Abstract:
An automatic lens delivery device using a linear actuator which is specially adapted for low torque, low heat applications, and can be used to insert a lens into a user&#39;s eye. The linear actuator uses two semiconductor devices which are moved one relative to the other. The movable device pushes a push rod that delivers a lens.

Description:
[0001]    This application is a Continuation-in-Part of U.S. application Ser. No. 08/275,835, filed Jul. 15, 1994, pending.  
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a device for automatically delivering an intraocular lens into a patient&#39;s eye. More specifically, the present invention defines a device operating using an improved miniaturized linear stepper motor to deliver an intraocular lens into a patient&#39;s eye.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0003]    A cataract is a hardened opaque portion on part of or all of the lens of an eye. Unchecked, a cataract could cause blindness and other complications. Cataract surgery is a procedure whereby the human lens is removed from the eye. In one method of cataract surgery, the hardened opaque lens is first fragmented and then aspirated out of the human eye.  
           [0004]    A thin, delicate, clear membrane surrounds the lens. This membrane is left intact during this surgery, except for the opening in the front through which the cataractous lens is removed. Commonly, this sac is temporarily filled with viscoelastic material. Then an artificial lens to replace the human lens is inserted. This is referred to as an intraocular lens or IOL. Currently, the preference is to place the IOL in the hollow sac.  
           [0005]    Phacoemulsification allows a surgeon to fragment and remove the cataract through a small incision in the eye. In recent years, there has been an interest in inserting the artificial implant lens into the eye through smaller and smaller wounds and even through the hole made for the phacoemulsification. This would allow replacement of the removed lens portion without enlarging the incision.  
           [0006]    Cataract-replacing lens parts are commonly made of rigid polymethylmethacrylate (PMMA). The typical way to insert these lenses has been by using a blade or knife to enlarge the incision after the cataract has been removed and inserting the IOL. Since these IOLs are rigid, they require a larger incision. Larger incisions, however, require a longer recovery time and provide more probability of infection and more unstable post operative refractions. In more recent years, foldable intraocular lenses have been replacing rigid PMMA lenses.  
           [0007]    Foldable lenses include three-piece looped designs, and a one piece plate design. The one-piece lens can be folded into a cylinder or a sphere. The folded lens can be inserted through the hole that has been used to remove the cataract (“the phaco hole”), into the eye. The artificial lens, if properly delivered, unfolds and takes the place of the removed human lens.  
           [0008]    The artificial lens is often delivered as shown in FIG. 25. The folded lens  1000  is located in cassette  1002 . The entire cassette, including the lens, is inserted into a chamber  1004  of the delivery device.  
           [0009]    While looking through a microscope, the surgeon holds the handle part  1010 , and inserts the end  1006  of the delivery device into the eye through the phaco hole. While still looking through the microscope, the surgeon reaches around with the other hand that is not holding the portion  1010  and actuates the control knob  1012 . This actuation may be a screw movement or a pushing movement.  
           [0010]    This puts the surgeon in an uncomfortable position while doing this crucial and exacting work. Specifically, the surgeon must operate the delivery device with both hands, one of which is placed in an unnatural and uncomfortable position due to an intervening optical microscope. In addition to the uncomfortable position, the surgeon&#39;s actuation of the control knob  1012  also may cause movement of the delivery end  1006  in the eye. These lenses, especially of the plate variety, must be inserted into the hollow sac occupied by the cataractous lens. This can produce a difficult situation, where the lens must be removed from the patient&#39;s eye or worse, can lead to serious postoperative vision problems.  
           [0011]    Another problem is that sometimes the lens gets stuck as it leaves the cassette  1002 , or the push rod jumps over the folded IOL and gets stuck half way out of the cassette. When this happens, the surgeon must decide how to remove the entire unit—possibly with a partially inserted lens—from the eye. The present invention, while not completely solving this problem, describes an arrangement which is far superior. The cassette can be easily detached from the inserter, leaving the IOL and cassette in the wound. Forceps can then be inserted and the IOL removed through the cassette without enlarging the wound or making other incisions to “lead” or pull the IOL out of the cassette, remove the cassette, then remove the IOL.  
           [0012]    The inventors wondered why such a system had not been previously mechanized. They decided that there would be significant advantages to such a make a mechanized system.  
           [0013]    The inventors found unexpectedly, however, that all commercially-available motors and actuators were unsuitable for the purpose. They found that rotary motors, e.g. those that produce a rotational force, were unsuitable in that they produced a torque on start up that could move the delivery tip, and hence increase failure rate. Also, most motors of this type were too large in size and mass, and would not fit within a conventional lens delivery device. The smaller motors that exist either could not produce enough force to push the IOL out of the cassette, or produced an unacceptable amount of heat which could cause danger for the surgeon or patient, or lacked very precise linear control. In addition, so-called micro motors are high speed and low torque. They require substantial gear reduction as well as conversion of rotary motion to linear displacement. This complexity adds to cost, increases weight and decreases reliability. If simply attached to the distal end of the device, it would be imbalanced. Linear actuators were also too large, not balanced, and consumed too much power.  
           [0014]    To solve these problems, the inventors devised a special linear actuator that was small, balanced, produced no rotary torque, had a small power consumption, was very precise and controlled, and for the first time was practical for attachment to deliver a folded lens into an eye, through a small incision.  
           [0015]    In view of the above, the inventors have invented a new method and apparatus for delivering an IOL into the eye. This technique uses a cassette-held folded lens, driven by a special linear actuator which produces virtually no torque on movement, produces very little heat and has a low weight. The preferred device uses the expansion and contraction of a member to deliver the force to press the lens along a path.  
           [0016]    In addition, while doing so, the present invention obtains significant operational advantages.  
           [0017]    The specific kind of linear actuator uses the shape change of piezoelectric materials that occurs when voltage is applied thereacross to generate linear motion.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    These and other aspects of the invention will now be described in detail with reference to the accompanying drawings, wherein:  
         [0019]    [0019]FIG. 1 is an enlarged, fragmentary, sectional view of a miniature linear motion actuator in accordance with the present invention, depicted within a support casing;  
         [0020]    [0020]FIG. 1A is a sectional view of the layers forming the moving parts of the first embodiment.  
