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Development and testing of a brush feeder
CIRP Annals - Manufacturing Technology 59 (2010) 17–20
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er. com/ci rp/ def a ult . asp
Development and testing of a brush feeder G. Fantoni *, M. Santochi (1) Department of Mechanical, Nuclear and Production Engineering, University of Pisa, Italy
A R T I C L E I N F O
A B S T R A C T
Keywords: Assembly Positioning Feeding
Some manufacturing processes and many packaging operations require oriented and aligned parts. When a high feed rate cannot be obtained by human operators or when sophisticated vision systems, able to guide the picking operations, are too expensive or too complex for a specific application, a different approach to solve the problem is necessary. In this paper a brush feeding system based on tilted brushes is presented. It allows the controlled motion and the correct alignment of products different in shape, weight and surface roughness. The brush feeder is analyzed both from a theoretical and experimental point of view. ß 2010 CIRP.
1. Introduction
2. The brush feeder
In mass production very often parts have to be aligned, oriented and located before being assembled or packaged: manual or automatic feeders are usually used. Examples can be found in many industries such as glass, foundry, steel, construction, recycling, pulp and paper, and plastics. Vibratory bowl or linear feeders are the most common automatic devices. The bowl feeder is a self-contained system, based on a storage area for randomly located parts, a helical track supplied with features able to orient the part, and a vibrating drive unit. A stick-slip action forces the parts to move up the helical track. The track is designed to sort and orient the parts in consistent and repeatable positions [1]. Delicate and fragile parts can be damaged by stick-slip friction and by reciprocal hits. For them vibratory brush feeder have been developed in the seventies [2] and improved until now [3]. Unfortunately, excepting very rare traces [4], there is practically no scientific documentation of this feeder. Conversely the handling and feeding of microparts by exploiting the coordinated motion of arrays of microactuators (cilia) is attracting the attention of several researchers. Cilia provide the movement, the orientation and the alignment of microparts by means of the static friction generated among cilia and objects. Their actuation is based on thermal [4], electrostatic [6], magnetic [7] and piezoelectric [8] principle. From a theoretical point of view, abstract representations of force fields demonstrate the possibility of designing the force field according to the number and shape of the parts to be aligned, oriented and fed [9]. The authors want to give a contribution to the understanding of the working principle and to test the brush feeders under different motion conditions obtainable by brushes with differently oriented tufts.
The basic design of the brush feeder is very simple and its main components are:
* Corresponding author. 0007-8506/$ – see front matter ß 2010 CIRP. doi:10.1016/j.cirp.2010.03.049
a base supporting modulus, an array of tilted tufts; each tuft is composed of, a certain number of plastic fibres (Fig. 1). The prototype of the brush feeder is composed of tufts formed by about 200 polyamide cylindrical fibres with a diameter of 0.4 mm, Young’s modulus = 3300 MPa, H = 25 mm and a = 708. Due to the manufacturing process, the brush upper surface is quite irregular: some fibres are longer than others, with a maximum difference in length of 0.5 mm. However, such imperfections do not alter the behaviour of the device. The brush feeder’s working principle is based on the following phenomena. The tilted tuft is deformed under the weight of the body in motion over the brush. Each fibre is bent under the part’s weight and can interact with the neighbouring fibres. Therefore, during the motion over the brush surface, the part encounters new un-deformed fibres and leaves behind deformed ones. Thus, three different conditions of motion and friction can be distinguished (Fig. 2): according to the tilting direction, against the tilting direction, during a hit. When the part moves over the brush surface according to the tilting direction of the tufts (Fig. 2a), the fibres bend under the weight and the part slides on the tilted fibres (nearly the same behaviour can be imagined during the lateral motion—along x). The resulting motion is very soft and regular. On the contrary going against the tilted tufts, some fibres stick with the surface imperfections (roughness and waviness). They bend according to the movement direction, hence the fibres rotate
18
G. Fantoni, M. Santochi / CIRP Annals - Manufacturing Technology 59 (2010) 17–20
Fig. 3. Example of a result obtained during tests.
Fig. 1. Brush feeder: geometry and tufts.
and such rotation lifts the body. The few bent fibres are highly deformed and, despite their low number, they obstacle the motion making it very irregular (Fig. 2b). To correctly feed, separate, orient and align parts it is possible to exploit the transition between areas with differently oriented tufts. Indeed when a component is in motion along the tilting direction, the fibres are deformed (and lowered) in the same direction by its weight. When the component finds tufts oriented against the
motion the new un-deformed tufts act instead as a barrier (a sort of step) for the moving part (Fig. 3 on the top). Such different behaviour can be used to build a chute where different areas have differently oriented tufts. The chute exploits gravity as the driving force and the differently tilted tufts as obstacles able to orient the parts during their up–down motion. Finally, when an object hits vertically the tilted tufts forming the brush surface (Fig. 2c) some of fibres’ tips remain stuck on the roughness or waviness of the part surface, they bend under the normal load and pass from a relaxed configuration to an instable one (Eulero’s). The fibres are compressed and store elastic energy until the energy is released and the object is pushed away along the tilting direction. Such behaviour can be exploited for building an active vibrating brush feeder. 3. Experimental setup for tuft characterisation 3.1. Tuft strain–stress analysis An Instron machine has been used to measure the strain-stress curve for a square matrix of 9 tufts. A PMMA smooth square block (50 50 mm) has been pushed along the Z direction against the brush surface. The force–displacement diagram has been measured for different speeds but the results remained constant. The brush behaviour is nearly linear and showed a high repeatability in several tests. The obtained stiffness for a single tuft is 50 kN/m. 3.2. Dynamic friction analysis The Instron machine with a fixed pulley has been used also to measure the friction coefficient in different directions, with different speeds and under different loads. The evaluation of the dynamic friction coefficient has been performed by moving a slider over the brush surface along: X direction, according to the tilting direction and against it; Y direction to determine the lateral friction force.
Fig. 2. Motion: (a) according, (b) against the tilting direction, and (c) during a hit.
In addition the transition between according tilted tufts and against tufts with respect to the motion has been investigated. The force measured by the sensor is shown in Fig. 3. During the according motion, the force acting on the brush increases at each entrance of a new row of tufts. At the beginning of each step the force increases, the fibres are bent and when all the rows are in contact the forces remain nearly constant. Conversely, when the tufts exit the inverse behaviour can be observed for each row. In synthesis, the dynamic friction coefficient is about 0.35 and there is a small difference between the one measured laterally, according and against the tuft’s tilt.
G. Fantoni, M. Santochi / CIRP Annals - Manufacturing Technology 59 (2010) 17–20
19
Fig. 4. Resulting motion due to two different impacts and frames from the High Speed Camera.
The results obtained measuring the transition between two opposite oriented areas are more interesting. Actually, when a part is in motion over an area according to tuft’s tilt and reaches a zone where tufts are oriented in the other way, it feels a repelling force until 10 times larger. Indeed, the moving part deforms the tufts lowering its centre of gravity, hence, when it comes up against the opposite, un-deformed tufts, they act as a real obstacle. Fig. 3 shows how the friction force increases by nearly one order of magnitude.
The motion of a steel disk (D = 70 mm, h = 5 mm, and Ra = 6 mm) starting from different positions at the top of the chute has been traced by a vision system and the traces are shown in Fig. 5b. The alignment capabilities were really good both for flat cylindrical parts and for flat blocks (70 140 10 mm aluminium plate, Ra = 3.2 mm). Moreover Fig. 5c presents also the motion of 7 steel disks thrown simultaneously from the top of the chute. Four positions of the disks along the chute are shown. As the figure indicates, the red disks are conveyed towards the central channel of brush feeder in 2.5 s.
