2.875 - Fall 2001 Mechanical Assembly and Its Role in Product Development Term Project: Report #2 Analyzing the Assembly Design of a Computer Mouse Using Datum Flow Chains October 31, 2001 Annabel Flores James Katzen Photos taken from: http://www.petergof.com/x-ray/mouse.htm http://www.mousemorf.com/images/mouse2b.jpg Analyzing the Assembly Design of a Computer Mouse1 Using Datum Flow Chains The Microsoft Mouse Version 2.0 is an ergonomic, dual-button mouse. The simple, ten-part design provides an opportunity to analyze the product’s assembly characteristics. In addition, we can apply assembly analysis tools such as a liaison diagram and datum flow chains to evaluate the current design and propose product redesigns. Below is a figure of the computer mouse. Figure 1: Computer Mouse Semi-Exploded View The Liaison Diagram for the mouse is shown below: Mouse Base (Part 8) Sticker Pad #1 (Part 3) Screw (Part 4) ce an ar pe Ap Circuit Board (Part 11) Functional (Gear aligned wrt Encoders) F (Ge unctio wrt ar ali nal En gne cod d ers ) Gear #1 (Part 7) Gear #2 (Part 7) Ball Holder (Part 1) Spring (Part 9) Ball (Part 2) Wheel (Part 10) Sticker Pad #2 (Part 3) nt ge an ll t is) Ba x l( ra na ea t io G nc ith Fu w s tton s) (Bu nal witche ctio S Fun ed wrt n Alig Cord (Part 6) Fun ction a with l (Ball ta Gea r ax ngent is) Mouse Cover (Part 5) Figure 2: Liaison Diagram for Microsoft® Mouse v2.2A Note that this diagram shows the numerous key characteristics that must be delivered in this device. A designer must pay attention to numerous aspects of the assembly in order to properly deliver the important functional and customer requirements. This diagram appears fairly 1 Refer to Bill of Materials and exploded view of mouse attached at end of product. straightforward, and shows that there is no coupling of key characteristics. Thus, we assume that each of these key characteristics can be met under nominal conditions. In observing the liaison diagram, as well as various different parts of a mouse, we found a number of key characteristics that we could have focused on for this report. For example, the alignment between the mouse base and cover is a key characteristic particularly of importance to the end user who would like a smooth transition between the parts. This key characteristic is therefore an appearance characteristic. Another key characteristic is the positioning of the mouse cover with respect to the circuit board, so that the buttons properly actuate the electronic switches. This key characteristic is therefore a functional characteristic. In choosing a key characteristic for the purpose of this analysis, we were compelled to choose one that was crucial in the functional performance of the mouse. We determined that other than the monitoring of switch inputs, the key driver of mouse functionality is its ability to convert mechanical motion into optical information that could be transferred onto a computer screen. A user will move the mouse on a surface that, in turn, will move the ball within. Refer to the figure below to follow our nomenclature. The ball transfers up/down and left/right motion to two independent gear axles that are in constant contact with the ball. The gear head rotates according to the ball’s speed and direction. The teeth on the gear head pass through optical sensors that record the speed and direction of the ball and hence the user’s movement. Key Characteristic Sensor Spacing Y X Gear Head Figure 3: Gear/Sensor with Co-ordinate System The position of the gear’s teeth with respect to the sensor is critical to provide the sensitivity necessary to capture the user’s movement. If the gear is grossly out of position in or about any direction, the sensors will not be able to process the data accurately. However, for the purpose of this analysis, we are focusing on the key characteristic that is the relative position of the gear and sensor in the direction parallel to the gear’s rotational axis. This key characteristic, and its associated coordinate system are denoted in the figure above. Note that we have chosen to analyze only one gear/sensor pair instead of both as the same analysis can be applied to both. The parts that deliver the key characteristic are the mouse base (part #8), circuit board (part #11), optical sensors (subassembly on part #11) and gear (part #7). The most likely root for this datum flow chain is the mouse base as this part locates all others. The datum flow chain for the gear/sensor subassembly is as follows: Circuit Board 10 6 7 8 1 9 11 2 Mouse Base 12 3 4 13 5 Sensors 15 Feature Coord Frame 16 14 Group Coord Frame Gear Figure 4: Datum Flow Chain Delivering Key Characteristic As the assembly root, the mouse base is the starting point to locate all other parts. The table below lists the important features on the base that locate the circuit board and the gear. Feature Number 1 2 3 4 5 6 7 8 9 10 11 12 13 Feature Support Pin 1 Pin 2 Tab 1 Tab 2 Bottom Surface Hole 1 Hole 2 Hole Set 1 Hole Set 2 Pegs Pegs Sensor Spacing Part Base Circuit Board Photo Eye Sensor LED Sensor Sensors 14 15 16 Teeth Peg End 1 Peg End 2 Gear Table 1: Features Delivering the KC The Support, Pin 1 & Pin 2 define the location of the circuit board within the mouse base. Tabs 1 & 2 locate the position of the gears with respect to the base. The injection-molded features of the base are shown in the figure below. The part’s coordinate frame locates the coordinate frame of the features. Tab 1 Tab 2 Pin 1 Support Pin 2 Figure 5: Mouse Base Features Delivering the KC The circuit board features that connect to those on the mouse base are the bottom surface and Holes 1 & 2. The circuit board’s coordinate frame is located in the assembly through these features. The part coordinate frame defines the frame of the Hole Sets 1 & 2 that define the position of the optical sensors. Figure 6 locates the above features on the circuit board. The circuit board’s coordinate frame is located through these features. Hole Set 2 Hole Set 1 Hole Set 2 Hole 1 Hole Set 1 Hole 2 Figure 6: Circuit Board Features Delivering the KC The two sensors that translate the mechanical motion of the gears are the photo eye sensor and the LED Sensor. The position of these sensors, and the spacing between them, is defined through the position of the circuit board’s hole sets. LED Sensor Photo Eye Sensor Figure 7: Sensor Features Delivering the KC As shown in Figure 8, the gear’s coordinate frame is located through its pegs and the respective tabs on the mouse base. Peg End 2 Teeth Peg End 1 Figure 8: Gear Features Delivering the KC The datum flow chain developed in Figure 4 is a direct representation of the assembly scheme. The circuit board and gear are located through features on the mouse base. The circuit board subassembly locates the sensors. The position of the gear with respect to the sensor spacing is the key characteristic under analysis. In studying the assembly scheme of the mouse, it became apparent that parts in the assembly were over-constrained. Adding the degrees of freedom to the datum flow diagram developed in Figure 4 results in the following figure. Circuit Board 10 6 Z, x, y 7 8 1 X, Y 2 X, Y, z Over-constraint 9 Overconstraint Mouse Base 11 12 3 4 5 13 X, Z, x, z Y Sensors 15 Feature Coord Frame 16 14 Group Coord Frame Gear Figure 9 Datum Flow Chain with Assembly Degrees of Freedom There are a number of potential redesigns of the computer mouse that can eliminate the overconstrained conditions. In addition, a product redesign can improve the deliver of the key characteristic. We have developed a number of design proposals that improve the product assembly with a more robust design and are described in detail below. Design Proposal 1: Revise Circuit Board – Mouse Base Locating Method Currently, the circuit board (Part #11) is oriented with respect to the mouse base (Part #8) through the use of two peg-hole mates. These are shown in the picture below: Figure 10: Assembly Features linking the mouse base and the circuit board As we have seen in this class, this is an inherently over-constrained design. The over-constraint in the x and y directions will cause numerous problems, such as assembly difficulty, and the locking-in of internal stresses. This over-constraint can be overcome by introducing a peg-slot mate at one of the features. This design is shown below: Figure 11: Proposed Assembly Features linking the mouse base and the circuit board Note that since the two pegs do not share a common x or y location, the slot must be placed on an angle. The long axis of the slot must be parallel to the line that connects the two center points of the pegs. This will result in a completely constrained assembly, with no over-constraint. The circuit board will be completely positioned and oriented properly with respect to the mouse base. This will likely result in reduced assembly efforts, and reduced “locked-in” stresses. Design Proposal 2: Revise Optical Encoder Sensors’ LED Unit – Circuit Board Locating Method Currently, the optical encoder sensors’ LED units are oriented with respect to the circuit board (Part #11) through the use of two peg-hole mates. These are shown in the picture below: Figure 12: Assembly Features linking the optical encoder sensors’ LED units and the circuit board This is recognized as an inherently over-constrained design. The over-constraint in the x and y directions will cause numerous problems, such as assembly difficulty, and the locking-in of internal stresses. It is assumed that these problems occur very regularly, since both the LED units are visibly misoriented about their x-axes on the unit we examined. We assume that this misorientation does not affect the amount of light produced by the LED units in the direction of the photo eye (due to a wide field of illumination). However, this over-constraint likely causes additional effort than should be needed in assembling these relatively simplistic parts. This over-constraint can be overcome by introducing a peg-slot mate at one of the features. This design is shown below: Figure 13: Proposed Assembly Features linking the optical encoder sensors’ LED units and the circuit board Although it has not been confirmed, it is assumed that the through holes in the circuit board are large enough to have clearance between the sensor element leads and the hole edges. If this is the case, the item is not over-constrained. However, if these items are soldered one lead at a time rather than both at once, the item will be over-constrained, since an adjustable contact feature was fixed before the mates were fixed. But since it is known that this part is made with a wave-soldering process, we can assume that the contacts are all affixed at the same time. This new design will result in a completely constrained assembly, with no over-constraint. The LED unit will be completely positioned and oriented properly with respect to the circuit board. This will likely result in reduced assembly efforts, and reduced “locked-in” stresses. Design Proposal 3: Revised Optical Encoder Sensors’ Photo Eye Unit – Circuit Board Locating Method Currently, the optical encoder sensors’ photo eye units are oriented with respect to the circuit board (Part #11) through the use of three collinear peg-hole mates. These are shown in the picture below: Figure 14: Assembly Features linking the optical encoder sensors’ photo eye units and the circuit board As with the circuit board – mouse base and the LED units – circuit board mates, this is recognized as an inherently over-constrained design. The over-constraint in the x and y directions will cause numerous problems, such as assembly difficulty, and the locking-in of internal stresses. It is assumed that these problems occur also very regularly, since both the photo eye units are visibly misoriented about their x-axes on the unit we examined. We assume that this misorientation does not affect the amount of light sensed by the photo eye units (due to a wide sensing field). However, this over-constraint likely causes additional effort than should be needed in assembling these relatively simplistic parts. Eliminating one of the three pegs and introducing a peg-slot mate at one of the features can overcome this over-constraint. This design is shown below: Figure 15: Proposed Assembly Features linking the optical encoder sensors’ photo eye units and the circuit board This will result in a completely constrained assembly, with no over-constraint. The photo eye unit will be completely positioned and oriented properly with respect to the circuit board. This will likely result in reduced assembly efforts, and reduced “locked-in” stresses. It is not known whether the new two-lead photo eye units would be compatible with the existing circuitry and sensing algorithms. Therefore, this change to correct an over-constrained condition may require additional analysis and changes. The same concern regarding the soldering process exists for this item, as it did for the LED units. Suggested Redesigns That Improve KC Delivery The Key Characteristic that has been identified is the alignment of the gear, the optical encoder sensor LED unit and the optical encoder sensor photo eye unit. This alignment must be tightly controlled, since the mechanical motion of the mouse is directly transferred to electrical signals via the use of the optical encoder. Figure 16 shows this nominal case. Y Y Gear X X Alignment Centerline Photo Eye Unit LED Unit Figure 16: Nominal case where the light transmitted by the optical encoder sensor LED unit is sensed by the optical encoder sensor photo eye unit If this alignment were in error, the amount of light passing through the gear (Part #7) would be affected. If large misalignments occur, no light could pass through, and even though the mouse is in motion, the unit would not sense the movement. The condition of lateral error is