the present invention, a mechanical actuation system is provided. A liquid source provides warmer and cooler liquid to a plurality of actuators. Each actuator includes a housing body with fluid ports and a liquid flow path, an interior chamber, and a piston bore in fluid communication with the chamber. A piston is in the chamber. A phase change material is in the chamber, which expands and contracts as it changes phases. A controller controls the liquid source. 
     In accordance with another aspect of the present invention, a method of actuating is provided. A polymer is disposed in a sealed polymer chamber. The temperature of the polymer chamber is varied causing the polymer to expand and contract forcing a piston to stroke. 
     In accordance with another aspect of the present invention, a method of controlling a plurality of pistons in provided. Liquid is warmed and circulated to melt the polymer, and it is cooled and circulated to freeze the polymer. 
     According to another aspect of the present invention, a mechanical actuating device is provided. An outer housing defines a sealed polymer chamber, wherein is located an expansible polymer. A piston responds to expansion of the polymer. The polymer expands in response to a thermal carrier transferring heat into the polymer. A spring applies an opposing force to the force applied on the piston by the polymer. 
     According to another aspect of the present invention, a clamping system is provided. A mechanical actuator includes a piston received in a sliding relationship in a piston bore, a volume of polymer in a polymer chamber, and a heat transfer conduit through which heat transfer fluid flows, adding and removing heat from the polymer. The actuator is attached to a base. The base includes a clamping surface opposite the piston, and a means of securing the actuator in position. The base is secured to a stationary surface. A power supply supplies heat transfer fluid to the actuator. The power supply includes hot, cool, and warm fluid reservoirs, each reservoir holding a volume of the heat transfer fluid at different temperatures. The hot reservoir holds fluid that will melt the polymer, the cool reservoir holds fluid that will solidify he polymer, and the warm reservoir holds fluid that will keep the polymer melted once it is in a liquid state. The power supply also includes a pump for moving the transfer fluid. 
     According to another aspect of the present invention, a method of automated machining is provided. A mechanical actuator is secured to a base by an animated inorganic entity. Supply lines are attached to the actuator utilizing quick-connect fittings. A part is clamped between an extended piston of the actuator and a portion of the base by passing warmer heat transfer fluid through the actuator. Work is done on the clamped part by a second animated inorganic entity. The part is unclamped by passing cooler heat transfer fluid through the actuator. 
     One advantage of the present invention resides in hydraulic strength force clamping levels. 
     Another advantage resides in the elimination of possible oil discharge. 
     Another advantage is the circulation of only biologically safe fluids. 
     Another advantage resides in the elimination of high pressure circulation lines. 
     Another advantage resides in the reduction of the possibility of damage to supply lines by automated mills. 
     Another advantage resides in quick connection and disconnection of circulating fluids. 
     Another advantage resides in reduced factory downtime. 
     Another advantage resides in the enablement of arrays of multiple clamps. 
     Another advantage resides in user controllable clamping force levels. 
     Another advantage resides in more force for warmer temperatures. 
     Another advantage resides in less force for cooler temperatures. 
     Yet another advantage resides in the reduction of manual labor. 
     Still further benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
     FIG. 1 is a longitudinal sectional view of a clamping device in accordance with the present invention; 
     FIG. 2 is a transverse sectional view of the clamping device; 
     FIG. 3 is an array of clamping devices in accordance with the present invention; 
     FIG. 4 is a perspective view of the clamping device; 
     FIG. 5 is a perspective view of the clamping device with attached end pieces and fittings, in accordance with the present invention; 
     FIG. 6 is a flow diagram of one or more clamping devices and an associated power supply, in accordance with the present invention; 
     FIG. 7A is a parallel combination of several chains of clamping devices, in accordance with the present invention; 
     FIG. 7B is a series combination of the chains of clamping devices. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1 and 2, a mechanical clamp  10  has an outer housing or body  12  which defines an internal chamber  14 . The internal chamber  14  is filled with a volume of polymer. In the preferred embodiment the polymer is chosen to have a melting (freezing) point relatively close to ambient room temperature, preferably above temperatures that commonly occur in the environment surrounding the clamps. For example, one preferred polymer is paraffin. When the polymer undergoes a liquid to solid phase transition, or the reverse thereof, it changes volume. The expansion when the polymer melts applies force on the surrounding housing  12  and a pair of actuation rods  16  such as pistons. As the polymer expands, it forces the pistons  16  to propagate outward along a longitudinal axis. The pistons are threadedly connected with interface elements  18  shaped and sized in accordance with the surface to be engaged. Alternately, the clamping force can be created by a mechanical spring and the piston is extended to compress the spring and drive the associated clamp open. If the piston  16  impinges upon a surface, such as a machine part, and the polymer is not fully expanded, pressure builds in the polymer chamber. This resultant pressure or clamping force is used to secure the surface in place. A return spring  20  biases the pistons  16  to withdraw as the polymer changes phases from a liquid to a solid. 