3.3. The brush in vibrating conditions 4.2. The brush feeder in vibrating conditions The vibration can be thought as a series of small hits, therefore a high speed camera has been used to monitor and understand a single hit. A series of parallel V-grooves (Vangle = 608, p = 1 mm, V-depth = 0.2 mm) has been milled on a flat transparent PMMA block which has been let fall on the brush surface. When the grooves were perpendicular to the tilting direction the block was pushed away along the tilting direction itself. The entity of the motion can be observed in the graph of Fig. 4 where the same object fell from h1 = 22 mm and h2 = 45 mm, respectively. Furthermore the frames captured by the high speed camera (frame rate = 0.01 s) confirmed the theoretical mechanism of motion. Conversely, when the grooves were parallel nearly no movement could be observed. The same behaviour was observed when a flat and smooth surface (Ra = 0.02 mm) hit the brush.
There are many parameters influencing the motion of an object over the vibrating brush feeder. Among them the weight of the object and its roughness have been recognised as the two most influencing. Therefore, a PMMA block (8 132 68 mm) has been used to study the motion under three different roughness conditions: smooth [Ra = 0.024 mm]; grooves [h = 0.2 mm,
4. Feeding results 4.1. The test of the brush feeder (chute configuration) A reconfigurable chute has been built in order to test the positioning and aligning capabilities. It allowed several arrangements of the brushes in order to align parts having different features (weight, roughness, shape, etc.). The chute dimensions were 1800 mm long and 600 mm wide, the slope of the chute was 158 and the brush module was formed by tufts tilted by an angle of 708, spaced px = py = 15 mm, composed of 200 polyamide fibres per tuft, as those previously characterized. The brushes were arranged in a funnel shape (Fig. 5a). The yellow arrows show the tilt of the tufts.
Fig. 5. Example of alignment results.
20
G. Fantoni, M. Santochi / CIRP Annals - Manufacturing Technology 59 (2010) 17–20
Fig. 6. ANOVA diagram: how roughness and weight influence body speed.
p = 1 mm]; rough [Ra = 3.2 mm]; and under two different loads: P0 = 78.65 g and P1 = 267 g. The vibration parameters have been determined by imposing that the body remains still under the lower load and in the smooth conditions. The parameters were: amplitude A = 1.2 mm and frequency f = 17 Hz. The ANOVA diagram presents the data organized in box plots: the red line represents the average values of the part speed m, while the blue trapeziums limits the area m s, finally the black points show the outliers. Results presented in the ANOVA show the speed of the object under different conditions of roughness and weight. When the roughness increases the speed increases as well, due to the higher number of fibres which stick to the surface. The higher is the weight the higher is the energy of the impact (proportional to the ratio component’s weight/surface) and according to Fig. 4 the higher is the displacement due to each single hit. The white arrows in the diagram show an increment of the speed when the roughness increases (for the same weight) and grey arrows when the weight does (for the same roughness) (Fig. 6). The vibrating brush feeder is shown in Fig. 7, and its dimensions are 300 mm 600 mm and the brush feeder has been arranged according to the funnel described in [10] and ending with a vortex as shown in [9]. The funnel shape is achieved through differently oriented brushes whose tilting direction is shown Fig. 7a by using colourer arrows. The blue arrows surrounded by yellow arrows form the funnel, while the green ones form the vortex. Several parts have been tested: they differ for their shape (from round to triangular shape, from square to cylindrical, etc.) for the pressure over the tufts (0.1–3 kPa) for their roughness (from Ra = 0.02–6 mm and more). The brush feeder in vibrating conditions demonstrated good performances both in positioning and in rotating. Actually, all the tested parts have been correctly fed and their paths followed the designed one (similar to that shown in Fig. 7b). In particular the two points A acted as the beginning of the funnel and were responsible of the alignment of long objects along the channel. B was the transition point between the funnel and the vortex whose centre is labelled with the letter C. It is the centre of rotation for all the parts which remain there and continue rotating until vibration is supplied. The general design rules deduced are: the surface of the object standing on the brushes must be always in contact with at least 4 not aligned tufts in order to avoid parts from falling down in the space among the tufts, the path for sorting and feeding must have about the same dimension of the minimal dimension of the surface on which the part stands, the lighter the part or the smother its surface, the higher the vibration frequency and/or the amplitude.
Fig. 7. Traces of triangular steel part during feeding and rotation.
