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3/19/2018 Chapter 5 Design for High Speed Automatic Assembly and Robot Assembly 1 Dr. Mohammad Abuhaiba

2 3/19/2018 5. 1 INTRODUCTION Fig. 5. 1: The slightly asymmetrical threaded stud would not present significant problems in manual handling and insertion For automatic handling an expensive vision system would be needed to recognize its orientation. If the part were made symmetrical, automatic handling would be simple. Dr. Mohammad Abuhaiba

3 3/19/2018 5. 1 INTRODUCTION if a part can be handled automatically, then it can usually be assembled automatically. When we consider design for automation, we will be paying close attention to the design of the parts for ease of automatic feeding and orienting. Dr. Mohammad Abuhaiba

4 3/19/2018 5. 1 INTRODUCTION In automatic assembly: We shall be mainly concerned with: 1. 2. 3. Time taken to complete an assembly does not control the assembly cost. It is the rate at which the assembly machine or system cycles. If the total rate (cost per unit time) for the machine or system and all the operators is known, the assembly cost can be calculated. Cost of all the equipment Number of operators and technicians Assembly rate at which the system is designed to operate Apportion the cost of product assembly between the individual parts and, for each part; we shall need to know the cost of feeding and orienting and the cost of automatic insertion. Dr. Mohammad Abuhaiba

5 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Cost of feeding & orienting parts depends on: 1. 2. Time between delivery of parts: reciprocal of the delivery rate. 1. Cost of the equipment required Time interval between delivery of successive parts. It is equal to cycle time of machine or system. Let Fr = required delivery or feed rate (parts/min), then the cost of feeding each part Cf is given by Dr. Mohammad Abuhaiba

6 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Rf = cost (cents/s) of using feeding equipment CF = feeder cost (\$) Eo = equipment factory overhead ratio Pb = payback period in months Sn = number of shifts worked per day The constant 5760 = number of available seconds in one shift working for one month divided by 100 to convert dollars to cents. Dr. Mohammad Abuhaiba

7 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Example: assume that a standard vibratory bowl feeder costs \$5000, payback period is 30 months with 2 shifts working, factory equipment overheads are 100% (Eo = 2), we get Rf = 5000 x 2/(5760 x 30 x 2) = 0. 03 cent/s It would cost 0. 03 cents to use the equipment for 1 second. Taking this figure as the rate for a "standard" feeder and assigning a relative cost factor Cr to any feeder under consideration, then Eq. (5. 1) becomes Cf = 0. 03(60/Fr)Cr (5. 3) Dr. Mohammad Abuhaiba

8 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Feeding cost per part is inversely proportional to required feed rate and proportional to feeder cost. For otherwise identical conditions, it would cost twice as much to feed each part to a machine with a 6 s cycle compared with the cost for a machine with a 3 s cycle. This illustrates why it is difficult to justify feeding equipment for assembly systems with long cycle times. It would cost twice as much to feed a part using a feeder costing \$10, 000 compared with a feeder costing \$5000. Dr. Mohammad Abuhaiba

9 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Fig. 5. 2: The faster the parts are required, the lower the feeding cost. This is true only as long as there is no limit on the speed at which a feeder can operate. There is an upper limit to the feed rate obtainable from a particular feeder. Fm = maximum feed rate Dr. Mohammad Abuhaiba

10 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Dr. Mohammad Abuhaiba

11 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Example: Let max feed rate from feeder = 10 parts/min. 1. If parts are required at a rate of 5 parts/min, feeder can simply be operated more slowly involving an increased feeding cost. 2. Suppose parts are required at a rate of 20 parts/min. 3. 4. Two feeders could be used, each at a rate of 10 parts/min. Feeding cost per part using two feeders to give twice max feed rate will be the same as one feeder delivering parts at its max feed rate. If required feed rate is greater than max feed rate obtainable from one feeder, feeding cost becomes constant and equal to cost of feeding when the feeder is operating at its max rate. This is shown in Fig. 5. 2 by the horizontal line. If multiple feeders are used for increased feed rates, then the line will be saw-toothed as shown. Dr. Mohammad Abuhaiba