     To expand and contract the polymer, heat is added and removed. A thermally transmissive conduit  22  carries a thermal carrier  24  such as hot or cold liquid. In the preferred embodiment, the thermal carrier is a liquid that is benign to its surroundings, such as water, or water based cutting fluid. However, the thermal carrier is not limited to liquids, for example steam or other gases can be utilized as thermal carriers. To maximize heat transfer to and from the polymer, longitudinal or helical fins  26  are attached to the tubing to increase surface contact with the polymer. The vanes are oriented to facilitate polymer flow toward the pistons and back. The tubing itself could be wound into a helical or convoluted pattern to increase contact area with the polymer. Multiple tubes are also contemplated. In the preferred embodiment, the tubing material is one with high thermal conductivity, but is also structurally solid to withstand the high pressures developed without compressing and reducing piston force. Brass and copper alloys are preferred materials for constructing the conduit  22 . The thermal tube  22  is threaded into opposing end fittings  28  which are cammed into a fluid sealing relationship with threaded end pieces  30  that define ends of the polymer chamber  14 . 
     In order to eliminate laminar boundary layers within the heat transfer medium along the surface of the tube  22 , fins  32  or other turbulence causing structures are disposed on the interior of the tube. The induced turbulence improves heat transfer to and from the polymer by promoting convection of the heat transfer fluid. 
     Many different polymers are available to be used in a clamping device. Based on the desired application, three criteria are considered. First is the melting temperature of the polymer. Its relation to the ambient temperature determines whether the polymer will naturally be in a solid or liquid state, hence in a contracted or expanded state, respectively. If the melt temperature is above the ambient temperature, then the polymer is naturally in a solid state, meaning the piston is withdrawn. The polymer is heated above ambient temperature to extend the piston. Consideration should also be given to maximum temperatures that occur in the environment. If the clamping temperature occurs in environmental conditions, the pistons may extend due to environmental rather than controlled factors. 
     Another option is to choose a polymer that is in the liquid state at ambient temperature. This embodiment presents a clamp that is closed at ambient temperature, and is cooled to effect a release of the clamp. A benefit of this embodiment is that once the clamp  10  is closed, it can be removed from the heat transfer fluid circulation system, and remain closed. This can ensure that positioning of the clamped material remains constant across multiple machining devices. 
     A second factor in choosing the polymer involves expansion and compressibility characteristics. These characteristics describe how the volume of the polymer behaves as the pressure changes. By examining these characteristics, a stroke, that is, an amount of displacement of the piston  16 , is determined, along with maximum clamping forces of the clamp  10 . 
     A third factor in consideration of the polymer is its viscosity. Knowing the viscosity of the polymer in its liquid state facilitates design of the polymer chamber  14  and the heat transfer tube. By designing for viscosity, the clamp becomes more predictable in closure times, pressure gradients, and maximum clamping forces. 
     With reference to FIG. 3, multiple clamping devices  10  can be connected together. This forms a clamping line that can secure a part with a much greater dimension, or multiple parts against a common, stationary surface. In this type of arrangement, the heat transfer fluid flows through each of the clamping devices  10  before returning to its source. The heat transfer tubes  22  of each clamping device  10  are interconnected to form a continuous path. With reference to FIGS. 1 and 4, the bodies  12  define bores  40  which receive dowels, rods, individual threaded connectors, or the like to align and connect multiple devices. Preferably, the bores  40  are alternatingly threaded to receive bolts or dowel rods, for clamping adjacent devices  10  together. Each of the clamp modules  10  has flat side faces  42  that are clamped together in a fluid tight seal around a thermal medium port  43  in which the threaded end pieces  30  are received. Optionally, a groove or other gasket locating structure  44  it. holds a gasket that promotes fluid sealing around the thermal medium port. Polymeric or soft metal washers can be received in the thermal medium port  43  that receives end pieces  30  and clamped into fluid sealing contact between adjoining end piece faces to promote sealing. 
     With reference to FIGS. 2,  3 , and  5 , end pieces  46  are clamped to the first and last clamping devices  10  in a line. The end pieces  46  are tapped to receive fittings  48  which are configured to connect quickly with various hoses and tubes that carry the heat transfer fluid. 
     In the preferred embodiment, and with reference to FIG. 6, a clamping device  10  or array of clamping devices are connected to a heat transfer system  50 . The heat transfer system  50  includes a hot fluid reservoir  52  and a cold fluid reservoir  54 . Optionally, a warm fluid reservoir  56  is also included. Hot, cold, and warm are relative to the melting point of the polymer. The hot fluid reservoir  52  contains fluid at a temperature sufficiently greater than the melting point of the polymer to melt it quickly. The cold fluid reservoir  54  contains fluid at a temperature sufficiently less than the melting point of the polymer to solidify it within a preselected time. The warm fluid reservoir  56  contains fluid at or slightly above the melt temperature of the polymer. Fluid from the warm fluid reservoir  56  is used to hold the polymer in its melted state. The warm reservoir can be used to melt the polymer, but the warm fluid melts the polymer more slowly. Optionally, a fourth reservoir can have liquid just below the melt temperature to hold the polymer close to its phase change temperature for faster actuation response. 
     When actuation of the device is desired, fluid is drawn from the hot fluid reservoir through the device, rapidly changing the temperature of the polymer. Once the polymer has changed phase, or after a preset time period, fluid flow is switched from the hot fluid reservoir to the warm fluid reservoir. 
     For example, given a polymer with a melting point of 46° Celsius, the hot and cold reservoirs  52 ,  54  are preferably 82° and 21° respectively. The warm reservoir  56  is preferably 49°, warm enough to keep the polymer melted, even in the presence of thermal losses in the system. In the preferred embodiment, the hot fluid reservoir  52  is not held above 82° for safety reasons. 
     Should a supply line be accidentally cut, scalding might occur if the fluid is too hot. The previous example is that of a polymer with a melting point above most ambient room temperatures. In another example, the melting point is below ambient temperatures, for example, 16° Celsius. 
     The temperatures of the fluid reservoirs would be shifted appropriately as per the needs of the application. 
     In the preferred embodiment, the heat transfer fluid is safe, non-toxic, and non-contaminative should it leak. Water is an ideal heat transfer fluid. Other fluids of particular interest are water based cutting fluids and electrical discharge machining (EDM) fluids. Certain criteria are considered in choosing the heat transfer fluid. First, the heat capacity and how well the fluid conducts heat is considered. The fluid is desired to easily store and give up heat, making clamping and unclamping of the clamping devices  10  faster processes. Environmentally friendly fluids are preferred. Fluids that do not contaminate other fluids being used are preferred. For instance, some cutting fluids and-EDM fluids are easily contaminated by hydraulic oil. Instead of using an oil as the heat transfer fluid, the same cutting fluid or EDM fluid is used. 
     Another temperature consideration addressed when choosing the heat transfer fluid is whether the fluid remains in its liquid state at both the hot and cold reservoir temperatures. In the preferred embodiment, the heat transfer fluid is circulated at a relatively low pressure, about 275 kPa (about 40 psi). This minimizes spraying should circulation hoses develop leaks. Moreover, it is the temperature and heat capacity of the fluid that primarily affects the polymer rather than the pressure. The preferred embodiment of the clamping system can effectively be maintained and actuated with a loss of 50% of the transfer fluid pressure. 