         [0021]    [0021]FIG. 2 is a fragmentary view of a sliding electrical contact wire;  
         [0022]    [0022]FIG. 3 is a sectional view taken along the line  3 - 3  of FIG. 1;  
         [0023]    [0023]FIG. 4 is a fragmentary, detail view depicting a second embodiment of the invention which uses double clamping;  
         [0024]    [0024]FIG. 5 is a simplified diagram depicting the control console and electrical connection to the elements of the miniature linear motion actuator in accordance with the present invention;  
         [0025]    [0025]FIG. 6 is a block diagram of the control system of the linear actuator;  
         [0026]    [0026]FIG. 7 is an electronic circuit diagram of an exemplary control circuit used according to the present invention;  
         [0027]    [0027]FIG. 8 is a graph depicting output force of an exemplary actuator as a function of clamping voltage and expandable member voltage;  
         [0028]    [0028]FIG. 9 is a graph depicting the velocity of the linear actuator as a function of the clamping voltage and output velocity;  
         [0029]    [0029]FIG. 10 is a timing diagram for the first embodiment;  
         [0030]    [0030]FIG. 11 is a timing diagram for the second embodiment;  
         [0031]    [0031]FIG. 12 is a graph depicting the velocity of the single clamping embodiment of the actuator as a function of clamping voltage for a variety of load sizes;  
         [0032]    [0032]FIG. 13 is a graph depicting the force generated by the single clamping embodiment to the actuator as a function of clamping voltage for a variety of clamping frequencies;  
         [0033]    [0033]FIG. 14 is a graph depicting the force generated by the single clamping embodiment of the actuator as a function of expandable member voltage for a variety of clamping voltages, with the phase between the clamping voltage and expandable member voltage as depicted in FIG. 8;  
         [0034]    [0034]FIG. 15 is a graph depicting the velocity of the single clamping embodiment of the actuator as a function of external load for a variety of clamping voltages;  
         [0035]    [0035]FIG. 16 is a graph depicting an estimate of glider velocity of the single clamping embodiment of the actuator as a function of load force for a variety of glider weights;  
         [0036]    [0036]FIG. 17 is a graph depicting the force generated by the single clamping embodiment of the actuator as a function of glider mass;  
         [0037]    [0037]FIG. 18 is a graph depicting the force generated by the single clamping embodiment of the actuator as a function of phase control variation of expandable member and clamp waveforms;  
         [0038]    [0038]FIG. 19 shows the lens delivery device part of the linear actuator of the present invention;  
         [0039]    [0039]FIG. 20 shows one attachment mechanism for the lens delivery device;  
         [0040]    [0040]FIG. 21 shows a matched attached mechanism which attaches to the FIG. 20 device;  
         [0041]    [0041]FIG. 22 shows the lens storage unit and its attachment tube;  
         [0042]    [0042]FIG. 23 shows a flattened intraocular lens;  
         [0043]    [0043]FIG. 24 shows a rolled intraocular lens;  
         [0044]    [0044]FIG. 25 shows a lens delivery device which manually screws to deliver a lens; and  
         [0045]    FIGS.  26 A- 26 D show a second embodiment of the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    A presently preferred embodiment will now be described in detail with reference to the accompanying drawings.  
         [0047]    [0047]FIG. 1 shows a miniature linear actuator in accordance with a first embodiment of the present invention. The structure of the first embodiment has a base and a glider which are continuously clamped to one another, and wherein movement is effected by selectively overcoming the clamping force. The actuator is formed of a base  22 , attached to the casing C, and a glider  24  which moves relative to the base, to provide force to a mass load  26 .  
         [0048]    The power for the operation is supplied over a plurality of wires  40 ,  76 ,  78 , and  80  supplied as a control wire trunk  28 . These wires are configured in a way that retains separation of the wires as the glider moves, to prevent electrical short circuits between the wires. Portions of these wires may be insulated to prevent any unintended short circuits. A more preferable technique is to use rigid wires as described herein.  
         [0049]    The casing for the device is shown generally in FIG. 1 with the reference designation C, and refers to a part of the device which remains fixed and immobile. The casing is preferably cylindrical, and includes a plug  32  held in the cylinder. The base  22  includes support element  30  and wafer base  34  which is attached to support element  30  by epoxy or the like. A detailed drawing of the layers forming the actuator is found in FIG. 1A. Support element  30  is connected to the plug at a first end  31 , and cantilevered therefrom at its other end. This connection of the support element  30  to the plug  32  prevents movement of the base in a direction parallel to the axial direction of the cylindrical casing. A top surface of the support element  30  is polished to have a surface height asperity of less than 1 μm/5 mm of linear length, and has an insulation layer  36  thereon to insulate between the support element  30  and the overlying wafer base  34 . Insulation layer  36  is most preferably a native oxide.  
         [0050]    The wafer base  34  is formed of silicon with an upper polished surface  38 . Surface  38  is covered by an insulating layer  39  which is preferably a native oxide layer of SiO 2 . Another layer of silicon nitride, Si 3 N 4 , layer  41 , is preferably, but not necessarily, grown over native oxide layer  39 . The Si 3 N 4  layer helps stabilize the native oxide layer  39  and also physically strengthens the layer.  
         [0051]    The resultant insulation layers  39 ,  41  are very smooth since they have been formed on the highly polished surface  38 .  
         [0052]    Any technique which is known in the semiconductor art can be used for forming the SiO 2 /Si 3 N 4  layers over the wafer base  34 . The most preferred technique is to heat the surface of the silicon element in the presence of oxygen to form the native oxide layer thereon. This has the added advantage that the connection strength between the silicon and the insulation is very high. Less preferred techniques include sputtering and chemical vapor deposition of the oxide.  
         [0053]    Wafer base  34  receives a potential through a wire  40  which is electrically connected therewith.  
         [0054]    Glider  24  includes clamping wafer  46  and expandable member  48 . The clamping wafer  46  is also preferably formed of silicon with a lower polished surface  44 . An alternate embodiment of this invention forms the insulating layers  39 ,  41  on the polished surface  44  of the clamping wafer  46 , instead of on the wafer base  38 .  
         [0055]    An insulating layer  52  is formed on the opposite surface of the clamping wafer  46 , opposite the polished layer  44 . Expandable member  48  is attached to insulating layer  52 . A portion  49  of expandable member  48  is cantilevered with respect to the underlying support elements. Expandable member  48  is formed of a material which changes in size responsive to application of a stimulus thereto. More preferably, expandable member  48  expands and/or contracts in size based on an electric field applied thereto. The material which is currently preferred is a piezoelectric material, such as PZT. Another preferred material is the PZT material known as LTZ-2M, available from Transducer Products in Connecticut. Other materials could also be used, including a shape memory material such as nitinol, an electrostrictive material such as PLZT, or a magneto-restrictive element that changes its dimension in response to an appropriate magnetic field. Any material can be used, so long as it allows the expandable member  48  to increase and decrease in size relatively rapidly responsive to the application of a stimulus field.  