12 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Eq. (5. 3) holds true only when required feed rate Fr

13 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING The meaning of the orienting efficiency E: Consider feeding of dies (cubes with faces numbered 1 to 6). If no orientation is needed, the dies can be delivered at a rate of 1 per second from a vibratory bowl feeder. If only those dies with the 6 side uppermost were of interest, a vision system could be employed to detect all other orientations and a solenoid operated pusher could be used to reject them. In this case the delivery rate would fall to an average of 1 die every 6 seconds or a feed rate of 1/6 per second. The factor 1/6 is defined as the orienting efficiency E and it can be seen that the max feed rate is proportional to the orienting efficiency (Eq. (5. 5)). Dr. Mohammad Abuhaiba

14 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING If dies were doubled in size and that feed speed on the feeder track were unaffected. It would then take twice as long to deliver each die. Max feed rate is inversely proportional to length of part in the feeding direction [Eq. (5. 5)]. Dr. Mohammad Abuhaiba

15 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Eq. 5. 4 shows that when Fr > Fm, the feeding cost per part is inversely proportional to Fm. Under these circumstances, cost of feeding is inversely proportional to orienting efficiency and proportional to length of part in the feeding direction. Automatic feeding and orienting methods are only applicable to "small" parts. Parts larger than about 8” in their major dimension cannot usually be fed economically. Dr. Mohammad Abuhaiba

16 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING When considering the design of a part and its feeding cost, the designer will know: 1. 2. The remaining two parameters that affect feeding cost, namely, the orienting efficiency E and the relative feeder cost Cr, will depend on: 1. 2. required feed rate Fr dimensions of the part, l part symmetry types of features that define its orientation. A portion of a classification system is presented in Figs. 5. 3 to 5. 5. Dr. Mohammad Abuhaiba

17 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Fig. 5. 3: 1 st digit of a 3 -digit shape code. Fig. 5. 4: 2 nd and 3 rd digits are determined for a selection of rotational parts (1 st digit 0, 1, or 2) and corresponding values of orienting efficiency E and relative feeder cost Cr. Fig. 5. 5: 2 nd and 3 rd digits are determined for a selection of non-rotational parts (1 st digit 6, 7, or 8). Dr. Mohammad Abuhaiba

18 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Dr. Mohammad Abuhaiba

19 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING Dr. Mohammad Abuhaiba

20 3/19/2018 5. 2 DESIGN OF PARTS FOR HIGHSPEED FEEDING AND ORIENTING FIG. 5. 5: 2 nd & 3 rd digits of geometrical classification for some non-rotational parts Dr. Mohammad Abuhaiba

21 5. 3 EXAMPLE Part shown in Fig. 5. 6 is to be delivered to an automatic assembly station working at a 5 s cycle. Use classification system and database to determine feeding cost assuming that cost of delivering simple parts at 1 per second using standard feeder of 0. 03 cents per part. Dr. Mohammad Abuhaiba 3/19/2018

22 3/19/2018 5. 3 EXAMPLE A = 30 mm, B = 20 mm, and C = 15 mm A/B = 1. 5 and A/C = 2 Fig. 5. 3: A/B < 3 and A/C < 4, part is cubic non-rotational and is assigned a 1 st digit of 8. Fig. 5. 5: part has no rotational symmetry about any of its axes. Dr. Mohammad Abuhaiba

