DESIGN OF THE TRANSMISSION MECHANISM USED IN A MULTIPOINT MORTISE LOCK Hsing-Hui Huang and Yi-Ming Lin Department of Vehicle Engineering, National PingTung University of Science and Technology, Taiwan, R.O.C. E-mail: sanlyhuang@mail.npust.edu.tw IMETI 2015, SG5009_SC No. 16-CSME-61, E.I.C. Accession 3947 ABSTRACT A multipoint lock is a useful lock which can provide more security and is convenient for the user. One of the aims of this article is to study how a multipoint lock is designed systematically by utilizing a mortise lock. Based on a systematic design methodology, the concepts and the atlas of designs are synthesized systematically. A feasible mechanism is further chosen for detailed design. The computer simulation is developed and the basic stress analysis is also constructed for verifying the design results. Finally, the prototype is also built. The results of this study provide a valuable reference for the design and analysis of a mortise lock s mechanism. Keywords: mortise lock; mechanism design. CONCEPTION DU MÉCANISME DE TRANSMISSION UTILISÉ DANS MULTILOCK RÉSUMÉ Un système de verrouillage de sécurité multilock est un système utile et pratique qui peut signifier plus de sécurité pour l utilisateur. Comment concevoir un système de conception systématique multilock en utilisant un type de serrure à mortaise, voilà le propos de cet article. Basé sur la méthodologie de conception systématique, le concept et l atlas des conceptions sont synthétisés systématiquement. Un mécanisme réalisable est choisi pour les détails de la conception. La simulation numérique est développée et l analyse de stress de base est aussi construite pour vérifier les résultats de la conception. Finalement le prototype est construit. Les résultats de cette étude offre une référence appréciable pour la conception et l analyse de mécanisme de serrure à mortaise. Mots-clés : serrure à mortaise; mécanisme de conception. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016 959
1. INTRODUCTION The mortise lock is a common lock with a long history, and it is commonly discussed in documents regarding locks. After a long period of improvement and evolution, a safer multipoint mortise lock has been developed. The design of this lock combines the installation methods of the traditional mortise lock and rim lock in which the rim lock becomes a part of the mortise lock, and the relationship between them is transmitted by linkages. A multipoint mortise lock can be designed and developed to have a primary lock and auxiliary lock where both of them are mortise locks [1]. This study collects and arranges the existing lock-related data and focuses on its aim, i.e., to carry out the analysis which is the foundation for the innovative design of the lock. And then, the bolt positions and moving functions of the existing mechanism are analyzed based on those of a multipoint lock so as to generalize its movement characteristics and set its design requirements and constraints; and so the design of the mechanism for the integration of a new multipoint lock is carried out. The better design is evaluated and selected according to the design atlas of integrated mechanisms, and then a feasible lock is designed in accordance with the dimensions and specifications. Next, a computer animation is carried out to make the actual mode. In light of the problems faced when practically using a multipoint mortise lock, a finite element analysis is used to analyze its motion and force endurance so as to find the maximum bearable moment of force and the components that can endure more force or its weak link; thus, a multipoint lock can be designed and fabricated. 2. DEFINITIONS AND ASSUMPTIONS Mechanical locks are very common devices in our daily lives. Mechanical locks can be classified into five types, mortise locks, rim locks, bored-in locks, combination locks, and padlocks, based on the difference in shape, operation, and installation method. The mortise lock is named so because it is inlaid in a wooden (or metal) door plank, its lock body is inserted into the door plank where the strike plate is installed on the wall, and the bolt of the lock body would fit into the strike plate. Where the mortise lock consists of latch bolt and dead bolt, its latch bolt is unlocked by the handle, while its dead bolt is unlocked by a key or knob, as shown in Fig. 1. The mortise lock is inlaid in the door plank with two bolts, so a higher strength can be achieved. From the above discussion, one can understand that a mortise lock is a lock with a mortise and tenon, and it must be inserted into the desired installation body. Locking is the snap-fit between the mortise and tenon, while unlocking is the separation between the mortise and tenon, as shown in Fig. 2. Therefore, a mortise lock can be defined as a lock with a bolt (mortise) and a strike plate (tenon); its lock body must be inserted into the target. Its bolt consists of a latch bolt and dead bolt that can be unlocked by a handle and key, respectively. Fig. 1. A mortise lock. 960 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016
