Operation of a Hydraulic Backhoe - Literature review Example

Operation of a Hydraulic Backhoe Name: Course: Tutor: Date: Introduction Backhoes are used at surface metal as well as non-metal mines for several types of applications. They are versatile machines and this makes them widely used elements of mobile equipment. Backhoes were built specifically for ditching and cleanup, but their use has been broadened to encompass loading and removal of overburden material. These operations need coordinated movement of the boom, arm and bucket so as to control the ripping of the bucket to follow a desired trajectory (Patel & Prajapati, 2011). Although backhoes are used for similar purposes as earth hydraulic excavators, they have a different action. Rather than being mounted on a boom, the cutting bucket of a backhoe is fitted to a hydraulic arm that pivots in two places. First, hydraulics rams extend the arm and then raise the bucket to the top of the cutting face. They then draw the bucket down and toward the power section in a clawing motion (Marshall Cavendish Corporation, 2003). This paper discusses the operating mechanism of the hydraulic backhoe with reference to the hydraulic system within. It also focuses on the process control system that operates the backhoe. Parts of a hydraulic excavator The major components of a hydraulic excavator are shown in the figure below. Figure 1 Source: Hitachi (2011) The major difference between a hydraulic excavator and regular automobiles that run or tyres is that these automobiles get power generated and transmitted directly from the engine. But hydraulic excavators move by changing the force from the engine directly into the required hydraulic power (Komatsu, 2012). The operation of the backhoe as well as the other parts of the excavators is based on controlling of hydraulic pressure through control valves as shown in the figure below. Figure 2: Transmission of hydraulic pressure through the hydraulic excavator Source: Komatsu (2012) Functioning of the hydraulic excavator Hydraulic excavators can generate a large amount of energy thanks to the hydraulic pressure created using oil in the hydraulic compartment. The basic structure of the hydraulic system involves oil being supplied from a pump and flowing into and out of two openings, the “rod side” and the “bottom side.” The direction of flow of oil either into the rod side or into the bottom side determines the position of the piston – that is whether it retracts or projects. This basic operation is illustrated in the figure below. Figure 3 Source: Hitachi (2011) The basic operation of a hydraulic system involves transmission of pressure from a narrow cylinder (master cylinder) to a wider cylinder (slave cylinder) where the resultant pressure is used to lift a load. This involves the use of an incompressible liquid (in this case oil) which transmits the pressure exerted at one point to another point without a change in its volume. For instance, when a relatively small pressure of 350 kgf/cm2 is applied to the narrow section of a cylinder in a hydraulic excavator, it can yield a pressure that can lift up to 15 tonnes on the other end of the wider cylinder. It is the resultant pressure that enables the backhoe to lift large loads during excavation, loading, digging and so forth. The hydraulic system can therefore convert a tiny amount of power into an enormous force (Hitachi, 2011). See figure 4 for an illustration of this mechanism. Figure 4 Source: Hitachi (2011) A hydraulic backhoe can be likened to a huge, energetic of version of a human arm. There are three steel segments: the boom, the stick or arm and the bucket – which are connected by three joints. Hydraulic cylinders in the system act as muscles in the human arm and give the backhoe the desired power. The segments of the backhoe are hinged together and each cylinder can either push a connected segment away or pull it closer (Brain & Harris, 2012a). See figure 5 for an illustration of the hydraulic rams in the backhoe arm. Figure 5: Hydraulic rams in the backhoe arm Source: Brain and Harris (2012a) Each of the cylinder pistons is controlled by its own spool valve. Thus when an operator digs with the backhoe, he or she is essentially controlling at least four different spools that move four different pistons (Brain & Harris, 2012a). All cylinders in the arm of a backhoe function in the same way. The backhoe also possesses two hydraulic pistons that are positioned near the base of the boom. The boom arm is connected to the excavator with a swing casting that enables the pistons to swing with the backhoe from one side to another. The pistons are synchronised such that when one is pushed, the other is pulled. Most European backhoes have the boom attached to a side-shift mechanism, which is a bracket that can shift the whole of the backhoe horizontally on the excavator. This enables the operator to dig in spaces that would be very difficult to access (Brain & Harris, 2012a). Control systems of the hydraulic backhoe As noted earlier, the arm of the backhoe swivels on four separate hinges (although some bucket designs have five) and the loader moves on either two or three hinges. In addition, the operator controls the stabilizer arms of the excavator and moves the tractor around while loading (Brain & Harris, 2012b). The main controls for the backhoe (specifically for a Caterpillar backhoe) are computer-type joysticks that have several functions. First, the joystick on the left moves the boom and enables the entire backhoe to swing from side to side. Second, the joystick on the right moves the stick or arm and the bucket. Third, pushing the joystick on the left side of the excavator to the left makes the entire backhoe to swing to the left, and pushing the joystick to the right makes the arm swing to the right. Additionally, pushing the joystick on the right hand side to the left scoops the bucket in, and pushing the same joystick to the right makes the bucket come out, hence scooping debris or overburden (Brain & Harris, 2012b). Operating the loader of the backhoe is relatively easy because it only dumps, lowers and raises the arm. The main loader control is a joystick located on the right-hand side of the operator. If the operator pulls the joystick back toward him/her, the first set of hydraulic rams will push to raise the arms. When the operator pushes the joystick from the sitting position, the arms are lowered. To empty the bucket, the operator moves the joystick to the right. To scoop the bucket in an area to be dug, the operator moves the joystick to the right (Brain & Harris, 2012b). All