23 3/19/2018 5. 3 EXAMPLE Outline of part in X direction: A step or projection in the basic rectangular shape This feature alone can always be used to determine part's orientation. This means that if the outline in the X direction is oriented as shown in Fig. 5. 6, part can be in only one orientation Therefore, 2 nd digit of the classification is 4. However, either groove apparent in the view in Y direction and step seen in the view in Z direction could also be used to determine the part's orientation. Select feature giving smallest 3 rd classification digit; in this case it is the step seen in X direction. Thus appropriate column number in Fig. 5. 5 is 0. Three-digit code: 840 Orienting efficiency: E = 0. 15 Relative feeder cost: Cr = 1 Dr. Mohammad Abuhaiba

24 3/19/2018 5. 3 EXAMPLE Longest part dimension l = 30 mm Orienting efficiency E = 0. 15 Eq. (5. 5) gives max feed rate obtainable from one feeder Fm =1500 E/ l = 1500 x 0. 15/30 = 7. 5 parts/min From the cycle time of 5 s the required feed rate Fr is 12 parts/min, which is higher than Fm. Since Fr > Fm we use Eq. (5. 4) Cr = 1 Feeding cost Cf = 0. 03(60/Fm)Cr = 0. 03(60/7. 5)1 = 0. 24 cents Dr. Mohammad Abuhaiba

25 3/19/2018 5. 4 ADDITIONAL FEEDING DIFFICULTIES Fig. 5. 7: If edges of parts are thin, shingling or overlapping can occur during feeding, leading to problems with the use of orienting devices on feeder track Dr. Mohammad Abuhaiba

26 3/19/2018 5. 4 ADDITIONAL FEEDING DIFFICULTIES Fig. 5. 8: for each combination of features, an approximate additional relative feeder cost is given that should be taken into account in estimating the cost of automatic feeding. Dr. Mohammad Abuhaiba

27 3/19/2018 5. 5 HIGH-SPEED AUTOMATIC INSERTION If a part can be sorted from bulk and delivered to a convenient location correctly oriented, a specialpurpose mechanism or work head can usually be designed that will place it in the assembly. Such work heads can generally be built to operate on a cycle as short as 1 second. For assembly machines operating on cycles greater than 1 sec, automatic insertion cost Ci is given by Fr = required assembly rate (or feed rate of parts) Ri = cost (cents/s) of using the automatic work head Dr. Mohammad Abuhaiba

28 3/19/2018 5. 5 HIGH-SPEED AUTOMATIC INSERTION The equipment rate Ri is given by Wc = work head cost (\$) Eo = equipment factory overhead ratio Pb = payback period in months Sn = number of shifts worked per day Assuming a standard work head costs \$10, 000, payback period is 30 months with two shifts working, and factory equipment overheads are 100% (Eo = 2), we get Ri = 10, 000 x 2/(5760 x 30 x 2) = 0. 06 cents/s Dr. Mohammad Abuhaiba

29 3/19/2018 5. 5 HIGH-SPEED AUTOMATIC INSERTION It would cost 0. 06 cents to use the equipment for 1 second. Taking this figure as the rate for a "standard" work head and assign a relative cost factor Wr to any work head under consideration, then Eq. (5. 6) becomes Insertion cost is inversely proportional to required assembly rate and proportional to work head cost. Dr. Mohammad Abuhaiba

30 3/19/2018 5. 5 HIGH-SPEED AUTOMATIC INSERTION Dr. Mohammad Abuhaiba

31 3/19/2018 5. 6 EXAMPLE Fig. 5. 6: For a cycle time of 5 s, assembly rate Fr is 12 parts/min and Eq. (5. 8) gives an insertion cost of: part is inserted horizontally into the assembly in the direction of arrow Y It is not easy to align and position Not secured on insertion Appropriate classification is row 1, column 2 in Fig. 5. 9 Automatic insertion code is thus 12, giving a relative work head cost of 1. 6. Ci= 0. 06(60/Fr) Wr = 0. 06(60/12)1. 6 = 0. 48 cents Total handling & insertion cost Ct = 0. 24 + 0. 48 = 0. 72 cents Dr. Mohammad Abuhaiba

32 3/19/2018 5. 7 ANALYSIS OF AN ASSEMBLY assembled at a rate of 9. 6 per minute Dr. Mohammad Abuhaiba

33 3/19/2018 5. 7 ANALYSIS OF AN ASSEMBLY FIG. 5. 11: Completed worksheets for high-speed automatic assembly analysis of the assemblies in Fig. 5. 10 - Original Design High speed automatic assembly No. Part or sub of or opern No. repe ats Orientat Relati Handli ion ve ng assembl feede code y r cost Max feed rate (parts/ min) Handli Inserti ng ng on difficul cost code ty (cents) Relati Insertio Inserti Total Figur ve n/ on cost e for work operati difficul (cent min head on cost ty s) parts cost (cents) Name of assemblyvalue Name of part, subassembly or operation ID RP HC OE CR FM DH CF IC WC DI CI CA NM 1 1 83100 0. 20 1 4. 8 12. 4 0. 40 00 1. 0 6. 3 0. 38 0. 69 1 Housing 2 1 02000 0. 40 1 21. 4 6. 3 0. 20 02 1. 5 0. 56 0. 63 1 Plunger 3 1 00840 . * ***. ** Manual assembly required 7. 13 0 Gasket 4 1 00800 . * * ***. ** Manual assembly required 6. 67 1 cover 5 2 21000 0. 90 1 122. 7 6. 3 0. 20 39 1. 44 0 screw 1. 8 11. 3 0. 68 Dr. Mohammad Abuhaiba

34 3/19/2018 5. 7 ANALYSIS OF AN ASSEMBLY FIG. 5. 11: Completed worksheets for high-speed automatic assembly analysis of the assemblies in Fig. 5. 10 – Re-Design High speed automatic assembly No. Part or sub of or opern No. repe ats Orientat Relati Handli ion ve ng Efficienc feede code y r cost Max feed rate (parts/ min) Handli Inserti ng ng on difficul cost code ty (cents) Relati Insertio Inserti Total Figur ve n/ on cost e for work operati difficul (cent min head on cost ty s) parts cost (cents) Name of assemblyvalue Name of part, subassembly or operation ID RP HC OE CR FM DH CF IC WC DI CI CA NM 1 1 83100 0. 20 1 4. 8 12. 6 0. 40 00 1. 0 6. 3 0. 29 0. 69 1 Housing 2 1 02000 0. 40 1 21. 4 6. 3 0. 20 02 1. 5 9. 4 0. 43 0. 63 1 Plunger 3 1 00040 0. 70 3 26. 3 18. 8 0. 61 00 1. 0 6. 3 0. 29 0. 90 0 Gasket 4 1 02000 0. 40 1 15. 0 6. 3 0. 20 38 0. 8 5. 0 0. 23 0. 43 1 cover Dr. Mohammad Abuhaiba

35 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION The 1. 2. 3. elimination of a part would eliminate: a complete station on an assembly machine-including the parts feeder special work head associated portion of the transfer device Dr. Mohammad Abuhaiba

36 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Automation can be facilitated by the introduction of guides and chamfers. Figs. 5. 12 and 5. 13 Sharp corners are removed so that the part can be guided into its correct position during assembly leading to: 1. 2. less control by the placement device or can even eliminate the need for a placement device. Dr. Mohammad Abuhaiba

37 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Dr. Mohammad Abuhaiba

38 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Dr. Mohammad Abuhaiba

39 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Screws that tend to centralize themselves in the hole give the best results in automatic assembly: 1. 2. 3. 4. 5. 6. Rolled thread point: very poor location; will not centralize without positive control on the outside diameter of the screws. Header point: only slightly better than (1) if of correct shape. Chamfer point: reasonable to locate. Dog point: reasonable to locate Cone point: very good to locate. Oval point: very good to locate. Dr. Mohammad Abuhaiba

40 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Assembly from above: Allow for assembly in sandwich or layer fashion, each part being placed on top of previous one. Work heads and feeding devices above the assembly station: Gravity can be used to assist in feeding and placing of parts. They will be accessible in event of a fault due to feeding of a defective part. Assembly assist in the problem of keeping parts in their correct positions during the machine index period, when dynamic forces in the horizontal plane might tend to displace them. With proper product design using self-locating parts, force due to gravity should be sufficient to hold the part until it is fastened or secured. Dr. Mohammad Abuhaiba

41 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Assembly from above is not possible: divide assembly into subassemblies. Fig. 5. 15: Difficult to position and drive the two cord grip screws from below. The two screws, cord grip, and plug base could be treated as a subassembly dealt with prior to main machine assembly. Dr. Mohammad Abuhaiba

42 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Have a base part on which assembly can be built. Figure 5. 16 a: Must have features to be suitable for quick and accurate location on the work carrier. If a force were applied at A, part would rotate unless adequate clamping was provided. To ensure that a base part is stable, Arrange that its center of gravity be contained within flat horizontal surfaces. Fig. 5. 16 b: A small ledge machined into part Dr. Mohammad Abuhaiba

43 3/19/2018 5. 8 GENERAL RULES FOR PRODUCT DESIGN FOR AUTOMATION Fig. 5. 17: Location of base part in the horizontal plane is often achieved by tapered dowel pins mounted in the work carrier to provide guidance Dr. Mohammad Abuhaiba

44 3/19/2018 5. 9 DESIGN OF PARTS FOR FEEDING AND ORIENTING versatile parts feeder is the vibratory bowl feeder. Three basic design principles: Most 1. 2. 3. Avoid designing parts that will tangle, nest, or shingle. Make the parts symmetrical. If parts cannot be made symmetrical, avoid slight asymmetry or asymmetry resulting from small or non-geometrical features. Dr. Mohammad Abuhaiba

45 3/19/2018 5. 9 DESIGN OF PARTS FOR FEEDING AND ORIENTING Dr. Mohammad Abuhaiba

46 3/19/2018 5. 9 DESIGN OF PARTS FOR FEEDING AND ORIENTING deliberately add asymmetrical features for the purpose of orienting. The features that require alignment are difficult to utilize in an orienting device, so corresponding external features are deliberately added. Dr. Mohammad Abuhaiba

47 3/19/2018 5. 9 DESIGN OF PARTS FOR FEEDING AND ORIENTING FIG 5. 20 a: a part that would be difficult to handle FIG 5. 20 b: redesigned part, which could be fed and oriented in a vibratory bowl feeder at a high rate. Dr. Mohammad Abuhaiba

48 3/19/2018 5. 9 DESIGN OF PARTS FOR FEEDING AND ORIENTING Parts that are easy to handle automatically will also be easy to handle manually. Very small parts or complicated shapes formed from thin strips are difficult to handle in an automatic environment. Manufacture the parts on the assembly machine or to separate them from the strip at the moment of assembly. Dr. Mohammad Abuhaiba

49 3/19/2018 5. 10 SUMMARY OF DESIGN RULES FOR HIGH-SPEED AUTOMATIC ASSEMBLY Rules for Product Design 1. Minimize number of parts 2. Ensure that product has a suitable base part on which to build the assembly 3. Ensure that base part has features that enable it to be readily located in a stable position in the horizontal plane. 4. Design product so that it can be built up in layers, each part being assembled from above and positively located so that there is no tendency for it to move under the action of horizontal forces during the machine index period. 5. Provide chamfers or tapers that help to guide and position parts in the correct position. 6. Avoid expensive and time-consuming fastening operations, such as screw fastening, soldering, and so on. Dr. Mohammad Abuhaiba

50 3/19/2018 5. 10 SUMMARY OF DESIGN RULES FOR HIGH-SPEED AUTOMATIC ASSEMBLY Rules for the Design of Parts 1. 2. 3. Avoid projections, holes, or slots that cause tangling with identical parts when placed in bulk in the feeder. Attempt to make the parts symmetrical If symmetry cannot be achieved, exaggerate asymmetrical features to facilitate orienting or, alternatively, provide corresponding asymmetrical features that can be used to orient the parts. Dr. Mohammad Abuhaiba

51 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY Three representative types of robot assembly systems : 1. 2. 3. Single-station with one robot arm Single-station with two robot arms Multi station with: Robots special-purpose work heads manual assembly stations Dr. Mohammad Abuhaiba

52 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY: Single-station system For reasons of safety it would usually be necessary to transfer the assembly to a location or fixture outside the working environment of the robot. Robot place the assembly on a transfer device that carries the assembly to the manual station. After manual operation has been completed, assembly can be returned in a similar manner to within reach of the robot. Dr. Mohammad Abuhaiba

53 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY: Single-station system Two 1. 2. insertion situations: Insertion or placement of part by the robot without it being secured immediately. followed by transfer of assembly to an external workstation to carry out the securing operation. A special-purpose work head is engineered to interact directly at the robot work fixture. Dr. Mohammad Abuhaiba

54 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY To determine assembly costs, it is necessary to obtain estimates of: 1. Total cost of all general-purpose equipment: 2. Total cost of all special-purpose equipment and tooling: 1. 2. 3. 4. 1. cost of robots Cost of transfer devices Cost of grippers. special-purpose work heads special fixtures special robot tools or grippers special-purpose feeders special magazines, pallets, or part trays Average assembly cycle time Cost per assembly of manual labor involved in: 1. 2. 3. machine supervision loading feeders, magazines, pallets, or part trays performing any manual assembly tasks Dr. Mohammad Abuhaiba

55 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY One classification & one data chart for each of the three basic robot assembly systems. Insertion or other required operations are classified according to difficulty For each classification, and depending on difficulty of operation, relative cost &time factors are given that can be used to estimate equipment costs & assembly times Dr. Mohammad Abuhaiba

56 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY Figure 5. 21: a portion of classification system and database for a single-station one-arm robot assembly system. Part is being added to assembly, but is not being secured immediately. Selection of appropriate row depends on direction of insertion. Selection of appropriate column depends on: whether part needs a special gripper, clamping temporarily after insertion whether it tends to align itself during insertion Dr. Mohammad Abuhaiba

57 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY Dr. Mohammad Abuhaiba

58 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY Example: A part is to be inserted along a horizontal axis, does not require a special gripper, requires temporary clamping, and is easy to align. Code =12 Relative robot cost AR =1. 5 If basic capital cost of an installed standard 4 DOF robot (capable of only vertical insertions) is \$60, 000, a cost of \$90, 000 is assumed. Relative additional gripper or tool cost =1. 0 Since the part needs temporary clamping, special tooling mounted on the work fixture would be required. Thus, if standard tooling or gripper cost \$5000, additional tooling needed would represent a cost penalty of \$5000 in the form of special purpose equipment. Dr. Mohammad Abuhaiba

59 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY Example: A part is to be inserted along a horizontal axis, does not require a special gripper, requires temporary clamping, and is easy to align. Relative basic operation time TP =1. 0 The basis for time estimates is the average time taken by robot to: move approximately 0. 5 m grasp the part Return insert the part when the motion is simple and no insertion problems exist For a typical present-generation robot, this process might take 3 s. Since relative time penalty for gripper or tool change is zero, no additional time penalty is incurred and total operation time is 3 s. A further time penalty must be added when the part to be inserted is not completely oriented by the part presentation device. The robot arm must perform final orientation with the aid of a simple vision system and an additional 2 to 3 s must be added to the operation time. Dr. Mohammad Abuhaiba