shown below: Y Y Gear X X Alignment Centerline Photo Eye Unit LED Unit Figure 17: Effect on the amount of light sensed by the optical encoder sensor photo eye unit as the result of lateral misalignment of the optical encoder sensor LED unit and the optical encoder sensor photo eye unit The condition of angular error is shown below: Y Y Gear X X Alignment Centerline Photo Eye Unit LED Unit Figure 18: Effect on the amount of light sensed by the optical encoder sensor photo eye unit as the result of angular misalignment of the optical encoder sensor LED unit and the optical encoder sensor photo eye unit Multiple design proposals are being offered to make the sensing system more robust to variation in the alignment of the optical encoder sensor LED unit and the optical encoder sensor photo eye unit. Design Proposal 4: Increase Diameter of Toothed Portion of Gear Since the passages that allow the passage of light are slots rather than point holes, the current design of the gear (part #7) is tolerant of some lateral error in the x-direction. A non-robust design for the gear, with point holes is shown below: Figure 19: Non-Robust design for optical encoder gear However, due to geometric concerns, the current gear cannot be made more tolerant of lateral error in the x-direction, since expanding the slots would soon weaken the gear tremendously. But, if the overall diameter of the gear is increased, the slots could then be lengthened, making the gear much more tolerant of lateral error. This design modification is shown below: Figure 20: Proposed design improvement for optical encoder gear Note that the accuracy of the device would be negatively affected as the lateral error in the xdirection increases. Knowing the elapsed time over which the light passes through a gap in the gear teeth, a rotational velocity can be calculated, as long as the distance of the gap is known. However, if this gap increases, the relation between the time and the corresponding rotational velocity is affected, and false readings can be created. This is precisely what would happen if the gear placement were in error. Because the width of the slot increases with increasing radius, this increased gap would fool the electronics into thinking that the mouse was moving slower than it was. However, existing computer software utilities exist that allow the computer user to customize the behavior of the mouse. Therefore, the customer could correct the slight calculation error in mouse position, and this integration of this design proposal is therefore feasible. Design Proposal 5: Decrease Distance Between Optical Encoder Sensor LED and Photo Eye Unit Changing the distance between the optical encoder sensor LED and sensing field of optical encoder sensor photo eye units will affect the robustness of the light sensing performance. Shortening this distance will result in an increased ability of the photo eye to detect the light illumination, even in the presence of LED / Sensor misalignment. The same angular misalignment that was shown in Figure 18 is repeated in Figure 21. However, in Figure 21, the distance between the LED and the photo eye unit is decreased. Gear Y X Alignment Centerline Photo Eye Unit LED Unit Figure 21: Improved robustness of sensing device created by the shortening of the distance between the sensor LED and the photo eye unit As can be seen, with a misalignment between the LED and the sensor unit, the photo eye “sees” more of the beam if the photo eye is brought closer to the LED. Therefore, this shortened distance would allow a higher amount of light to be sensed. This change would therefore improve the KC delivery by reducing the sensitivity of the system performance by reducing the effect of variation in the alignment of the optical encoder sensor LED unit and the optical encoder sensor photo eye unit. Upon examination of the assembly, it does appear that some of the distance between the two components can be eliminated. Examining the following photograph can see this: Figure 22: Distance between Optical Encoder Sensor LED and Photo Eye Unit A rough estimate predicts that almost 50 per cent of the existing distance can be eliminated. Placing the components closer together would require adding more material to the circuit board (which may introduce some cost), but is well within the realm of possibility. Design Proposal 6: Change Field of Illumination of Optical Encoder Sensor LED and Sensing Field of Photo Eye Unit Changing the field of illumination of optical encoder sensor LED and sensing field of optical encoder sensor photo eye units will also affect the robustness of the light sensing