Validating the instrumented ball outputs with simple trajectories Sudarshan Martins a, * , Wei Li a , Peter Radziszewski a , Sylvain Caron b , Marc Aguanno a , Michael Bakhos a , Emma Lee Petch a a Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, Québec, Canada H3A 2K6 b COREM, 1180 rue de la Minéralogie, Québec, Canada H3A 2K6 article info Article history: Received 20 December 2007 Accepted 30 May 2008 Available online 23 July 2008 Keywords: Process instrumentation Modeling abstract An instrumented ball capable of measuring a number of physical quantities within a highly dynamic environment, such as a tumbling mill, has been designed, built and tested. To ensure that the instru- mented ball is operating as designed, it is made to follow a number of known trajectories. The physical quantities measured by the instrumented ball are consistent with the expected results along the trajec- tories. An example of the use of a properly functioning instrument is also shown. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Milling is not an efficient process. According to Mishra (2003), only 20% of the supplied energy is directed towards comminution processes. The remaining energy is wasted. This inefficiency has driven the effort to understand the dynamics of a mill; a greater understanding of milling processes could lead to an increased effi- ciency. Measurements are the basis of any improved understand- ing – they underpin new models and theories. A review by Caron and Roy (2004) found only a limited number of instruments having stemmed from all the recent research effort – the development of measurement instruments for a tumbling mill is a challenging problem, particularly if internal physical quantities are to be mea- sured. An instrument dedicated to the measurement of an internal physical quantity usually implies that, while in operation, the instrument must withstand and survive the action of the mill, without affecting the dynamics of the mill. One possible internal measurement system is the instrumented ball. Once deployed within an operating mill, the instrumented ball is subject to the same environment as the charge (Martins et al., 2006; Rolf, 1999; Dunn and Martin, 1978). Any measure- ments thus obtained provide some insight into the internal dynamics of a mill. The objective of the present work is to demonstrate that (i) the instrumented ball is an accurate measurement system and (ii) to demonstrate a possible application of the instrumented ball. 2. Instrumented ball The development of the McGill University instrumented ball (iBall) was motivated by major advancement in electronics. During the development of the prior instrumented balls, very high density computer memory and MEMs (micro-electromechanical systems) sensors were not commercially available. In addition, the current consumer electronics market has driven the production of small, low-power electronic components. These new advances in elec- tronics are leveraged by the McGill University iBall. The iBall, pic- tured in Fig. 1, consists of an electronic data acquisition system embedded within a protective shell. Several subsystems form the electronics: 1. Power supply. 2. Microcontroller and clock. 3. Storage (data and instructions). 4. Input/output subsystem (analog and digital). 5. Measurement sensors. In the current configuration, the measurement sensors are com- posed of one 3-axis accelerometer, three angular rate sensors and a temperature sensor. The adjustable sample frequency is set at 1 kHz. From the measured data, a number of physical quantities, such as the rotational kinetic energy, E rotational KE , the net applied mo- ment, ~ M Applied , the net applied force, ~ F Applied and the angular momentum, L * , can be found (Goldstein, 1980). E rotational KE ¼ 1 2 x * T I $ x * ð1Þ L * ¼ I $ ~ x ð2Þ 0892-6875/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2008.05.016 * Corresponding author. E-mail address: sudarshan.martins@mcgill.ca (S. Martins). Minerals Engineering 21 (2008) 782–788 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng