Sensor-Based Data Recording of Use Conditions for Product Takeback

Sensor-Based Data Recording of Use Conditions for Product Takeback Markus Klausner* and Wolfgang M. Gimm Robert Bosch GmbH Corporate Research and Development P.O. Box 10 60 50,70049 Stuttgart, Germany

Chns Hendrickson and Arpad Howath Green Design Initiative Carnegie Mellon University Pittsburgh, PA 15213-3890 Abstract - Information on product properties and the history of product use are essential for higher levels of product recovery like the reuse of components or remanufacturing.These product recovery options are economically more attractive than materials recycling. In this paper, the ISPR (Information System for Product Recovery) is proposed. Its key component is an electronic device, the so-called EDL (Electronic Data Log), which i s integrated in a product to record and store data strongly correlated with the degradation of components during the use stage of a product. The data recorded and processed during the use stage are retrieved and analyzed by the ISPR when the product is returned. The objectives for the development of the EDL, its implementation and its economical efficiency are discussed in detail.

I. INTRODUCTION While consumers traditionally dispose of products at the end of their life, product takeback shifts this responsibility from consumers to manufacturers, implying that manufacturers collect end-of-life products and control their recovery or disposal. Product recovery encompasses reuse of the product or its components, refurbishing, remanufacturing, materials recycling, etc. [l]. Legislation, current and pending, is a major driving force behind product takeback. Policies of Extended Producer Responsibility (EPR) [2], which make manufacturers responsible for a product’s entire life cycle including disposal, encourage manufacturers to take product recovery into account when designing a product. Each option of product recovery requires certain information about the product. For example, materials recycling may require information about materials composition, additives, hazardous content and disassembly sequences. The reuse of certain components of a product requires an assessment of the reuse potential, whtch is primarily influenced by the intensity of use, the treatment of the product by the customer, and environmental conditions during product use (e.g., temperature, humidity, voltage). Industry has been responding to the need of providing information to facilitate product recovery. Today’s products have plastic parts

marked to support the identification of materials in the postconsumer stage. At Bosch, for example, an environmental profile is required for new products containing information on materials composition, recyclability, the content of hazardous materials, etc. Designers are required to comply with design-for-environment guidelines that focus on disassemblability, recyclability, and avoidance of hazardous substances. While materials recycling is the most likely recovery option for the majority of consumer products, the reuse of components of returned products is limited: It is only suitable for high-value components that will not become obsolete in a next life cycle. Take an electric motor with a rated lifetime of 1000 hours as an example. If the motor was only used for 50 hours during the first use stage, why not reuse the motor? The problem is that no information on the remaining lifetime and the quality of a used motor is available. Inferior quality of used components, uncertainty about the remaining life time, and technological innovation are often cited arguments against the reuse of components. Yet reusing components of returned products may be economically more attractive than materials recycling. Reuse of components requires reliable methods for assessing the quality of used components. Tests have been developed to assess the reuse potential of certain components. For example, Xerox Corp. developed an acoustical test to discriminate between good and bad used motors for assessing the reuse potential of AC induction motors which are used as document handler motors for copiers [3].An alternative to testing is the recording of data indicating the degradation of components during the use stage of a product by an electronic device integrated in the product [4]. In the next section, the idea behind an Information System for Product Recovery (ISPR) is outlined. Recording data during the use stage of a product is an essential element of the ISPR. A technical solution for product-integrated data recording is presented in Section 111. In the same section, we also discuss economic aspects of the EDL. Finally, a summary in Section IV concludes the paper.

* Corresponding author. Email: [email protected]

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11. PRODUCT-INTEGRATED DATARECORDING FORPRODUCT RECOVERY ANDTHEISPR CONCEPT

A. Product-ZntegratedData Recording Very few concepts have been proposed for storing data for product recovery using a product-integrated electronic device.. An approach reported in [ 5 ] uses a so-called “identification unit” that stores static and dynamic “green data” which are accessed via a “green port”. An industry consortium of electronics manufacturers intends to develop such an identification unit and “green port” for electronic products [6]. Independently of those efforts, Bosch has already developed an integrated Electronic Data Log (EDL) that stores data obtained from sensors indicating the degradation of electronic and electromechanical components. The EDL has been implemented in electric motors as described in Section 111.

design &manufacture date & place of mfg. materials composition * toxic content disassembly sequence MTBF (mean time between failure) of components environmental conditions recycled content specs for batteries, oils, etc. etc.

use conditions, e.g.: number of use cycles runtime in each use cycle temperature humidity voltage, current, power service data, e.g.: data on service inspections parts replaced or repaired

STATIC DATA

DYNAMIC DATA

I I

The ISPR compiles data relevant to product recovery. Fig. I illustrates the data processed by the ISPR.