60 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY In addition to cost of robot and special tools or grippers, costs of part presentation must be estimated. In practice there are usually only two choices: The special-purpose feeder The manually loaded magazine, pallet, or part tray. 1. 2. Costs associated with part presentation can be divided into: Labor costs: material handling (loading parts feeders or magazines) system tending (freeing jams in feeders, handling parts trays, etc. ) system changeover costs (changing of work fixture, feeders, and magazines and robot reprogramming) Equipment costs: 1. 2. feeder depreciation of special fixtures, special tooling, magazines, pallets, or part trays. Dr. Mohammad Abuhaiba

61 3/19/2018 5. 11 PRODUCT DESIGN FOR ROBOT ASSEMBLY Bulk material handling costs are negligible compared with cost of manually loading individual parts one-by-one into magazines, pallets, or part trays. 3 significant factors needed to estimate cost of part presentation: 1. Special-purpose feeders: Manually loaded magazines: 1. cost of a special-purpose feeder, fully tooled and operating on the robot system, is assumed to be a min of \$5000. Actual cost of a feeder, for a particular part, can be obtained from the data presented earlier in this chapter. cost of one set of special magazines, pallets, or part trays for one part type is assumed to be \$1000. For large parts this figure may considerably underestimate the actual cost and extra allowance should be made. Loading of magazines: time needed to hand-load one part into a magazine can be estimated to be part -handling time, obtained from data in Chapter 3, plus 1 s. a typical value of 4 s may be used. Dr. Mohammad Abuhaiba

62 3/19/2018 5. 11. 1 Summary of Design Rules for Robot Assembly 1. 2. 3. Reduce part count Include features such as leads, lips, chamfers, etc. , to make parts self-aligning in assembly. Ensure that parts which are not secured immediately on insertion are self-locating in the assembly. Dr. Mohammad Abuhaiba

63 3/19/2018 5. 11. 1 Summary of Design Rules for Robot Assembly 4. Design parts so that they can all be gripped and inserted using the same robot gripper. 5. 6. Each change to a special gripper and then back to standard gripper is approximately equal to two assembly operations. Design products so that they can be assembled in layer fashion from directly above. Avoid the need for reorienting the partial assembly or for manipulating previously assembled parts. 4. These operations increase robot assembly cycle time without adding value to assembly. If the partial assembly has to be turned to a different resting aspect during assembly process, then this will usually result in increased work fixture cost and the need to use a more expensive 6 DOF robot arm. Dr. Mohammad Abuhaiba

64 3/19/2018 5. 11. 1 Summary of Design Rules for Robot Assembly 7. Design parts that can be easily handled from bulk. Avoid parts that Nest or tangle in bulk Are flexible Have thin or tapered edges that can overlap or "shingle" as they move along a conveyor or feed track Are so delicate or fragile that recirculation in a feeder would cause damage Are sticky or magnetic so that a force comparable to the weight of the part is required for separation Are abrasive and will wear the surfaces of automatic handling systems Are light so that air resistance will create conveying problems Dr. Mohammad Abuhaiba

65 3/19/2018 5. 11. 1 Summary of Design Rules for Robot Assembly If parts are to be presented using automatic feeders, then ensure that they can be oriented using simple tooling. 9. If parts are to be presented using automatic feeders, then ensure that they can be delivered in an orientation from which they can be gripped and inserted without any manipulation. 8. Dr. Mohammad Abuhaiba

66 3/19/2018 5. 11. 1 Summary of Design Rules for Robot Assembly 10. If parts are to be presented in magazines or part trays, then ensure that they have a stable resting aspect from which they can be gripped and inserted without any manipulation by the robot. If the production conditions are appropriate, the use of robots holds advantages over the use of special purpose work heads and some design rules can be relaxed. For example, a robot can be programmed to acquire parts presented in an array—such as in a pallet or part tray which has been loaded manually, thus avoiding many of the problems arising with automatic feeding from bulk. Dr. Mohammad Abuhaiba