these functions are enabled by the controls that manage the hydraulic rams. See figure 6. Figure 6: The standard mechanical connection control system from a backhoe. Source: Brain and Harris (2012b) When the stick on the far left is moved, it controls the spool valves that shift the boom from side to side and backward and forward. Additionally, the stick on the far right control the spool valves that shift the stick and the bucket. The two controls at the centre move the spool valves that extend and retract the stabilizer supports of the excavator (Brain & Harris, 2012b) (therefore these may be optional in case the excavator does not have these stabilizers). The main hydraulic pumps of the backhoe are controlled electronically and depend on the speed of the engine. The illustrations below (figure 7) show the various positions moved by the backhoe. Figure 7: A typical excavator and its coordinate frames (left) and on the right, the moving items of a typical backhoe excavator, as well as the assignment of their coordinate frames. Source: Patel and Prajapati (2011, p. 1991) Control systems of the bucket position The bucket position of the hydraulic backhoe is very important because it determines when to scoop and when to dump. The automatic control of the bucket position of the backhoe in the realization of a rectilinear trajectory requires a number of items: (1) the synchronized command of three mechanisms (that is the manoeuvring mechanisms of the boom, the stick or arm and the bucket) with the correlation of their movements; (2) sensors that can indicate the position of the bucket; and (3) a regulator that emits command signals in the view of the attaining of the desired trajectory of the bucket (Alexandru & Vladeanu, 2011). Several types of control of the bucket position are used in the hydraulic backhoe and they are highlighted next. a) Systems with transducers On such excavator equipment, there are three angle transducers mounted in the positions shown in figure 8: (1) a transducer that indicates the relative angular displacement between the boom and the platform of rotation; (2) a transducer that designates the relative angular displacement between the arm and the boom; and (3) a transducer that shows the relative angular displacement between the bucket and the arm. By considering the signal transmitted by the position of the sensors of the boom, bucket and arm using a special calculus, the position of the cutting edge of the bucket is determined and displayed on a screen for the operator to view (Alexandru & Vladeanu, 2011). Figure 8 Source: Alexandru and Vladeanu (2011, p. 165). b) Systems that use laser In this case a, laser transmitter generates a reference plane towards which the bucket position is determined with the aid of a laser sensor mounted on the working equipment (Alexandru & Vladeanu, 2011). c) Systems that use GPS In these systems, the position of the excavator and that of the bucket is established with the help of radio waves that are broadcasted and received by the devices that are mounted on the satellites, on fixed stations positioned on the earth as well as on the excavator, on the arm on the boom and on the bucket. The position of the cutting edge of the bucket is then calculated and displayed on the screen situated within the cab of the excavator (Alexandru & Vladeanu, 2011). Aside from the systems that display the position of the bucket on the screen within the cab of the excavator, automatic systems of controlling the bucket position have been realised at the laser and GPS versions as well as angle transducers. The introduction of the systems that control the bucket position of the hydraulic backhoe is justified from the economic perspective because in the case of the manual command the rectilinear path of the cutting edge of the bucket is determined with difficulty and needs a high qualification of the operator and this also lowers the precision of execution of the work as well as productivity (Alexandru & Vladeanu, 2011). Conclusion In conclusion, this paper has discussed the main operating mechanism of a hydraulic backhoe. It has been shown that the hydraulic systems form the basis of operation of the backhoe. These systems make use of an incompressible liquid (oil) which is used to transmit pressure from the point of control by the operator to the point where a lot of pressure is required to lift a load, dig or dump. The backhoe has three major components: the boom, the stick/arm and the bucket. These parts are hinged together to give the backhoe the desired power during operation. They are connected by hydraulic rams that are controlled to achieve the required functionality. The operator uses controls in the form of joysticks to controls the various parts to aid in the desired job. To enhance accuracy of the position of the bucket, modern excavators have backhoes fitted with sensors in the form of transducers, laser devices or GPS systems, which enable the operator to accurately determine the position of the backhoe and therefore perform the desired function such as digging, scooping or dumping more precisely. Modern systems also have hydraulic rams that are controlled electronically to enable faster and more synchronised movement of the boom, stick and bucket of the hydraulic backhoe. The hydraulic rams also facilitate backward and forward as well as side to side movement to make the backhoe more versatile. References Brain, M. & Harris, T. (2012a). “How Caterpillar Backhoe Loaders Work.” Retrieved 09 January 2012, from http://science.howstuffworks.com/transport/engines-equipment/backhoe-loader5.htm Brain, M. & Harris, T. (2012b). “How Caterpillar Backhoe Loaders Work.” Retrieved 09 January 2012, from http://science.howstuffworks.com/transport/engines-equipment/backhoe-loader7.htm Hitachi (2011). “Environmental activities.” Retrieved 09 January 2012, from http://www.hitachi.com/environment/showcase/speco_technique/zaxis/01.html Komatsu (2012). “Everything about construction equipment.” Retrieved 09 January 2012, from http://www.kenkenkikki.jp/special/no01/e_jyobu.htm Marshall Cavendish Corporation (2003). How it Works: Science and Technology (3rd edition). New York: Marshall Cavendish. Patel, B. P. & Prajapati, J. M. (2011). “A review on kinematics of hydraulic excavator’s backhoe attachment.” International Journal of Engineering Science and Technology (IJEST), Vol. 3, No. 3, pp. 1990-1997. Vladeanu, A. & Vladeanu, G. (2011). “The control of the bucket position at the hydraulic excavators with backhoe attachment.” SISOM 2011 and Session of the Commission of Acoustics, Bucharest 25-26 May. Read More