Data correlated with the degradation of the product and its components are not static. They are measured, processed and stored by a product-integrated electronic device which may be equipped with sensors. One possible design of this device is the EDL. It is suggested to enable the reuse of the product or its components and may facilitate refurbishing or remanufacturing. It must be implemented in each product manufactured, thus implying to minimize its cost. Since materials recycling does not require the EDL, it should only be implemented in products for which the reuse of components, refurbishing and remanufacturing are likely recovery options besides materials recycling. However, if it is obvious at the design stage that a product will be recycled exclusively for its materials, a passive transponder could be used instead of the EDL. The transponder would store a product identification which is retrieved after product return to provide a link between the product and the static data on the product stored in the external database.

I CATION EDL implemented in product

Extemal database

B. Outline of the ISPR Concept

The first data describing a product’s recovery potential are created at the design stage of a product, when, for example, the materials composition is chosen by designers. Since these data will not change during a product’s lifetime, they are static. During the manufacturing stage, hrther static data emerge that may be relevant for product recovery such as the toxic content or recommended disassembly sequence. Static data describing the product are suggested to be stored in an external database.

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external up-to-date information, e.g., demand for spare parts demand and prices for components, materials, etc. disassembly cost 0 recycling cost chemicals prohibited FIG. I DATA PROCESSED BY THE ISPR AT A PRODUCT’S END OF LIFE.

When the product is retumed at end-of-life, the data stored in the EDL are retrieved and subsequently compiled by the ISPR. For this purpose, software is required to process the data set retrieved and to assess the reuse potential of components. A unique identification code stored in the EDL links the set of static data in the database to the dynamic data in the EDL. External information on secondary markets, internal demand for spare parts, cost figures for disassembly and recycling, etc., allow the ISPR to assess distinct product recovery options. This concept differs from that described in [ 5 ] , which is based on storing all relevant data in the memory integrated in the product. We propose to store only those data in the EDL that cannot be stored or processed outside the product. The reasons for this different approach are: 0 the cost of the EDL must be minimized since it must be implemented in all products, thus implying to minimize the cost of the EDL memory; 0 most of the static data like materials composition and disassembly sequence apply to all products of a certain product line and thus would be stored redundantly if they were stored in the EDL. To reduce the manufacturer’s burden to compile a centralized database is the reason for proposals that favour to store static

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data in the product and not in an external database [6]. However, this is only meaningful if product recovery is left to independent recyclers, which is unllkely for a large-scale takeback program that is either handled by the manufacturer or by contracted recyclers. The latter would have access to a centralized database.

The current EDL prototype can record data for a cumulated runtime of approximately 2300+ hours. This is achieved by assigning the parameters measured to classes, which significantly reduces the data memory size of the EDL. For example, the temperature range of interest is divided into 15 classes. The EDL stores the runtime of the motor in each temperature class.

111. IMPLEMENTATION OF THE ELECTRONIC DATALOG(EDL) At Bosch, we developed and implemented an EDL for electric motors, i.e., a product-integrated device used to measure, compute and store parameters correlated with the degradation of an electric motor. The rationale for the development of the EDL is a takeback concept based on the reuse of electric motors and other components of electromechanical products.

A. Current EDL Prototype Two main objectives were associated with the development of the EDL for small low-cost motors: minimization of cost, since each product using an electric motor has to be equipped with the EDL, which results in higher initial manufacturing cost; small size, because the EDL has to be implemented in highly integrated products without modifying thc housing and the geometric dimensions. The EDL prototype described in the following meets both objectives. It consists of the following components: e a circuit board including a microcontroller and EEPROM memory; 0 sensors for the measurement o f temperature and current; 0 a low-current LED for data transmission from the EDL to an electronic reader; 0 a power supply that provides the required DC voltage. The power supply is not required for a wide range of battery-powered products like cordless power tools, where the DC voltage from batteries can be used. The EDL is located inside the housing of a product like a power tool, without modifying its design. The power supply of the EDL is connected to the terminals of the motor. We did not experience problems when we implemented the EDL prototype in other consumer products. During the use stage of the product, the EDL counts the number of starts and stops of the motor, stores the runtime in each individual use cycle as well as the cumulated runtime, records and compiles a set of sensor information such as the motor temperature and the power consumption in each individual use cycle, classifies and evaluates the recorded data, computes and stores peak and average values of all parameters of interest.