         [0056]    The expandable member  48  is glued to the insulating layer  52  which overlies clamping wafer  46  by an epoxy adhesive. Electric lead wires  54  and  56  provide an electrical potential across the expandable member  48  to control its expansion and contraction.  
         [0057]    Mass load  26  represents schematically the device which receives the output force produced by the movement of the glider relative to the wafer base. Mass load  26  includes a work interface rod  64  which is connected to the device which is intended to receive the payload. The expandable member  48  is preferably attached to mass load  26  is by an insulating bonding adhesive  60 , such as epoxy. The movement of the glider assembly  24  is thereby translated into linear motion of the mass load  26 . The mass load  26  is preferably of a shape to contact the interior surfaces of the cylindrical casing C and thereby maintain a seal within the cylinder. Workbase seal  66  seals between mass load  26  and casing C in order to prevent liquid leakage into the motor. Seal  66  can be an annular truncated cone, or an “O” ring seal.  
         [0058]    In order to allow more sensitive control of the present invention, a sensor  300  may be placed in contact with the mass load. Sensor  300  could be a force sensor, accelerometer, or the like. The sensor can be wireless or wire-connected, and is used to provide feedback as described herein.  
         [0059]    Force levels encountered at the distal tip are directly transmitted back to expanding member  48  and the interface between gliding wafer  46  and base wafer  34 . Controller  120  may directly sense any load changes on work interface  64  from a workpiece through monitoring voltage, current and phase angle changes. Controller  120  can be programmed to automatically respond to these changes through feedback mechanisms to adjust one or more settings to adjust the glider waveform control, voltage amplitude, frequency control  132 , expandable member waveform control  134 , expandable member voltage control  136 , expandable member frequency control  138 , and phase control  126  as described. Thus, a specific force displacement relationship can be maintained within the power and mechanical limits of the system. It is also anticipated that other sensors may be added to the system to assist in feedback control of the present invention.  
         [0060]    In operation, the device operates to produce motion as follows. It should be understood that while the explanation given herein is an explanation of forward motor motion, the opposite sense operation produces a reverse movement of the motor.  
         [0061]    A first step of the operation provides a clamping force by applying an electrical force between clamping wafer  46  and wafer base  34 . This clamping force is carefully controlled as explained herein such that it holds the position clamping member relative to the wafer base under most circumstances, including slow expansion of expandable member  48 . The force is not so strong a force as to prevent separation between the clamping wafer  46  and wafer base when sufficient inertial force is applied thereto from maximum-speed contraction of expandable member  48 . The clamping force is important since the clamping force must be sufficient to hold the connection between the wafers while pushing forward the mass load.  
         [0062]    The clamping force is one of the important parts of this motor. It is well known from physics that an electrostatic clamping force is expressed as follows:  
               F   clamp     =       ε                   AV   2         x   2               (   1   )                               
 
         [0063]    where ε is the dielectric constant of the insulating material, A is the surface area of the wafers, V is the voltage applied between the two wafers, and x is the separation between the two wafers. The separation between the wafers, of course, is the thickness of the insulating layer  39 , 41 . Equation (1), therefore, shows that the clamping force is inversely proportional to the square of the thickness of the insulating layer that separates the base from the glider. As this thickness increases, the area of the clamping layers must increase proportionally as the square of this thickness. It can therefore be seen that a thicker insulation layer between the wafer base and the glider will necessitate that the wafer base and the glider be much larger in area to provide a comparable force.  
         [0064]    The Judy et al. design used a teflon sleeve between the layers. This teflon sleeve was about 63.5 μm in thickness. In order to obtain sufficient clamping force between the base and glider, therefore, the surface areas of these two elements needed to be relatively large in comparison to the present invention.  
         [0065]    In contrast, the present invention teaches using semiconductor materials, which allow the use of very thin insulating layers, e.g. 50 Å-2 μm in thickness. Silicon and other such materials can be very accurately processed using conventional semiconductor miniaturization techniques. This processing allows very thin insulating layers with a high degree of polish. While the insulating layers can be as thin as 50 Å, the preferred thickness for the insulating layer  42 , according to the present invention, is 1 μm in thickness. This is almost two orders of magnitude thinner than the Judy et al. insulating layer, and therefore allows the resultant structure to be four orders of magnitude smaller (since the area is not a squared term, but the distance is) for a similar clamping force.  
         [0066]    This reduced size for the same clamping force allows increased miniaturization.  
         [0067]    Returning to operation, then, once the glider is clamped to the base with an appropriate amount of clamping force, the expandable member  48  is increased in length slowly, e.g., gradually over 1 ms. This increase in length pushes mass load  26  in the direction of the length increase. This slow increase does not overcome the clamping force between the glider and the base. The overall result is that the mass load is pushed forward by an amount proportional to the amount of expansion possible of the expandable member.  
         [0068]    At this point, the voltage across the expandable member is quickly reduced, e.g. in 200-500 ns, to cause the expandable member to decrease in size in its minimum possible time. Inertial force from the fast contraction produces sufficient force between the glider and the wafer base to overcome the clamping force, and causes the glider to lift off from the wafer base. This overcomes the clamping force and moves the glider forward on the wafer base. The clamping force amount is explained in more detail herein, but it should be seen that the clamping force must set sufficiently high so that when the expandable member is increased in length slowly, the clamping force is sufficient to resist this force and maintain the position of the glider relative to the wafer. However, the clamping force is not sufficiently high that it will resist the inertia caused when the expandable member decreases in size at its maximum rate. This high inertia overcomes the inertial force and causes the glider  24  to move relative to the wafer base  34  against the force caused by the clamping. This completes the cycle of operation, and the next cycle is then initiated to move the mass load  26  further forward.  
         [0069]    As can therefore be seen from the above, the present invention, by using semiconductor wafer materials and technology, allows the clamping wafers to be more closely spaced than was possible in the prior art. This increases the output force and velocity for a similarly sized device, and allows the device to be much smaller. In fact, the device of the present invention could be 63 2 =3969 times smaller than the Judy et al. device for similar force characteristics.  
         [0070]    Another advantage of the present invention is obtained from the different mode of operation used according to the present invention. Judy et al. described that, during every cycle, the electrostatic clamp was turned off during the time when the glider was to be moved relative to the wafer base. However, during the time the clamp is turned off, the effects of gravity may affect the position of the glider relative to the base. This means that the device would operate differently depending on the position it was being held.  
         [0071]    In contrast, the techniques of the present invention maintain the clamp force at all times. The present invention does not turn off the clamp, but instead appropriately sets the clamping force at an appropriate value that can be maintained constant. In a first mode of this first embodiment of the invention, the clamp voltage is maintained at a constant value. In a second mode of this embodiment, described in more detail herein, the clamping voltage varies cyclically. This cyclic variation removes accumulated charge in the substrate.  