performance. Using elements that have a large field of illumination and/or elements that have a large sensing region will transmit and sense a constant amount of light, even in the presence of LED / Sensor misalignment. The same angular misalignment that was shown in Figure 18 is repeated in Figure 23. However, in Figure 23, the field of illumination and the sensing field have been increased in area. Gear Y X Alignment Centerline Photo Eye Unit LED Unit Figure 23: Improved robustness of sensing device created by the use of electronic components with wider field of illumination and sensing areas As can be seen, with a misalignment between the LED and the sensor unit, the photo eye “sees” more of the beam if the optical properties are widened. Therefore, these upgraded components would allow a constant amount of light to be sensed, even in the presence of LED / Sensor misalignment. As in the prior proposal, this change would therefore improve the KC delivery by reducing the sensitivity of the system performance by reducing the effect of variation in the alignment of the optical encoder sensor LED unit and the optical encoder sensor photo eye unit. It is expected that this design change will not increase per-piece cost of the finished unit. Optical LED and photo-eyes are commodity electronic components, and are made with multiple values for illumination field and sensing area. It is very likely that improved components can be found that will still satisfy overall quality and price design requirements. Design Proposal 7: Incorporate Optical Encoder Sensor LED and Photo Eye Unit Into One Component We have seen that an important Key Characteristic (and one that can be addressed) is the alignment of the gear face with the axis connecting the optical encoder sensor LED unit and the optical encoder sensor photo eye unit. This KC is obviously affected by the horizontal position, the vertical position, and the rotational position about the horizontal and vertical axes. To achieve this properly, both the optical encoder sensor LED and the optical encoder sensor photo eye unit must be placed accurately, relatively to each other. However, currently these components are separately mounted to the circuit board. Therefore, much care must be taken to ensure their alignment. Often, these components are placed improperly, as seen below: Figure 24: Misalignment between optical encoder sensor LED and photo eye unit The importance of the relative position of the optical encoder sensor LED and the optical encoder sensor photo eye unit can be eliminated if these two items are incorporated into one unit. In effect, the two items will become their own, fully constrained, sub-assembly. These integrated photo eye gates are common electronic devices, and it is expected that one can be found that would meet the quality and cost requirements. Note that it is likely that this integrated unit will at least three external leads (power, signal, ground) that will be used to mount the unit to the circuit board (Part #11). Care should be taken that the mounting of these three leads does not create an over-constrained condition similar to the one that currently exists with the optical sensor units’ photo eye sensors. Design Proposal 8: Replacement of Mouse Wheel/Trackball, Gear, and Optical Encoder Technology with Alternative Motion Sensing Technology The objective of the entire ball (Part #2), gear (Part #7), and optical encoder electronics systems linkage (Part #11) is to reliably translate planar motion (input by a human user) into an electrical signal (output to a integrated circuit for analysis). The original mouse, developed by Douglas Engelbart in 1968, utilized this wheel/trackball technology. This design is shown below: Figure 25: Underside view of mouse developed by Douglas Englebart2 Note the horizontal and vertical discs protruding from the underside of the mouse. Since this early design, this method has been improved upon incrementally, and evolved to its current form. The figure below is a partially disassembled view of an original Apple mouse from 1983. This mouse incorporated the ball into the design to transfer mechanical motion into optical information. There are significant differences in this design as the key characteristic is integral to the circuit board subassembly. Figure 26: 1983 Apple Mouse The figure below is an earlier version of the Microsoft Mouse we have studied thus far. Figure 27: 1998 Microsoft Mouse 2.0 2 http://www.superkids.com/aweb/pages/features/mouse/mouse.html While there were a number of design improvements, the key characteristic is still delivered via the same