5. Conclusions The brush feeder demonstrated good positioning and aligning capabilities both in passive configuration (the chute) and in the active one (vibrating feeder). Several configurations of the feeder have been successfully tested with different components. The paper presents some experimental evidences of the achieved results. The analysis presented here focused on the most influencing parameters, but other parameters and feeder characteristics will be object of future investigations both theoretical and empirical. Acknowledgments The research has been supported by Toscana Spazzole Industriali and by the Tuscany Region. The authors thank Mr. Moncini, Mr. Tambellini, Mr. Tincani and the technical staff of the DIMNP. References [1] Boothroyd G (1986) Product Design For Assembly. Boothroyd Dewhurst Inc., Wakefield. [2] Mead D.E. (1970) Vibratory Pile Feeder, US3667590. [3] Giovinazzo F. (2007) Vibratory Conveyor With Non-biased Oscillations, US20070017784. [4] Kru¨ger J, Lien TK, Verl A (2009) Cooperation of Human and Machines in Assembly Lines. CIRP Annals—Manufacturing Technology 58(2):628–646. [6] Bo¨hringer KF, Donald BR, MacDonald NC (1996) Single Crystal Silicon Actuator Arrays for Micro Manipulation Tasks. Proceedings of the IEEE Workshop on Micro Electro Mechanical Systems, San Diego, CA, . [7] Liu C, Tsao T, Tai YC, Ho CM (1994) Surface Micromachined Magnetic Actuators. Tech. Dig. IEEE Workshop Micro ElectroMech. Syst., Oiso, Japan, 57–62. [8] Ferreira A, Boudjabi S, Fontaine J-G (2002) Dynamic Model of an Arrayed-type Ultrasonic Microconveyer for Control Design. IEEE International Conference on Robotics and Automation Washington DC (USA) 3205–3211. [9] Bo¨hringer KF, Donald BR, Kavraki LE, Lamiraux F (2000) Part Orientation with One or Two Stable Equilibria Using Programmable Force Fields. IEEE Transactions on Robotics and Automation 16(2):731–747. [10] Coutinho MG, Will PM (1998) A general theory for positioning and orienting 2d polygonal or curved parts using intelligent motion surfaces. IEEE International Conference on Robotics and Automation 1:856–862.
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er. com/ci rp/ def a ult . asp
Development and testing of a brush feeder G. Fantoni *, M. Santochi (1) Department of Mechanical, Nuclear and Production Engineering, University of Pisa, Italy
A R T I C L E I N F O
A B S T R A C T
Keywords: Assembly Positioning Feeding
Some manufacturing processes and many packaging operations require oriented and aligned parts. When a high feed rate cannot be obtained by human operators or when sophisticated vision systems, able to guide the picking operations, are too expensive or too complex for a specific application, a different approach to solve the problem is necessary. In this paper a brush feeding system based on tilted brushes is presented. It allows the controlled motion and the correct alignment of products different in shape, weight and surface roughness. The brush feeder is analyzed both from a theoretical and experimental point of view. ß 2010 CIRP.
1. Introduction
2. The brush feeder
In mass production very often parts have to be aligned, oriented and located before being assembled or packaged: manual or automatic feeders are usually used. Examples can be found in many industries such as glass, foundry, steel, construction, recycling, pulp and paper, and plastics. Vibratory bowl or linear feeders are the most common automatic devices. The bowl feeder is a self-contained system, based on a storage area for randomly located parts, a helical track supplied with features able to orient the part, and a vibrating drive unit. A stick-slip action forces the parts to move up the helical track. The track is designed to sort and orient the parts in consistent and repeatable positions [1]. Delicate and fragile parts can be damaged by stick-slip friction and by reciprocal hits. For them vibratory brush feeder have been developed in the seventies [2] and improved until now [3]. Unfortunately, excepting very rare traces [4], there is practically no scientific documentation of this feeder. Conversely the handling and feeding of microparts by exploiting the coordinated motion of arrays of microactuators (cilia) is attracting the attention of several researchers. Cilia provide the movement, the orientation and the alignment of microparts by means of the static friction generated among cilia and objects. Their actuation is based on thermal [4], electrostatic [6], magnetic [7] and piezoelectric [8] principle. From a theoretical point of view, abstract representations of force fields demonstrate the possibility of designing the force field according to the number and shape of the parts to be aligned, oriented and fed [9]. The authors want to give a contribution to the understanding of the working principle and to test the brush feeders under different motion conditions obtainable by brushes with differently oriented tufts.