         [0072]    Any semiconductor material, as well as many metals, could be used for the clamping wafers. Crystalline silicon is the preferred material, however, since it is readily available, strong, easily able to form a native insulative layer of SiO 2  thereon and also easily processed using conventional semiconductor techniques. Amorphous or polycrystalline silicon could also be used. Germanium and gallium arsenide are also good materials, but are more brittle. They are usable, but less preferred. Also usable, but even less preferred, include silicon carbide, gallium nitride, and gallium phosphide. Metals also can be used, for example aluminum, but its native oxide is not reliable. A stainless steel thin film can be used, but the thin layer of oxide would need to be sputtered thereon. This forms a more granular surface. Copper, brass and gold could also be used.  
         [0073]    The preferred process of making the device, therefore, includes obtaining a silicon wafer, polishing the surface to obtain a flat surface, growing the oxide by heating the surface in the presence of oxygen, and then forming the Si 3 N 4  on the SiO 2  by a conventional chemical vapor deposition technique.  
         [0074]    [0074]FIG. 2 shows a detailed connection diagram of each of the wires  76 ,  78 ,  80  and their accompanying cylinders  70 ,  72 ,  74 . Each of the wires  76 ,  78  and  80  are formed of a rigid rod, connected at one end through the control wire trunk  28 , and having a fixed length. Each wire, e.g.,  76 , is of a length such that it will remain within its associated cylinder  70  at all possible glider positions. Each of the cylinders is connected by a lead wire, e.g.,  50 , to its connected location. Each of the wires  76 ,  78 ,  80  from the control wire trunk  28  are slightly smaller in outer diameter than the inner diameter of the cylinder, but include a kink  120  therein at which point they contact the inside of the cylinder. Therefore, the wires  76 ,  78 ,  80  contact the inside of their associated cylinder  70 ,  72 ,  74 , and form a sliding connection as the expandable members move relative to one another. The wires slide relative to the cylinder during this time. The cylinder itself, however, does not move, and the connection  50  does not move.  
         [0075]    [0075]FIG. 3 shows a cross-sectional view along the line  3 - 3  in FIG. 1 showing the positions of the cylinders  70 ,  72  and  74  and their connections to the layers.  
         [0076]    [0076]FIG. 4 shows a second embodiment of the present invention which is a linear actuator using a more conventional double-clamping technique. The FIG. 4 embodiment shows only a portion of the overall device, that portion being the part which differs from the portion of FIG. 1.  
         [0077]    [0077]FIG. 4 includes a similar support member  30  and wafer base  34  with insulating layer  44  thereon.  
         [0078]    The glider  84  of the FIG. 4 embodiment is totally different than the glider of the first embodiment. Glider  84  includes two separated pieces, including a proximal glider  86  and a distal glider  88 . Each of the glider pieces include a respective lead wire,  90 ,  96  attached thereto. Each of the gliders also includes a bottom-most polished surface. The proximal glider  86  includes polished surface  92  and the distal glider includes polished surface  98 . Each of these polished surfaces abuts against the insulating layer  39  on the wafer base, it being understood that the insulator could be similar to the insulator of FIG. 1, 1A and alternately could be formed on the bottom surface of the glider.  
         [0079]    The operation of the system of FIG. 4 is somewhat different than the operation of the single clamping motor of FIG. 1. FIG. 4 uses a double clamping technique, whereby different glider portions are repetitively clamped, followed by expansion or contraction of the expandable element  48  to move it forward. The device can be moved in the direction to the right of FIG. 4 in the following way. First, the proximal glider  86  is clamped with the expandable member  48  in its maximally contracted position. The distal glider  84  is not clamped at this time. The expandable member  60  is then expanded to its maximum expansion state, thereby pushing the mass load  26  to the right of FIG. 4. At this time, the distal glider  84  is clamped, and the proximal glider  86  is released. The expandable member  60  is then returned to its contracted length to pull the proximal glider to the right in FIG. 4. At this time the proximal glider  86  is again clamped, and the cycle begins anew.  
         [0080]    The FIG. 4 embodiment is highly miniaturizable due to the semiconductor materials that are used.  
         [0081]    The movement of both embodiments of the invention are controlled by various parameters including voltage for clamping, voltage across the piezoelectric expandable elements, frequency of the repetitive voltage, and voltage waveform shape, i.e., change of voltage with respect to time.  
         [0082]    [0082]FIG. 5 shows the power control console  120  which controls the operation of these input parameters. Power control console  120  controls all voltages, frequencies and phases of the various elements.  
         [0083]    The magnitude of the clamping voltage is adjusted to control the actuator operation according to desired characteristics. As explained above, the force between the base and glider is proportional to the amount of voltage used for clamping. Hence, the clamping voltage sets the base level of force holding together the glider and the base. When the expandable member expands, and pushes against the mass load, that mass load will only move forward if the force produced by pushing against the load does not overcome the clamping voltage between the glider and the base. Therefore, a clamping voltage must be set keeping in mind the load; too small a clamping voltage will not produce sufficient force to drive a specified load.  
         [0084]    On the other hand, the clamping voltage must be overcome by the inertia of the expandable member contracting quickly. Too high a clamping voltage prevents the expandable member from snapping back sufficiently, and therefore shortens the step length.  
         [0085]    As described above, the expandable member is repetitively expanded and contracted. The frequency of this expansion and contraction is based on physical characteristics of the system. The expandable member, for example, takes a certain amount of time to expand and to contract. In the embodiment described above, the expansion is done relatively slowly, e.g. 1 ms. The contraction occurs at the maximum possible speed of the material, but this also takes a certain finite amount of time, e.g. 250 ns. The frequency of the repetitive operation cannot be faster than the time which is physically necessary for these materials to expand and contract.  
         [0086]    It has also been determined by the inventors that the phase between the voltage waveform of the expandable member and the voltage waveform of the clamping member effects the amount of force that can be supplied by the device. An experimental plot of this information is shown in FIG. 18. It should be seen that usually the phase should be around zero, but some small adjustments may improve certain characteristics.  
         [0087]    [0087]FIG. 5 shows the control console including a glider control unit  122 , expandable member control unit  124 , and a relative phase control unit  126 . The glider base control unit  122  includes rotatable potentiometer knobs shown schematically as waveform control  128 , amplitude control  130 , and frequency control  132 . These potentiometers correspond to those in FIG. 7 described herein, and it should be understood that control circuit  120  may have more knobs than those shown.  