Since the number of write cycles in its EEPROM memory limits the lifetime of the EDL, an algorithm was developed which reallocates the memory cells that are accessed most frequently. This ensures that all memory cells of the EEPROM are accessed evenly. Due to its modular design concept, the EDL can be easily customized. For example, both temperature and current measurement are optional. If the current measurement is not desired, data memory will become availabe to increase measurement precision, Three bytes in the EDL memory store a unique product identification like a serial number which can be used to llnk the set of dynamic data in the EDL to external static information on the product (see Fig. I). B. Interface and Electronic Reader Based on the main objective to minimize the cost of all parts of the EDL implemented in a product, a low-cost device was developed for transmitting the data stored in the EDL. A lowcurrent LED, located at an easily accessible part of the product's housing, was selected to wirelessly transmit data from the EDL. When the odoff switch of the product is pressed, the data set stored in the EDL is sent via the LED. The reader, which must be pointed towards the LED tc receive the data transmitted, consists of photo diodes and an electronic device to amplify and convert the data transmitted via the LED. It is connected to the RS 232 port of a computer. The LED, which is actually the only indication for a customer that a product is equipped with an EDL, can also be utilized for other purposes, e.g., that a service inspection is due since the brushes are worn out. We also investigated other options for transmitting the data stored in the EDL such as infrared transmission and high frequency. The LED represents the lowest-cost option. In contrast to this approach, the "green port" that is under development at a consortium o f electronics manufacturers basically represents an active transponder, using an antenna for bidirectional data transfer [6]. C. Software f o r Data Visualization and Interpretation Software has been developed to visualize, store and analyze the data retrieved from the EDL. Data such as total runtime, individual runtime in each use cycle, the associated motor temperature and current, and peak and average values of those variables are visualized on the screen. A classification algorithm allows us to discriminate between reusable and

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nonreusable used motors based on the recorded data. This software represents a part of the ISPR (see Fig. I). Further research is needed to determine the parameters of the most significant impacts on motor degradation so that a reliable estimate for the remaining lifetime can be provided. This will determine future strategies for data measurement and processing.

saved by equipping the motors with an EDL and reusing them. This clearly shows that reusing motors with the aid of the EDL may be associated with a significant cost-savings potential. $45 20

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D. Economic Eficiency of the EDL 1) Manufacturing Cost Savings: While the consortium of electronics manufacturers working on the “green port” has a unit cost target of $0.50 [ 6 ] , we argue that the cost target should be determined by the economic efficiency of motor reuse based on EDLs. Using an EDL in each product sold ought to improve the overall economic efficiency of product recovery by bypassing expensive tests, improving the recovery rate, etc. All motors of a product line have to be equipped with an EDL, and thus the initial manufacturing cost will increase due to the additional cost of the EDL and its integration in the product. Unfortunately, only a fraction of the motors equipped with the EDL is ldcely to be returned, and only a fraction of the returned motors can actually be reused. Therefore, a manufacturer is faced with the question whether the additional cost of the EDL is justified by the savings resulting from the reuse of a fraction of motors equipped with the EDL. Therefore, we compare the total cost of equipping all motors with an EDL and reusing a fraction of them (cost C,,) to the total cost of newly manufactured motors not equipped with an EDL (cost Cnew).Taking into account the costs of screening and reclaiming used motors, we developed a cost model that quantifies the net present value of the difference between C,, and C,,,, over two motor life cycles [4]. Fig. I1 shows the unit cost savings (total cost scaled to the number of motors manufactured) resulting from reusing motors based on EDLs for different unit costs of newly manufactured motors as a function of the recovery rate. The recovery rate is determined by multiplying the return rate (fraction of products sold that are returned) with the yield (fraction of motors returned that are classified as reusable). As Fig. I1 indicates, the recovery rate needed to obtain a positive profit from motor reuse decreases as the motor manufacturing cost increases. For a large-scale application of the EDL with the same functionality as the prototype described above, our cost target is $2. The AC induction motor investigated for reuse at Xerox Corp. costs about $35 [3]. In the case of copier machines, it can be expected that the return rate is close to 100 per cent. For example, a yield of 80% would lead to a cost saving per motor of approximately $15 (see Fig. 11) and thus, approximately 43% of the manufacturing cost over two life cycles would be

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FIG. 11. UNIT MOTOR COST SAVINGS POTENTLAL DUE TO MOTOR REUSE BASED ON THE EDL FOR A COST OF $2 FOR THE EDL.

2) Cost of Misclassifications: Ideally, the classification software correctlv classifies all motors as reusable or nonreusable. In actuality, misclassifications will inevitably occur (Fig. 111).

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FIG. 111. ERRORS IN THE CLASSIFICATION OF USED MOTORS.

Consequently, a fraction of motors classified as reusable may actually fail in the second life cycle (false positives) and a fraction of motors rejected for reuse may be actually reusable (false negatives). We are interested in the full cost of used motor misclassifications. An approach to this problem is described in [7], where cost values are assigned to the misclassifications in testing for carcinogenicity to quantify the social cost of misclassifications. We adopted this methodology to the problem of motor classification (Fig.111). In actuality, estimating the TP, FP, FN and TN is very difficult. The yield is equivalent to the sum of TP and FP and is known. However, the relation between TP and FP is

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generally unknown so that estimates must be based on engineers' guesses. Repair statistics should not be used to estimate FP since the eventual fate o f a product equipped with a defective motor can hardly be predicted. The product may be disposed of, stored, etc., so that a manufacturer has no complete information on the actual number of failures during the entire use stage of a product. Statistically determining the frequency of a FN would require extensively testing all motors rejected for reuse, ideally even simulating an entire life cycle. In industrial practice, the actual values of FN and FP should be very small and thus, a large sample size would have to be tested to determine those values. 0

The cost of a FN, c, is the cost of substituting a newly manufactured motor for a motor rejected for reuse. For reasons of simplicity, we assume that motors rejected for reuse do not incur costs to a manufacturer. While estimating c,, is not difficult, estimating the cost of a FP,, , ,c is much harder. A motor classified as reusable which fails later when implemented in a product may lead to serious consequences, e.g., loss of future contracts and negative impact on the image of a manufacturer. Therefore, quantifying cFp is subjective and hard to justify. While the most conservative estimate for cFpmay be the cost of repair for a product equipped with a defective motor, a manufacturer concerned about quality may use an extremly high cost estimate, taking into account that the indirect effects of motor failure are prohibitively expensive. The cost of misclassifications were incorporated into the cost model in [4]. This allows us to determine the number of FP which must not be exceeded to obtain a profit from motor reuse. Hence, it represents an analytical way to determine the classification accuracy of the software processing the EDL data. Fig. IV visualizes the number of FP in parts per million (ppm) which must not be exceeded depending on the cost assigned to a FP and the recovery rate. Fig. IV is based on a unit manufacturing cost of $25 for a newly manufactured motor and a cost of $2 for the EDL. IV. SUMMARY

To make product recovery for electronic and electromechanical products economically attractive, informations on product properties and the history of the product are needed. In this paper, the ISPR (Information System for Product Recovery) is proposed. For this purpose, the information

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FIG. IV. MAXIMUM OF FP WHICH MUST NOT BE EXCEEDED DEPENDING ON BOTH THE COST VALUE ASSIGNED TO A FP AND THE RECOVERY RATE.

required for product recovery is classified into different types of information in terms of the product history, its static or dynamic nature, and the location where the information ought to be collected, stored and updated. An essential component of the ISPR is a product-integrated electronic device, the so-called EDL (Electronic Data Log). The EDL is an electronic device integrated in a product, where it gathers information on the actual usage of the product by measuring data closely correlated with the degradation of the product and its components over the entire lifetime. These data are considered to be essential to assess the reuse potential of components and facilitate remanufacturing. For this purpose, the EDL stores each switch-odswitch-off cycle, the absolute and mean runtime and a set of sensor data including peak and average values. In order to study the applicability and reliability of the EDL, it was implemented in electrical motors used in consumer products. An electronic reader was developed to retrieve data from the EDL for further visualization and processing. Based on a cost model, we showed that motor reuse may indeed result in a significant manufacturing cost savings potential even if only a fraction of the motors equipped with EDLs is retumed and only a fraction of the retumed motors can be reused. We also outlined a framework for the cost of misclassifications which allows us to derive the required accuracy of the classification software. ACKNOWLEDGMENTS

The authors wish to thank Professor Wolf-Henning Rech at the Fachhochschule Pforzheim and graduate student Harald Horber at the University of Stuttgart for their dedicated support on the development of the EDL hardware. Also, we want to thank Professor Lester Lave at Camegie Mellon University for his valuable contribution to the economic model outlined in this paper.

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REFERENCES [l] Thierry, M., M. Salomon, J.V. Nunen and L.V. Wassenhove, “Strategic Issues in Product Recovery Management,” California Management Review, Vol. 37, No. 2, 1995, pp. 114-135. [2] Lifset, R.J., “Take it Back Extended Producer Responsibility as a Form of Incentive-based Environmental Policy,” The Journal of Resource Management and Technology, Vol. 21, No. 4, 1993, pp. 163-175. [3] Reyes, W. et al., “Reliability Assessment of Used Parts: An Enabler for Asset Recovery,” Proceedings 1995 IEEE International Symposium on Electronics and the Environment, Orlando, Florida, 1995, pp. 89-94. [4] Klausner, M., W. G r i m and C. Hendrickson, “Case Study on the Reuse of Electric Motors of Consumer Products,” submitted for review to the Journal of Industrial Ecology, September 1997. [5] Scheidt, L.-G. and S. Zong, “An Approach to Achieve Reusability of Electronic Modules,” Proceedings 1994 IEEE International Symposium on Electronics and the Environment,

San Francisco, CA, 1994, pp. 331-336. [6] Product Stewardship Advisor. Cutter Information Corp., October 1997.

[7] Lave, L.B. and G.S. Omenn, “Cost-effectiveness of short-term tests for carcinogenicity,” Nature, Vol. 324, No. 6092, 1986, pp. 29-34.

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