Fig. 2. Mortise and tenon. Fig. 3. The interrelationship of the mechanism of the multipoint mortise lock. A multipoint mortise lock consists of one primary lock and at least one auxiliary lock. Nowadays, the common design has already changed the auxiliary lock to the mortise lock that is inserted into the door plank (mortise latch lock or mortise dead lock). The direction of motion of the bolt in the auxiliary lock is parallel to that of the bolt in the primary lock, and it is driven by a transmission mechanism when the primary lock moves. Therefore, the auxiliary lock cannot be unlocked when the primary lock is locked, and it is impossible to unlock the primary lock through any operation in the auxiliary lock directly. On the contrary, the auxiliary lock would be unlocked automatically if the primary lock can be unlocked correctly. The interior mechanism of a multipoint mortise lock is complicated and the motion mechanism would also be different under different operations. Thus, this study refers to the U.S. patent of the existing relevant design 6266981 B1 [2] to categorize the mechanism of motion into four sub-mechanisms for discussion, including a latch-bolt lock (latch-bolt mortise lock), dead-bolt lock (dead-bolt mortise lock), dead-latch bolt lock (dead-latch bolt mortise lock), and transmission mechanism as shown in Fig. 3. To illustrate the main functions of every sub-mechanism clearly, the operational condition and operating method of every sub-mechanism is illustrated in Fig. 4. 3. MECHANISM ANALYSIS Regardless of the type, latch-bolt locks, dead-bolt locks, and dead-latch bolt locks, are all feasible mortise locks. Therefore, the mortise lock comprises four parts: an input source, transmission mechanism, stop mechanism, and output (locking device). The biggest difference between a latch-bolt lock and dead-bolt lock is that the latch-bolt lock does not have stop transmission; appearances and motions of dead-bolt lock and Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016 961
Fig. 4. Operating conditions of mechanisms. Fig. 5. Composition of a mortise lock mechanism. latch-bolt lock are also different, as shown in Fig. 5. Since there is not much variation in the locking device, this study discusses the transmission mechanism and stop mechanism to analyze the design differences in the transmission mechanism and stop mechanism of different patents [3 6] as shown in Fig. 6. As a result, the basic design requirements of a multipoint mortise lock are obtained and listed as follows: 1. It should have a lock body. 2. It should have a primary lock, auxiliary lock, and transmission mechanism; the primary lock includes a latch-bolt lock and dead-bolt lock, while the auxiliary lock includes a dead-latch bolt. 962 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016
Fig. 6. Analytical diagram of structures. To define the differences between a latch-bolt lock, dead-bolt lock, and dead-latch bolt lock clearly, their design requirements and restrictions are set respectively according to the analytical result. A. The transmission mechanism of a latch-bolt lock The basic design requirements for the transmission mechanism of a latch-bolt lock are as follows: 1. It should have a fixed arm (lock body). 2. It should have an input arm (handle). 3. It should have an output arm (latch bolt). 4. The latch bolt should spring back into place after closing the door. 5. The handle should not revolve when closing the door. The following design restrictions are finalized based on functional requirements and practical issues: 1. The joint of the fixed arm cannot have 2 degrees of freedom. 2. The fixed arm must be the linkage with the most joints. 3. The input arm and output arm must be dual-joint arms. 4. The joint between the input arm and fixed arm must form a revolute pair. 5. The joint between the output arm and fixed arm must form a sliding pair, and only the output arm must have a sliding pair. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016 963
6. The input arm must be on top of the output arm, and the latch-bolt lock should get unlocked when turning the output arm clockwise. 7. At least one joint with a cam pair must be included. 8. Only the joint with 2 degrees of freedom can be paired with the input arm or output arm. 9. The multijoint arm must be adjacent to the fixed arm. B. The transmission mechanism of a dead-bolt lock Given that the stop arm situation is not considered, the design requirements for the transmission mechanism of dead-bolt lock are as follows: 1. It should have a fixed arm (lock body). 2. It should have an input arm (key or knob). 3. It should have an output arm (dead bolt). 4. The input arm must not be affected when the handle revolves after locking. 5. It should accommodate key holes of European and American specifications. The following design restrictions are finalized based on functional requirements and practical issues: 1. The joint of fixed arm cannot be the joint with 2 degree of freedoms. 2. The fixed arm must be the linkage with the most joints. 3. The input arm and output arm must be dual-joint arms. 4. The joint between input arm and fixed arm must be revolute pair, and the joint of another must be gear pair. 5. The joint between output arm and fixed arm must be sliding pair, and only output arm has sliding pair. 6. The input arm is on top of the output arm, and the dead-bolt will be pushed out of the lock body when turning the output arm anti-clockwise. 7. The joint with 2 degree of freedoms can only be paired with the input arm or output arm. 8. Multi-joint arm must be adjacent to the fixed arm. 9. The dual-joint arm cannot have two joints whose degrees of freedom are 2. C. The transmission mechanism of dead-latch bolt lock Given that the stop arm situation is not considered, the design requirements for the transmission mechanism of dead-latch bolt lock are as follows: 1. It should have a fixed arm (lock body). 2. It should have an input arm (linkage). 3. It should have an output arm (dead-latch bolt). 964 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016
4. The dead-latch bolt should bounce back into position after closing the door. 5. The input arm should not move when closing the door. The following design restrictions are finalized based on functional requirements and practical issues: 1. The joint of fixed arm cannot have 2 degrees of freedom. 2. The fixed arm must be the linkage with the most joints. 3. The input arm and output arm must be dual-joint arms. 4. The joint between input arm and fixed arm must form a sliding pair, and the joint of output arm and fixed arm must form a sliding pair as well. 5. The dead-latch bolt lock should get unlocked when the input arm moves upwards. 6. At least one joint with a gear pair must be included. 7. Only the joint with 2 degrees of freedom can be paired with the input arm or output arm. 8. The multijoint arm must be adjacent to the fixed arm. 9. The dual-joint arm cannot have two joints with 2 degrees of freedom. 4. MECHANISM SYNTHESIS Since the multipoint mortise lock is synthesized through four sub-mechanisms, this study discusses the transmission mechanism of a latch-bolt lock to explain every step of the synthesis. 4.1. Design Specifications The environments where they are used, sizes, specifications, and restrictions of mortise locks are different, and the mechanisms of mortise locks are also different. Thus, the number of linkages used for design can differ. The adjoining auxiliary relationships between joints are different as well. Consequently, the design specifications have to be finalized besides the above-mentioned design restrictions and requirements, including the number of linkages, mechanism type, joint type, degrees of freedom, and mechanical element type. The design specifications are as follows: 1. The number of linkages must be at least 3 and at most 5. 2. The degree of freedom must be 1, and the condition for separation of the linkages when moving should be ignored. 3. A revolute pair, sliding pair, cam pair, gear pair, pin-in slot, and five joint types are used. For a joint with 2 degrees of freedom, its number must be more than 0 but less than 3. 4. There is no restriction for the type of mechanical element. 4.2. Feasible Generalized Chain Atlas When analyzing the topological structure of a mechanism, the corresponding generalized chain can be obtained according to the procedures of generalization. Generalization [7] is a method to transform the linkages and joints from the original mechanical device to generalized linkages and generalized joints. When synthesizing the design, the feasible generalized chain atlas showing the required number of joints and linkages would be obtained through the number synthesis according to the design specifications that are set by the designer as shown in Fig. 7. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016 965
Fig. 7. Feasible generalized chain atlas of transmission mechanisms of the latch-bolt lock. Fig. 8. Design atlas of transmission mechanisms of the latch-bolt lock. 4.3. Feasible Specialized Chain Atlas Specialization is the method to assign the points from the generalized chain atlas as the specialized joints and the lines as the processes of specialized linkages [7]. The required type of linkage and joint is assigned to at least one generalized chain according to the design requirements so as to obtain the corresponding specialized chain that can satisfy the design restrictions; this is called the feasible specialized chain. 966 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016
Fig. 9. New multipoint mortiselock. 4.4. Particularization When particularizing, it is necessary to pay attention to redraw the feasible device according to the shape and arrangement of linkages and joints so as to give the characteristics of appearance back to the original one by one; the design atlas is shown in Fig. 8. 4.5. The Mechanism Diagram of a New Multipoint Mortise Lock From the synthesized, particularized design atlas, appropriate designs are selected for the latch-bolt lock, dead-bolt lock, and dead-latch bolt lock, respectively, through evaluation, and then the primary and auxiliary locks are placed in position. Next, the appropriate stop mechanism and linkage mechanism are collocated with the selected transmission mechanism. The diagram of the mechanism of a new multipoint mortise lock can then be synthesized as shown in Fig. 9(a). 5. DIMENSIONAL DESIGN The detailed dimensional design is carried out according to the evaluated design concept. In order to allow the design dimension to be compatible with the motion requirements of actual locks, the American patent 6266981 B1[8] with its production specifications is used as the prototype to design the lock that can satisfy the following dimension restrictions: 1. The locking displacement quantity of the dead-bolt should be 25 mm. 2. The unlocking displacement quantity of the latch bolt should be 11 mm. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016 967
Fig. 10. Material nature and analytical result of preliminary stress. 3. The unlocking displacement quantity of the dead-latch bolt should be 20 mm. 4. The sectional area of the primary lock body should be 64 197 mm 2. 5. The sectional area of the auxiliary lock body should be 42 120 mm 2. 6. Three fitting holes are needed for the primary lock for the fixed positions, and two are needed for the auxiliary lock. 7. When turning the key (or knob) anticlockwise by 90, the dead-bolt should get locked. 8. When turning the key (or knob) by 90, the dead-bolt should get unlocked. 9. When turning the handle by 45, the latch bolt and dead bolt should get unlocked. The dimensional design and calculation for the mechanism of synthesized sub-mechanisms is carried out. Its structures are shown in Fig. 9. 6. STRESS ANALYSIS The finite element analysis is used to carry out stress analysis, and the boundary conditions of the preliminary setting are as follows, which express the important point as shown in Fig. 10: 968 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016
1. C4 and C4(2) can have only 1 degree of freedom along the direction X. 2. C2, temp(2), D1, D2, D3, A4, temp(3), and C2(2) can have only 1 degree of freedom along the direction Y. 3. A2, A2, C2, and C2(2) can have only 1 degree of freedom that revolves around the Z axis. The initial moment of force, M, that revolves around the Z axis is given to component A2 simultaneously so as to move the entire machine. The stress changes that are produced from every component are observed. The maximum area of stress is shown in Fig. 10. From Fig. 10(a), one can find out there are three points with the maximum stress. However, from the continuous motion analysis, one can find that the regions that are shown in Figs. 10(b) and 10(c) continue to produce greater stress, they could be easily destroyed, and they are the more fragile links in the entire mechanism. When the given exerted pressure of force reaches 2800N mm, the maximum stress that is produced by the mechanism can reach 800 MPa, which greatly exceeds the tensile strength of steel, 500 MPa. Furthermore, the stress values of many points from the mechanism exceed the yield strength of steel, 250 MPa, and plasticity deformation that causes the mechanism to deform could occur; thus, the mechanism could be destroyed at this moment. 7. CONCLUSIONS This study designs and analyzes the multipoint mortise lock and the four major sub-mechanisms are also generalized, including the latch-bolt lock, dead-bolt lock, dead-latch bolt lock, and linkage mechanism. The simplified procedures of a multipoint mortise lock are applied to the structural synthesis of the new type of mechanism. Besides, the existing design is analyzed, the characteristics of the mechanism are generalized, and the design restrictions and requirements of multipoint locks are finalized. Eventually, the design concept and dimensions of the mechanism of a new multipoint mortise lock are obtained, and are verified by computerized simulation and a practical model. Moreover, the preliminary motion analysis of the mechanism is done and the design aspects that are needed to be strengthened are obtained. Since relevant analyses partly result in simplification of the model, not all conditions could be considered. As a result, the prospective study should soundly consider the damping effect of a spring, strengthen the setting of the contact, and detail the grid setting further so that an analytical result that is more practical is obtained. REFERENCES 1. Huang, H.H., Yan, H.S. and Lin, Y.M., The design of new type multipoint mortise locks, in Proceedings of the 24th National Conference on Mechanical Engineering, Chung Li, (NSC 95-2622-E-168-016- CC395WFDA700061), November 2007. 2. Resch, J.V., Renz, W., Gründler, D. and Dieners, U., Lock, in particular mortise lock for an exterior door, U.S. Patent No. 6,226,981 B1, July 31, 2001. 3. Renz, W., Röger, W. and Henzler, T., Locking device for a door, window or the like, U.S. Patent No. 6,389,855 B2, May 21, 2002. 4. Vanderburgh, G.W., Exit device, U.S. Patent No. 3,819,213, June 25, 1974. 5. Weller, G., Lock, U.S. Patent No. 1,290,439, January 7, 1919. 6. Yu, J.M., Combine door latch and deadbolt arrangement, U.S. Patent No. 4,578,967, April 1, 1986. 7. Yan, H.S., Creative Design of Mechanical Devices, Springer, Singapore, 1998. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 5, 2016 969