         [0088]    The glider waveform control  128  generally controls the shape of the glider waveform. The voltage amplitude control  130  controls the amount of voltage between the wafer  46  and wafer base  34  to change the amount of electrostatic attraction. Because of the characteristics of the materials, a linear change in voltage amplitude may cause non-linear effects. The voltage amplitude control knob can be weighted, e.g., logarithmically, to compensate for those effects. Frequency control  132  controls the repetitive rate at which the waveforms are produced. For the preferred mode, this frequency is kept between around 10 Hz and 1000 Hz.  
         [0089]    The expandable member control unit  124  similarly comprises an expandable member waveform control  134  which controls the characteristics of the waveform applied to the expandable member. For the first embodiment, this waveform should be a slowly rising, but quickly falling waveform. For the second embodiment, the waveform could have any desired characteristics. Adjustable voltage amplitude control  136  controls the amplitude of the voltages used for clamping. The adjustable frequency control  138  changes the frequency of this voltage.  
         [0090]    Phase control unit  126  controls the timing between the clamp voltage and the expansion voltage. The preferred timing characteristics are described herein.  
         [0091]    A block diagram of the circuit within the control console of FIG. 5 is shown in FIG. 6. Frequency generator  204  produces the frequencies which will be used to drive the linear actuator. These frequencies are adjustable over a certain range. The output of frequency generator  204  is received by phase control unit  206  which produces two outputs, separated in phase by a selectable time. One of the outputs drives the piezo waveform generator  218 , and the other output is divided to drive the clamp waveform generator  216 . It should be noted that while the preferred embodiment of the invention provides a clamp waveform, it is also contemplated, but less preferred, to drive the motor using a constant clamp voltage. Direction control  212  controls the direction in which the motor is running, and is connected to the piezo wave generator  218 , and to the clamp voltage actuator  214  which actuates clamp waveform generator  216 .  
         [0092]    Clamp voltage device  210  produces the clamping voltage that will be used to clamp the glider to the base. According to a preferred embodiment of the invention, the output of force sensor  300  is used to address the magnitude of this voltage in order to produce a desired amount of force.  
         [0093]    As explained above, expandable member  48  expands or contracts as controlled by control console  120 . Three separate controllable parameters, expandable member waveform control  134 , voltage control  136  and frequency control  138 , affect expansion and contraction of expandable member  48 . Voltage control  136  generally controls the magnitude of change of length of expandable member  48 . Frequency control  138  controls the periodic motion of expandable member  48 . Expandable member waveform control generally controls the inertial properties of expandable member  48  and its attached mass load  26 .  
         [0094]    A specific embodiment of an electrical control circuit for providing control over the parameters discussed above for the first embodiment is depicted in FIG. 7 as control circuit  200 . The circuit depicted in FIG. 7 can be wholly or partially fabricated in one of the silicon wafer(s) carried within the linear actuator of the present invention, preferably in the base  30  at area  500 , using conventional semiconductor techniques.  
         [0095]    DC power supply  202  includes high voltage DC source  220  for energizing and expanding the piezoelectric element and a lower voltage source  222  for driving the logic e.g. at 12 V. Voltage source  220  may be variable by the operator and/or by feedback from sensor  300  for achieving the optimal power from the linear actuator. The output value from voltage source  220  may range between 15 and 1000 volts, with the preferred voltage being around 500 V.  
         [0096]    The frequency generator  204  in FIG. 7 produces a frequency which is used to produce the wafer driving waveforms. Frequency generator circuit  204  includes an internal frequency oscillator  224 , and an external input port  226 . The internal oscillator  224  uses an operational amplifier oscillator to produce a frequency based on the magnitude of the feedback resistance in the operational amplifier  236 . Frequency selector switch  230  controllably switches feedback resistors  232 , to form an RC network between those feedback resistors  232  and the capacitor  234 . The system oscillates at a frequency dependant on the RC time constant, and hence produces a frequency based on the position of switch  230 . Bias resistors  238 ,  240  and  242  provide a bias voltage to the inverting input of the operational amplifier.  
         [0097]    The frequency generator circuit  224  could alternately be a variable divider attached to the output of a crystal, or could be a programmable frequency divider integrated circuit.  
         [0098]    In this embodiment, an external frequency can also be added through terminal  226 . Operational amplifier  244  compares the input frequency with a DC bias from adjustable resistor  246  to adjust its amplitude to match the characteristics of the system.  
         [0099]    The frequencies from external input  226  and from internal frequency oscillator  224  are input to two contacts of switch  228 . The output of the switch  228  is passed to the phase shift control unit  206 .  
         [0100]    Phase shift control unit  206  provides two output frequencies, selected such that the phase lag between those output frequencies has a desired characteristic between 0 and approximate 0.1 μs. The phase control circuit  250  and phase control circuit  252  each have separately-adjustable delay characteristics. Circuit  250  includes fixed resistor  254  and variable resistor  256  as well as a capacitor  258 . The combination of these resistances and capacitances form an RC circuit which delays the rise of the waveform. The RC time constant by varying the value of resistor  256 . This delays the passage of the waveform and hence changes the phase angle thereof. Similarly, adjustment of resistor  266  delays the passage of the waveform to the output.  
         [0101]    A switch  276  controls whether or not the phase shifting will be used. In a first position, the switch  276  directly connects the inputs of the phase shift unit to the outputs, thereby preventing any phase shift. In the second position, the phase shifts are controllable.  
         [0102]    The signal output from circuit  250 , either phase-shifted or directly connected, is coupled to frequency divider  208 . Divider  208  is simply a D-type flip-flop with its Q not output connected to its D input to thereby divide the input frequency by 2. The output is coupled through a variable resistor. The output voltage is supplied to the clamp waveform generator  216 . Of course, this could also be a programmable divide by N counter or any other divider known in the art.  
         [0103]    The voltage for the electrostatic clamping of the base to the glider is produced by clamp voltage generator  284 . Element  284  includes a voltage divider  290 ,  292 ,  294 , connected to the inverting input of an operational amplifier  288 . The output of the operational amplifier  288  drives the gate of a power MOSFET  286  which has a grounded drain, and a source connected to the output with a bias resistor  285 . The source is also directed through a feedback loop with sensor  300  and resistance  302  to the non-inverting input of the operational amplifier. It will be appreciated that operational amplifier  288  is connected as a comparator, and the output thereof determines the voltage drop across the MOSFET  286 .  
         [0104]    The source of the MOSFET  286  is connected to a filtering capacitor  298  whose output produces the voltage at output terminal  296 . This output voltage  296  becomes the clamping voltage.  