The basic design of the brush feeder is very simple and its main components are:
* Corresponding author. 0007-8506/$ – see front matter ß 2010 CIRP. doi:10.1016/j.cirp.2010.03.049
a base supporting modulus, an array of tilted tufts; each tuft is composed of, a certain number of plastic fibres (Fig. 1). The prototype of the brush feeder is composed of tufts formed by about 200 polyamide cylindrical fibres with a diameter of 0.4 mm, Young’s modulus = 3300 MPa, H = 25 mm and a = 708. Due to the manufacturing process, the brush upper surface is quite irregular: some fibres are longer than others, with a maximum difference in length of 0.5 mm. However, such imperfections do not alter the behaviour of the device. The brush feeder’s working principle is based on the following phenomena. The tilted tuft is deformed under the weight of the body in motion over the brush. Each fibre is bent under the part’s weight and can interact with the neighbouring fibres. Therefore, during the motion over the brush surface, the part encounters new un-deformed fibres and leaves behind deformed ones. Thus, three different conditions of motion and friction can be distinguished (Fig. 2): according to the tilting direction, against the tilting direction, during a hit. When the part moves over the brush surface according to the tilting direction of the tufts (Fig. 2a), the fibres bend under the weight and the part slides on the tilted fibres (nearly the same behaviour can be imagined during the lateral motion—along x). The resulting motion is very soft and regular. On the contrary going against the tilted tufts, some fibres stick with the surface imperfections (roughness and waviness). They bend according to the movement direction, hence the fibres rotate
18
G. Fantoni, M. Santochi / CIRP Annals - Manufacturing Technology 59 (2010) 17–20
Fig. 3. Example of a result obtained during tests.
Fig. 1. Brush feeder: geometry and tufts.
and such rotation lifts the body. The few bent fibres are highly deformed and, despite their low number, they obstacle the motion making it very irregular (Fig. 2b). To correctly feed, separate, orient and align parts it is possible to exploit the transition between areas with differently oriented tufts. Indeed when a component is in motion along the tilting direction, the fibres are deformed (and lowered) in the same direction by its weight. When the component finds tufts oriented against the
motion the new un-deformed tufts act instead as a barrier (a sort of step) for the moving part (Fig. 3 on the top). Such different behaviour can be used to build a chute where different areas have differently oriented tufts. The chute exploits gravity as the driving force and the differently tilted tufts as obstacles able to orient the parts during their up–down motion. Finally, when an object hits vertically the tilted tufts forming the brush surface (Fig. 2c) some of fibres’ tips remain stuck on the roughness or waviness of the part surface, they bend under the normal load and pass from a relaxed configuration to an instable one (Eulero’s). The fibres are compressed and store elastic energy until the energy is released and the object is pushed away along the tilting direction. Such behaviour can be exploited for building an active vibrating brush feeder. 3. Experimental setup for tuft characterisation 3.1. Tuft strain–stress analysis An Instron machine has been used to measure the strain-stress curve for a square matrix of 9 tufts. A PMMA smooth square block (50 50 mm) has been pushed along the Z direction against the brush surface. The force–displacement diagram has been measured for different speeds but the results remained constant. The brush behaviour is nearly linear and showed a high repeatability in several tests. The obtained stiffness for a single tuft is 50 kN/m. 3.2. Dynamic friction analysis The Instron machine with a fixed pulley has been used also to measure the friction coefficient in different directions, with different speeds and under different loads. The evaluation of the dynamic friction coefficient has been performed by moving a slider over the brush surface along: X direction, according to the tilting direction and against it; Y direction to determine the lateral friction force.
Fig. 2. Motion: (a) according, (b) against the tilting direction, and (c) during a hit.