parts. The part features on the base that locate the circuit board are redesigned though it is still over-constrained. Pin/Hole Pin/Hole Figure 28: 1998 Microsoft Mouse – Base & Circuit Board Locating Features However, there are numerous other technologies that can sense planar motion. A number of these are solid-state components (i.e. dual axis accelerometers, texture recognition cameras, etc.) that require no moving parts. Solid-state electronics provide multiple advantages, such as: the reduction in total parts; the elimination of the need to periodically clean the device; and the reduction in overall weight (due to the lack of the need to create friction between the ball and the table surface). The reduction in parts as a result of using solid-state technology will likely yield lower material costs, lower tooling costs, lower assembly costs times, and overall higher reliability. Additional effort may be needed to process and filter the input signals to obtain the required resolution and bandwidth, however, these algorithms are readily available, and would be simple to integrate. This design approach has been implemented by a number of computer mouse manufacturers. Optical mice have come to the forefront of the market, and are currently displacing the wheel/trackball mouse as the dominant technology. The following Figures present different optical mouse designs that are currently on the market. Figure 29: Microsoft® Optical Mouse3 Figure 30: Macally Peripherals® Optical Mouse4 3 4 http://www.overclockers.co.uk/acatalog/ms_intellimouse_optical.jpg http://www.macally.com/gif/products/usb/micromouse.gif Figure 31: Logitech® Optical Mouse5 Other technologies that monitor input motion include virtual reality gloves and hand mounted ring devices that use accelerometers to accurately track the desired motion and resolve it into planar motion. Perhaps the computer mouse will eventually be replaced! 5 http://www.theshipcarver.com/images/products/peripherals/log_ifeel_optical.gif Appendix 1: List of Figures FIGURE 1: COMPUTER MOUSE SEMI-EXPLODED VIEW 2 FIGURE 2: LIAISON DIAGRAM FOR MICROSOFT® MOUSE V2.2A 2 FIGURE 3: GEAR/SENSOR WITH CO-ORDINATE SYSTEM 3 FIGURE 4: DATUM FLOW CHAIN DELIVERING KEY CHARACTERISTIC 4 FIGURE 5: MOUSE BASE FEATURES DELIVERING THE KC 5 FIGURE 6: CIRCUIT BOARD FEATURES DELIVERING THE KC 6 FIGURE 7: SENSOR FEATURES DELIVERING THE KC 6 FIGURE 8: GEAR FEATURES DELIVERING THE KC 6 FIGURE 9 DATUM FLOW CHAIN WITH ASSEMBLY DEGREES OF FREEDOM 7 FIGURE 10: ASSEMBLY FEATURES LINKING THE MOUSE BASE AND THE CIRCUIT BOARD 8 FIGURE 11: PROPOSED ASSEMBLY FEATURES LINKING THE MOUSE BASE AND THE CIRCUIT BOARD 8 FIGURE 12: ASSEMBLY FEATURES LINKING THE OPTICAL ENCODER SENSORS’ LED UNITS AND THE CIRCUIT BOARD 9 FIGURE 13: PROPOSED ASSEMBLY FEATURES LINKING THE OPTICAL ENCODER SENSORS’ LED UNITS AND THE CIRCUIT BOARD 9 FIGURE 14: ASSEMBLY FEATURES LINKING THE OPTICAL ENCODER SENSORS’ PHOTO EYE UNITS AND THE CIRCUIT BOARD 10 FIGURE 15: PROPOSED ASSEMBLY FEATURES LINKING THE OPTICAL ENCODER SENSORS’ PHOTO EYE UNITS AND THE CIRCUIT BOARD 11 FIGURE 16: NOMINAL CASE WHERE THE LIGHT TRANSMITTED BY THE OPTICAL ENCODER SENSOR LED UNIT IS SENSED BY THE OPTICAL ENCODER SENSOR PHOTO EYE UNIT 11 FIGURE 17: EFFECT ON THE AMOUNT OF LIGHT SENSED BY THE OPTICAL ENCODER SENSOR PHOTO EYE UNIT AS THE RESULT OF LATERAL MISALIGNMENT OF THE OPTICAL ENCODER SENSOR LED UNIT AND THE OPTICAL ENCODER SENSOR PHOTO EYE UNIT 12 FIGURE 18: EFFECT ON THE AMOUNT OF LIGHT SENSED BY THE OPTICAL ENCODER SENSOR PHOTO EYE UNIT AS THE RESULT OF ANGULAR MISALIGNMENT OF THE OPTICAL ENCODER SENSOR LED UNIT AND THE OPTICAL ENCODER SENSOR PHOTO EYE UNIT 12 FIGURE 19: NON-ROBUST DESIGN FOR OPTICAL ENCODER GEAR 13 FIGURE 20: PROPOSED DESIGN IMPROVEMENT FOR OPTICAL ENCODER GEAR 13 FIGURE 21: IMPROVED ROBUSTNESS OF SENSING DEVICE CREATED BY THE SHORTENING OF THE DISTANCE BETWEEN THE SENSOR LED AND THE PHOTO EYE UNIT 14 FIGURE 22: DISTANCE BETWEEN OPTICAL ENCODER SENSOR LED AND PHOTO EYE UNIT 14 FIGURE 23: IMPROVED ROBUSTNESS OF SENSING DEVICE CREATED BY THE USE OF ELECTRONIC COMPONENTS WITH WIDER FIELD OF ILLUMINATION AND SENSING AREAS 15 FIGURE 24: MISALIGNMENT BETWEEN OPTICAL ENCODER SENSOR LED AND PHOTO EYE UNIT 16 FIGURE 25: UNDERSIDE VIEW OF MOUSE DEVELOPED BY DOUGLAS ENGLEBART 17 FIGURE 25: 1983 APPLE MOUSE 17 FIGURE 26: 1998 MICROSOFT MOUSE 2.0 17 FIGURE 27: 1998 MICROSOFT MOUSE – BASE & CIRCUIT BOARD LOCATING FEATURES 18 FIGURE 28: MICROSOFT® OPTICAL MOUSE 19 FIGURE 29: MACALLY PERIPHERALS® OPTICAL MOUSE 19 FIGURE 30: LOGITECH® OPTICAL MOUSE 20 Appendix 2: List of Tables TABLE 1: FEATURES DELIVERING THE KC 5