         [0105]    Element  212  is a motor direction control. By closing one of the two switches, the motor can be selectively reversed in direction. The switches selectively operate the clamp voltage activator  214 , which includes comparator amplifiers  308  and  310 . Each comparator  308 ,  310  has its negative input connected to a variable voltage from voltage divider  312 . Depending on the positions of the switches  304  and  306 , output voltages from the amplifiers  308 ,  310  are connected to the inverting inputs of operational amplifiers  316 ,  318  within the clamp waveform generator  216 . The positive inputs of these operational amplifiers receive the output voltage from divide by two circuit  208 . Each of the amplifier circuits in the clamp waveform generator have a similar construction. Operational amplifier  316  has an output which drives the base of MOSFET  320  which is configured as a follower. The source of this transistor  320  is connected through a variable resistor to the gate of another MOSFET  322 , also configured as a follower. The source of the follower-configured MOSFET  322  has an output terminal  346 .  
         [0106]    Similarly, the circuit including op-amp  318  produces an output voltage at terminal  348 . The output terminals  346  and  348  are respectively connected to the glider  46  and wafer base  34 . It should be appreciated that by changing the positions of the switches  306 ,  308 , the voltage between those values is also changed to thereby change the direction of operation of the motor.  
         [0107]    The other output of the phase control unit, from variable resistor  278 , is coupled to the input of piezoelectric element waveform generator  218 . This second phase control element is connected to inverting inputs of operational amplifiers  352 ,  354 . The non-inverting inputs of both of these operational amplifiers receive respective signals from the switches  304 ,  306 . The operational amplifiers, configured as comparators, electrically control the gates of MOSFETS  364 ,  366 . These MOSFETS are connected as followers, with the source of each MOSFET connected through a variable resistor  372 ,  374  and a resistor to ground,  380 ,  382 , to a power MOSFET  376  also connected as a follower. The sources of MOSFETS  376  and  378  produce voltages which are coupled to output terminals  388 ,  392 . These terminals are connected to the electrical leads  54 ,  56  and thereby control the expansion and contraction of expandable member  48 .  
         [0108]    In operation, the circuit of FIG. 7 produces voltage waveforms for the electrostatic clamp(s) and the expandable element. When switch  304  is closed, the respective amplifiers  352  and  308  are turned on thereby applying a specific voltage to amplifiers  316  and  318 . These voltages are applied to operational amplifiers  316 ,  318  in clamp waveform generator  216 . The other inputs of the operational amplifiers are driven by the output of the divide by 2 divider  208 . This results in a continuously-reversing voltage across the output terminals  346 ,  348  at half the frequency of driving of the expandable member. The actual shape of the voltage curve depends on the RC time constant controlled by using variable resistors  328 ,  330 . Closure of switch  306  turns on the opposite-sense voltage drivers.  
         [0109]    Switches  304  and  306  also control the operation of the piezoelement waveform generator  218 . When both switches  304  and  306  are open, waveform generator  218  is idle. Closing switch  304  also provides a low level voltage to the positive input of operational amplifier  352 , thereby turning it on and allowing it to pass the output voltage received from the phase control  206 . Alternately, switch  306  turns on the amplifier  354 , thereby allowing it to operate using that same voltage. It can be seen that the overall effect of closing switches  304 ,  306  is to control the direction of motion of the linear actuator. By just closing switch  304 , the waveform generator circuit that powers MOSFET  376  is initiated. By closing switch  306 , the waveform across terminals  388  and  392  is inverted.  
         [0110]    As described above, velocity of the actuator is controlled by changing the frequency output signal from frequency generator  204 . However, for any given input power, the velocity output must be traded off against work load. The expandable member voltage most directly controls the power. The clamp voltage controls the tradeoff between speed and force. A low clamp voltage allows a higher speed but less force. Since the clamp voltage is lower, the clamping force between the glider and the base can be maintained only for a lower amount of force. However, since the clamping force is relatively lower, the inertial snapback operation allows the glider to move forward a little further.  
         [0111]    The relationship between velocity and force is more complicated and less linear. The characteristics are more easily modelled, which has been done by the inventors and will be explained with reference to the following preferred embodiment.  
         [0112]    The linear actuator of the present invention uses a piezoelectric element which is preferably 38.1 mm in length. The preferred piezoelement width is 6.35 mm. This provides a preferred clamp surface area of 234 square millimeters. The preferred thickness is 0.8 mm. More generally, however, the actuator can be between 1 and 250 mm in length, between 0.1 and 50 mm in width, and 0.01 to 5 mm in thickness.  
         [0113]    The preferred piezoelement has a mass of 1.4 grams, although it can range between 0.01 and 450 grams. The preferred glider mass is 30 grams, although it is conceivable to make the glider mass between 1 gram and 10 kilograms.  
         [0114]    The insulating layer  39  is preferably formed of SiO 2  and Si 3 N 4  as shown in FIG. 1A. Preferably, the SiO 2  layer has a thickness of about 0.75 μm and the Si 3 N 4  layer about 0.15 μm. Both layers could be as thick as 2-3 μm or as thin as 50 Å.  
         [0115]    The silicon clamping wafer preferably has a thickness of 0.036 mm, but more generally between 0.01 and 1 mm.  
         [0116]    The system operates according to the following preferred parameters:  
                                           PARAMETER   PREFERRED   MINIMUM   MAXIMUM                   Electrostatic Clamp   300   30   2000       Voltage   volts   volts   volts       Piezoelectric Drive   500   15   1000       Voltage   volts   volts   volts       Drive Frequency   400   0.1   3000           Hz   Hz   Hz       Silicon Clamping Wafer   1   0.001   100       Resistivity   ohm-cm   ohm-cm   ohm-cm       Incremental Step Size   6.25 μm   0.01 μm   50 μm       Velocity   0.25 cm/s   0 cm/s   2 cm/s       Electrostatic clamping   10   0   500       force   Newtons   Newtons   Newtons       Output Force    6   0   100           Newtons   Newtons   Newtons                  
 
         [0117]    It should be apparent from the above that the performance characteristics of the linear actuator are dependent on the physical properties of the system. FIGS. 8 and 9 show general performance envelopes for a linear actuator, it being understood that the absolute values of the curves could depend on the actual loads and inertial masses chosen in the clamp surface areas. The point of FIGS. 8 and 9 is that for each mass range and clamp area, a different set of curves define the performance envelopes, and values on these curves can be chosen to optimize different characteristics.  
         [0118]    By specifying different values for any given application, usually the largest inertial mass and clamp surface area will be selected. FIG. 8 shows the output force reaching its optimum value at point  146 . An increase in clamp voltage initially produces a higher output force because it causes the glider wafer to be more tightly held in place as the expandable member is expanded. Too much clamping voltage, however, lowers the output force, because it prevents the expandable member from moving forward when the expandable member voltage is released. The clamp surface area and voltage are related to one another, and as the clamp surface is increased, the voltage necessary to produce the same amount of clamping force decreases.  