     With further reference to FIG. 6, An operator manipulates a control  60 , such as a foot pedal which is connected with control electronics  62 . In one preferred embodiment, the operator controls the valves remotely with an RF, infrared, or other remote device, allowing distance between himself and mill components. The controller controls output valves  64   a  and input valves  64   b  to send hot water to actuate the clamps  10 , then warm water to maintain actuation. A timer  66  causes the controller to switch the valves from the hot water reservoir to the warm water reservoir after a preselected duration. A pump  68  provides the fluid with motive force to travel from the reservoirs, to the clamping devices  10 , and back. Filters  69  are disposed between the reservoirs and the outgoing valves  64   a  to cleanse the heat transfer fluid of impurities before it is circulated to the clamping devices  10 . 
     In order to keep the hot and cold reservoirs  52 ,  54  at temperature, the heat transfer subsystem  30  includes at least one heater  70  and at least one cooler system  72 . In the preferred embodiment, the heater  70  heats transfer fluid returning to the hot fluid reservoir  52  from the clamping devices  10  as well as sedentary fluid directly from the hot fluid reservoir  52 . This ensures that the hot fluid reservoir is held at the appropriate temperature. Similarly, the cooler system  72  removes heat from fluid returning from the clamping devices  10  to the cold fluid reservoir  54 . The exact type of cooling system depends on the desired temperature of the cold reservoir  54 . If the cold reservoir is to be held close to room temperature, then a fan and a simple heat exchanger is preferred. For colder temperatures, more complex refrigeration systems are preferred. 
     In order to lessen heat pollution from one reservoir to another, a heat sensor  74  is disposed on a return path to the reservoirs  52 ,  54 ,  56  before the return valve  64   b . The heat sensor measures when the temperature of the heat transfer fluid changes. The control electronics  62  causes the valve  64   b  to direct the fluid to the most appropriate reservoir. When the sensor  74  senses the hot fluid returning from the devices  10 , the controller causes the valves  64   b  to return the fluid to the hot fluid reservoir. The controller switches flow from the hot fluid reservoir  52  to the warm fluid reservoir  56 . For a time, the sensor  74  still senses hot fluid, and returns it to the hot fluid reservoir  52  until arm fluid is detected by the sensor  74 . Of course, if he warm fluid reservoir is too cool, the hot return fluid an be used to warm it. 
     In FIG. 7A, the clamping devices are arranged in a parallel combination; and in FIG. 7B, a series combination is illustrated. Depending on the application, the number of clamping devices in a chain, and other factors, one arrangement might be preferred over another. For example, The parallel lines can be controlled individually to actuate the sets of clamps sequentially. The parallel arrangement has less temperature drop across each line of clamp modules, but has a greater pressure/flow speed drop that can affect heat transfer rates. 
     For maintaining safety of a commercial product, the preferred embodiment includes various safety features. One is a temperature sensor. A warning indicator  76  actuates if a fluid reservoir strays from a preset temperature range, especially if it presents a possibly for unscheduled unclamping of the devices. Such a temperature deviation could indicate a problem with heating and/or cooling elements. Another sensor is concerned with the water level of the reservoirs. If the reservoirs become depleted (e.g. because of a cut supply line) a warning signal warns the operator so appropriate measures can be taken to avoid unwanted actuation or deactuation of the devices. Additionally, safety indicators and alarms can be used to indicate when a device reaches a preset clamping force, or the like. Optionally, pressure gauges give a visual readout of the instantaneous pressure. 
     In an alternate embodiment, only one supply is utilized. A flash heater is used to heat the transfer fluid to desired temperatures. This embodiment is most compatible with an open system (e.g. a tap water feed to a drain). 
     With reference again to FIG. 1, the actuator  10  is secured to a clamping base  80  with actuator securing bolts  82 . Alternately, lever release securing clamps  84  could be used to secure the actuator  10  to the base, as ghosted in FIG. 1. A lever release is preferable in a fully automated setting in which a robot can release a plurality of actuators  10  and reposition them with a relativly simple range of motions. In the preferred embodiment, the base  80  provides a platform for securing the actuators  10  as well as clamping surfaces  86  opposite the piston caps  18 . In operation, a piece to be clamped is inserted in a gap between the piston cap  18  and the clamping surface  86 . The piston actuates, pressing the piece against the clamping surface  86 , securing it in place while the piston  16  is actuated. The base  80  is secured to a table  88  or other stationary platform with base securing bolts  90 . 
     The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.