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1 is operated through a crank that is attached directly to the upper wheel. The upper wheel has been designed with a proper small size whose diameter that can range from 40 cm to 60 cm and it can be installed with the center at a height of 40 cm to 70 cm from the ground, as at-tempted in the prototype of Fig. 1. This design solution, although amenable for components in manufacturing and assembling in rural sites, can give problems fora human operator in rotating the crank with proper force in a long operation. Com-fort issues will require the crank at a height that does not need too many other motion of the human body of an operator and the driving force can be transmitted to the upper wheel at a proper ratio from human action. Comfort and proper human action have motivated a conception of a new fairly simple solution by using the mechanism in Fig. 3. 3 A Design Solution with a Driving Linkage Design problem for enhancing the rural water pump in Fig.1 has been focused for a better efficiency with comfort solution for an operator working the pump in standing up position with a limited man power. In addition, constraints were con-sidered in planning not to modify the original structure of the rural system and its sizes and materials as in Fig. b). Thus a solution has been conceived by proposing to add a mechanism to the axle of the upper wheel with the aim to achieve a prop-er functioning with suitable comfort of an operator. Thu, the scheme of Fig.3 has been considered as based on a 4-bar linkage whose crank is connected to the upper wheel and the input link can be powered through an handle by a human operator in a standing up position to alternate the input motion though the designed fol-lower behavior. Ergonomic features are represented by the length h for the handle link and the swinging angle Δθ as function of the motion capability of human operators. Efficiency is considered by sizing the 4-bar linkage so that the required torque Mw for the upper wheel is obtained with a force Fh at the handle with values that can be feasible for human operators in rural places. Beside the sizes of links as l1, l2, l3, l4, the linkage is characterized the by handle link with length H and a frame whose position can be adjusted with respect to the upper wheel frame through distances L1, D1, and b. the frame link has a size l1 given by ()212121 2 / D L b L l − + + =
(1) A suitable comfort operation is related to a suitable approximate straight path of handle corresponding to a proper value of Δθ4 for l4. In order to achieve a de-sign solution with a computation procedure that can be easily understood and even updates on site, the scheme of Fig.4 has been used for the dead centre configura-tions of a 4-bar linkage as in [3] ()23 2 1 4 12421 l l cos l l 2 l l + = ψ − + (2) ()22 3 2 4 12421 l l cos l l 2 l l − = ψ − + with θ + β − π = ψ1 ; θ − β − π = ψ2 ; − ++π= β −11 1L2 / D L btan2 By using Eqs. (1) -(2) and Fig.4 data are obtained for design solution for differ-ent cases as reported in Table 1. As regarding force transmission for operation efficiency, a 4-bar linkage offers the possibility of a fairly simple computation of the relationship between a re-quired driving torque Mw for the upper wheel and human action Fh1 at the input link handle in the form ϕω =cos VM Fh2 wh (3) with Mw = Fw rw where Fw is the weight and force due to the lifting rope with wa-ter acting at the radius rw of the upper wheel. An analysis has been carried out to derive computation expressions also for the force transmission as based on geo-metrical schemes that both help for intuitive understanding and allow handsome computations. Referring to the scheme in Fig.5, by using expressions for lines IA and IB with I as instantaneous center of rotation for link l3, [3], the velocity Vh of the handle point and its orientation angle ϕ with respect to the horizontal human driving force Fh can be computed after some algebraic manipulations as IA lIB lV422 h ω = and B 1Bx lycos−= ϕ (4) with IB as distance of I from B and IA as distance of I from A. The coordinates of I can be computed as intersection of lines IA and IB as B AB 1It tt lx−−= and I A I x t y = (5) where tA = yA /xA and tB = yB / (xB- l1), when xA = l2 sin(θ2) and yA = l22 cos(θ2). The coordinates of B are obtained by intersecting the mobility circles that are centered in A with radius l2 and centered at frame joint of follower with radius l4 as a 2c a 4 b bx2B− + −= and B 12B2124 B x l 2 x l l y + − − = (6) with () 2A2A 1 y 4 x l 4 a − − = , ()( ) 2321242A2A A 12A 1 l l l y x x l 4 y l 8 b − − + + − + − = ()( )2 2321242A2A21242A l l l y x l l y 4 c − − + + + − − = Design results from Eqs. (3) to (6) as related to the design solutions in Table 1 give suitable values of human action force with maximum values below 100 N when the speed of the driving upper wheel is moved for a speed of 360 deg /sec. In particular, the above expressions Eqs. (3) to (6) can be computed through a drawing scheme like in Fig.5 from which parameters can be easily obtained for a handsome calculations with only geometrical data to obtain the required force Fh to operate the water pump as BB 1242w wyx lIBIAllhr FFh−ω=
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