         [0119]    [0119]FIG. 9 shows a similar relationship between the force and clamping voltage. A peak velocity can be selected by adjusting the clamp voltage. However, when the clamp voltage becomes too high, the velocity begins to drop because of the increased difficulty in overcoming the clamping force to move forward. The output force also increases with increased voltage.  
         [0120]    The step length is a function of the elastic limit of the expandable material and of the voltage applied to the expandable material.  
         [0121]    As can be seen from the drawings of FIG. 8, optimum force and velocity can be separately set, and the values may need to be set at different values to achieve different results.  
         [0122]    [0122]FIG. 10 shows a typical set of waveforms generated by the control console  120  for control of the actuator of the preferred mode of the first embodiment of the present invention. For purposes of this time chart, we assume that the expandable member  48  is oriented such that when the voltage on electrical lead  54  is positive, member  48  is expanded in length.  
         [0123]    Voltage  148  represents the voltage applied to the wafer base, and voltage  150  represents the voltage on the glider. The voltage difference between voltages  148  and  150  represents the clamping voltage. According to one mode of the present invention, the clamping voltage is simply kept at a constant value at all times. This produces satisfactory results, but is less preferred than the technique described herein.  
         [0124]    It was found by the present inventors that when a constant clamping voltage was maintained at all times, this caused buildup of charge across the elements and also caused increased attraction between the wafers, causing the separation distance between the glider  24  and base  22  to decrease. According to the preferred mode of the present invention, the voltage across the glider and base is maintained for a relatively short time, e.g., 1-4 ms. At the end of that 1-4 ms time, the voltage across the glider/base is reversed in polarity. This causes a momentary time during which the voltage across the glider base approaches zero. At this time, the glider and base separate slightly, followed by an increased attraction. This increased attraction, however, has opposite sense charge layer characteristics so that charge buildup is avoided.  
         [0125]    Turning then to the time chart, prior to point  170 , the time chart shows that the voltage between the glider and the base is negative: that is, the voltage on the glider is less than the voltage on the base. At time point  170 , the voltage across the electrical leads are reversed. This momentarily loosens the electrostatic clamping force between the clamping wafer  46  and the wafer base  34 , but essentially immediately re-tightens the clamping force. At this point, the voltage  154 , which is the voltage controlling the expansion of the electrostatic element, is dropped to zero as quickly as possible. This causes a quick contraction of the expandable member within hundreds of nanoseconds. As described above, the quick contraction causes the glider to overcome the clamping force and move slightly forward.  
         [0126]    At time point  172 , voltage  154  begins slowly increasing. This causes a slow increase in the length of the expandable member  48 . This slow increase pushes forward the mass load rather than overcoming the clamping force. When the expandable member  48  is completely expanded, at time  174 , the voltage across member  48  drops to zero again, thereby repeating the previous step causing a further forward movement.  
         [0127]    By repeating these steps, the system has a continuously-intermittent forward motion. Backward motion is carried out the opposite of the forward motion as shown on the negative sense line  155 , at time  176  etc.  
         [0128]    The waveforms for the second embodiment are slightly different and are shown in FIG. 11. One cycle may be considered to begin at time point  180 , when the voltage potential on the curve  166 , which represents the potential on the electrical lead  90  driving the proximal glider  86 , is dropped to zero. At the same time, the voltage on line  168 , connected to the distal glider  84 , rises. This allows the proximal glider  86  to slide freely relative to the wafer base, but clamps the distal glider  84  relative to the wafer base.  
         [0129]    At this time, the voltage  154 , which drives the expandable member  48  is reduced, so that the expandable member contracts in size. Since the distal glider has been clamped, the proximal glider  86  is moved to the right in FIG. 4. After full contraction, at time  182 , the voltages are reversed, with the distal glider being freed, and the proximal glider being clamped. The voltage across the expandable member  48  then increases, causing the distal glider to move to the right in FIG. 4. Of course, opposite direction motion is carried out using precisely the opposite steps.  
         [0130]    FIGS.  12 - 18  show the interrelationships between clamping voltage, expandable member voltage, voltage amplitude, waveform, frequency, phase angle difference and clamping force. FIGS.  12 - 18  show actual values for specific prototypes used according to the present invention.  
         [0131]    [0131]FIG. 12 shows the velocity of an element plotted as a function of electrostatic clamp voltage for various external loads. For each design, there is an optimum range where too little or too much clamp voltage produces inferior results. If the clamp voltage is too low, e.g., less than 50 volts as shown in FIG. 13, then no movement may be possible at all.  
         [0132]    [0132]FIG. 13 shows the output force plotted as a function of electrostatic clamping voltage for various clamping cycle frequencies. The clamp voltage increase produces an output force which increases until it plateaus. Lower frequencies have less overall effect than the highest frequency tested. The control frequencies of the voltage inputs to the expandable member and the clamping wafer generally control the repetitive rate of actuator steps.  
         [0133]    [0133]FIG. 14 shows a plot between the voltage applied to the expandable member and the force produced for various clamping voltages. It should be seen that for the different clamping voltages, different expansion voltages for the piezo electric element are possible.  
         [0134]    [0134]FIG. 15 shows a relationship between the velocity and the mass of the external load for different clamp voltages.  
         [0135]    [0135]FIG. 16 shows a three dimensional plot between the velocity, the loading, and the force of the load.  
         [0136]    [0136]FIG. 17 shows the force as a function of glider mass data, showing that the output force increases linearally, at least over a specified range, with the glider mass.  
         [0137]    [0137]FIG. 18 shows a plot of the force versus phase of the PZT clamps.  
         [0138]    [0138]FIGS. 8, 9 and  12 - 18  show the large range of operating characteristics that are controllable by way of mathematical and experimental modeling which produce an application-specific design procedure. The actual use of a linear actuator constructed according to the present invention yields a required total displacement, a minimum step size, a maximum velocity, a volumetric size constraint and a maximum force. The design procedures include prediction of whether such a set of constraints can be satisfied and then guide the design of a complete linear actuator, according to the present invention for that task.  
         [0139]    Another advantage of the present invention is the ability to control motion by either displacement, force or a combination of both. Traditional linear motors can only be driven by specifying displacements because there is high mechanical impedance between the motor and the workpiece, i.e., the load created by the work piece at the distal end of the linear motor. For example, in the case of a rotary motor driving through a rotary-to-linear coupling, such as a worm and worm gear, even medium levels of force at the distal end are not transmitted back to the motor due to the mechanical advantage of the high gear ratio. This condition renders force control impossible without extra sensors added to the distal end to workpiece interface.  