In addition the transition between according tilted tufts and against tufts with respect to the motion has been investigated. The force measured by the sensor is shown in Fig. 3. During the according motion, the force acting on the brush increases at each entrance of a new row of tufts. At the beginning of each step the force increases, the fibres are bent and when all the rows are in contact the forces remain nearly constant. Conversely, when the tufts exit the inverse behaviour can be observed for each row. In synthesis, the dynamic friction coefficient is about 0.35 and there is a small difference between the one measured laterally, according and against the tuft’s tilt.
G. Fantoni, M. Santochi / CIRP Annals - Manufacturing Technology 59 (2010) 17–20
19
Fig. 4. Resulting motion due to two different impacts and frames from the High Speed Camera.
The results obtained measuring the transition between two opposite oriented areas are more interesting. Actually, when a part is in motion over an area according to tuft’s tilt and reaches a zone where tufts are oriented in the other way, it feels a repelling force until 10 times larger. Indeed, the moving part deforms the tufts lowering its centre of gravity, hence, when it comes up against the opposite, un-deformed tufts, they act as a real obstacle. Fig. 3 shows how the friction force increases by nearly one order of magnitude.
The motion of a steel disk (D = 70 mm, h = 5 mm, and Ra = 6 mm) starting from different positions at the top of the chute has been traced by a vision system and the traces are shown in Fig. 5b. The alignment capabilities were really good both for flat cylindrical parts and for flat blocks (70 140 10 mm aluminium plate, Ra = 3.2 mm). Moreover Fig. 5c presents also the motion of 7 steel disks thrown simultaneously from the top of the chute. Four positions of the disks along the chute are shown. As the figure indicates, the red disks are conveyed towards the central channel of brush feeder in 2.5 s.
3.3. The brush in vibrating conditions 4.2. The brush feeder in vibrating conditions The vibration can be thought as a series of small hits, therefore a high speed camera has been used to monitor and understand a single hit. A series of parallel V-grooves (Vangle = 608, p = 1 mm, V-depth = 0.2 mm) has been milled on a flat transparent PMMA block which has been let fall on the brush surface. When the grooves were perpendicular to the tilting direction the block was pushed away along the tilting direction itself. The entity of the motion can be observed in the graph of Fig. 4 where the same object fell from h1 = 22 mm and h2 = 45 mm, respectively. Furthermore the frames captured by the high speed camera (frame rate = 0.01 s) confirmed the theoretical mechanism of motion. Conversely, when the grooves were parallel nearly no movement could be observed. The same behaviour was observed when a flat and smooth surface (Ra = 0.02 mm) hit the brush.
There are many parameters influencing the motion of an object over the vibrating brush feeder. Among them the weight of the object and its roughness have been recognised as the two most influencing. Therefore, a PMMA block (8 132 68 mm) has been used to study the motion under three different roughness conditions: smooth [Ra = 0.024 mm]; grooves [h = 0.2 mm,
4. Feeding results 4.1. The test of the brush feeder (chute configuration) A reconfigurable chute has been built in order to test the positioning and aligning capabilities. It allowed several arrangements of the brushes in order to align parts having different features (weight, roughness, shape, etc.). The chute dimensions were 1800 mm long and 600 mm wide, the slope of the chute was 158 and the brush module was formed by tufts tilted by an angle of 708, spaced px = py = 15 mm, composed of 200 polyamide fibres per tuft, as those previously characterized. The brushes were arranged in a funnel shape (Fig. 5a). The yellow arrows show the tilt of the tufts.
Fig. 5. Example of alignment results.
20
G. Fantoni, M. Santochi / CIRP Annals - Manufacturing Technology 59 (2010) 17–20
Fig. 6. ANOVA diagram: how roughness and weight influence body speed.