         [0140]    The present invention preferably uses sensor  300 , which senses force or displacement and feeds back a signal indicative thereof. Alternately, however, controller  120  may directly sense any load changes on work interface  64  from a workpiece through monitoring voltage, current and phase angle changes. Controller  120  can be programmed to automatically respond to these changes through feedback mechanisms to adjust one or more settings for the following: glider waveform control  128 , voltage amplitude control  130 , adjustable frequency control  132 , expandable member frequency control  138 , and phase control  126 . Thus, a specific force/displacement relationship can be maintained within the power and mechanical limits of the system.  
         [0141]    The device of the present invention is capable of small precision steps in the range of 10-30 nanometers throughout the entire displacement range of the device which can be between 3.3 cm and 12 cm. The actual theoretical displacement is limited only by the length of the wafer base. However, according to another preferred modification of the present invention, glider  24  is connected to casing C by a spring which limits the length of movement of the glider relative to the base. This spring can preferably bias glider into a specific position; whereby when the clamping force is released between the glider and the base, the spring biases the combination back to a zero position.  
         [0142]    The preferred device fits within a ⅜ inch tube, but still produces {fraction (1.2)} foot pounds of force over its range.  
         [0143]    The inventors of the present invention tested the above-described linear actuator, and found that failures occasionally occurred therein, although the general concept was quite sound. After extensive tests, the inventors had concluded that the SiN surfaces would be the most wear-resistant surfaces. However, after expensive testing they found that if both surfaces were formed of the same material, those surfaces tended to stick to one another over time. When the two surfaces were made of dissimilar materials, they did not stick.  
         [0144]    After testing special materials, the inventors decided that the base material should be polished silicon and that the clamp material surface should be SiN, more preferably a silicon wafer with a 500 Å thick silicon dioxide layer, covered with 2000 Å of SiN. In this way, the SiN layer slides relative to the silicon base. Although the silicon base may oxidize over time to form an SiO2 layer, the two materials in contact would always be different materials.  
         [0145]    Another problem was found in the way the materials were made. The silicon wafers are made as long wafers, and cuts are made to seperate the silicon wafers using a mechanical cutting saw. This, however, caused chips on the silicon wafer. Each of these chips formed a sharp edge. This sharp edge tended to cause arcing, especially when the high voltage and high frequency voltages were applied.  
         [0146]    The inventors obviated this problem by changing the cutting technique. The silicon wafers are 400 μm thick. A diamond saw is used to cut a trench 25 μm wide and 300 μm in depth into this silicon wafer. The 300 μm trench goes ¾ of the way through the material. The materials are snapped apart at this trench. The facing surface of these materials is the cut part, not the snapped part. This cut part has no chips or rough edges thereon, and therefore no arcing or sparking occurs when the final unit is formed.  
         [0147]    [0147]FIG. 19 shows a first lens delivery tip of the present invention. The mass loading arm  64  according to this preferred mode pushes on a force-delivering element, moving mass  1900 . Element  1900  is moved within the chamber  1902  by the motion of the stepper motor.  
         [0148]    Any surgical element, and especially an eye surgery element, is used in a moisture-intensive environment. The inventors found that the preferred rotary motor of the present invention, however, would not operate properly once moist. To overcome this problem, an O-ring seal  1901  seals between the movable piece and the casing to avoid liquid seepage into the motor during sterilization. O-ring  1901  must be located in a cylindrical area to ensure the best seal, and the farther forward the better. O-ring is shown sealing between the pushing element  1910 , and the guide element  1912 . O-ring  1901  could alternately be located behind mass  1900 .  
         [0149]    Chamber  1902  also includes a ridge area  1904  thereon which engages a corresponding notch  1906  within the force delivering area  1900 . This prevents any rotary torque. The ridge is preferably formed of a minimal friction material, such as teflon, to ensure smoothest possible forward and reverse motion. The ridge  1904  prevents placement of O-ring  1901  at a location close thereto.  
         [0150]    A pushing element  1910  includes a rod which is movable through guide element  1912 , within which the shaft  1910  passes.  
         [0151]    The end of the shaft  1910  includes a pusher element  1914  which fits within the inside of lens cassette  1916 . Pusher element  1914  presses against lens  1918 . As the arm is pushed forward by the motor, the cylindrically-rolled lens is pushed through the cylindrical delivery shaft  1930 , and finally into the eye.  
         [0152]    According to the present invention, the materials used to deliver the lens in the eye are formed of a number of connectable pieces. The housing portion is formed of a cylinder  1920  and an attachment portion  1922 . Attachment portion  1922  is shown in more detail in FIG. 20. It includes a notched groove  1924  thereon. The detachable delivery piece  1940  includes a peg  1942  which fits within the notched groove  1924 , and twists therein to maintain contact therebetween. The lens delivery cassette  1950  fits within the lens delivery device  1960  which includes lens delivery tube  1930 . The cassette element  1950  fits within an appropriate groove  1944  within the delivery device  1940 .  
         [0153]    Lens  1918  is shown in FIG. 23 in the unfolded condition, and in FIG. 24 in the folded condition. The folded lens fits within the cassette  1950 . The plunger  1914  pulls the lens from the cassette and pushes it into the eye.  
         [0154]    A second, and currently preferred, embodiment of the lens delivery system is shown in FIGS. 26 a - 26   d . The moving mass  2600  has a special shape. The push rod  1910  includes an insulated non-conductive insert  2602 . This insert has a non-conductive portion  2604 , formed of insulating material, which is screwed into the moving mass  2600 . The rod  1910  has a threaded area  2606  which is screwed into the insulated area. This non-conductive insert protects the rod from receiving any charge from the stepper is motor. Otherwise, residual charge might conceivably creep into the rod.  
         [0155]    Moving mass  2600  moves back and forth within the chamber  1902 . In this embodiment, the element is sealed at location  2610  by an O-ring  2612 . An attachment mechanism, including at least tip  1930  is removable from the O-ring portion  2612 .  
         [0156]    Although only a few embodiments have been described in detail above, those having ordinary skill in the art will certainly understand that many modifications are possible in the preferred embodiment without departing from the teachings thereof.  
         [0157]    For example, mechanical equivalents for the electrostatic clamps may be used. Mechanical biasing methods for increasing the friction at the glider wafer to base wafer interface would have the advantage of providing the performance achieved with continuous electrostatic clamping. In addition, the substitution of mechanical biasing methods could eliminate the additional electronic controlling required by the electrostatic clamps.  
         [0158]    All such modifications are intended to be encompassed within the following claims.