p = 1 mm]; rough [Ra = 3.2 mm]; and under two different loads: P0 = 78.65 g and P1 = 267 g. The vibration parameters have been determined by imposing that the body remains still under the lower load and in the smooth conditions. The parameters were: amplitude A = 1.2 mm and frequency f = 17 Hz. The ANOVA diagram presents the data organized in box plots: the red line represents the average values of the part speed m, while the blue trapeziums limits the area m s, finally the black points show the outliers. Results presented in the ANOVA show the speed of the object under different conditions of roughness and weight. When the roughness increases the speed increases as well, due to the higher number of fibres which stick to the surface. The higher is the weight the higher is the energy of the impact (proportional to the ratio component’s weight/surface) and according to Fig. 4 the higher is the displacement due to each single hit. The white arrows in the diagram show an increment of the speed when the roughness increases (for the same weight) and grey arrows when the weight does (for the same roughness) (Fig. 6). The vibrating brush feeder is shown in Fig. 7, and its dimensions are 300 mm 600 mm and the brush feeder has been arranged according to the funnel described in [10] and ending with a vortex as shown in [9]. The funnel shape is achieved through differently oriented brushes whose tilting direction is shown Fig. 7a by using colourer arrows. The blue arrows surrounded by yellow arrows form the funnel, while the green ones form the vortex. Several parts have been tested: they differ for their shape (from round to triangular shape, from square to cylindrical, etc.) for the pressure over the tufts (0.1–3 kPa) for their roughness (from Ra = 0.02–6 mm and more). The brush feeder in vibrating conditions demonstrated good performances both in positioning and in rotating. Actually, all the tested parts have been correctly fed and their paths followed the designed one (similar to that shown in Fig. 7b). In particular the two points A acted as the beginning of the funnel and were responsible of the alignment of long objects along the channel. B was the transition point between the funnel and the vortex whose centre is labelled with the letter C. It is the centre of rotation for all the parts which remain there and continue rotating until vibration is supplied. The general design rules deduced are: the surface of the object standing on the brushes must be always in contact with at least 4 not aligned tufts in order to avoid parts from falling down in the space among the tufts, the path for sorting and feeding must have about the same dimension of the minimal dimension of the surface on which the part stands, the lighter the part or the smother its surface, the higher the vibration frequency and/or the amplitude.
Fig. 7. Traces of triangular steel part during feeding and rotation.
5. Conclusions The brush feeder demonstrated good positioning and aligning capabilities both in passive configuration (the chute) and in the active one (vibrating feeder). Several configurations of the feeder have been successfully tested with different components. The paper presents some experimental evidences of the achieved results. The analysis presented here focused on the most influencing parameters, but other parameters and feeder characteristics will be object of future investigations both theoretical and empirical. Acknowledgments The research has been supported by Toscana Spazzole Industriali and by the Tuscany Region. The authors thank Mr. Moncini, Mr. Tambellini, Mr. Tincani and the technical staff of the DIMNP. References [1] Boothroyd G (1986) Product Design For Assembly. Boothroyd Dewhurst Inc., Wakefield. [2] Mead D.E. (1970) Vibratory Pile Feeder, US3667590. [3] Giovinazzo F. (2007) Vibratory Conveyor With Non-biased Oscillations, US20070017784. [4] Kru¨ger J, Lien TK, Verl A (2009) Cooperation of Human and Machines in Assembly Lines. CIRP Annals—Manufacturing Technology 58(2):628–646. [6] Bo¨hringer KF, Donald BR, MacDonald NC (1996) Single Crystal Silicon Actuator Arrays for Micro Manipulation Tasks. Proceedings of the IEEE Workshop on Micro Electro Mechanical Systems, San Diego, CA, . [7] Liu C, Tsao T, Tai YC, Ho CM (1994) Surface Micromachined Magnetic Actuators. Tech. Dig. IEEE Workshop Micro ElectroMech. Syst., Oiso, Japan, 57–62. [8] Ferreira A, Boudjabi S, Fontaine J-G (2002) Dynamic Model of an Arrayed-type Ultrasonic Microconveyer for Control Design. IEEE International Conference on Robotics and Automation Washington DC (USA) 3205–3211. [9] Bo¨hringer KF, Donald BR, Kavraki LE, Lamiraux F (2000) Part Orientation with One or Two Stable Equilibria Using Programmable Force Fields. IEEE Transactions on Robotics and Automation 16(2):731–747. [10] Coutinho MG, Will PM (1998) A general theory for positioning and orienting 2d polygonal or curved parts using intelligent motion surfaces. IEEE International Conference on Robotics and Automation 1:856–862.